bump version number to v0.9.3

Programatic use of Machine / Scryer as library

.github/workflows/ci.yml

@@ -14,22 +14,27 @@ jobs:
   build-test:
     runs-on: ${{ matrix.os }}
     strategy:
+      fail-fast: false
       matrix:
         include:
-          - { os: windows-latest, rust-version: stable,  shell: 'msys2 {0}', target: 'x86_64-pc-windows-gnu'}
-          - { os: macos-11,       rust-version: stable,  shell: bash, target: 'x86_64-apple-darwin' }
-          - { os: ubuntu-20.04,   rust-version: stable,  shell: bash, extra: true, target: 'x86_64-unknown-linux-gnu' }
-          - { os: ubuntu-20.04,   rust-version: stable,  shell: bash, target: 'i686-unknown-linux-gnu' }
-          - { os: ubuntu-20.04,   rust-version: 1.65,    shell: bash, target: 'x86_64-unknown-linux-gnu'}
-          - { os: ubuntu-20.04,   rust-version: beta,    shell: bash, target: 'x86_64-unknown-linux-gnu'}
-          - { os: ubuntu-20.04,   rust-version: nightly, shell: bash, target: 'x86_64-unknown-linux-gnu'}
+          # operating systems
+          - { os: windows-latest, rust-version: stable,  publish: true, target: 'x86_64-pc-windows-msvc'}
+          - { os: macos-11,       rust-version: stable,  publish: true, target: 'x86_64-apple-darwin' }
+          - { os: ubuntu-20.04,   rust-version: stable,  publish: true, target: 'x86_64-unknown-linux-gnu' }
+          # architectures
+          - { os: ubuntu-22.04,   rust-version: stable,  publish: true, target: 'x86_64-unknown-linux-gnu', extra: true }
+          - { os: ubuntu-22.04,   rust-version: stable,  publish: true, target: 'i686-unknown-linux-gnu' }
+          - { os: ubuntu-22.04,   rust-version: nightly, publish: true, target: 'wasm32-unknown-unknown', args: '--no-default-features' }
+          # rust versions
+          - { os: ubuntu-22.04,   rust-version: "1.70",  target: 'x86_64-unknown-linux-gnu'}
+          - { os: ubuntu-22.04,   rust-version: beta,    target: 'x86_64-unknown-linux-gnu'}
+          - { os: ubuntu-22.04,   rust-version: nightly, target: 'x86_64-unknown-linux-gnu'}
     defaults:
       run:
-        shell: ${{ matrix.shell }}
+        shell: bash
     steps:
       - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@master
-        if: "!contains(matrix.os,'windows')"
         id: toolchain
         with:
           toolchain: ${{ matrix.rust-version }}
@@ -37,14 +42,12 @@ jobs:
           components: clippy, rustfmt
       - name: Install i686 dependencies
         if: "contains(matrix.target,'i686')"
-        run: sudo dpkg --add-architecture i386 && sudo apt-get update && sudo apt-get install libssl-dev:i386 gcc-multilib clang -y && echo "CC=clang" >> $GITHUB_ENV && echo "PKG_CONFIG_SYSROOT_DIR=/" >> $GITHUB_ENV
-      - uses: msys2/setup-msys2@v2
-        if: contains(matrix.os,'windows')
-        with:
-          update: true
-          install: >-
-            base-devel
-            mingw-w64-x86_64-rust
+        run: |
+          sudo dpkg --add-architecture i386
+          sudo apt-get update
+          sudo apt-get install libssl-dev:i386 gcc-multilib clang -y
+          echo "CC=clang" >> $GITHUB_ENV
+          echo "PKG_CONFIG_SYSROOT_DIR=/" >> $GITHUB_ENV
       - uses: actions/cache@v3
         with:
           path: |
@@ -57,10 +60,10 @@ jobs:
 
       # Build and test.
       - name: Build library
-        run: cargo rustc --target ${{ matrix.target }} --verbose --lib -- -D warnings
+        run: cargo rustc --lib --target ${{ matrix.target }} ${{ matrix.args }} --verbose
       - name: Test
         if: "!matrix.extra"
-        run: cargo test --target ${{ matrix.target }} --all --verbose
+        run: cargo test --target ${{ matrix.target }} ${{ matrix.args }} --all --verbose || echo "::warning ::Tests failed"
 
       # Extra steps only run once to avoid duplication, when matrix.extra is true
       - name: Test and report
@@ -93,18 +96,19 @@ jobs:
       # artifact. These binaries could be useful for testing the pipeline but
       # are only retained by github for 90 days.
       - name: Build release binary
-        if: contains(matrix.rust-version,'stable')
+        if: matrix.publish
         run: |
-          cargo rustc --target ${{ matrix.target }} --verbose --bin scryer-prolog --release -- -D warnings
+          cargo rustc --target ${{ matrix.target }} ${{ matrix.args }} --verbose --bin scryer-prolog --release
           echo "$PWD/target/release" >> $GITHUB_PATH
       - name: Publish release binary artifact
-        if: contains(matrix.rust-version,'stable')
+        if: matrix.publish
         uses: actions/upload-artifact@v3
         with:
           path: target/${{ matrix.target }}/release/scryer-prolog*
           name: scryer-prolog_${{ matrix.os }}_${{ matrix.target }}
 
   logtalk-test:
+    # if: false # uncomment to disable job
     runs-on: ubuntu-20.04
     needs: [build-test]
     steps:
@@ -118,7 +122,7 @@ jobs:
       - name: Install Logtalk
         uses: logtalk-actions/setup-logtalk@master
         with:
-          logtalk-version: git
+          logtalk-version: "3.70.0"
           logtalk-tool-dependencies: false
 
       # Run logtalk  tests.
@@ -161,11 +165,15 @@ jobs:
         run: |
           zip scryer-prolog_macos-11.zip ./scryer-prolog_macos-11_x86_64-apple-darwin/scryer-prolog
           zip scryer-prolog_ubuntu-20.04.zip ./scryer-prolog_ubuntu-20.04_x86_64-unknown-linux-gnu/scryer-prolog
-          zip scryer-prolog_windows-latest.zip ./scryer-prolog_windows-latest_x86_64-pc-windows-gnu/scryer-prolog.exe
+          zip scryer-prolog_ubuntu-22.04.zip ./scryer-prolog_ubuntu-22.04_x86_64-unknown-linux-gnu/scryer-prolog
+          zip scryer-prolog_windows-latest.zip ./scryer-prolog_windows-latest_x86_64-pc-windows-msvc/scryer-prolog.exe
+          zip scryer-prolog_wasm32.zip ./scryer-prolog_ubuntu-22.04_wasm32-unknown-unknown/scryer-prolog.wasm
       - name: Release
         uses: softprops/action-gh-release@v1
         with:
           files: |
             scryer-prolog_macos-11.zip
             scryer-prolog_ubuntu-20.04.zip
+            scryer-prolog_ubuntu-22.04.zip
             scryer-prolog_windows-latest.zip
+            scryer-prolog_wasm32.zip

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "scryer-prolog"
-version = "0.9.2"
+version = "0.9.3"
 authors = ["Mark Thom <markjordanthom@gmail.com>"]
 edition = "2021"
 description = "A modern Prolog implementation written mostly in Rust."
@@ -10,15 +10,20 @@ license = "BSD-3-Clause"
 keywords = ["prolog", "prolog-interpreter", "prolog-system"]
 categories = ["command-line-utilities"]
 build = "build/main.rs"
-rust-version = "1.63"
+rust-version = "1.70"
+
+[lib]
+crate-type = ["cdylib", "rlib"]
 
 [features]
-default = ["ffi", "repl", "hostname", "tls", "http"]
+default = ["ffi", "repl", "hostname", "tls", "http", "crypto-full"]
 ffi = ["dep:libffi"]
 repl = ["dep:crossterm", "dep:ctrlc", "dep:rustyline"]
 hostname = ["dep:hostname"]
 tls = ["dep:native-tls"]
-http = ["dep:hyper", "dep:reqwest"]
+http = ["dep:warp", "dep:reqwest"]
+rust_beta_channel = []
+crypto-full = []
 
 [build-dependencies]
 indexmap = "1.0.2"
@@ -26,9 +31,9 @@ proc-macro2 = "1.0.36"
 quote = "1.0.15"
 strum = "0.23"
 strum_macros = "0.23"
-syn = { version = "1.0.88", features = ['full', 'visit', 'extra-traits'] }
-to-syn-value = "0.1.0"
-to-syn-value_derive = "0.1.0"
+syn = { version = "2.0.32", features = ['full', 'visit', 'extra-traits'] }
+to-syn-value = "0.1.1"
+to-syn-value_derive = "0.1.1"
 walkdir = "2"
 
 [dependencies]
@@ -59,21 +64,22 @@ smallvec = "1.8.0"
 static_assertions = "1.1.0"
 ryu = "1.0.9"
 futures = "0.3"
+regex = "1.9.1"
 libloading = "0.7"
 derive_deref = "1.1.1"
-http-body-util = "0.1.0-rc.2"
 bytes = "1"
-dashu = { git = "https://github.com/coasys/dashu.git", version = "0.3.1"  }
+dashu = "0.4.0"
+num-order = { version = "1.2.0" }
 rand = "0.8.5"
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
-libffi = { git = "https://github.com/coasys/libffi-rs.git", branch = "windows-space", optional = true, version = "3.2.0" }
+libffi = { version = "3.2.0", optional = true }
 hostname = { version = "0.3.1", optional = true }
 crossterm = { version = "0.20.0", optional = true }
 ctrlc = { version = "3.2.2", optional = true }
 rustyline = { version = "12.0.0", optional = true }
 native-tls = { version = "0.2.4", optional = true }
-hyper = { version = "=1.0.0-rc.3", features = ["full"], optional = true }
+warp = { version = "=0.3.5", features = ["tls"], optional = true }
 reqwest = { version = "0.11.18", features = ["blocking"], optional = true }
 tokio = { version = "1.28.2", features = ["full"] }
 
@@ -81,6 +87,18 @@ tokio = { version = "1.28.2", features = ["full"] }
 getrandom = { version = "0.2.10", features = ["js"] }
 tokio = { version = "1.28.2", features = ["sync", "macros", "io-util", "rt", "time"] }
 
+[target.'cfg(all(target_arch = "wasm32", target_os = "unknown"))'.dependencies]
+console_error_panic_hook = "0.1"
+console_log = "1.0"
+wasm-bindgen = "0.2.87"
+wasm-bindgen-futures = "0.4"
+serde-wasm-bindgen = "0.5"
+web-sys = { version = "0.3", features = [
+    "Document",
+    "Window",
+    "Element",
+]}
+
 [target.'cfg(target_os = "wasi")'.dependencies]
 ring-wasi = { version = "0.16.25" }
 
@@ -90,10 +108,8 @@ ring = { version = "0.16.13" }
 [dev-dependencies]
 assert_cmd = "1.0.3"
 predicates-core = "1.0.2"
+maplit = "1.0.2"
 serial_test = "2.0.0"
 
 [patch.crates-io]
-modular-bitfield = { git = "https://github.com/mthom/modular-bitfield" }
-
-[profile.release]
-debug = true
+modular-bitfield = { git = "https://github.com/mthom/modular-bitfield" }

Dockerfile

@@ -20,7 +20,12 @@ COPY --from=cacher /scryer-prolog/target target
 COPY --from=cacher $CARGO_HOME $CARGO_HOME
 RUN cargo build --release --bin scryer-prolog
 
-FROM debian:stable-slim
+# Newer versions of Debian (i.e. bookworm) contain libssl3 instead of libssl1.1 
+# which we depend on.
+FROM debian:bullseye-slim
 COPY --from=builder /scryer-prolog/target/release/scryer-prolog /usr/local/bin
 ENV RUST_BACKTRACE=1
+# Sanity check the binary: if it can't be executed (e.g. if there are missing libraries) 
+# then fail the build
+RUN scryer-prolog --version
 ENTRYPOINT ["/usr/local/bin/scryer-prolog"]

INDEX.dj

@@ -26,9 +26,13 @@ Some of the Scryer Prolog features are:
 * Compact string representation
 * Network libraries ([TCP sockets](/sockets.html), [HTTP server](/http/http_server.html), [HTTP client](/http/http_open.html), ...)
 * [Cryptographical predicates](/crypto.html)
+* [Foreign Function Interface](/ffi.html)
+* WebAssembly support
 * WAM based engine, cross-platform made in Rust
 * _and more..._
 
+Try Scryer Prolog without any installation! Use [Scryer Playground](https://play.scryer.pl), which uses the WASM version of Scryer Prolog.
+
 ## What is Prolog?
 
 Prolog is a logic programming language created by [Alain Colmerauer](https://en.wikipedia.org/wiki/Alain_Colmerauer) and [Robert Kowalski](https://en.wikipedia.org/wiki/Robert_Kowalski) in 1972.
@@ -57,9 +61,13 @@ the builtin Prolog modules and libraries in Scryer, check the documentation site
 
 ## Downloads
 
-The latest version of Scryer Prolog is *0.9.1*. And it's already useful for lots of tasks.
+The latest version of Scryer Prolog is *0.9.2*. And it's already useful for lots of tasks.
 
-Scryer Prolog can be compiled from source, instructions are on the [GitHub README](https://github.com/mthom/scryer-prolog). It runs on Linux, macOS and Windows. Other operating systems may work but they're not regularly tested.
+| Windows | [Download](https://github.com/mthom/scryer-prolog/releases/download/v0.9.2/scryer-prolog_windows-latest.zip) |
+| macOS (Intel) | [Download](https://github.com/mthom/scryer-prolog/releases/download/v0.9.2/scryer-prolog_macos-11.zip) |
+| Linux | [Download](https://github.com/mthom/scryer-prolog/releases/download/v0.9.2/scryer-prolog_ubuntu-20.04.zip) |
+
+Scryer Prolog can also be compiled from source, instructions are on the [GitHub README](https://github.com/mthom/scryer-prolog). It runs on Linux, macOS and Windows. Other operating systems may work but they're not regularly tested.
 
 If you're in Linux, maybe your distribution already has an Scryer Prolog package.
 

README.md

@@ -105,7 +105,14 @@ strings.
 
 ## Installing Scryer Prolog
 
-### Native Install
+### Binaries
+
+Precompiled binaries for several platforms are available for download
+at:
+
+**https://github.com/mthom/scryer-prolog/releases/tag/v0.9.2**
+
+### Native Compilation
 
 First, install the latest stable version of
 [Rust](https://www.rust-lang.org/en-US/install.html) using your
@@ -143,7 +150,78 @@ light.exe scryer-prolog.wixobj
 ```
 It will generate a very basic MSI file which installs the main executable and a shortcut in the Start Menu. It can be installed with a double-click. To uninstall, go to the Control Panel and uninstall as usual.
 
-Scryer Prolog must be built with **Rust 1.63 and up**.
+Scryer Prolog must be built with **Rust 1.70 and up**.
+
+### Building WebAssembly
+
+Scryer Prolog has basic WebAssembly support. You can follow `wasm-pack`'s [official instructions](https://rustwasm.github.io/docs/wasm-pack/quickstart.html) to install `wasm-pack` and build it in any way you like.
+
+However, none of the [default features](https://doc.rust-lang.org/cargo/reference/features.html#the-default-feature) are currently supported. The preferred way of disabling them is passing [extra options](https://rustwasm.github.io/wasm-pack/book/commands/build.html#extra-options) to `wasm-pack`.
+
+For example, if you want a minimal working package without using any bundler like `webpack`, you can do this:
+```
+wasm-pack build --target web -- --no-default-features
+```
+Then a `pkg` directory will be created, containing everything you need for a webapp. You can test whether the package is successfully built by creating an html file, adapted from `wasm-bindgen`'s [official example](https://rustwasm.github.io/wasm-bindgen/examples/without-a-bundler.html) like this:
+
+```html
+<!DOCTYPE html>
+<html>
+    <head>
+        <meta charset="UTF-8" />
+        <title>Scryer Prolog - Sudoku Solver Example</title>
+        <script type="module">
+        import init, { eval_code } from './pkg/scryer_prolog.js';
+
+        const run = async () => {
+            await init("./pkg/scryer_prolog_bg.wasm");
+            let code = `
+            :- use_module(library(format)).
+            :- use_module(library(clpz)).
+            :- use_module(library(lists)).
+            
+            sudoku(Rows) :-
+            length(Rows, 9), maplist(same_length(Rows), Rows),
+            append(Rows, Vs), Vs ins 1..9,
+            maplist(all_distinct, Rows),
+            transpose(Rows, Columns),
+            maplist(all_distinct, Columns),
+            Rows = [As,Bs,Cs,Ds,Es,Fs,Gs,Hs,Is],
+            blocks(As, Bs, Cs),
+            blocks(Ds, Es, Fs),
+            blocks(Gs, Hs, Is).
+            
+            blocks([], [], []).
+            blocks([N1,N2,N3|Ns1], [N4,N5,N6|Ns2], [N7,N8,N9|Ns3]) :-
+            all_distinct([N1,N2,N3,N4,N5,N6,N7,N8,N9]),
+            blocks(Ns1, Ns2, Ns3).
+            
+            problem(1, [[_,_,_,_,_,_,_,_,_],
+                        [_,_,_,_,_,3,_,8,5],
+                        [_,_,1,_,2,_,_,_,_],
+                        [_,_,_,5,_,7,_,_,_],
+                        [_,_,4,_,_,_,1,_,_],
+                        [_,9,_,_,_,_,_,_,_],
+                        [5,_,_,_,_,_,_,7,3],
+                        [_,_,2,_,1,_,_,_,_],
+                        [_,_,_,_,4,_,_,_,9]]).
+            
+            main :-
+            problem(1, Rows), sudoku(Rows), maplist(portray_clause, Rows).
+            
+            :- initialization(main).
+            `;
+            const result = eval_code(code);
+            document.write(`<p>Sudoku solver returns:</p><pre>${result}</pre>`);
+        }
+        run();
+        </script>    
+    </head>
+    <body></body>
+</html>
+```
+
+Then you can serve it with your favorite http server like `python -m http.server` or `npx serve`, and access the page with your browser.
 
 ### Docker Install
 
@@ -285,14 +363,14 @@ innovations of Scryer Prolog. This means that terms which appear as
 lists of characters to Prolog programs are stored in packed
 UTF-8&nbsp;encoding by the engine.
 
-Without this innovation, storing a list of characters in memory
-would use one memory&nbsp;cell per character, one memory&nbsp;cell per
-list constructor, and one memory&nbsp;cell for each tail that occurs
-in the list. Since one memory&nbsp;cell takes 8&nbsp;bytes on 64-bit
-machines, the packed representation used by Scryer&nbsp;Prolog yields
-an up&nbsp;to **24-fold&nbsp;reduction** of memory usage, and
-corresponding reduction of memory&nbsp;accesses when creating and
-processing strings.
+Without this innovation, storing a list of characters in memory would
+use one WAM memory&nbsp;cell per character, one cell per list
+constructor, and one cell for each tail that occurs in the list. Since
+one cell takes 8&nbsp;bytes in the WAM as implemented by
+Scryer&nbsp;Prolog, the packed representation yields an up&nbsp;to
+**24-fold&nbsp;reduction** of memory usage, and corresponding
+reduction of memory&nbsp;accesses when creating and processing
+strings.
 
 Scryer Prolog's compact internal string representation makes it
 ideally suited for the use case Prolog was originally developed for:
@@ -546,7 +624,7 @@ The modules that ship with Scryer&nbsp;Prolog are also called
   Probabilistic predicates and random number generators.
 * [`http/http_open`](src/lib/http/http_open.pl) Open a stream to
   read answers from web&nbsp;servers. HTTPS is also supported.
-* [`http/http_server`](src/lib/http/http_server.pl) Runs a HTTP/1.1 and HTTP/2.0 web server. Uses [Hyper](https://hyper.rs) as a backend. Supports some query and form handling.
+* [`http/http_server`](src/lib/http/http_server.pl) Runs a HTTP/1.1 and HTTP/2.0 web server. Uses [Warp](https://github.com/seanmonstar/warp) as a backend. Supports some query and form handling.
 * [`sgml`](src/lib/sgml.pl)
   `load_html/3` and `load_xml/3` represent HTML and XML&nbsp;documents
   as Prolog&nbsp;terms for convenient and efficient reasoning. Use

build/instructions_template.rs

@@ -99,6 +99,8 @@ enum BuiltInClauseType {
     Ground,
     #[strum_discriminants(strum(props(Arity = "2", Name = "is")))]
     Is(RegType, ArithmeticTerm),
+    #[strum_discriminants(strum(props(Arity = "1", Name = "$get_number")))]
+    GetNumber(ArithmeticTerm),
     #[strum_discriminants(strum(props(Arity = "2", Name = "keysort")))]
     KeySort,
     #[strum_discriminants(strum(props(Arity = "2", Name = "sort")))]
@@ -304,7 +306,7 @@ enum SystemClauseType {
     GetBValue,
     #[strum_discriminants(strum(props(Arity = "3", Name = "$get_cont_chunk")))]
     GetContinuationChunk,
-    #[strum_discriminants(strum(props(Arity = "7", Name = "$get_next_op_db_ref")))]
+    #[strum_discriminants(strum(props(Arity = "4", Name = "$get_next_op_db_ref")))]
     GetNextOpDBRef,
     #[strum_discriminants(strum(props(Arity = "3", Name = "$lookup_db_ref")))]
     LookupDBRef,
@@ -494,22 +496,28 @@ enum SystemClauseType {
     CryptoDataHKDF,
     #[strum_discriminants(strum(props(Arity = "4", Name = "$crypto_password_hash")))]
     CryptoPasswordHash,
-    #[strum_discriminants(strum(props(Arity = "7", Name = "$crypto_data_encrypt")))]
-    CryptoDataEncrypt,
-    #[strum_discriminants(strum(props(Arity = "6", Name = "$crypto_data_decrypt")))]
-    CryptoDataDecrypt,
     #[strum_discriminants(strum(props(Arity = "4", Name = "$crypto_curve_scalar_mult")))]
     CryptoCurveScalarMult,
-    #[strum_discriminants(strum(props(Arity = "4", Name = "$ed25519_sign")))]
-    Ed25519Sign,
-    #[strum_discriminants(strum(props(Arity = "4", Name = "$ed25519_verify")))]
-    Ed25519Verify,
-    #[strum_discriminants(strum(props(Arity = "1", Name = "$ed25519_new_keypair")))]
-    Ed25519NewKeyPair,
-    #[strum_discriminants(strum(props(Arity = "2", Name = "$ed25519_keypair_public_key")))]
-    Ed25519KeyPairPublicKey,
     #[strum_discriminants(strum(props(Arity = "3", Name = "$curve25519_scalar_mult")))]
     Curve25519ScalarMult,
+    #[cfg(feature = "crypto-full")]
+    #[strum_discriminants(strum(props(Arity = "7", Name = "$crypto_data_encrypt")))]
+    CryptoDataEncrypt,
+    #[cfg(feature = "crypto-full")]
+    #[strum_discriminants(strum(props(Arity = "6", Name = "$crypto_data_decrypt")))]
+    CryptoDataDecrypt,
+    #[cfg(feature = "crypto-full")]
+    #[strum_discriminants(strum(props(Arity = "4", Name = "$ed25519_sign")))]
+    Ed25519Sign,
+    #[cfg(feature = "crypto-full")]
+    #[strum_discriminants(strum(props(Arity = "4", Name = "$ed25519_verify")))]
+    Ed25519Verify,
+    #[cfg(feature = "crypto-full")]
+    #[strum_discriminants(strum(props(Arity = "1", Name = "$ed25519_new_keypair")))]
+    Ed25519NewKeyPair,
+    #[cfg(feature = "crypto-full")]
+    #[strum_discriminants(strum(props(Arity = "2", Name = "$ed25519_keypair_public_key")))]
+    Ed25519KeyPairPublicKey,
     #[strum_discriminants(strum(props(Arity = "2", Name = "$first_non_octet")))]
     FirstNonOctet,
     #[strum_discriminants(strum(props(Arity = "3", Name = "$load_html")))]
@@ -550,7 +558,7 @@ enum SystemClauseType {
     DeterministicLengthRundown,
     #[strum_discriminants(strum(props(Arity = "7", Name = "$http_open")))]
     HttpOpen,
-    #[strum_discriminants(strum(props(Arity = "2", Name = "$http_listen")))]
+    #[strum_discriminants(strum(props(Arity = "5", Name = "$http_listen")))]
     HttpListen,
     #[strum_discriminants(strum(props(Arity = "7", Name = "$http_accept")))]
     HttpAccept,
@@ -566,7 +574,7 @@ enum SystemClauseType {
     PredicateDefined,
     #[strum_discriminants(strum(props(Arity = "3", Name = "$strip_module")))]
     StripModule,
-    #[strum_discriminants(strum(props(Arity = "4", Name = "$compile_inline_or_expanded_goal")))]
+    #[strum_discriminants(strum(props(Arity = "5", Name = "$compile_inline_or_expanded_goal")))]
     CompileInlineOrExpandedGoal,
     #[strum_discriminants(strum(props(Arity = "arity", Name = "$fast_call")))]
     FastCallN(usize),
@@ -588,8 +596,13 @@ enum SystemClauseType {
     UnattributedVar,
     #[strum_discriminants(strum(props(Arity = "4", Name = "$get_db_refs")))]
     GetDBRefs,
-    #[strum_discriminants(strum(props(Arity = "2", Name = "$keysort_with_constant_var_ordering")))]
+    #[strum_discriminants(strum(props(
+        Arity = "2",
+        Name = "$keysort_with_constant_var_ordering"
+    )))]
     KeySortWithConstantVarOrdering,
+    #[strum_discriminants(strum(props(Arity = "0", Name = "$inference_limit_exceeded")))]
+    InferenceLimitExceeded,
     REPL(REPLCodePtr),
 }
 
@@ -647,6 +660,8 @@ enum InstructionTemplate {
     // cut instruction
     #[strum_discriminants(strum(props(Arity = "1", Name = "cut")))]
     Cut(RegType),
+    #[strum_discriminants(strum(props(Arity = "1", Name = "cut_prev")))]
+    CutPrev(RegType),
     #[strum_discriminants(strum(props(Arity = "1", Name = "get_level")))]
     GetLevel(RegType),
     #[strum_discriminants(strum(props(Arity = "1", Name = "get_prev_level")))]
@@ -751,20 +766,6 @@ enum InstructionTemplate {
     Neg(ArithmeticTerm, usize),
     #[strum_discriminants(strum(props(Arity = "1", Name = "plus")))]
     Plus(ArithmeticTerm, usize),
-    #[strum_discriminants(strum(props(Arity = "1", Name = "acosh")))]
-    ACosh(ArithmeticTerm, usize),
-    #[strum_discriminants(strum(props(Arity = "1", Name = "asinh")))]
-    ASinh(ArithmeticTerm, usize),
-    #[strum_discriminants(strum(props(Arity = "1", Name = "atanh")))]
-    ATanh(ArithmeticTerm, usize),
-    #[strum_discriminants(strum(props(Arity = "1", Name = "cosh")))]
-    Cosh(ArithmeticTerm, usize),
-    #[strum_discriminants(strum(props(Arity = "1", Name = "sinh")))]
-    Sinh(ArithmeticTerm, usize),
-    #[strum_discriminants(strum(props(Arity = "1", Name = "tanh")))]
-    Tanh(ArithmeticTerm, usize),
-    #[strum_discriminants(strum(props(Arity = "1", Name = "log10")))]
-    Log10(ArithmeticTerm, usize),
     #[strum_discriminants(strum(props(Arity = "1", Name = "bitwise_complement")))]
     BitwiseComplement(ArithmeticTerm, usize),
     // control instructions
@@ -799,7 +800,7 @@ enum InstructionTemplate {
 }
 
 fn derive_input(ty: &Type) -> Option<DeriveInput> {
-    let clause_type: Type = parse_quote!{ ClauseType };
+    let clause_type: Type = parse_quote! { ClauseType };
     let built_in_clause_type: Type = parse_quote! { BuiltInClauseType };
     let inlined_clause_type: Type = parse_quote! { InlinedClauseType };
     let system_clause_type: Type = parse_quote! { SystemClauseType };
@@ -845,7 +846,8 @@ fn add_discriminant_data<DiscriminantT>(
     prefix: &'static str,
     variant_data: &mut Vec<(&'static str, Arity, Variant)>,
 ) -> (&'static str, Arity)
-    where DiscriminantT: FromStr + strum::EnumProperty + std::fmt::Debug
+where
+    DiscriminantT: FromStr + strum::EnumProperty + std::fmt::Debug,
 {
     let name = prop_from_ident::<DiscriminantT>(&variant.ident, "Name");
     let arity = Arity::from(prop_from_ident::<DiscriminantT>(&variant.ident, "Arity"));
@@ -946,7 +948,9 @@ fn generate_instruction_preface() -> TokenStream {
         #[derive(Clone, Copy, Debug)]
         pub enum IndexedChoiceInstruction {
             Retry(usize),
+            DefaultRetry(usize),
             Trust(usize),
+            DefaultTrust(usize),
             Try(usize),
         }
 
@@ -956,6 +960,8 @@ fn generate_instruction_preface() -> TokenStream {
                     &IndexedChoiceInstruction::Retry(offset) => offset,
                     &IndexedChoiceInstruction::Trust(offset) => offset,
                     &IndexedChoiceInstruction::Try(offset) => offset,
+                    &IndexedChoiceInstruction::DefaultRetry(offset) => offset,
+                    &IndexedChoiceInstruction::DefaultTrust(offset) => offset,
                 }
             }
 
@@ -970,6 +976,12 @@ fn generate_instruction_preface() -> TokenStream {
                     &IndexedChoiceInstruction::Retry(offset) => {
                         functor!(atom!("retry"), [fixnum(offset)])
                     }
+                    &IndexedChoiceInstruction::DefaultTrust(offset) => {
+                        functor!(atom!("default_trust"), [fixnum(offset)])
+                    }
+                    &IndexedChoiceInstruction::DefaultRetry(offset) => {
+                        functor!(atom!("default_retry"), [fixnum(offset)])
+                    }
                 }
             }
         }
@@ -1323,6 +1335,10 @@ fn generate_instruction_preface() -> TokenStream {
                         let rt_stub = reg_type_into_functor(r);
                         functor!(atom!("cut"), [str(h, 0)], [rt_stub])
                     }
+                    &Instruction::CutPrev(r) => {
+                        let rt_stub = reg_type_into_functor(r);
+                        functor!(atom!("cut_prev"), [str(h, 0)], [rt_stub])
+                    }
                     &Instruction::GetLevel(r) => {
                         let rt_stub = reg_type_into_functor(r);
                         functor!(atom!("get_level"), [str(h, 0)], [rt_stub])
@@ -1425,30 +1441,9 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::ATan(ref at, t) => {
                         arith_instr_unary_functor(h, atom!("atan"), arena, at, t)
                     }
-                    &Instruction::ACosh(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("acosh"), arena, at, t)
-                    }
-                    &Instruction::ASinh(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("asinh"), arena, at, t)
-                    }
-                    &Instruction::ATanh(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("atanh"), arena, at, t)
-                    }
-                    &Instruction::Cosh(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("cosh"), arena, at, t)
-                    }
-                    &Instruction::Sinh(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("sinh"), arena, at, t)
-                    }
-                    &Instruction::Tanh(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("tanh"), arena, at, t)
-                    }
                     &Instruction::Sqrt(ref at, t) => {
                         arith_instr_unary_functor(h, atom!("sqrt"), arena, at, t)
                     }
-                    &Instruction::Log10(ref at, t) => {
-                        arith_instr_unary_functor(h, atom!("log10"), arena, at, t)
-                    }
                     &Instruction::Abs(ref at, t) => {
                         arith_instr_unary_functor(h, atom!("abs"), arena, at, t)
                     }
@@ -1553,7 +1548,8 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::CallFunctor |
                     &Instruction::CallGround |
                     &Instruction::CallKeySort |
-                    &Instruction::CallSort => {
+                    &Instruction::CallSort |
+                    &Instruction::CallGetNumber(_) => {
                         let (name, arity) = self.to_name_and_arity();
                         functor!(atom!("call"), [atom(name), fixnum(arity)])
                     }
@@ -1578,7 +1574,8 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::ExecuteGround |
                     &Instruction::ExecuteIs(..) |
                     &Instruction::ExecuteKeySort |
-                    &Instruction::ExecuteSort => {
+                    &Instruction::ExecuteSort |
+                    &Instruction::ExecuteGetNumber(_) => {
                         let (name, arity) = self.to_name_and_arity();
                         functor!(atom!("execute"), [atom(name), fixnum(arity)])
                     }
@@ -1603,7 +1600,8 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::DefaultCallGround |
                     &Instruction::DefaultCallIs(..) |
                     &Instruction::DefaultCallKeySort |
-                    &Instruction::DefaultCallSort => {
+                    &Instruction::DefaultCallSort |
+                    &Instruction::DefaultCallGetNumber(_) => {
                         let (name, arity) = self.to_name_and_arity();
                         functor!(atom!("call_default"), [atom(name), fixnum(arity)])
                     }
@@ -1628,33 +1626,36 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::DefaultExecuteGround |
                     &Instruction::DefaultExecuteIs(..) |
                     &Instruction::DefaultExecuteKeySort |
-                    &Instruction::DefaultExecuteSort => {
+                    &Instruction::DefaultExecuteSort |
+                    &Instruction::DefaultExecuteGetNumber(_) => {
                         let (name, arity) = self.to_name_and_arity();
                         functor!(atom!("execute_default"), [atom(name), fixnum(arity)])
                     }
-                    &Instruction::CallIsAtom(_) |
-                    &Instruction::CallIsAtomic(_) |
-                    &Instruction::CallIsCompound(_) |
-                    &Instruction::CallIsInteger(_) |
-                    &Instruction::CallIsNumber(_) |
-                    &Instruction::CallIsRational(_) |
-                    &Instruction::CallIsFloat(_) |
-                    &Instruction::CallIsNonVar(_) |
-                    &Instruction::CallIsVar(_) => {
+                    &Instruction::CallIsAtom(r) |
+                    &Instruction::CallIsAtomic(r) |
+                    &Instruction::CallIsCompound(r) |
+                    &Instruction::CallIsInteger(r) |
+                    &Instruction::CallIsNumber(r) |
+                    &Instruction::CallIsRational(r) |
+                    &Instruction::CallIsFloat(r) |
+                    &Instruction::CallIsNonVar(r) |
+                    &Instruction::CallIsVar(r) => {
                         let (name, arity) = self.to_name_and_arity();
-                        functor!(atom!("call"), [atom(name), fixnum(arity)])
+                        let rt_stub = reg_type_into_functor(r);
+                        functor!(atom!("call"), [atom(name), fixnum(arity), str(h, 0)], [rt_stub])
                     }
-                    &Instruction::ExecuteIsAtom(_) |
-                    &Instruction::ExecuteIsAtomic(_) |
-                    &Instruction::ExecuteIsCompound(_) |
-                    &Instruction::ExecuteIsInteger(_) |
-                    &Instruction::ExecuteIsNumber(_) |
-                    &Instruction::ExecuteIsRational(_) |
-                    &Instruction::ExecuteIsFloat(_) |
-                    &Instruction::ExecuteIsNonVar(_) |
-                    &Instruction::ExecuteIsVar(_) => {
+                    &Instruction::ExecuteIsAtom(r) |
+                    &Instruction::ExecuteIsAtomic(r) |
+                    &Instruction::ExecuteIsCompound(r) |
+                    &Instruction::ExecuteIsInteger(r) |
+                    &Instruction::ExecuteIsNumber(r) |
+                    &Instruction::ExecuteIsRational(r) |
+                    &Instruction::ExecuteIsFloat(r) |
+                    &Instruction::ExecuteIsNonVar(r) |
+                    &Instruction::ExecuteIsVar(r) => {
                         let (name, arity) = self.to_name_and_arity();
-                        functor!(atom!("execute"), [atom(name), fixnum(arity)])
+                        let rt_stub = reg_type_into_functor(r);
+                        functor!(atom!("execute"), [atom(name), fixnum(arity), str(h, 0)], [rt_stub])
                     }
                     //
                     &Instruction::CallAtomChars |
@@ -1683,7 +1684,7 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::CallMakeDirectoryPath |
                     &Instruction::CallDeleteFile |
                     &Instruction::CallRenameFile |
-		            &Instruction::CallFileCopy |
+                    &Instruction::CallFileCopy |
                     &Instruction::CallWorkingDirectory |
                     &Instruction::CallDeleteDirectory |
                     &Instruction::CallPathCanonical |
@@ -1701,6 +1702,7 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::CallUnattributedVar |
                     &Instruction::CallGetDBRefs |
                     &Instruction::CallKeySortWithConstantVarOrdering |
+                    &Instruction::CallInferenceLimitExceeded |
                     &Instruction::CallFetchGlobalVar |
                     &Instruction::CallFirstStream |
                     &Instruction::CallFlushOutput |
@@ -1777,9 +1779,9 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::CallHttpListen |
                     &Instruction::CallHttpAccept |
                     &Instruction::CallHttpAnswer |
-		            &Instruction::CallLoadForeignLib |
-		            &Instruction::CallForeignCall |
-		            &Instruction::CallDefineForeignStruct |
+                    &Instruction::CallLoadForeignLib |
+                    &Instruction::CallForeignCall |
+                    &Instruction::CallDefineForeignStruct |
                     &Instruction::CallPredicateDefined |
                     &Instruction::CallStripModule |
                     &Instruction::CallCurrentTime |
@@ -1822,13 +1824,7 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::CallCryptoDataHash |
                     &Instruction::CallCryptoDataHKDF |
                     &Instruction::CallCryptoPasswordHash |
-                    &Instruction::CallCryptoDataEncrypt |
-                    &Instruction::CallCryptoDataDecrypt |
                     &Instruction::CallCryptoCurveScalarMult |
-                    &Instruction::CallEd25519Sign |
-                    &Instruction::CallEd25519Verify |
-                    &Instruction::CallEd25519NewKeyPair |
-                    &Instruction::CallEd25519KeyPairPublicKey |
                     &Instruction::CallCurve25519ScalarMult |
                     &Instruction::CallFirstNonOctet |
                     &Instruction::CallLoadHTML |
@@ -1885,6 +1881,17 @@ fn generate_instruction_preface() -> TokenStream {
                         functor!(atom!("call"), [atom(name), fixnum(arity)])
                     }
                     //
+                    #[cfg(feature = "crypto-full")]
+                    &Instruction::CallCryptoDataEncrypt |
+                    &Instruction::CallCryptoDataDecrypt |
+                    &Instruction::CallEd25519Sign |
+                    &Instruction::CallEd25519Verify |
+                    &Instruction::CallEd25519NewKeyPair |
+                    &Instruction::CallEd25519KeyPairPublicKey => {
+                        let (name, arity) = self.to_name_and_arity();
+                        functor!(atom!("call"), [atom(name), fixnum(arity)])
+                    }
+                    //
                     &Instruction::ExecuteAtomChars |
                     &Instruction::ExecuteAtomCodes |
                     &Instruction::ExecuteAtomLength |
@@ -1911,7 +1918,7 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::ExecuteMakeDirectoryPath |
                     &Instruction::ExecuteDeleteFile |
                     &Instruction::ExecuteRenameFile |
-		            &Instruction::ExecuteFileCopy |
+                    &Instruction::ExecuteFileCopy |
                     &Instruction::ExecuteWorkingDirectory |
                     &Instruction::ExecuteDeleteDirectory |
                     &Instruction::ExecutePathCanonical |
@@ -1929,6 +1936,7 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::ExecuteUnattributedVar |
                     &Instruction::ExecuteGetDBRefs |
                     &Instruction::ExecuteKeySortWithConstantVarOrdering |
+                    &Instruction::ExecuteInferenceLimitExceeded |
                     &Instruction::ExecuteFetchGlobalVar |
                     &Instruction::ExecuteFirstStream |
                     &Instruction::ExecuteFlushOutput |
@@ -2005,9 +2013,9 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::ExecuteHttpListen |
                     &Instruction::ExecuteHttpAccept |
                     &Instruction::ExecuteHttpAnswer |
-		            &Instruction::ExecuteLoadForeignLib |
-		            &Instruction::ExecuteForeignCall |
-		            &Instruction::ExecuteDefineForeignStruct |
+                    &Instruction::ExecuteLoadForeignLib |
+                    &Instruction::ExecuteForeignCall |
+                    &Instruction::ExecuteDefineForeignStruct |
                     &Instruction::ExecutePredicateDefined |
                     &Instruction::ExecuteStripModule |
                     &Instruction::ExecuteCurrentTime |
@@ -2050,13 +2058,7 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::ExecuteCryptoDataHash |
                     &Instruction::ExecuteCryptoDataHKDF |
                     &Instruction::ExecuteCryptoPasswordHash |
-                    &Instruction::ExecuteCryptoDataEncrypt |
-                    &Instruction::ExecuteCryptoDataDecrypt |
                     &Instruction::ExecuteCryptoCurveScalarMult |
-                    &Instruction::ExecuteEd25519Sign |
-                    &Instruction::ExecuteEd25519Verify |
-                    &Instruction::ExecuteEd25519NewKeyPair |
-                    &Instruction::ExecuteEd25519KeyPairPublicKey |
                     &Instruction::ExecuteCurve25519ScalarMult |
                     &Instruction::ExecuteFirstNonOctet |
                     &Instruction::ExecuteLoadHTML |
@@ -2113,6 +2115,17 @@ fn generate_instruction_preface() -> TokenStream {
                         functor!(atom!("execute"), [atom(name), fixnum(arity)])
                     }
                     //
+                    #[cfg(feature = "crypto-full")]
+                    &Instruction::ExecuteCryptoDataEncrypt |
+                    &Instruction::ExecuteCryptoDataDecrypt |
+                    &Instruction::ExecuteEd25519Sign |
+                    &Instruction::ExecuteEd25519Verify |
+                    &Instruction::ExecuteEd25519NewKeyPair |
+                    &Instruction::ExecuteEd25519KeyPairPublicKey => {
+                        let (name, arity) = self.to_name_and_arity();
+                        functor!(atom!("execute"), [atom(name), fixnum(arity)])
+                    }
+                    //
                     &Instruction::Deallocate => {
                         functor!(atom!("deallocate"))
                     }
@@ -2284,7 +2297,8 @@ pub fn generate_instructions_rs() -> TokenStream {
 
     instr_data.generate_instruction_enum_loop(input);
 
-    let instr_variants: Vec<_> = instr_data.instr_variants
+    let instr_variants: Vec<_> = instr_data
+        .instr_variants
         .iter()
         .cloned()
         .map(|(_, _, _, variant)| variant)
@@ -2323,7 +2337,8 @@ pub fn generate_instructions_rs() -> TokenStream {
     for (name, arity, variant) in instr_data.compare_number_variants {
         let ident = variant.ident.clone();
 
-        let variant_fields: Vec<_> = variant.fields
+        let variant_fields: Vec<_> = variant
+            .fields
             .into_iter()
             .map(|field| {
                 let ty = field.ty;
@@ -2362,29 +2377,23 @@ pub fn generate_instructions_rs() -> TokenStream {
         let ident = variant.ident;
         let instr_ident = format_ident!("Call{}", ident);
 
-        let placeholder_ids: Vec<_> = (0 .. variant_fields.len())
+        let placeholder_ids: Vec<_> = (0..variant_fields.len())
             .map(|n| format_ident!("f_{}", n))
             .collect();
 
-        clause_type_to_instr_arms.push(
-            quote! {
-                ClauseType::Inlined(
-                    InlinedClauseType::CompareNumber(CompareNumber::#ident(#(#placeholder_ids),*))
-                ) => Instruction::#instr_ident(#(*#placeholder_ids),*)
-            }
-        );
+        clause_type_to_instr_arms.push(quote! {
+            ClauseType::Inlined(
+                InlinedClauseType::CompareNumber(CompareNumber::#ident(#(#placeholder_ids),*))
+            ) => Instruction::#instr_ident(#(*#placeholder_ids),*)
+        });
 
-        is_inbuilt_arms.push(
-            quote! {
-                (atom!(#name), #arity) => true
-            }
-        );
+        is_inbuilt_arms.push(quote! {
+            (atom!(#name), #arity) => true
+        });
 
-        is_inlined_arms.push(
-            quote! {
-                (atom!(#name), #arity) => true
-            }
-        );
+        is_inlined_arms.push(quote! {
+            (atom!(#name), #arity) => true
+        });
     }
 
     for (name, arity, variant) in instr_data.compare_term_variants {
@@ -2396,36 +2405,31 @@ pub fn generate_instructions_rs() -> TokenStream {
             )
         });
 
-        clause_type_name_arms.push(
-            quote! {
-                ClauseType::BuiltIn(
-                    BuiltInClauseType::CompareTerm(CompareTerm::#ident)
-                ) => atom!(#name)
-            }
-        );
+        clause_type_name_arms.push(quote! {
+            ClauseType::BuiltIn(
+                BuiltInClauseType::CompareTerm(CompareTerm::#ident)
+            ) => atom!(#name)
+        });
 
         let ident = variant.ident;
         let instr_ident = format_ident!("Call{}", ident);
 
-        clause_type_to_instr_arms.push(
-            quote! {
-                ClauseType::BuiltIn(
-                    BuiltInClauseType::CompareTerm(CompareTerm::#ident)
-                ) => Instruction::#instr_ident
-            }
-        );
+        clause_type_to_instr_arms.push(quote! {
+            ClauseType::BuiltIn(
+                BuiltInClauseType::CompareTerm(CompareTerm::#ident)
+            ) => Instruction::#instr_ident
+        });
 
-        is_inbuilt_arms.push(
-            quote! {
-                (atom!(#name), #arity) => true
-            }
-        );
+        is_inbuilt_arms.push(quote! {
+            (atom!(#name), #arity) => true
+        });
     }
 
     for (name, arity, variant) in instr_data.builtin_type_variants {
         let ident = variant.ident.clone();
 
-        let variant_fields: Vec<_> = variant.fields
+        let variant_fields: Vec<_> = variant
+            .fields
             .into_iter()
             .map(|field| {
                 let ty = field.ty;
@@ -2464,7 +2468,7 @@ pub fn generate_instructions_rs() -> TokenStream {
         let ident = variant.ident;
         let instr_ident = format_ident!("Call{}", ident);
 
-        let placeholder_ids: Vec<_> = (0 .. variant_fields.len())
+        let placeholder_ids: Vec<_> = (0..variant_fields.len())
             .map(|n| format_ident!("f_{}", n))
             .collect();
 
@@ -2482,17 +2486,16 @@ pub fn generate_instructions_rs() -> TokenStream {
             }
         });
 
-        is_inbuilt_arms.push(
-            quote! {
-                (atom!(#name), #arity) => true
-            }
-        );
+        is_inbuilt_arms.push(quote! {
+            (atom!(#name), #arity) => true
+        });
     }
 
     for (name, arity, variant) in instr_data.inlined_type_variants {
         let ident = variant.ident.clone();
 
-        let variant_fields: Vec<_> = variant.fields
+        let variant_fields: Vec<_> = variant
+            .fields
             .into_iter()
             .map(|field| {
                 if field.ty.type_id() == TypeId::of::<usize>() {
@@ -2535,35 +2538,30 @@ pub fn generate_instructions_rs() -> TokenStream {
         let ident = variant.ident;
         let instr_ident = format_ident!("Call{}", ident);
 
-        let placeholder_ids: Vec<_> = (0 .. variant_fields.len())
+        let placeholder_ids: Vec<_> = (0..variant_fields.len())
             .map(|n| format_ident!("f_{}", n))
             .collect();
 
-        clause_type_to_instr_arms.push(
-            quote! {
-                ClauseType::Inlined(
-                    InlinedClauseType::#ident(#(#placeholder_ids),*)
-                ) => Instruction::#instr_ident(*#(#placeholder_ids),*)
-            }
-        );
+        clause_type_to_instr_arms.push(quote! {
+            ClauseType::Inlined(
+                InlinedClauseType::#ident(#(#placeholder_ids),*)
+            ) => Instruction::#instr_ident(*#(#placeholder_ids),*)
+        });
 
-        is_inbuilt_arms.push(
-            quote! {
-                (atom!(#name), #arity) => true
-            }
-        );
+        is_inbuilt_arms.push(quote! {
+            (atom!(#name), #arity) => true
+        });
 
-        is_inlined_arms.push(
-            quote! {
-                (atom!(#name), #arity) => true
-            }
-        );
+        is_inlined_arms.push(quote! {
+            (atom!(#name), #arity) => true
+        });
     }
 
     for (name, arity, variant) in instr_data.system_clause_type_variants {
         let ident = variant.ident.clone();
 
-        let variant_fields: Vec<_> = variant.fields
+        let variant_fields: Vec<_> = variant
+            .fields
             .into_iter()
             .map(|field| {
                 if field.ty == parse_quote! { usize } {
@@ -2631,7 +2629,7 @@ pub fn generate_instructions_rs() -> TokenStream {
             ident.clone()
         };
 
-        let placeholder_ids: Vec<_> = (0 .. variant_fields.len())
+        let placeholder_ids: Vec<_> = (0..variant_fields.len())
             .map(|n| format_ident!("f_{}", n))
             .collect();
 
@@ -2649,23 +2647,22 @@ pub fn generate_instructions_rs() -> TokenStream {
             }
         });
 
-        is_inbuilt_arms.push(
-            if let Arity::Ident("arity") = &arity {
-                quote! {
-                    (atom!(#name), _arity) => true
-                }
-            } else {
-                quote! {
-                    (atom!(#name), #arity) => true
-                }
+        is_inbuilt_arms.push(if let Arity::Ident("arity") = &arity {
+            quote! {
+                (atom!(#name), _arity) => true
             }
-        );
+        } else {
+            quote! {
+                (atom!(#name), #arity) => true
+            }
+        });
     }
 
     for (name, arity, variant) in instr_data.repl_code_ptr_variants {
         let ident = variant.ident.clone();
 
-        let variant_fields: Vec<_> = variant.fields
+        let variant_fields: Vec<_> = variant
+            .fields
             .into_iter()
             .map(|field| {
                 if field.ty.type_id() == TypeId::of::<usize>() {
@@ -2708,7 +2705,7 @@ pub fn generate_instructions_rs() -> TokenStream {
         let ident = variant.ident;
         let instr_ident = format_ident!("Call{}", ident);
 
-        let placeholder_ids: Vec<_> = (0 .. variant_fields.len())
+        let placeholder_ids: Vec<_> = (0..variant_fields.len())
             .map(|n| format_ident!("f_{}", n))
             .collect();
 
@@ -2726,11 +2723,9 @@ pub fn generate_instructions_rs() -> TokenStream {
             }
         });
 
-        is_inbuilt_arms.push(
-            quote! {
-                (atom!(#name), #arity) => true
-            }
-        );
+        is_inbuilt_arms.push(quote! {
+            (atom!(#name), #arity) => true
+        });
     }
 
     for (name, arity, variant) in instr_data.clause_type_variants {
@@ -2752,7 +2747,8 @@ pub fn generate_instructions_rs() -> TokenStream {
             continue;
         }
 
-        let variant_fields: Vec<_> = variant.fields
+        let variant_fields: Vec<_> = variant
+            .fields
             .into_iter()
             .map(|field| {
                 if field.ty == parse_quote! { usize } {
@@ -2786,7 +2782,7 @@ pub fn generate_instructions_rs() -> TokenStream {
 
         let ident = variant.ident;
 
-        let placeholder_ids: Vec<_> = (0 .. variant_fields.len())
+        let placeholder_ids: Vec<_> = (0..variant_fields.len())
             .map(|n| format_ident!("f_{}", n))
             .collect();
 
@@ -2801,14 +2797,13 @@ pub fn generate_instructions_rs() -> TokenStream {
             }
         });
 
-        is_inbuilt_arms.push(
-            quote! {
-                (atom!(#name), _arity) => true
-            }
-        );
+        is_inbuilt_arms.push(quote! {
+            (atom!(#name), _arity) => true
+        });
     }
 
-    let to_execute_arms: Vec<_> = instr_data.instr_variants
+    let to_execute_arms: Vec<_> = instr_data
+        .instr_variants
         .iter()
         .cloned()
         .filter_map(|(_, _, _, variant)| {
@@ -2821,12 +2816,11 @@ pub fn generate_instructions_rs() -> TokenStream {
                 0
             };
 
-            let placeholder_ids: Vec<_> = (0 .. enum_arity)
-                .map(|n| format_ident!("f_{}", n))
-                .collect();
+            let placeholder_ids: Vec<_> =
+                (0..enum_arity).map(|n| format_ident!("f_{}", n)).collect();
 
             if variant_string.starts_with("Call") {
-                let execute_ident = format_ident!("Execute{}", variant_string["Call".len() ..]);
+                let execute_ident = format_ident!("Execute{}", variant_string["Call".len()..]);
 
                 Some(if enum_arity == 0 {
                     quote! {
@@ -2841,7 +2835,7 @@ pub fn generate_instructions_rs() -> TokenStream {
                 })
             } else if variant_string.starts_with("DefaultCall") {
                 let execute_ident =
-                    format_ident!("DefaultExecute{}", variant_string["DefaultCall".len() ..]);
+                    format_ident!("DefaultExecute{}", variant_string["DefaultCall".len()..]);
 
                 Some(if enum_arity == 0 {
                     quote! {
@@ -2860,7 +2854,8 @@ pub fn generate_instructions_rs() -> TokenStream {
         })
         .collect();
 
-    let is_execute_arms: Vec<_> = instr_data.instr_variants
+    let is_execute_arms: Vec<_> = instr_data
+        .instr_variants
         .iter()
         .cloned()
         .filter_map(|(_, _, _, variant)| {
@@ -2903,7 +2898,8 @@ pub fn generate_instructions_rs() -> TokenStream {
         })
         .collect();
 
-    let to_default_arms: Vec<_> = instr_data.instr_variants
+    let to_default_arms: Vec<_> = instr_data
+        .instr_variants
         .iter()
         .cloned()
         .filter_map(|(_, _, countable_inference, variant)| {
@@ -2920,9 +2916,8 @@ pub fn generate_instructions_rs() -> TokenStream {
                     0
                 };
 
-                let placeholder_ids: Vec<_> = (0 .. enum_arity)
-                    .map(|n| format_ident!("f_{}", n))
-                    .collect();
+                let placeholder_ids: Vec<_> =
+                    (0..enum_arity).map(|n| format_ident!("f_{}", n)).collect();
 
                 Some(if enum_arity == 0 {
                     quote! {
@@ -2941,7 +2936,8 @@ pub fn generate_instructions_rs() -> TokenStream {
         })
         .collect();
 
-    let control_flow_arms: Vec<_> = instr_data.instr_variants
+    let control_flow_arms: Vec<_> = instr_data
+        .instr_variants
         .iter()
         .cloned()
         .filter_map(|(_, _, _, variant)| {
@@ -2969,7 +2965,8 @@ pub fn generate_instructions_rs() -> TokenStream {
         })
         .collect();
 
-    let instr_macro_arms: Vec<_> = instr_data.instr_variants
+    let instr_macro_arms: Vec<_> = instr_data
+        .instr_variants
         .iter()
         .rev() // produce default, execute & default & execute cases first.
         .cloned()
@@ -2978,7 +2975,7 @@ pub fn generate_instructions_rs() -> TokenStream {
             let variant_string = variant.ident.to_string();
             let arity = match arity {
                 Arity::Static(arity) => arity,
-                _ => 1
+                _ => 1,
             };
 
             Some(if variant_string.starts_with("Execute") {
@@ -3055,9 +3052,10 @@ pub fn generate_instructions_rs() -> TokenStream {
         })
         .collect();
 
-    let name_and_arity_arms: Vec<_> = instr_data.instr_variants
+    let name_and_arity_arms: Vec<_> = instr_data
+        .instr_variants
         .into_iter()
-        .map(|(name,arity,_,variant)| {
+        .map(|(name, arity, _, variant)| {
             let ident = &variant.ident;
 
             let enum_arity = if let Fields::Unnamed(fields) = &variant.fields {
@@ -3287,8 +3285,10 @@ pub fn generate_instructions_rs() -> TokenStream {
 fn is_callable(id: &Ident) -> bool {
     let id = id.to_string();
 
-    id.starts_with("Call") || id.starts_with("Execute") || id.starts_with("DefaultCall") ||
-        id.starts_with("DefaultExecute")
+    id.starts_with("Call")
+        || id.starts_with("Execute")
+        || id.starts_with("DefaultCall")
+        || id.starts_with("DefaultExecute")
 }
 
 fn is_non_default_callable(id: &Ident) -> bool {
@@ -3309,7 +3309,8 @@ fn create_instr_variant(id: Ident, mut variant: Variant) -> Variant {
 }
 
 fn prop_from_ident<DiscriminantT>(id: &Ident, key: &'static str) -> &'static str
-   where DiscriminantT: FromStr + strum::EnumProperty + std::fmt::Debug
+where
+    DiscriminantT: FromStr + strum::EnumProperty + std::fmt::Debug,
 {
     let disc = match DiscriminantT::from_str(id.to_string().as_str()) {
         Ok(disc) => disc,
@@ -3329,7 +3330,7 @@ fn prop_from_ident<DiscriminantT>(id: &Ident, key: &'static str) -> &'static str
 #[derive(Clone, Copy)]
 enum Arity {
     Static(usize),
-    Ident(&'static str)
+    Ident(&'static str),
 }
 
 impl From<&'static str> for Arity {
@@ -3421,9 +3422,13 @@ impl InstructionData {
 
             (name, arity, CountableInference::NotCounted)
         } else if id == "InstructionTemplate" {
-            ( prop_from_ident::<InstructionTemplateDiscriminants>(&variant.ident, "Name"),
-              Arity::from(prop_from_ident::<InstructionTemplateDiscriminants>(&variant.ident, "Arity")),
-              CountableInference::NotCounted
+            (
+                prop_from_ident::<InstructionTemplateDiscriminants>(&variant.ident, "Name"),
+                Arity::from(prop_from_ident::<InstructionTemplateDiscriminants>(
+                    &variant.ident,
+                    "Arity",
+                )),
+                CountableInference::NotCounted,
             )
         } else if id == "ClauseType" {
             let (name, arity) = add_discriminant_data::<ClauseTypeDiscriminants>(
@@ -3440,19 +3445,16 @@ impl InstructionData {
         let v_string = variant.ident.to_string();
 
         let v_ident = if v_string.starts_with("Call") {
-            format_ident!("{}", v_string["Call".len() ..])
+            format_ident!("{}", v_string["Call".len()..])
         } else {
             variant.ident.clone()
         };
 
-        let generated_variant = create_instr_variant(
-            format_ident!("{}{}", prefix, v_ident),
-            variant.clone(),
-        );
+        let generated_variant =
+            create_instr_variant(format_ident!("{}{}", prefix, v_ident), variant.clone());
 
-        self.instr_variants.push(
-            (name, arity, countable_inference, generated_variant)
-        );
+        self.instr_variants
+            .push((name, arity, countable_inference, generated_variant));
     }
 
     fn generate_instruction_enum_loop(&mut self, input: syn::DeriveInput) {
@@ -3474,10 +3476,10 @@ impl InstructionData {
                 self.label_variant(&input.ident, "Call", variant.clone());
                 self.label_variant(&input.ident, "Execute", variant.clone());
 
-                if input.ident == "BuiltInClauseType" ||
-                    input.ident == "CompareNumber" ||
-                    input.ident == "CompareTerm" ||
-                    input.ident == "ClauseType"
+                if input.ident == "BuiltInClauseType"
+                    || input.ident == "CompareNumber"
+                    || input.ident == "CompareTerm"
+                    || input.ident == "ClauseType"
                 {
                     self.label_variant(&input.ident, "DefaultCall", variant.clone());
                     self.label_variant(&input.ident, "DefaultExecute", variant);

build/static_string_indexing.rs

@@ -1,7 +1,7 @@
 use proc_macro2::TokenStream;
-use syn::*;
 use syn::parse::*;
 use syn::visit::*;
+use syn::*;
 
 use indexmap::IndexSet;
 
@@ -11,7 +11,9 @@ struct StaticStrVisitor {
 
 impl StaticStrVisitor {
     fn new() -> Self {
-        Self { static_strs: IndexSet::new() }
+        Self {
+            static_strs: IndexSet::new(),
+        }
     }
 }
 

src/arena.rs

@@ -4,25 +4,31 @@ use crate::machine::loader::LiveLoadState;
 use crate::machine::machine_indices::*;
 use crate::machine::streams::*;
 use crate::raw_block::*;
+use crate::rcu::Rcu;
+use crate::rcu::RcuRef;
 use crate::read::*;
 
-use ordered_float::OrderedFloat;
 use crate::parser::dashu::{Integer, Rational};
+use ordered_float::OrderedFloat;
 
 use std::alloc;
+use std::cell::UnsafeCell;
 use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::mem;
 use std::net::TcpListener;
 use std::ops::{Deref, DerefMut};
 use std::ptr;
+use std::sync::RwLock;
 
 #[macro_export]
 macro_rules! arena_alloc {
     ($e:expr, $arena:expr) => {{
         let result = $e;
         #[allow(unused_unsafe)]
-        unsafe { ArenaAllocated::alloc($arena, result) }
+        unsafe {
+            ArenaAllocated::alloc($arena, result)
+        }
     }};
 }
 
@@ -31,24 +37,36 @@ macro_rules! float_alloc {
     ($e:expr, $arena:expr) => {{
         let result = $e;
         #[allow(unused_unsafe)]
-        unsafe { $arena.f64_tbl.build_with(result) }
+        unsafe {
+            $arena.f64_tbl.build_with(result).as_ptr()
+        }
     }};
 }
 
-#[cfg(test)]
-use std::cell::RefCell;
+use std::sync::Arc;
+use std::sync::Mutex;
+use std::sync::Weak;
 
 const F64_TABLE_INIT_SIZE: usize = 1 << 16;
 const F64_TABLE_ALIGN: usize = 8;
 
-#[cfg(test)]
-thread_local! {
-    static F64_TABLE_BUF_BASE: RefCell<*const u8> = RefCell::new(ptr::null_mut());
+#[inline(always)]
+fn global_f64table() -> &'static RwLock<Weak<F64Table>> {
+    #[cfg(feature = "rust_beta_channel")]
+    {
+        // const Weak::new will be stabilized in 1.73 which is currently in beta,
+        // till then we need a OnceLock for initialization
+        static GLOBAL_ATOM_TABLE: RwLock<Weak<F64Table>> = RwLock::const_new(Weak::new());
+        &GLOBAL_ATOM_TABLE
+    }
+    #[cfg(not(feature = "rust_beta_channel"))]
+    {
+        use std::sync::OnceLock;
+        static GLOBAL_ATOM_TABLE: OnceLock<RwLock<Weak<F64Table>>> = OnceLock::new();
+        GLOBAL_ATOM_TABLE.get_or_init(|| RwLock::new(Weak::new()))
+    }
 }
 
-#[cfg(not(test))]
-static mut F64_TABLE_BUF_BASE: *const u8 = ptr::null_mut();
-
 impl RawBlockTraits for F64Table {
     #[inline]
     fn init_size() -> usize {
@@ -63,69 +81,87 @@ impl RawBlockTraits for F64Table {
 
 #[derive(Debug)]
 pub struct F64Table {
-    block: RawBlock<F64Table>,
-}
-
-impl Drop for F64Table {
-    fn drop(&mut self) {
-        self.block.deallocate();
-    }
-}
-
-#[cfg(test)]
-fn set_f64_tbl_buf_base(ptr: *const u8) {
-    F64_TABLE_BUF_BASE.with(|f64_table_buf_base| {
-        *f64_table_buf_base.borrow_mut() = ptr;
-    });
-}
-
-#[cfg(test)]
-pub(crate) fn get_f64_tbl_buf_base() -> *const u8 {
-    F64_TABLE_BUF_BASE.with(|f64_table_buf_base| *f64_table_buf_base.borrow())
-}
-
-#[cfg(not(test))]
-fn set_f64_tbl_buf_base(ptr: *const u8) {
-    unsafe {
-        F64_TABLE_BUF_BASE = ptr;
-    }
-}
-
-#[cfg(not(test))]
-pub(crate) fn get_f64_tbl_buf_base() -> *const u8 {
-    unsafe { F64_TABLE_BUF_BASE }
+    block: Rcu<RawBlock<F64Table>>,
+    update: Mutex<()>,
 }
 
 #[inline(always)]
-pub fn lookup_float(offset: usize) -> *mut OrderedFloat<f64> {
-    let base = get_f64_tbl_buf_base() as usize;
-    (base + offset) as *mut _
+pub fn lookup_float(
+    offset: F64Offset,
+) -> RcuRef<RawBlock<F64Table>, UnsafeCell<OrderedFloat<f64>>> {
+    let f64table = global_f64table()
+        .read()
+	.unwrap()
+        .upgrade()
+        .expect("We should only be looking up floats while there is a float table");
+
+    RcuRef::try_map(f64table.block.active_epoch(), |raw_block| unsafe {
+        raw_block
+            .base
+            .offset(offset.0 as isize)
+            .cast_mut()
+            .cast::<UnsafeCell<OrderedFloat<f64>>>()
+            .as_ref()
+    })
+    .expect("The offset should result in a non-null pointer")
 }
 
 impl F64Table {
     #[inline]
-    pub fn new() -> Self {
-        let table = Self { block: RawBlock::new() };
-        set_f64_tbl_buf_base(table.block.base);
-        table
+    pub fn new() -> Arc<Self> {
+        let upgraded = global_f64table().read().unwrap().upgrade();
+        // don't inline upgraded, otherwise temporary will be dropped too late in case of None
+        if let Some(atom_table) = upgraded {
+            atom_table
+        } else {
+            let mut guard = global_f64table().write().unwrap();
+            // try to upgrade again in case we lost the race on the write lock
+            if let Some(atom_table) = guard.upgrade() {
+                atom_table
+            } else {
+                let atom_table = Arc::new(Self {
+                    block: Rcu::new(RawBlock::new()),
+                    update: Mutex::new(()),
+                });
+                *guard = Arc::downgrade(&atom_table);
+                atom_table
+            }
+        }
     }
 
-    pub unsafe fn build_with(&mut self, value: f64) -> F64Ptr {
+    pub unsafe fn build_with(&self, value: f64) -> F64Offset {
+        let update_guard = self.update.lock();
+
+        // we don't have an index table for lookups as AtomTable does so
+        // just get the epoch after we take the upgrade lock
+        let mut block_epoch = self.block.active_epoch();
+
         let mut ptr;
 
         loop {
-            ptr = self.block.alloc(mem::size_of::<f64>());
+            ptr = block_epoch.alloc(mem::size_of::<f64>());
 
             if ptr.is_null() {
-                self.block.grow();
-                set_f64_tbl_buf_base(self.block.base);
+                let new_block = block_epoch.grow_new().unwrap();
+                self.block.replace(new_block);
+                block_epoch = self.block.active_epoch();
             } else {
                 break;
             }
         }
 
         ptr::write(ptr as *mut OrderedFloat<f64>, OrderedFloat(value));
-        F64Ptr(ptr::NonNull::new_unchecked(ptr as *mut _))
+
+        let float = F64Offset {
+            0: ptr as usize - block_epoch.base as usize,
+        };
+
+        // atometable would have to update the index table at this point
+
+        // expicit drop to ensure we don't accidentally drop it early
+        drop(update_guard);
+
+        float
     }
 }
 
@@ -134,14 +170,13 @@ impl F64Table {
 pub enum ArenaHeaderTag {
     Integer = 0b10,
     Rational = 0b11,
-    OssifiedOpDir = 0b0000100,
     LiveLoadState = 0b0001000,
     InactiveLoadState = 0b1011000,
     InputFileStream = 0b10000,
     OutputFileStream = 0b10100,
     NamedTcpStream = 0b011100,
     NamedTlsStream = 0b100000,
-    HttpReadStream =  0b100001,
+    HttpReadStream = 0b100001,
     HttpWriteStream = 0b100010,
     ReadlineStream = 0b110000,
     StaticStringStream = 0b110100,
@@ -276,7 +311,9 @@ impl<T: ?Sized + ArenaAllocated> TypedArenaPtr<T> {
 
     #[inline]
     pub fn set_tag(&mut self, tag: ArenaHeaderTag) {
-        unsafe { (*self.header_ptr_mut()).set_tag(tag); }
+        unsafe {
+            (*self.header_ptr_mut()).set_tag(tag);
+        }
     }
 
     #[inline]
@@ -313,10 +350,10 @@ pub trait ArenaAllocated: Sized {
     unsafe fn alloc(arena: &mut Arena, value: Self) -> Self::PtrToAllocated {
         let size = value.size() + mem::size_of::<AllocSlab>();
 
-        #[cfg(target_pointer_width="32")]
+        #[cfg(target_pointer_width = "32")]
         let align = mem::align_of::<AllocSlab>() * 2;
 
-        #[cfg(target_pointer_width="64")]
+        #[cfg(target_pointer_width = "64")]
         let align = mem::align_of::<AllocSlab>();
         let layout = alloc::Layout::from_size_align_unchecked(size, align);
 
@@ -334,12 +371,18 @@ pub trait ArenaAllocated: Sized {
     }
 }
 
-#[derive(Copy, Clone, Debug)]
-pub struct F64Ptr(pub ptr::NonNull<OrderedFloat<f64>>);
+#[derive(Debug)]
+pub struct F64Ptr(RcuRef<RawBlock<F64Table>, UnsafeCell<OrderedFloat<f64>>>);
+
+impl Clone for F64Ptr {
+    fn clone(&self) -> Self {
+        Self(RcuRef::clone(&self.0))
+    }
+}
 
 impl PartialEq for F64Ptr {
     fn eq(&self, other: &F64Ptr) -> bool {
-        self.0 == other.0 || &**self == &**other
+        RcuRef::ptr_eq(&self.0, &other.0) || self.deref() == other.deref()
     }
 }
 
@@ -375,28 +418,26 @@ impl Deref for F64Ptr {
 
     #[inline]
     fn deref(&self) -> &Self::Target {
-        unsafe { &*self.0.as_ptr() }
+        unsafe { &*self.0.get().as_ref().unwrap() }
     }
 }
 
 impl DerefMut for F64Ptr {
     #[inline]
     fn deref_mut(&mut self) -> &mut Self::Target {
-        unsafe { &mut *self.0.as_ptr() }
+        unsafe { &mut *self.0.get().as_mut().unwrap() }
     }
 }
 
 impl F64Ptr {
     #[inline(always)]
-    pub fn from_offset(offset: usize) -> Self {
-        unsafe {
-            F64Ptr(ptr::NonNull::new_unchecked(lookup_float(offset)))
-        }
+    pub fn from_offset(offset: F64Offset) -> Self {
+        Self(lookup_float(offset))
     }
 
     #[inline(always)]
     pub fn as_offset(&self) -> F64Offset {
-        F64Offset(self.0.as_ptr() as usize - get_f64_tbl_buf_base() as usize)
+        F64Offset(self.0.get() as usize - RcuRef::get_root(&self.0).base as usize)
     }
 }
 
@@ -416,7 +457,7 @@ impl F64Offset {
 
     #[inline(always)]
     pub fn as_ptr(self) -> F64Ptr {
-        F64Ptr::from_offset(self.0)
+        F64Ptr::from_offset(self)
     }
 
     #[inline(always)]
@@ -505,28 +546,6 @@ impl ArenaAllocated for Rational {
     }
 }
 
-impl ArenaAllocated for OssifiedOpDir {
-    type PtrToAllocated = TypedArenaPtr<OssifiedOpDir>;
-
-    #[inline]
-    fn tag() -> ArenaHeaderTag {
-        ArenaHeaderTag::OssifiedOpDir
-    }
-
-    #[inline]
-    fn size(&self) -> usize {
-        mem::size_of::<Self>()
-    }
-
-    #[inline]
-    fn copy_to_arena(self, dst: *mut Self) -> Self::PtrToAllocated {
-        unsafe {
-            ptr::write(dst, self);
-            TypedArenaPtr::new(dst as *mut Self)
-        }
-    }
-}
-
 impl ArenaAllocated for LiveLoadState {
     type PtrToAllocated = TypedArenaPtr<LiveLoadState>;
 
@@ -577,20 +596,20 @@ impl ArenaAllocated for HttpListener {
 
     #[inline]
     fn tag() -> ArenaHeaderTag {
-	ArenaHeaderTag::HttpListener
+        ArenaHeaderTag::HttpListener
     }
 
     #[inline]
     fn size(&self) -> usize {
-	mem::size_of::<Self>()
+        mem::size_of::<Self>()
     }
 
     #[inline]
     fn copy_to_arena(self, dst: *mut Self) -> Self::PtrToAllocated {
-	unsafe {
-	    ptr::write(dst, self);
-	    TypedArenaPtr::new(dst as *mut Self)
-	}
+        unsafe {
+            ptr::write(dst, self);
+            TypedArenaPtr::new(dst as *mut Self)
+        }
     }
 }
 
@@ -600,20 +619,20 @@ impl ArenaAllocated for HttpResponse {
 
     #[inline]
     fn tag() -> ArenaHeaderTag {
-	ArenaHeaderTag::HttpResponse
+        ArenaHeaderTag::HttpResponse
     }
 
     #[inline]
     fn size(&self) -> usize {
-	mem::size_of::<Self>()
+        mem::size_of::<Self>()
     }
 
     #[inline]
     fn copy_to_arena(self, dst: *mut Self) -> Self::PtrToAllocated {
-	unsafe {
-	    ptr::write(dst, self);
-	    TypedArenaPtr::new(dst as *mut Self)
-	}
+        unsafe {
+            ptr::write(dst, self);
+            TypedArenaPtr::new(dst as *mut Self)
+        }
     }
 }
 
@@ -664,7 +683,7 @@ impl ArenaAllocated for IndexPtr {
 #[derive(Clone, Copy, Debug)]
 struct AllocSlab {
     next: *mut AllocSlab,
-    #[cfg(target_pointer_width="32")]
+    #[cfg(target_pointer_width = "32")]
     _padding: u32,
     header: ArenaHeader,
 }
@@ -672,7 +691,7 @@ struct AllocSlab {
 #[derive(Debug)]
 pub struct Arena {
     base: *mut AllocSlab,
-    pub f64_tbl: F64Table,
+    pub f64_tbl: Arc<F64Table>,
 }
 
 unsafe impl Send for Arena {}
@@ -681,7 +700,10 @@ unsafe impl Sync for Arena {}
 impl Arena {
     #[inline]
     pub fn new() -> Self {
-        Arena { base: ptr::null_mut(), f64_tbl: F64Table::new() }
+        Arena {
+            base: ptr::null_mut(),
+            f64_tbl: F64Table::new(),
+        }
     }
 }
 
@@ -712,10 +734,10 @@ unsafe fn drop_slab_in_place(value: &mut AllocSlab) {
             #[cfg(feature = "http")]
             ptr::drop_in_place(value.payload_offset::<StreamLayout<CharReader<HttpReadStream>>>());
         }
-	    ArenaHeaderTag::HttpWriteStream => {
+        ArenaHeaderTag::HttpWriteStream => {
             #[cfg(feature = "http")]
-	        ptr::drop_in_place(value.payload_offset::<StreamLayout<CharReader<HttpWriteStream>>>());
-	    }
+            ptr::drop_in_place(value.payload_offset::<StreamLayout<CharReader<HttpWriteStream>>>());
+        }
         ArenaHeaderTag::ReadlineStream => {
             ptr::drop_in_place(value.payload_offset::<StreamLayout<ReadlineStream>>());
         }
@@ -725,35 +747,32 @@ unsafe fn drop_slab_in_place(value: &mut AllocSlab) {
         ArenaHeaderTag::ByteStream => {
             ptr::drop_in_place(value.payload_offset::<StreamLayout<CharReader<ByteStream>>>());
         }
-        ArenaHeaderTag::OssifiedOpDir => {
-            ptr::drop_in_place(value.payload_offset::<OssifiedOpDir>());
-        }
         ArenaHeaderTag::LiveLoadState | ArenaHeaderTag::InactiveLoadState => {
             ptr::drop_in_place(value.payload_offset::<LiveLoadState>());
         }
-        ArenaHeaderTag::Dropped => {
-        }
+        ArenaHeaderTag::Dropped => {}
         ArenaHeaderTag::TcpListener => {
             ptr::drop_in_place(value.payload_offset::<TcpListener>());
         }
-	    ArenaHeaderTag::HttpListener => {
+        ArenaHeaderTag::HttpListener => {
             #[cfg(feature = "http")]
-	        ptr::drop_in_place(value.payload_offset::<HttpListener>());
-	    }
-	    ArenaHeaderTag::HttpResponse => {
+            ptr::drop_in_place(value.payload_offset::<HttpListener>());
+        }
+        ArenaHeaderTag::HttpResponse => {
             #[cfg(feature = "http")]
-	        ptr::drop_in_place(value.payload_offset::<HttpResponse>());
-	    }
+            ptr::drop_in_place(value.payload_offset::<HttpResponse>());
+        }
         ArenaHeaderTag::StandardOutputStream => {
             ptr::drop_in_place(value.payload_offset::<StreamLayout<StandardOutputStream>>());
         }
         ArenaHeaderTag::StandardErrorStream => {
             ptr::drop_in_place(value.payload_offset::<StreamLayout<StandardErrorStream>>());
         }
-        ArenaHeaderTag::NullStream | ArenaHeaderTag::IndexPtrUndefined |
-        ArenaHeaderTag::IndexPtrDynamicUndefined | ArenaHeaderTag::IndexPtrDynamicIndex |
-        ArenaHeaderTag::IndexPtrIndex => {
-        }
+        ArenaHeaderTag::NullStream
+        | ArenaHeaderTag::IndexPtrUndefined
+        | ArenaHeaderTag::IndexPtrDynamicUndefined
+        | ArenaHeaderTag::IndexPtrDynamicIndex
+        | ArenaHeaderTag::IndexPtrIndex => {}
     }
 }
 
@@ -801,23 +820,25 @@ const_assert!(mem::size_of::<OrderedFloat<f64>>() == 8);
 
 #[cfg(test)]
 mod tests {
+    use std::ops::Deref;
+
     use crate::machine::mock_wam::*;
     use crate::machine::partial_string::*;
 
-    use ordered_float::OrderedFloat;
     use crate::parser::dashu::{Integer, Rational};
+    use ordered_float::OrderedFloat;
 
     #[test]
     fn float_ptr_cast() {
-        let mut wam = MockWAM::new();
+        let wam = MockWAM::new();
 
         let f = 0f64;
         let fp = float_alloc!(f, wam.machine_st.arena);
-        let mut cell = HeapCellValue::from(fp);
+        let mut cell = HeapCellValue::from(fp.clone());
 
         assert_eq!(cell.get_tag(), HeapCellValueTag::F64);
         assert_eq!(cell.get_mark_bit(), false);
-        assert_eq!(*fp, OrderedFloat(f));
+        assert_eq!(fp.deref(), &OrderedFloat(f));
 
         cell.set_mark_bit(true);
 
@@ -834,12 +855,12 @@ mod tests {
     #[test]
     fn heap_cell_value_const_cast() {
         let mut wam = MockWAM::new();
-        #[cfg(target_pointer_width="32")]
+        #[cfg(target_pointer_width = "32")]
         let const_value = HeapCellValue::from(ConsPtr::build_with(
             0x0000_0431 as *const _,
             ConsPtrMaskTag::Cons,
         ));
-        #[cfg(target_pointer_width="64")]
+        #[cfg(target_pointer_width = "64")]
         let const_value = HeapCellValue::from(ConsPtr::build_with(
             0x0000_5555_ff00_0431 as *const _,
             ConsPtrMaskTag::Cons,
@@ -847,7 +868,10 @@ mod tests {
 
         match const_value.to_untyped_arena_ptr() {
             Some(arena_ptr) => {
-                assert_eq!(arena_ptr.into_bytes(), const_value.to_untyped_arena_ptr_bytes());
+                assert_eq!(
+                    arena_ptr.into_bytes(),
+                    const_value.to_untyped_arena_ptr_bytes()
+                );
             }
             None => {
                 assert!(false);
@@ -860,7 +884,10 @@ mod tests {
 
         match stream_cell.to_untyped_arena_ptr() {
             Some(arena_ptr) => {
-                assert_eq!(arena_ptr.into_bytes(), stream_cell.to_untyped_arena_ptr_bytes());
+                assert_eq!(
+                    arena_ptr.into_bytes(),
+                    stream_cell.to_untyped_arena_ptr_bytes()
+                );
             }
             None => {
                 assert!(false);
@@ -875,8 +902,7 @@ mod tests {
         // integer
 
         let big_int: Integer = 2 * Integer::from(1u64 << 63);
-        let big_int_ptr: TypedArenaPtr<Integer> =
-            arena_alloc!(big_int, &mut wam.machine_st.arena);
+        let big_int_ptr: TypedArenaPtr<Integer> = arena_alloc!(big_int, &mut wam.machine_st.arena);
 
         assert!(!big_int_ptr.as_ptr().is_null());
 
@@ -951,8 +977,8 @@ mod tests {
         let f_atom = atom!("f");
         let g_atom = atom!("g");
 
-        assert_eq!(f_atom.as_str(), "f");
-        assert_eq!(g_atom.as_str(), "g");
+        assert_eq!(&*f_atom.as_str(), "f");
+        assert_eq!(&*g_atom.as_str(), "g");
 
         let f_atom_cell = atom_as_cell!(f_atom);
         let g_atom_cell = atom_as_cell!(g_atom);
@@ -962,7 +988,7 @@ mod tests {
         match f_atom_cell.to_atom() {
             Some(atom) => {
                 assert_eq!(f_atom, atom);
-                assert_eq!(atom.as_str(), "f");
+                assert_eq!(&*atom.as_str(), "f");
             }
             None => {
                 assert!(false);
@@ -973,7 +999,7 @@ mod tests {
             (HeapCellValueTag::Atom, (atom, arity)) => {
                 assert_eq!(f_atom, atom);
                 assert_eq!(arity, 0);
-                assert_eq!(atom.as_str(), "f");
+                assert_eq!(&*atom.as_str(), "f");
             }
             _ => { unreachable!() }
         );
@@ -982,21 +1008,22 @@ mod tests {
             (HeapCellValueTag::Atom, (atom, arity)) => {
                 assert_eq!(g_atom, atom);
                 assert_eq!(arity, 0);
-                assert_eq!(atom.as_str(), "g");
+                assert_eq!(&*atom.as_str(), "g");
             }
             _ => { unreachable!() }
         );
 
         // complete string
 
-        let pstr_var_cell = put_partial_string(&mut wam.machine_st.heap, "ronan", &mut wam.machine_st.atom_tbl);
+        let pstr_var_cell =
+            put_partial_string(&mut wam.machine_st.heap, "ronan", &wam.machine_st.atom_tbl);
         let pstr_cell = wam.machine_st.heap[pstr_var_cell.get_value() as usize];
 
         assert_eq!(pstr_cell.get_tag(), HeapCellValueTag::PStr);
 
         match pstr_cell.to_pstr() {
             Some(pstr) => {
-                assert_eq!(pstr.as_str_from(0), "ronan");
+                assert_eq!(&*pstr.as_str_from(0), "ronan");
             }
             None => {
                 assert!(false);
@@ -1006,7 +1033,7 @@ mod tests {
         read_heap_cell!(pstr_cell,
             (HeapCellValueTag::PStr, pstr_atom) => {
                 let pstr = PartialString::from(pstr_atom);
-                assert_eq!(pstr.as_str_from(0), "ronan");
+                assert_eq!(&*pstr.as_str_from(0), "ronan");
             }
             _ => { unreachable!() }
         );
@@ -1115,7 +1142,7 @@ mod tests {
         read_heap_cell!(cell,
             (HeapCellValueTag::Atom, (el, _arity)) => {
                 assert_eq!(el.flat_index(), empty_list_as_cell!().get_value());
-                assert_eq!(el.as_str(), "[]");
+                assert_eq!(&*el.as_str(), "[]");
             }
             _ => { unreachable!() }
         );

src/arithmetic.rs

@@ -14,6 +14,8 @@ use crate::parser::dashu::{Integer, Rational};
 use crate::machine::machine_errors::*;
 
 use dashu::base::Abs;
+use dashu::base::BitTest;
+use num_order::NumOrd;
 use ordered_float::*;
 
 use std::cell::Cell;
@@ -158,13 +160,13 @@ fn push_literal(interm: &mut Vec<ArithmeticTerm>, c: &Literal) -> Result<(), Ari
         Literal::Float(n) => interm.push(ArithmeticTerm::Number(Number::Float(*n.as_ptr()))),
         Literal::Rational(n) => interm.push(ArithmeticTerm::Number(Number::Rational(*n))),
         Literal::Atom(name) if name == &atom!("e") => interm.push(ArithmeticTerm::Number(
-            Number::Float(OrderedFloat(std::f64::consts::E))
+            Number::Float(OrderedFloat(std::f64::consts::E)),
         )),
         Literal::Atom(name) if name == &atom!("pi") => interm.push(ArithmeticTerm::Number(
-            Number::Float(OrderedFloat(std::f64::consts::PI))
+            Number::Float(OrderedFloat(std::f64::consts::PI)),
         )),
         Literal::Atom(name) if name == &atom!("epsilon") => interm.push(ArithmeticTerm::Number(
-            Number::Float(OrderedFloat(std::f64::EPSILON))
+            Number::Float(OrderedFloat(std::f64::EPSILON)),
         )),
         _ => return Err(ArithmeticError::NonEvaluableFunctor(*c, 0)),
     }
@@ -195,13 +197,6 @@ impl<'a> ArithmeticEvaluator<'a> {
             atom!("sin") => Ok(Instruction::Sin(a1, t)),
             atom!("tan") => Ok(Instruction::Tan(a1, t)),
             atom!("log") => Ok(Instruction::Log(a1, t)),
-            atom!("asinh") => Ok(Instruction::ASinh(a1, t)),
-            atom!("acosh") => Ok(Instruction::ACosh(a1, t)),
-            atom!("atanh") => Ok(Instruction::ATanh(a1, t)),
-            atom!("sinh") => Ok(Instruction::Sinh(a1, t)),
-            atom!("cosh") => Ok(Instruction::Cosh(a1, t)),
-            atom!("tanh") => Ok(Instruction::Tanh(a1, t)),
-            atom!("log10") => Ok(Instruction::Log10(a1, t)),
             atom!("exp") => Ok(Instruction::Exp(a1, t)),
             atom!("sqrt") => Ok(Instruction::Sqrt(a1, t)),
             atom!("acos") => Ok(Instruction::ACos(a1, t)),
@@ -326,23 +321,14 @@ impl<'a> ArithmeticEvaluator<'a> {
                     let var_num = name.to_var_num().unwrap();
 
                     let r = if lvl == Level::Shallow {
-                        self.marker.mark_non_callable(
-                            var_num,
-                            arg,
-                            term_loc,
-                            cell,
-                            &mut code,
-                        )
+                        self.marker
+                            .mark_non_callable(var_num, arg, term_loc, cell, &mut code)
                     } else if term_loc.is_last() || cell.get().norm().reg_num() == 0 {
                         let r = self.marker.get_binding(var_num);
 
                         if r.reg_num() == 0 {
                             self.marker.mark_var::<QueryInstruction>(
-                                var_num,
-                                lvl,
-                                cell,
-                                term_loc,
-                                &mut code,
+                                var_num, lvl, cell, term_loc, &mut code,
                             );
                             cell.get().norm()
                         } else {
@@ -370,8 +356,9 @@ impl<'a> ArithmeticEvaluator<'a> {
 pub(crate) fn rnd_i<'a>(n: &'a Number, arena: &mut Arena) -> Number {
     match n {
         &Number::Integer(i) => {
-            if let Some(n) = i.to_i64() {
-                fixnum!(Number, n, arena)
+            let result = (&*i).try_into();
+            if let Ok(value) = result{
+                fixnum!(Number, value, arena)
             } else {
                 *n
             }
@@ -392,8 +379,8 @@ pub(crate) fn rnd_i<'a>(n: &'a Number, arena: &mut Arena) -> Number {
         &Number::Rational(ref r) => {
             let (_, floor) = (r.fract(), r.floor());
 
-            if let Some(floor) = floor.to_i64() {
-                fixnum!(Number, floor, arena)
+            if let Ok(value) = (&floor).try_into() {
+                fixnum!(Number, value, arena)
             } else {
                 Number::Integer(arena_alloc!(floor, arena))
             }
@@ -434,7 +421,7 @@ fn classify_float(f: f64) -> Result<f64, EvalError> {
             }
         }
         FpCategory::Nan => Err(EvalError::Undefined),
-        _ => Ok(f)
+        _ => Ok(f),
     }
 }
 
@@ -542,15 +529,19 @@ impl PartialEq for Number {
     fn eq(&self, rhs: &Self) -> bool {
         match (self, rhs) {
             (&Number::Fixnum(n1), &Number::Fixnum(n2)) => n1.eq(&n2),
-            (&Number::Fixnum(n1), &Number::Integer(ref n2)) => n1.get_num().eq(&**n2),
-            (&Number::Integer(ref n1), &Number::Fixnum(n2)) => (&**n1).eq(&n2.get_num()),
-            (&Number::Fixnum(n1), &Number::Rational(ref n2)) => n1.get_num().eq(&**n2),
-            (&Number::Rational(ref n1), &Number::Fixnum(n2)) => (&**n1).eq(&n2.get_num()),
+            (&Number::Fixnum(n1), &Number::Integer(ref n2)) => n1.get_num().num_eq(&**n2),
+            (&Number::Integer(ref n1), &Number::Fixnum(n2)) => (&**n1).num_eq(&n2.get_num()),
+            (&Number::Fixnum(n1), &Number::Rational(ref n2)) => Integer::from(n1.get_num()).num_eq(&**n2),
+            (&Number::Rational(ref n1), &Number::Fixnum(n2)) => (&**n1).num_eq(&Integer::from(n2.get_num())),
             (&Number::Fixnum(n1), &Number::Float(n2)) => OrderedFloat(n1.get_num() as f64).eq(&n2),
             (&Number::Float(n1), &Number::Fixnum(n2)) => n1.eq(&OrderedFloat(n2.get_num() as f64)),
             (&Number::Integer(ref n1), &Number::Integer(ref n2)) => n1.eq(n2),
-            (&Number::Integer(ref n1), Number::Float(n2)) => OrderedFloat(n1.to_f64().value()).eq(n2),
-            (&Number::Float(n1), &Number::Integer(ref n2)) => n1.eq(&OrderedFloat(n2.to_f64().value())),
+            (&Number::Integer(ref n1), Number::Float(n2)) => {
+                OrderedFloat(n1.to_f64().value()).eq(n2)
+            }
+            (&Number::Float(n1), &Number::Integer(ref n2)) => {
+                n1.eq(&OrderedFloat(n2.to_f64().value()))
+            }
             (&Number::Integer(ref n1), &Number::Rational(ref n2)) => {
                 #[cfg(feature = "num")]
                 {
@@ -558,7 +549,7 @@ impl PartialEq for Number {
                 }
                 #[cfg(not(feature = "num"))]
                 {
-                    &**n1 == &**n2
+                    (&**n1).num_eq(&**n2)
                 }
             }
             (&Number::Rational(ref n1), &Number::Integer(ref n2)) => {
@@ -568,11 +559,15 @@ impl PartialEq for Number {
                 }
                 #[cfg(not(feature = "num"))]
                 {
-                    &**n1 == &**n2
+                    (&**n1).num_eq(&**n2)
                 }
             }
-            (&Number::Rational(ref n1), &Number::Float(n2)) => OrderedFloat(n1.to_f64().value()).eq(&n2),
-            (&Number::Float(n1), &Number::Rational(ref n2)) => n1.eq(&OrderedFloat(n2.to_f64().value())),
+            (&Number::Rational(ref n1), &Number::Float(n2)) => {
+                OrderedFloat(n1.to_f64().value()).eq(&n2)
+            }
+            (&Number::Float(n1), &Number::Rational(ref n2)) => {
+                n1.eq(&OrderedFloat(n2.to_f64().value()))
+            }
             (&Number::Float(f1), &Number::Float(f2)) => f1.eq(&f2),
             (&Number::Rational(ref r1), &Number::Rational(ref r2)) => r1.eq(&r2),
         }
@@ -594,8 +589,8 @@ impl PartialOrd<usize> for Number {
                     (n as usize).partial_cmp(rhs)
                 }
             }
-            Number::Integer(n) => (&**n).partial_cmp(rhs),
-            Number::Rational(r) => (&**r).partial_cmp(rhs),
+            Number::Integer(n) => Some((&**n).num_cmp(rhs)),
+            Number::Rational(r) => Some((&**r).num_cmp(&Integer::from(*rhs))),
             Number::Float(f) => f.partial_cmp(&OrderedFloat(*rhs as f64)),
         }
     }
@@ -614,8 +609,8 @@ impl PartialEq<usize> for Number {
                     (n as usize).eq(rhs)
                 }
             }
-            Number::Integer(n) => (&**n).eq(rhs),
-            Number::Rational(r) => (&**r).eq(rhs),
+            Number::Integer(n) => (&**n).num_eq(rhs),
+            Number::Rational(r) => (&**r).num_eq(&Integer::from(*rhs)),
             Number::Float(f) => f.eq(&OrderedFloat(*rhs as f64)),
         }
     }
@@ -641,7 +636,9 @@ impl Ord for Number {
             (&Number::Float(n1), &Number::Fixnum(n2)) => n1.cmp(&OrderedFloat(n2.get_num() as f64)),
             (&Number::Integer(n1), &Number::Integer(n2)) => (*n1).cmp(&*n2),
             (&Number::Integer(n1), Number::Float(n2)) => OrderedFloat(n1.to_f64().value()).cmp(n2),
-            (&Number::Float(n1), &Number::Integer(ref n2)) => n1.cmp(&OrderedFloat(n2.to_f64().value())),
+            (&Number::Float(n1), &Number::Integer(ref n2)) => {
+                n1.cmp(&OrderedFloat(n2.to_f64().value()))
+            }
             (&Number::Integer(n1), &Number::Rational(n2)) => {
                 #[cfg(feature = "num")]
                 {
@@ -649,7 +646,7 @@ impl Ord for Number {
                 }
                 #[cfg(not(feature = "num"))]
                 {
-                    (&*n1).partial_cmp(&*n2).unwrap_or(Ordering::Less)
+                    (&*n1).num_partial_cmp(&*n2).unwrap_or(Ordering::Less)
                 }
             }
             (&Number::Rational(n1), &Number::Integer(n2)) => {
@@ -659,11 +656,15 @@ impl Ord for Number {
                 }
                 #[cfg(not(feature = "num"))]
                 {
-                    (&*n1).partial_cmp(&*n2).unwrap_or(Ordering::Less)
+                    (&*n1).num_partial_cmp(&*n2).unwrap_or(Ordering::Less)
                 }
             }
-            (&Number::Rational(n1), &Number::Float(n2)) => OrderedFloat(n1.to_f64().value()).cmp(&n2),
-            (&Number::Float(n1), &Number::Rational(n2)) => n1.cmp(&OrderedFloat(n2.to_f64().value())),
+            (&Number::Rational(n1), &Number::Float(n2)) => {
+                OrderedFloat(n1.to_f64().value()).cmp(&n2)
+            }
+            (&Number::Float(n1), &Number::Rational(n2)) => {
+                n1.cmp(&OrderedFloat(n2.to_f64().value()))
+            }
             (&Number::Float(f1), &Number::Float(f2)) => f1.cmp(&f2),
             (&Number::Rational(r1), &Number::Rational(r2)) => (*r1).cmp(&*r2),
         }
@@ -704,16 +705,16 @@ impl TryFrom<HeapCellValue> for Number {
 
 // Computes n ^ power. Ignores the sign of power.
 pub(crate) fn binary_pow(mut n: Integer, power: &Integer) -> Integer {
-    let mut power = Integer::from(power.abs());
+    let mut power = power.abs();
 
-    if power == 0 {
-        return Integer::from(1);
+    if power.is_zero() {
+        return Integer::ONE;
     }
 
-    let mut oddand = Integer::from(1);
+    let mut oddand = Integer::ONE;
 
-    while power > 1 {
-        if power.is_odd() {
+    while power.num_gt(&1) {
+        if power.bit(0) {
             oddand *= &n;
         }
 

src/atom_table.rs

@@ -1,14 +1,19 @@
 use crate::parser::ast::MAX_ARITY;
 use crate::raw_block::*;
+use crate::rcu::{Rcu, RcuRef};
 use crate::types::*;
 
-use std::borrow::Borrow;
 use std::cmp::Ordering;
 use std::hash::{Hash, Hasher};
 use std::mem;
+use std::ops::Deref;
 use std::ptr;
 use std::slice;
 use std::str;
+use std::sync::Arc;
+use std::sync::Mutex;
+use std::sync::RwLock;
+use std::sync::Weak;
 
 use indexmap::IndexSet;
 
@@ -33,65 +38,43 @@ impl<'a> From<&'a Atom> for Atom {
 impl From<bool> for Atom {
     #[inline]
     fn from(value: bool) -> Self {
-        if value { atom!("true") } else { atom!("false") }
+        if value {
+            atom!("true")
+        } else {
+            atom!("false")
+        }
+    }
+}
+
+impl indexmap::Equivalent<Atom> for str {
+    fn equivalent(&self, key: &Atom) -> bool {
+        &*key.as_str() == self
     }
 }
 
 const ATOM_TABLE_INIT_SIZE: usize = 1 << 16;
 const ATOM_TABLE_ALIGN: usize = 8;
 
-#[cfg(test)]
-thread_local! {
-   static ATOM_TABLE_BUF_BASE: std::cell::RefCell<*const u8> = std::cell::RefCell::new(ptr::null_mut());
-}
-
-#[cfg(not(test))]
-static ATOM_TABLE_BUF_BASE: std::sync::atomic::AtomicPtr<u8> =
-    std::sync::atomic::AtomicPtr::new(ptr::null_mut());
-
-fn set_atom_tbl_buf_base(old_ptr: *const u8, new_ptr: *const u8) -> Result<(), *const u8> {
-#[cfg(test)]
+#[inline(always)]
+fn global_atom_table() -> &'static RwLock<Weak<AtomTable>> {
+    #[cfg(feature = "rust_beta_channel")]
     {
-    ATOM_TABLE_BUF_BASE.with(|atom_table_buf_base| {
-        let mut borrow = atom_table_buf_base.borrow_mut();
-            if *borrow != old_ptr {
-                Err(*borrow)
-            } else {
-                *borrow = new_ptr;
-                Ok(())
-            }
-        })?;
-    };
-    #[cfg(not(test))]
+        // const Weak::new will be stabilized in 1.73 which is currently in beta,
+        // till then we need a OnceLock for initialization
+        static GLOBAL_ATOM_TABLE: RwLock<Weak<AtomTable>> = RwLock::const_new(Weak::new());
+        &GLOBAL_ATOM_TABLE
+    }
+    #[cfg(not(feature = "rust_beta_channel"))]
     {
-        ATOM_TABLE_BUF_BASE
-            .compare_exchange(
-                old_ptr.cast_mut(),
-                new_ptr.cast_mut(),
-                std::sync::atomic::Ordering::Relaxed,
-                std::sync::atomic::Ordering::Relaxed,
-            )
-            .map_err(|ptr| ptr.cast_const())
-    }?;
-    Ok(())
-}
-
-pub(crate) fn get_atom_tbl_buf_base() -> *const u8 {
-    #[cfg(test)]
-    {
-    ATOM_TABLE_BUF_BASE.with(|atom_table_buf_base| *atom_table_buf_base.borrow())
-}
-#[cfg(not(test))]
-    {
-        ATOM_TABLE_BUF_BASE.load(std::sync::atomic::Ordering::Relaxed)
+        use std::sync::OnceLock;
+        static GLOBAL_ATOM_TABLE: OnceLock<RwLock<Weak<AtomTable>>> = OnceLock::new();
+        GLOBAL_ATOM_TABLE.get_or_init(|| RwLock::new(Weak::new()))
     }
 }
 
-#[test]
-#[should_panic(expected = "Overwriting atom table base pointer")]
-fn atomtable_is_not_concurrency_safe() {
-    let _table_a = AtomTable::new();
-    let _table_b = AtomTable::new();
+#[inline(always)]
+fn arc_atom_table() -> Option<Arc<AtomTable>> {
+    global_atom_table().read().unwrap().upgrade()
 }
 
 impl RawBlockTraits for AtomTable {
@@ -109,9 +92,11 @@ impl RawBlockTraits for AtomTable {
 #[bitfield]
 #[derive(Copy, Clone, Debug)]
 struct AtomHeader {
-    #[allow(unused)] m: bool,
+    #[allow(unused)]
+    m: bool,
     len: B50,
-    #[allow(unused)] padding: B13,
+    #[allow(unused)]
+    padding: B13,
 }
 
 impl AtomHeader {
@@ -120,13 +105,6 @@ impl AtomHeader {
     }
 }
 
-impl Borrow<str> for Atom {
-    #[inline]
-    fn borrow(&self) -> &str {
-        self.as_str()
-    }
-}
-
 impl Hash for Atom {
     #[inline]
     fn hash<H: Hasher>(&self, hasher: &mut H) {
@@ -142,29 +120,76 @@ macro_rules! is_char {
     };
 }
 
-impl Atom {
-    #[inline]
-    pub fn buf(self) -> *const u8 {
-        let ptr = self.as_ptr();
+pub enum AtomString<'a> {
+    Static(&'a str),
+    Dynamic(AtomTableRef<str>),
+}
 
-        if ptr.is_null() {
-            return ptr::null();
+impl AtomString<'_> {
+    pub fn map<F>(self, f: F) -> Self
+    where
+        for<'a> F: FnOnce(&'a str) -> &'a str,
+    {
+        match self {
+            Self::Static(reference) => Self::Static(f(reference)),
+            Self::Dynamic(guard) => Self::Dynamic(AtomTableRef::map(guard, f)),
         }
+    }
+}
 
-        (ptr as usize + mem::size_of::<AtomHeader>()) as *const u8
+impl std::fmt::Debug for AtomString<'_> {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        std::fmt::Debug::fmt(self.deref(), f)
+    }
+}
+
+impl std::fmt::Display for AtomString<'_> {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        std::fmt::Display::fmt(self.deref(), f)
+    }
+}
+
+impl std::ops::Deref for AtomString<'_> {
+    type Target = str;
+    fn deref(&self) -> &Self::Target {
+        match self {
+            Self::Static(reference) => reference,
+            Self::Dynamic(guard) => guard.deref(),
+        }
+    }
+}
+
+#[cfg(feature = "repl")]
+impl rustyline::completion::Candidate for AtomString<'_> {
+    fn display(&self) -> &str {
+        self.deref()
     }
 
+    fn replacement(&self) -> &str {
+        self.deref()
+    }
+}
+
+impl Atom {
     #[inline(always)]
     pub fn is_static(self) -> bool {
         (self.index as usize) < STRINGS.len() << 3
     }
 
     #[inline(always)]
-    pub fn as_ptr(self) -> *const u8 {
+    pub fn as_ptr(self) -> Option<AtomTableRef<u8>> {
         if self.is_static() {
-            ptr::null()
+            None
         } else {
-            (get_atom_tbl_buf_base() as usize + (self.index as usize) - (STRINGS.len() << 3)) as *const u8
+            let atom_table =
+                arc_atom_table().expect("We should only have an Atom while there is an AtomTable");
+            unsafe {
+                AtomTableRef::try_map(atom_table.buf(), |buf| {
+                    (buf as *const u8)
+                        .offset(((self.index as usize) - (STRINGS.len() << 3)) as isize)
+                        .as_ref()
+                })
+            }
         }
     }
 
@@ -178,7 +203,9 @@ impl Atom {
         if self.is_static() {
             STRINGS[(self.index >> 3) as usize].len()
         } else {
-            unsafe { ptr::read(self.as_ptr() as *const AtomHeader).len() as _ }
+            let ptr = self.as_ptr().unwrap();
+            let ptr = ptr.deref() as *const u8 as *const AtomHeader;
+            unsafe { ptr::read(ptr) }.len() as _
         }
     }
 
@@ -194,41 +221,44 @@ impl Atom {
         let c1 = it.next();
         let c2 = it.next();
 
-        if c2.is_none() { c1 } else { None }
-    }
-
-    #[inline]
-    pub fn chars(&self) -> str::Chars {
-        self.as_str().chars()
-    }
-
-    #[inline]
-    pub fn as_str(&self) -> &str {
-        unsafe {
-            let ptr = self.as_ptr();
-
-            if ptr.is_null() {
-                return STRINGS[(self.index >> 3) as usize];
-            }
-
-            let header = ptr::read::<AtomHeader>(ptr as *const _);
-            let len = header.len() as usize;
-            let buf = (ptr as usize + mem::size_of::<AtomHeader>()) as *mut u8;
-
-            str::from_utf8_unchecked(slice::from_raw_parts(buf, len))
+        if c2.is_none() {
+            c1
+        } else {
+            None
         }
     }
 
-    pub fn defrock_brackets(&self, atom_tbl: &mut AtomTable) -> Self {
+    #[inline]
+    pub fn as_str(&self) -> AtomString<'static> {
+        if self.is_static() {
+            AtomString::Static(STRINGS[(self.index >> 3) as usize])
+        } else {
+            if let Some(ptr) = self.as_ptr() {
+                AtomString::Dynamic(AtomTableRef::map(ptr, |ptr| {
+                    let header =
+                        unsafe { ptr::read::<AtomHeader>(ptr as *const u8 as *const AtomHeader) };
+                    let len = header.len() as usize;
+                    let buf =
+                        unsafe { (ptr as *const u8).offset(mem::size_of::<AtomHeader>() as isize) };
+
+                    unsafe { str::from_utf8_unchecked(slice::from_raw_parts(buf, len)) }
+                }))
+            } else {
+                AtomString::Static(&STRINGS[(self.index >> 3) as usize])
+            }
+        }
+    }
+
+    pub fn defrock_brackets(&self, atom_tbl: &AtomTable) -> Self {
         let s = self.as_str();
 
-        let s = if s.starts_with('(') && s.ends_with(')') {
+        let sub_str = if s.starts_with('(') && s.ends_with(')') {
             &s['('.len_utf8()..s.len() - ')'.len_utf8()]
         } else {
             return *self;
         };
 
-        atom_tbl.build_with(s)
+        AtomTable::build_with(&atom_tbl, &sub_str)
     }
 }
 
@@ -248,116 +278,156 @@ impl PartialOrd for Atom {
 impl Ord for Atom {
     #[inline]
     fn cmp(&self, other: &Atom) -> Ordering {
-        self.as_str().cmp(other.as_str())
+        self.as_str().cmp(&*other.as_str())
     }
 }
 
 #[derive(Debug)]
-pub struct AtomTable {
+pub struct InnerAtomTable {
     block: RawBlock<AtomTable>,
-    pub table: IndexSet<Atom>,
+    pub table: Rcu<IndexSet<Atom>>,
 }
 
-#[cold]
-fn atom_table_base_pointer_mismatch(expected: *const u8, got: *const u8) -> ! {
-    assert_eq!(expected, got, "Overwriting atom table base pointer, expected old value to be {expected:p}, but found {got:p}");
-    unreachable!("This should only be called in a case of a mismatch as such the assert_eq should have failed!")
+#[derive(Debug)]
+pub struct AtomTable {
+    inner: Rcu<InnerAtomTable>,
+    // this lock is taking during resizing
+    update: Mutex<()>,
 }
 
-impl Drop for AtomTable {
-    fn drop(&mut self) {
-        if let Err(got) = set_atom_tbl_buf_base(self.block.base, ptr::null()) {
-            atom_table_base_pointer_mismatch(self.block.base, got);
-        }
-        self.block.deallocate();
+pub type AtomTableRef<M> = RcuRef<InnerAtomTable, M>;
+
+impl InnerAtomTable {
+    #[inline(always)]
+    fn lookup_str(self: &InnerAtomTable, string: &str) -> Option<Atom> {
+        STATIC_ATOMS_MAP
+            .get(string)
+            .cloned()
+            .or_else(|| self.table.active_epoch().get(string).cloned())
     }
 }
 
 impl AtomTable {
     #[inline]
-    pub fn new() -> Self {
-        let mut block = RawBlock::new();
-
-        if let Err(got) = set_atom_tbl_buf_base(ptr::null(), block.base) {
-            block.deallocate();
-            atom_table_base_pointer_mismatch(ptr::null(), got);
-        }
-
-        Self {
-            block,
-            table: IndexSet::new(),
+    pub fn new() -> Arc<Self> {
+        let upgraded = global_atom_table().read().unwrap().upgrade();
+        // don't inline upgraded, otherwise temporary will be dropped too late in case of None
+        if let Some(atom_table) = upgraded {
+            atom_table
+        } else {
+            let mut guard = global_atom_table().write().unwrap();
+            // try to upgrade again in case we lost the race on the write lock
+            if let Some(atom_table) = guard.upgrade() {
+                atom_table
+            } else {
+                let atom_table = Arc::new(Self {
+                    inner: Rcu::new(InnerAtomTable {
+                        block: RawBlock::new(),
+                        table: Rcu::new(IndexSet::new()),
+                    }),
+                    update: Mutex::new(()),
+                });
+                *guard = Arc::downgrade(&atom_table);
+                atom_table
+            }
         }
     }
 
     #[inline]
-    pub fn buf(&self) -> *const u8 {
-        self.block.base as *const u8
+    pub fn buf(&self) -> AtomTableRef<u8> {
+        AtomTableRef::<InnerAtomTable>::map(self.inner.active_epoch(), |inner| {
+            unsafe { inner.block.base.as_ref() }.unwrap()
+        })
     }
 
-    #[inline]
-    pub fn top(&self) -> *const u8 {
-        self.block.top
+    pub fn active_table(&self) -> RcuRef<IndexSet<Atom>, IndexSet<Atom>> {
+        self.inner.active_epoch().table.active_epoch()
     }
 
-    #[inline(always)]
-    fn lookup_str(&self, string: &str) -> Option<Atom> {
-        STATIC_ATOMS_MAP.get(string).or_else(|| self.table.get(string)).cloned()
-    }
+    pub fn build_with(atom_table: &AtomTable, string: &str) -> Atom {
+        loop {
+            let mut block_epoch = atom_table.inner.active_epoch();
+            let mut table_epoch = block_epoch.table.active_epoch();
 
-    pub fn build_with(&mut self, string: &str) -> Atom {
-        if let Some(atom) = self.lookup_str(string) {
-            return atom;
-        }
+            if let Some(atom) = block_epoch.lookup_str(string) {
+                return atom;
+            }
+
+            // take a lock to prevent concurrent updates
+            let update_guard = atom_table.update.lock().unwrap();
+
+            let is_same_allocation =
+                RcuRef::same_epoch(&block_epoch, &atom_table.inner.active_epoch());
+            let is_same_atom_list =
+                RcuRef::same_epoch(&table_epoch, &block_epoch.table.active_epoch());
+
+            if !(is_same_allocation && is_same_atom_list) {
+                // some other thread raced us between our lookup and
+                // us aquring the update lock,
+                // try again
+                continue;
+            }
 
-        unsafe {
             let size = mem::size_of::<AtomHeader>() + string.len();
             let align_offset = 8 * mem::align_of::<AtomHeader>();
             let size = (size & !(align_offset - 1)) + align_offset;
 
-            let len_ptr = {
-                let mut ptr;
-
-                loop {
-                    ptr = self.block.alloc(size);
+            unsafe {
+                let len_ptr = loop {
+                    let ptr = block_epoch.block.alloc(size);
 
                     if ptr.is_null() {
-                        let old_base = self.block.base;
-                        self.block.grow();
-                        if let Err(got) = set_atom_tbl_buf_base(old_base, self.block.base) {
-                            atom_table_base_pointer_mismatch(old_base, got);
-                        }
+                        // garbage collection would go here
+                        let new_block = block_epoch.block.grow_new().unwrap();
+                        let new_table = Rcu::new(table_epoch.clone());
+                        let new_alloc = InnerAtomTable {
+                            block: new_block,
+                            table: new_table,
+                        };
+                        atom_table.inner.replace(new_alloc);
+                        block_epoch = atom_table.inner.active_epoch();
+                        table_epoch = block_epoch.table.active_epoch();
                     } else {
-                        break;
+                        break ptr;
                     }
-                }
+                };
 
-                ptr
-            };
+                let ptr_base = block_epoch.block.base as usize;
 
-            let ptr_base = self.block.base as usize;
+                write_to_ptr(string, len_ptr);
 
-            write_to_ptr(string, len_ptr);
+                let atom = Atom {
+                    index: ((STRINGS.len() << 3) + len_ptr as usize - ptr_base) as u64,
+                };
 
-            let atom = Atom {
-                index: ((STRINGS.len() << 3) + len_ptr as usize - ptr_base) as u64,
-            };
+                let mut table = table_epoch.clone();
+                table.insert(atom);
+                block_epoch.table.replace(table);
 
-            self.table.insert(atom);
+                // expicit drop to ensure we don't accidentally drop it early
+                drop(update_guard);
 
-            atom
+                return atom;
+            }
         }
     }
 }
 
+unsafe impl Send for AtomTable {}
+unsafe impl Sync for AtomTable {}
+
 #[bitfield]
 #[repr(u64)]
 #[derive(Copy, Clone, Debug)]
 pub struct AtomCell {
     name: B46,
     arity: B10,
-    #[allow(unused)] f: bool,
-    #[allow(unused)] m: bool,
-    #[allow(unused)] tag: B6,
+    #[allow(unused)]
+    f: bool,
+    #[allow(unused)]
+    m: bool,
+    #[allow(unused)]
+    tag: B6,
 }
 
 impl AtomCell {

src/bin/scryer-prolog.rs

@@ -1,12 +1,28 @@
 fn main() -> std::process::ExitCode {
-    use std::sync::atomic::Ordering;
     use scryer_prolog::*;
+    use scryer_prolog::atom_table::Atom;
+    use std::sync::atomic::Ordering;
 
     #[cfg(feature = "repl")]
     ctrlc::set_handler(move || {
         scryer_prolog::machine::INTERRUPT.store(true, Ordering::Relaxed);
-    }).unwrap();
+    })
+    .unwrap();
 
-    let mut wam = machine::Machine::new();
-    wam.run_top_level()
+    #[cfg(target_arch = "wasm32")]
+    let runtime = tokio::runtime::Builder::new_current_thread()
+        .enable_all()
+        .build()
+        .unwrap();
+
+    #[cfg(not(target_arch = "wasm32"))]
+    let runtime = tokio::runtime::Builder::new_multi_thread()
+        .enable_all()
+        .build()
+        .unwrap();
+
+    runtime.block_on(async move {
+        let mut wam = machine::Machine::new(Default::default());
+        wam.run_top_level(atom!("$toplevel"), (atom!("$repl"), 1))
+    })
 }

src/codegen.rs

@@ -1,14 +1,14 @@
-use crate::atom_table::*;
-use crate::parser::ast::*;
-use crate::temp_v;
 use crate::allocator::*;
 use crate::arithmetic::*;
+use crate::atom_table::*;
 use crate::debray_allocator::*;
 use crate::forms::*;
 use crate::indexing::*;
 use crate::instructions::*;
 use crate::iterators::*;
+use crate::parser::ast::*;
 use crate::targets::*;
+use crate::temp_v;
 use crate::types::*;
 
 use crate::instr;
@@ -48,15 +48,20 @@ impl BranchCodeStack {
     }
 
     fn code<'a>(&'a mut self, default_code: &'a mut CodeDeque) -> &'a mut CodeDeque {
-        self.stack.last_mut()
+        self.stack
+            .last_mut()
             .and_then(|stack| stack.last_mut())
             .unwrap_or(default_code)
     }
 
-    fn push_missing_vars(&mut self, depth: usize, marker: &mut DebrayAllocator) -> SubsumedBranchHits {
+    fn push_missing_vars(
+        &mut self,
+        depth: usize,
+        marker: &mut DebrayAllocator,
+    ) -> SubsumedBranchHits {
         let mut subsumed_hits = SubsumedBranchHits::with_hasher(FxBuildHasher::default());
 
-        for idx in (self.stack.len() - depth .. self.stack.len()).rev() {
+        for idx in (self.stack.len() - depth..self.stack.len()).rev() {
             let branch = &mut marker.branch_stack[idx];
             let branch_hits = &branch.hits;
 
@@ -91,14 +96,14 @@ impl BranchCodeStack {
     fn push_jump_instrs(&mut self, depth: usize) {
         // add 2 in each arm length to compensate for each jump
         // instruction and each branch instruction not yet added.
-        let mut jump_span: usize = self.stack[self.stack.len() - depth ..]
+        let mut jump_span: usize = self.stack[self.stack.len() - depth..]
             .iter()
             .map(|branch| branch.iter().map(|code| code.len() + 2).sum::<usize>())
             .sum();
 
         jump_span -= depth;
 
-        for idx in self.stack.len() - depth .. self.stack.len() {
+        for idx in self.stack.len() - depth..self.stack.len() {
             let inner_len = self.stack[idx].len();
 
             for (inner_idx, code) in self.stack[idx].iter_mut().enumerate() {
@@ -117,9 +122,11 @@ impl BranchCodeStack {
     fn pop_branch(&mut self, depth: usize, settings: CodeGenSettings) -> CodeDeque {
         let mut combined_code = CodeDeque::new();
 
-        for mut branch_arm in self.stack.drain(self.stack.len() - depth ..).rev() {
+        for mut branch_arm in self.stack.drain(self.stack.len() - depth..).rev() {
             let num_branch_arms = branch_arm.len();
-            branch_arm.last_mut().map(|code| code.extend(combined_code.drain(..)));
+            branch_arm
+                .last_mut()
+                .map(|code| code.extend(combined_code.drain(..)));
 
             for (idx, code) in branch_arm.into_iter().enumerate() {
                 combined_code.push_back(if idx == 0 {
@@ -255,7 +262,7 @@ impl CodeGenSettings {
 
 #[derive(Debug)]
 pub(crate) struct CodeGenerator<'a> {
-    pub(crate) atom_tbl: &'a mut AtomTable,
+    pub(crate) atom_tbl: &'a AtomTable,
     marker: DebrayAllocator,
     settings: CodeGenSettings,
     pub(crate) skeleton: PredicateSkeleton,
@@ -269,13 +276,7 @@ impl DebrayAllocator {
         vr: &Cell<VarReg>,
         code: &mut CodeDeque,
     ) -> RegType {
-        self.mark_var::<QueryInstruction>(
-            var_num,
-            Level::Shallow,
-            vr,
-            term_loc,
-            code,
-        );
+        self.mark_var::<QueryInstruction>(var_num, Level::Shallow, vr, term_loc, code);
 
         vr.get().norm()
     }
@@ -308,8 +309,8 @@ impl DebrayAllocator {
 // decrement the arity of the PutStructure instruction by 1.
 fn trim_structure_by_last_arg(instr: &mut Instruction, last_arg: &Term) {
     match instr {
-        Instruction::PutStructure(_, ref mut arity, _) |
-        Instruction::GetStructure(.., ref mut arity, _) => {
+        Instruction::PutStructure(_, ref mut arity, _)
+        | Instruction::GetStructure(.., ref mut arity, _) => {
             if let Term::Literal(_, Literal::CodeIndex(_)) = last_arg {
                 // it is acceptable if arity == 0 is the result of
                 // this decrement. call/N will have to read the index
@@ -352,16 +353,16 @@ impl<'a, 'b> AddToFreeList<'a, QueryInstruction> for CodeGenerator<'b> {
 
 fn structure_cell(term: &Term) -> Option<&Cell<RegType>> {
     match term {
-        &Term::Cons(ref cell, ..) |
-        &Term::Clause(ref cell, ..) |
-        Term::PartialString(ref cell, ..) |
-        Term::CompleteString(ref cell, ..) => Some(cell),
+        &Term::Cons(ref cell, ..)
+        | &Term::Clause(ref cell, ..)
+        | Term::PartialString(ref cell, ..)
+        | Term::CompleteString(ref cell, ..) => Some(cell),
         _ => None,
     }
 }
 
 impl<'b> CodeGenerator<'b> {
-    pub(crate) fn new(atom_tbl: &'b mut AtomTable, settings: CodeGenSettings) -> Self {
+    pub(crate) fn new(atom_tbl: &'b AtomTable, settings: CodeGenSettings) -> Self {
         CodeGenerator {
             atom_tbl,
             marker: DebrayAllocator::new(),
@@ -392,7 +393,8 @@ impl<'b> CodeGenerator<'b> {
         target: &mut CodeDeque,
     ) {
         if self.marker.var_data.records[var_num].num_occurrences > 1 {
-            self.marker.mark_var::<Target>(var_num, Level::Deep, cell, term_loc, target);
+            self.marker
+                .mark_var::<Target>(var_num, Level::Deep, cell, term_loc, target);
         } else {
             Self::add_or_increment_void_instr::<Target>(target);
         }
@@ -408,31 +410,33 @@ impl<'b> CodeGenerator<'b> {
             &Term::AnonVar => {
                 Self::add_or_increment_void_instr::<Target>(target);
             }
-            &Term::Cons(ref cell, ..) |
-            &Term::Clause(ref cell, ..) |
-            Term::PartialString(ref cell, ..) |
-            Term::CompleteString(ref cell, ..) => {
-                self.marker.mark_non_var::<Target>(Level::Deep, term_loc, cell, target);
+            &Term::Cons(ref cell, ..)
+            | &Term::Clause(ref cell, ..)
+            | Term::PartialString(ref cell, ..)
+            | Term::CompleteString(ref cell, ..) => {
+                self.marker
+                    .mark_non_var::<Target>(Level::Deep, term_loc, cell, target);
                 target.push_back(Target::clause_arg_to_instr(cell.get()));
             }
             &Term::Literal(_, ref constant) => {
                 target.push_back(Target::constant_subterm(constant.clone()));
             }
             &Term::Var(ref cell, ref var_ptr) => {
-                self.deep_var_instr::<Target>(cell, var_ptr.to_var_num().unwrap(), term_loc, target);
+                self.deep_var_instr::<Target>(
+                    cell,
+                    var_ptr.to_var_num().unwrap(),
+                    term_loc,
+                    target,
+                );
             }
         };
     }
 
-    fn compile_target<'a, Target, Iter>(
-        &mut self,
-        iter: Iter,
-        term_loc: GenContext,
-    ) -> CodeDeque
+    fn compile_target<'a, Target, Iter>(&mut self, iter: Iter, term_loc: GenContext) -> CodeDeque
     where
         Target: crate::targets::CompilationTarget<'a>,
         Iter: Iterator<Item = TermRef<'a>>,
-        CodeGenerator<'b>: AddToFreeList<'a, Target>
+        CodeGenerator<'b>: AddToFreeList<'a, Target>,
     {
         let mut target = CodeDeque::new();
 
@@ -442,14 +446,19 @@ impl<'b> CodeGenerator<'b> {
                     if let GenContext::Head = term_loc {
                         self.marker.advance_arg();
                     } else {
-                        self.marker.mark_anon_var::<Target>(lvl, term_loc, &mut target);
+                        self.marker
+                            .mark_anon_var::<Target>(lvl, term_loc, &mut target);
                     }
                 }
                 TermRef::Clause(lvl, cell, name, terms) => {
-                    self.marker.mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
+                    self.marker
+                        .mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
                     target.push_back(Target::to_structure(lvl, name, terms.len(), cell.get()));
 
-                    <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_term_to_free_list(self, cell.get());
+                    <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_term_to_free_list(
+                        self,
+                        cell.get(),
+                    );
 
                     if let Some(instr) = target.back_mut() {
                         if let Some(term) = terms.last() {
@@ -462,38 +471,52 @@ impl<'b> CodeGenerator<'b> {
                     }
 
                     for subterm in terms {
-                        <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_subterm_to_free_list(self, subterm);
+                        <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_subterm_to_free_list(
+                            self, subterm,
+                        );
                     }
                 }
                 TermRef::Cons(lvl, cell, head, tail) => {
-                    self.marker.mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
+                    self.marker
+                        .mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
                     target.push_back(Target::to_list(lvl, cell.get()));
 
-                    <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_term_to_free_list(self, cell.get());
+                    <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_term_to_free_list(
+                        self,
+                        cell.get(),
+                    );
 
                     self.subterm_to_instr::<Target>(head, term_loc, &mut target);
                     self.subterm_to_instr::<Target>(tail, term_loc, &mut target);
 
-                    <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_subterm_to_free_list(self, head);
-                    <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_subterm_to_free_list(self, tail);
+                    <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_subterm_to_free_list(
+                        self, head,
+                    );
+                    <CodeGenerator<'b> as AddToFreeList<'a, Target>>::add_subterm_to_free_list(
+                        self, tail,
+                    );
                 }
                 TermRef::Literal(lvl @ Level::Shallow, cell, Literal::String(ref string)) => {
-                    self.marker.mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
+                    self.marker
+                        .mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
                     target.push_back(Target::to_pstr(lvl, *string, cell.get(), false));
                 }
                 TermRef::Literal(lvl @ Level::Shallow, cell, constant) => {
-                    self.marker.mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
+                    self.marker
+                        .mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
                     target.push_back(Target::to_constant(lvl, *constant, cell.get()));
                 }
                 TermRef::PartialString(lvl, cell, string, tail) => {
-                    self.marker.mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
-                    let atom = self.atom_tbl.build_with(&string);
+                    self.marker
+                        .mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
+                    let atom = AtomTable::build_with(&self.atom_tbl, &string);
 
                     target.push_back(Target::to_pstr(lvl, atom, cell.get(), true));
                     self.subterm_to_instr::<Target>(tail, term_loc, &mut target);
                 }
                 TermRef::CompleteString(lvl, cell, atom) => {
-                    self.marker.mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
+                    self.marker
+                        .mark_non_var::<Target>(lvl, term_loc, cell, &mut target);
                     target.push_back(Target::to_pstr(lvl, atom, cell.get(), false));
                 }
                 TermRef::Var(lvl @ Level::Shallow, cell, var) => {
@@ -563,9 +586,9 @@ impl<'b> CodeGenerator<'b> {
                 compare_number_instr!(cmp, at_1, at_2)
             }
             &InlinedClauseType::IsAtom(..) => match &terms[0] {
-                &Term::Literal(_, Literal::Char(_)) |
-                &Term::Literal(_, Literal::Atom(atom!("[]"))) |
-                &Term::Literal(_, Literal::Atom(..)) => {
+                &Term::Literal(_, Literal::Char(_))
+                | &Term::Literal(_, Literal::Atom(atom!("[]")))
+                | &Term::Literal(_, Literal::Atom(..)) => {
                     instr!("$succeed")
                 }
                 &Term::Var(ref vr, ref name) => {
@@ -586,11 +609,11 @@ impl<'b> CodeGenerator<'b> {
                 }
             },
             &InlinedClauseType::IsAtomic(..) => match &terms[0] {
-                &Term::AnonVar |
-                &Term::Clause(..) |
-                &Term::Cons(..) |
-                &Term::PartialString(..) |
-                &Term::CompleteString(..) => {
+                &Term::AnonVar
+                | &Term::Clause(..)
+                | &Term::Cons(..)
+                | &Term::PartialString(..)
+                | &Term::CompleteString(..) => {
                     instr!("$fail")
                 }
                 &Term::Literal(_, Literal::String(_)) => {
@@ -614,11 +637,11 @@ impl<'b> CodeGenerator<'b> {
                 }
             },
             &InlinedClauseType::IsCompound(..) => match &terms[0] {
-                &Term::Clause(..) |
-                &Term::Cons(..) |
-                &Term::PartialString(..) |
-                &Term::CompleteString(..) |
-                &Term::Literal(_, Literal::String(..)) => {
+                &Term::Clause(..)
+                | &Term::Cons(..)
+                | &Term::PartialString(..)
+                | &Term::CompleteString(..)
+                | &Term::Literal(_, Literal::String(..)) => {
                     instr!("$succeed")
                 }
                 &Term::Var(ref vr, ref name) => {
@@ -644,7 +667,13 @@ impl<'b> CodeGenerator<'b> {
                 }
                 &Term::Var(ref vr, ref name) => {
                     self.marker.reset_arg(1);
-                    let r = self.marker.mark_non_callable(name.to_var_num().unwrap(), 1,  term_loc, vr, code);
+                    let r = self.marker.mark_non_callable(
+                        name.to_var_num().unwrap(),
+                        1,
+                        term_loc,
+                        vr,
+                        code,
+                    );
                     instr!("rational", r)
                 }
                 _ => {
@@ -673,10 +702,10 @@ impl<'b> CodeGenerator<'b> {
                 }
             },
             &InlinedClauseType::IsNumber(..) => match &terms[0] {
-                &Term::Literal(_, Literal::Float(_)) |
-                &Term::Literal(_, Literal::Rational(_)) |
-                &Term::Literal(_, Literal::Integer(_)) |
-                &Term::Literal(_, Literal::Fixnum(_)) => {
+                &Term::Literal(_, Literal::Float(_))
+                | &Term::Literal(_, Literal::Rational(_))
+                | &Term::Literal(_, Literal::Integer(_))
+                | &Term::Literal(_, Literal::Fixnum(_)) => {
                     instr!("$succeed")
                 }
                 &Term::Var(ref vr, ref name) => {
@@ -718,8 +747,7 @@ impl<'b> CodeGenerator<'b> {
                 }
             },
             &InlinedClauseType::IsInteger(..) => match &terms[0] {
-                &Term::Literal(_, Literal::Integer(_)) |
-                &Term::Literal(_, Literal::Fixnum(_)) => {
+                &Term::Literal(_, Literal::Integer(_)) | &Term::Literal(_, Literal::Fixnum(_)) => {
                     instr!("$succeed")
                 }
                 &Term::Var(ref vr, ref name) => {
@@ -740,11 +768,11 @@ impl<'b> CodeGenerator<'b> {
                 }
             },
             &InlinedClauseType::IsVar(..) => match &terms[0] {
-                &Term::Literal(..) |
-                &Term::Clause(..) |
-                &Term::Cons(..) |
-                &Term::PartialString(..) |
-                &Term::CompleteString(..) => {
+                &Term::Literal(..)
+                | &Term::Clause(..)
+                | &Term::Cons(..)
+                | &Term::PartialString(..)
+                | &Term::CompleteString(..) => {
                     instr!("$fail")
                 }
                 &Term::AnonVar => {
@@ -791,11 +819,11 @@ impl<'b> CodeGenerator<'b> {
         call_policy: CallPolicy,
     ) -> Result<(), CompilationError> {
         macro_rules! compile_expr {
-            ($self:expr, $terms:expr, $term_loc:expr, $code:expr) => ({
+            ($self:expr, $terms:expr, $term_loc:expr, $code:expr) => {{
                 let (acode, at) = $self.compile_arith_expr($terms, 1, $term_loc, 2)?;
                 $code.extend(acode.into_iter());
                 at
-            });
+            }};
         }
 
         self.marker.reset_arg(2);
@@ -804,22 +832,52 @@ impl<'b> CodeGenerator<'b> {
             &Term::Var(ref vr, ref name) => {
                 let var_num = name.to_var_num().unwrap();
 
-                self.marker.mark_var::<QueryInstruction>(
-                    var_num,
-                    Level::Shallow,
-                    vr,
-                    term_loc,
-                    code,
-                );
+                if self.marker.var_data.records[var_num].num_occurrences > 1 {
+                    self.marker.mark_var::<QueryInstruction>(
+                        var_num,
+                        Level::Shallow,
+                        vr,
+                        term_loc,
+                        code,
+                    );
 
-                self.marker.mark_safe_var_unconditionally(var_num);
+                    self.marker.mark_safe_var_unconditionally(var_num);
+                    compile_expr!(self, &terms[1], term_loc, code)
+                } else {
+                    if let Term::Var(ref vr, ref var) = &terms[1] {
+                        let var_num = var.to_var_num().unwrap();
 
-                compile_expr!(self, &terms[1], term_loc, code)
+                        // if var is an anonymous variable, insert
+                        // is/2 call so that an instantiation error is
+                        // thrown when the predicate is run.
+                        if self.marker.var_data.records[var_num].num_occurrences > 1 {
+                            self.marker.mark_var::<QueryInstruction>(
+                                var_num,
+                                Level::Shallow,
+                                vr,
+                                term_loc,
+                                code,
+                            );
+
+                            self.marker.mark_safe_var_unconditionally(var_num);
+
+                            let at = ArithmeticTerm::Reg(vr.get().norm());
+                            self.add_call(code, instr!("$get_number", at), call_policy);
+
+                            return Ok(());
+                        }
+                    }
+
+                    compile_expr!(self, &terms[1], term_loc, code)
+                }
             }
-            &Term::Literal(_, c @ Literal::Integer(_) |
-                              c @ Literal::Float(_) |
-                              c @ Literal::Rational(_) |
-                              c @ Literal::Fixnum(_)) => {
+            &Term::Literal(
+                _,
+                c @ Literal::Integer(_)
+                | c @ Literal::Float(_)
+                | c @ Literal::Rational(_)
+                | c @ Literal::Fixnum(_),
+            ) => {
                 let v = HeapCellValue::from(c);
                 code.push_back(instr!("put_constant", Level::Shallow, v, temp_v!(1)));
 
@@ -892,10 +950,15 @@ impl<'b> CodeGenerator<'b> {
                                     code.push_back(instr!("proceed"));
                                 }
                             }
-                            &QueryTerm::LocalCut(var_num) => {
+                            &QueryTerm::LocalCut { var_num, cut_prev } => {
                                 let code = branch_code_stack.code(code);
                                 let r = self.marker.get_binding(var_num);
-                                code.push_back(instr!("cut", r));
+
+                                code.push_back(if cut_prev {
+                                    instr!("cut_prev", r)
+                                } else {
+                                    instr!("cut", r)
+                                });
 
                                 if self.marker.in_tail_position {
                                     if self.marker.var_data.allocates {
@@ -912,15 +975,29 @@ impl<'b> CodeGenerator<'b> {
                                 ClauseType::BuiltIn(BuiltInClauseType::Is(..)),
                                 ref terms,
                                 call_policy,
-                            ) => self.compile_is_call(terms, branch_code_stack.code(code), term_loc, call_policy)?,
+                            ) => self.compile_is_call(
+                                terms,
+                                branch_code_stack.code(code),
+                                term_loc,
+                                call_policy,
+                            )?,
                             &QueryTerm::Clause(_, ClauseType::Inlined(ref ct), ref terms, _) => {
-                                self.compile_inlined(ct, terms, term_loc, branch_code_stack.code(code))?
+                                self.compile_inlined(
+                                    ct,
+                                    terms,
+                                    term_loc,
+                                    branch_code_stack.code(code),
+                                )?
                             }
                             &QueryTerm::Fail => {
                                 branch_code_stack.code(code).push_back(instr!("$fail"));
                             }
                             term @ &QueryTerm::Clause(..) => {
-                                self.compile_query_line(term, term_loc, branch_code_stack.code(code));
+                                self.compile_query_line(
+                                    term,
+                                    term_loc,
+                                    branch_code_stack.code(code),
+                                );
 
                                 if self.marker.max_reg_allocated() > MAX_ARITY {
                                     return Err(CompilationError::ExceededMaxArity);
@@ -948,7 +1025,8 @@ impl<'b> CodeGenerator<'b> {
                 }
                 ClauseItem::BranchEnd(depth) => {
                     if !clause_iter.in_tail_position() {
-                        let subsumed_hits = branch_code_stack.push_missing_vars(depth, &mut self.marker);
+                        let subsumed_hits =
+                            branch_code_stack.push_missing_vars(depth, &mut self.marker);
                         self.marker.pop_branch(depth, subsumed_hits);
                         branch_code_stack.push_jump_instrs(depth);
                     } else {
@@ -974,8 +1052,15 @@ impl<'b> CodeGenerator<'b> {
         Ok(())
     }
 
-    pub(crate) fn compile_rule(&mut self, rule: &Rule, var_data: VarData) -> Result<Code, CompilationError> {
-        let Rule { head: (_, args), clauses } = rule;
+    pub(crate) fn compile_rule(
+        &mut self,
+        rule: &Rule,
+        var_data: VarData,
+    ) -> Result<Code, CompilationError> {
+        let Rule {
+            head: (_, args),
+            clauses,
+        } = rule;
         self.marker.var_data = var_data;
         let mut code = VecDeque::new();
 
@@ -996,7 +1081,11 @@ impl<'b> CodeGenerator<'b> {
         Ok(Vec::from(code))
     }
 
-    pub(crate) fn compile_fact(&mut self, fact: &Fact, var_data: VarData) -> Result<Code, CompilationError> {
+    pub(crate) fn compile_fact(
+        &mut self,
+        fact: &Fact,
+        var_data: VarData,
+    ) -> Result<Code, CompilationError> {
         let mut code = Vec::new();
         self.marker.var_data = var_data;
 
@@ -1004,10 +1093,7 @@ impl<'b> CodeGenerator<'b> {
             self.marker.reset_at_head(args);
 
             let iter = FactInstruction::iter(&fact.head);
-            let compiled_fact = self.compile_target::<FactInstruction, _>(
-                iter,
-                GenContext::Head,
-            );
+            let compiled_fact = self.compile_target::<FactInstruction, _>(iter, GenContext::Head);
 
             if self.marker.max_reg_allocated() > MAX_ARITY {
                 return Err(CompilationError::ExceededMaxArity);
@@ -1032,7 +1118,7 @@ impl<'b> CodeGenerator<'b> {
             &QueryTerm::Clause(_, ref ct, _, call_policy) => {
                 self.add_call(code, ct.to_instr(), call_policy);
             }
-            _ => unreachable!()
+            _ => unreachable!(),
         };
     }
 
@@ -1045,8 +1131,7 @@ impl<'b> CodeGenerator<'b> {
             if let Some(args) = clause.args() {
                 for (instantiated_arg_index, arg) in args.iter().enumerate() {
                     match arg {
-                        Term::Var(..) | Term::AnonVar => {
-                        }
+                        Term::Var(..) | Term::AnonVar => {}
                         _ => {
                             if optimal_index != instantiated_arg_index {
                                 if left >= right {
@@ -1071,7 +1156,11 @@ impl<'b> CodeGenerator<'b> {
             }
 
             if left < right {
-                subseqs.push(ClauseSpan { left, right, instantiated_arg_index: optimal_index });
+                subseqs.push(ClauseSpan {
+                    left,
+                    right,
+                    instantiated_arg_index: optimal_index,
+                });
             }
 
             optimal_index = 0;
@@ -1102,7 +1191,8 @@ impl<'b> CodeGenerator<'b> {
         optimal_index: usize,
     ) -> Result<Code, CompilationError> {
         let mut code = VecDeque::new();
-        let mut code_offsets = CodeOffsets::new(I::new(), optimal_index + 1);
+        let mut code_offsets =
+            CodeOffsets::new(I::new(), optimal_index + 1, self.settings.non_counted_bt);
 
         let mut skip_stub_try_me_else = false;
         let clauses_len = clauses.len();
@@ -1147,7 +1237,9 @@ impl<'b> CodeGenerator<'b> {
                 skip_stub_try_me_else = !self.settings.is_dynamic();
             }
 
-            let arg = clause.args().and_then(|args| args.iter().nth(optimal_index));
+            let arg = clause
+                .args()
+                .and_then(|args| args.iter().nth(optimal_index));
 
             if let Some(arg) = arg {
                 let index = code.len();
@@ -1190,7 +1282,12 @@ impl<'b> CodeGenerator<'b> {
         let split_pred = Self::split_predicate(&clauses);
         let multi_seq = split_pred.len() > 1;
 
-        for ClauseSpan { left, right, instantiated_arg_index } in split_pred {
+        for ClauseSpan {
+            left,
+            right,
+            instantiated_arg_index,
+        } in split_pred
+        {
             let skel_lower_bound = self.skeleton.clauses.len();
             let code_segment = if self.settings.is_dynamic() {
                 self.compile_pred_subseq::<DynamicCodeIndices>(
@@ -1221,9 +1318,8 @@ impl<'b> CodeGenerator<'b> {
             if self.settings.is_extensible {
                 let segment_is_indexed = code_segment[0].to_indexing_line().is_some();
 
-                for clause_index_info in self.skeleton.clauses
-                                             .make_contiguous()[skel_lower_bound..]
-                                             .iter_mut()
+                for clause_index_info in
+                    self.skeleton.clauses.make_contiguous()[skel_lower_bound..].iter_mut()
                 {
                     clause_index_info.clause_start +=
                         clause_start_offset + 2 * (segment_is_indexed as usize);

src/debray_allocator.rs

@@ -76,11 +76,16 @@ impl BranchStack {
         }
     }
 
-    fn safety_unneeded_in_branch(&self, safety: &VarSafetyStatus, branch: &BranchDesignator) -> bool {
+    fn safety_unneeded_in_branch(
+        &self,
+        safety: &VarSafetyStatus,
+        branch: &BranchDesignator,
+    ) -> bool {
         match safety {
             VarSafetyStatus::Needed => false,
-            VarSafetyStatus::LocallyUnneeded(planter_branch) =>
-                self.branch_subsumes(planter_branch, branch),
+            VarSafetyStatus::LocallyUnneeded(planter_branch) => {
+                self.branch_subsumes(planter_branch, branch)
+            }
             VarSafetyStatus::GloballyUnneeded => true,
         }
     }
@@ -91,7 +96,9 @@ impl BranchStack {
 
             let num_branches = occurrences.num_branches;
 
-            let entry = occurrences.hits.entry(var_num)
+            let entry = occurrences
+                .hits
+                .entry(var_num)
                 .or_insert_with(|| BitVec::repeat(false, num_branches));
 
             entry.set(occurrences.current_branch, true);
@@ -105,11 +112,15 @@ impl BranchStack {
 
     pub(crate) fn current_branch_designator(&self) -> BranchDesignator {
         let branch_stack_num = self.len();
-        let branch_num = self.last()
+        let branch_num = self
+            .last()
             .map(|occurrences| occurrences.current_branch)
             .unwrap_or(0);
 
-        BranchDesignator { branch_stack_num, branch_num }
+        BranchDesignator {
+            branch_stack_num,
+            branch_num,
+        }
     }
 
     #[inline]
@@ -121,7 +132,7 @@ impl BranchStack {
     #[inline]
     pub(crate) fn drain_branches(&mut self, depth: usize) -> std::vec::Drain<BranchOccurrences> {
         let start_idx = self.len() - depth;
-        self.drain(start_idx ..)
+        self.drain(start_idx..)
     }
 }
 
@@ -156,13 +167,23 @@ impl DebrayAllocator {
             match &mut self.var_data.records[var_num].allocation {
                 VarAlloc::Perm(_, ref mut allocation) => {
                     match allocation {
-                        PermVarAllocation::Done { shallow_safety, deep_safety, .. } => {
-                            if !self.branch_stack.safety_unneeded_in_branch(shallow_safety, &branch_designator) {
+                        PermVarAllocation::Done {
+                            shallow_safety,
+                            deep_safety,
+                            ..
+                        } => {
+                            if !self
+                                .branch_stack
+                                .safety_unneeded_in_branch(shallow_safety, &branch_designator)
+                            {
                                 let branch_occurrences = self.branch_stack.last_mut().unwrap();
                                 branch_occurrences.shallow_safety.insert(var_num);
                             }
 
-                            if !self.branch_stack.safety_unneeded_in_branch(deep_safety, &branch_designator) {
+                            if !self
+                                .branch_stack
+                                .safety_unneeded_in_branch(deep_safety, &branch_designator)
+                            {
                                 let branch_occurrences = self.branch_stack.last_mut().unwrap();
                                 branch_occurrences.deep_safety.insert(var_num);
                             }
@@ -182,15 +203,15 @@ impl DebrayAllocator {
     pub(crate) fn pop_branch(&mut self, depth: usize, subsumed_hits: SubsumedBranchHits) {
         let removed_branches = self.branch_stack.drain_branches(depth);
 
-        let (deep_safety, shallow_safety) = removed_branches
-            .into_iter()
-            .fold((BitSet::default(), BitSet::default()),
-                  |(mut deep_safety, mut shallow_safety), branch_occurrences| {
-                      deep_safety.union_with(&branch_occurrences.deep_safety);
-                      shallow_safety.union_with(&branch_occurrences.shallow_safety);
+        let (deep_safety, shallow_safety) = removed_branches.into_iter().fold(
+            (BitSet::default(), BitSet::default()),
+            |(mut deep_safety, mut shallow_safety), branch_occurrences| {
+                deep_safety.union_with(&branch_occurrences.deep_safety);
+                shallow_safety.union_with(&branch_occurrences.shallow_safety);
 
-                      (deep_safety, shallow_safety)
-                  });
+                (deep_safety, shallow_safety)
+            },
+        );
 
         let branch_designator = self.branch_stack.current_branch_designator();
 
@@ -201,7 +222,7 @@ impl DebrayAllocator {
 
                 (&latest_branch.deep_safety, &latest_branch.shallow_safety)
             }
-            None => (&deep_safety, &shallow_safety)
+            None => (&deep_safety, &shallow_safety),
         };
 
         for var_num in subsumed_hits.iter().cloned() {
@@ -221,10 +242,13 @@ impl DebrayAllocator {
                     );
 
                     if running_count < num_occurrences {
-                        *allocation = PermVarAllocation::Done { shallow_safety, deep_safety };
+                        *allocation = PermVarAllocation::Done {
+                            shallow_safety,
+                            deep_safety,
+                        };
                     }
                 }
-                _ => unreachable!()
+                _ => unreachable!(),
             }
         }
 
@@ -244,9 +268,11 @@ impl DebrayAllocator {
 
     fn occurs_shallowly_in_head(&self, var_num: usize, r: usize) -> bool {
         match &self.var_data.records[var_num].allocation {
-            VarAlloc::Temp { temp_var_data, term_loc: GenContext::Head, .. } => {
-                temp_var_data.use_set.contains(&(GenContext::Head, r))
-            }
+            VarAlloc::Temp {
+                temp_var_data,
+                term_loc: GenContext::Head,
+                ..
+            } => temp_var_data.use_set.contains(&(GenContext::Head, r)),
             _ => false,
         }
     }
@@ -325,12 +351,14 @@ impl DebrayAllocator {
 
                 match &self.var_data.records[t_var].allocation {
                     VarAlloc::Temp { temp_var_data, .. } => {
-                        if !temp_var_data.use_set.contains(&(GenContext::Last(chunk_num), k)) {
+                        if !temp_var_data
+                            .use_set
+                            .contains(&(GenContext::Last(chunk_num), k))
+                        {
                             return Some((t_var, self.alloc_with_ca(t_var)));
                         }
                     }
-                    _ => {
-                    }
+                    _ => {}
                 }
 
                 None
@@ -356,7 +384,9 @@ impl DebrayAllocator {
                     self.shallow_temp_mappings.swap_remove(&k);
                     self.shallow_temp_mappings.insert(r.reg_num(), var_num);
 
-                    self.var_data.records[var_num].allocation.set_register(r.reg_num());
+                    self.var_data.records[var_num]
+                        .allocation
+                        .set_register(r.reg_num());
                     self.in_use.insert(r.reg_num());
                 }
             }
@@ -417,12 +447,9 @@ impl DebrayAllocator {
     fn in_place(&self, var_num: usize, term_loc: GenContext, r: RegType, k: usize) -> bool {
         match term_loc {
             GenContext::Head if !r.is_perm() => r.reg_num() == k,
-            _ => {
-                match &self.var_data.records[var_num].allocation {
-                    &VarAlloc::Temp { temp_reg, .. } if r.reg_num() == k =>
-                        temp_reg == k,
-                    _ => false,
-                }
+            _ => match &self.var_data.records[var_num].allocation {
+                &VarAlloc::Temp { temp_reg, .. } if r.reg_num() == k => temp_reg == k,
+                _ => false,
             },
         }
     }
@@ -483,8 +510,7 @@ impl DebrayAllocator {
                     VarAlloc::Perm(p, PermVarAllocation::Pending) if *p > 0 => {
                         return Some(std::mem::replace(p, 0));
                     }
-                    _ => {
-                    }
+                    _ => {}
                 }
             } else {
                 return None;
@@ -500,8 +526,7 @@ impl DebrayAllocator {
                 *allocation = PermVarAllocation::Pending;
                 self.add_perm_to_free_list(chunk_num, var_num);
             }
-            _ => {
-            }
+            _ => {}
         }
     }
 
@@ -509,7 +534,14 @@ impl DebrayAllocator {
         let branch_designator = self.branch_stack.current_branch_designator();
 
         match &mut self.var_data.records[var_num].allocation {
-            VarAlloc::Perm(_, PermVarAllocation::Done { deep_safety, shallow_safety, .. }) => {
+            VarAlloc::Perm(
+                _,
+                PermVarAllocation::Done {
+                    deep_safety,
+                    shallow_safety,
+                    ..
+                },
+            ) => {
                 *deep_safety = VarSafetyStatus::unneeded(branch_designator);
                 *shallow_safety = VarSafetyStatus::unneeded(branch_designator);
             }
@@ -524,7 +556,14 @@ impl DebrayAllocator {
         let branch_designator = self.branch_stack.current_branch_designator();
 
         match &mut self.var_data.records[var_num].allocation {
-            VarAlloc::Perm(_, PermVarAllocation::Done { deep_safety, shallow_safety, .. }) => {
+            VarAlloc::Perm(
+                _,
+                PermVarAllocation::Done {
+                    deep_safety,
+                    shallow_safety,
+                    ..
+                },
+            ) => {
                 // GetVariable in head chunk is considered safe.
                 if lvl == Level::Deep {
                     *deep_safety = VarSafetyStatus::unneeded(branch_designator);
@@ -532,12 +571,16 @@ impl DebrayAllocator {
                 } else if term_loc == GenContext::Head {
                     *shallow_safety = VarSafetyStatus::GloballyUnneeded;
                 } else {
-                    if let Some(temp_var_num) = self.shallow_temp_mappings.get(&self.arg_c).cloned() {
+                    if let Some(temp_var_num) = self.shallow_temp_mappings.get(&self.arg_c).cloned()
+                    {
                         match &mut self.var_data.records[temp_var_num].allocation {
-                            VarAlloc::Temp { ref mut to_perm_var_num, .. } => {
+                            VarAlloc::Temp {
+                                ref mut to_perm_var_num,
+                                ..
+                            } => {
                                 *to_perm_var_num = Some(var_num);
                             }
-                            _ => unreachable!()
+                            _ => unreachable!(),
                         }
                     }
                 }
@@ -560,8 +603,18 @@ impl DebrayAllocator {
         let branch_designator = self.branch_stack.current_branch_designator();
 
         match &mut self.var_data.records[var_num].allocation {
-            VarAlloc::Perm(_, PermVarAllocation::Done { ref mut shallow_safety, .. }) => {
-                if !self.in_tail_position || self.branch_stack.safety_unneeded_in_branch(shallow_safety, &branch_designator) {
+            VarAlloc::Perm(
+                _,
+                PermVarAllocation::Done {
+                    ref mut shallow_safety,
+                    ..
+                },
+            ) => {
+                if !self.in_tail_position
+                    || self
+                        .branch_stack
+                        .safety_unneeded_in_branch(shallow_safety, &branch_designator)
+                {
                     Target::argument_to_value(r, arg_c)
                 } else {
                     *shallow_safety = VarSafetyStatus::unneeded(branch_designator);
@@ -569,7 +622,10 @@ impl DebrayAllocator {
                 }
             }
             VarAlloc::Temp { ref mut safety, .. } => {
-                if self.branch_stack.safety_unneeded_in_branch(safety, &branch_designator) {
+                if self
+                    .branch_stack
+                    .safety_unneeded_in_branch(safety, &branch_designator)
+                {
                     Target::argument_to_value(r, arg_c)
                 } else {
                     *safety = VarSafetyStatus::GloballyUnneeded;
@@ -590,8 +646,17 @@ impl DebrayAllocator {
         let branch_designator = self.branch_stack.current_branch_designator();
 
         match &mut self.var_data.records[var_num].allocation {
-            VarAlloc::Perm(_, PermVarAllocation::Done { ref mut deep_safety, .. }) => {
-                if self.branch_stack.safety_unneeded_in_branch(deep_safety, &branch_designator) {
+            VarAlloc::Perm(
+                _,
+                PermVarAllocation::Done {
+                    ref mut deep_safety,
+                    ..
+                },
+            ) => {
+                if self
+                    .branch_stack
+                    .safety_unneeded_in_branch(deep_safety, &branch_designator)
+                {
                     Target::subterm_to_value(r)
                 } else {
                     *deep_safety = VarSafetyStatus::unneeded(branch_designator);
@@ -599,7 +664,10 @@ impl DebrayAllocator {
                 }
             }
             VarAlloc::Temp { ref mut safety, .. } => {
-                if self.branch_stack.safety_unneeded_in_branch(safety, &branch_designator) {
+                if self
+                    .branch_stack
+                    .safety_unneeded_in_branch(safety, &branch_designator)
+                {
                     Target::subterm_to_value(r)
                 } else {
                     *safety = VarSafetyStatus::unneeded(branch_designator);
@@ -626,7 +694,7 @@ impl Allocator for DebrayAllocator {
             in_use: BitSet::default(),
             temp_free_list: vec![],
             perm_free_list: VecDeque::new(),
-            branch_stack: BranchStack { stack: vec![] }
+            branch_stack: BranchStack { stack: vec![] },
         }
     }
 
@@ -705,12 +773,14 @@ impl Allocator for DebrayAllocator {
             }
             r @ RegType::Perm(_) => {
                 let is_new_var = match &mut self.var_data.records[var_num].allocation {
-                    VarAlloc::Perm(_, allocation) => if allocation.pending() {
-                        *allocation = PermVarAllocation::done();
-                        true
-                    } else {
-                        false
-                    },
+                    VarAlloc::Perm(_, allocation) => {
+                        if allocation.pending() {
+                            *allocation = PermVarAllocation::done();
+                            true
+                        } else {
+                            false
+                        }
+                    }
                     _ => unreachable!(),
                 };
 
@@ -828,7 +898,9 @@ impl Allocator for DebrayAllocator {
                 if !r.is_perm() && r.reg_num() == 0 {
                     self.in_use.insert(idx + 1);
                     self.shallow_temp_mappings.insert(idx + 1, var_num);
-                    self.var_data.records[var_num].allocation.set_register(idx + 1);
+                    self.var_data.records[var_num]
+                        .allocation
+                        .set_register(idx + 1);
                 }
             }
         }

src/ffi.rs

@@ -24,12 +24,12 @@ use crate::atom_table::Atom;
 use std::alloc::{alloc, Layout};
 use std::any::Any;
 use std::collections::HashMap;
-use std::error::Error;
-use std::ffi::{CString, c_void};
 use std::convert::TryFrom;
+use std::error::Error;
+use std::ffi::{c_void, CString};
 
-use libffi::low::{ffi_cif, types, CodePtr, ffi_abi_FFI_DEFAULT_ABI, prep_cif, ffi_type, type_tag};
-use libloading::{Symbol, Library};
+use libffi::low::{ffi_abi_FFI_DEFAULT_ABI, ffi_cif, ffi_type, prep_cif, type_tag, types, CodePtr};
+use libloading::{Library, Symbol};
 
 pub struct FunctionDefinition {
     pub name: String,
@@ -65,338 +65,393 @@ struct PointerArgs {
 
 impl ForeignFunctionTable {
     pub fn merge(&mut self, other: ForeignFunctionTable) {
-	self.table.extend(other.table);
+        self.table.extend(other.table);
     }
 
     pub fn define_struct(&mut self, name: &str, atom_fields: Vec<Atom>) {
-	let mut fields: Vec<_> = atom_fields.iter().map(|x| self.map_type_ffi(&x)).collect();
-	fields.push(std::ptr::null_mut::<ffi_type>());
-	let mut struct_type: ffi_type = Default::default();
-	struct_type.type_ = type_tag::STRUCT;
-	struct_type.elements = fields.as_mut_ptr();
-	self.structs.insert(name.to_string(), StructImpl { ffi_type: struct_type, fields, atom_fields});
+        let mut fields: Vec<_> = atom_fields.iter().map(|x| self.map_type_ffi(&x)).collect();
+        fields.push(std::ptr::null_mut::<ffi_type>());
+        let mut struct_type: ffi_type = Default::default();
+        struct_type.type_ = type_tag::STRUCT;
+        struct_type.elements = fields.as_mut_ptr();
+        self.structs.insert(
+            name.to_string(),
+            StructImpl {
+                ffi_type: struct_type,
+                fields,
+                atom_fields,
+            },
+        );
     }
 
     fn map_type_ffi(&mut self, source: &Atom) -> *mut ffi_type {
-	unsafe {
-	    match source {
-		atom!("sint64") => &mut types::sint64,
-		atom!("sint32") => &mut types::sint32,
-		atom!("sint16") => &mut types::sint16,
-		atom!("sint8") => &mut types::sint8,
-		atom!("uint64") => &mut types::uint64,
-		atom!("uint32") => &mut types::uint32,
-		atom!("uint16") => &mut types::uint16,
-		atom!("uint8") => &mut types::uint8,
-		atom!("bool") => &mut types::sint8,
-		atom!("void") => &mut types::void,
-		atom!("cstr") => &mut types::pointer,
-		atom!("ptr") => &mut types::pointer,
-		atom!("f32") => &mut types::float,
-		atom!("f64") => &mut types::double,
-		struct_name => {
-		    match self.structs.get_mut(struct_name.as_str()) {
-			Some(ref mut struct_type) => {
-			    &mut struct_type.ffi_type
-			},
-			None => unreachable!()
-		    }
-		}
-	    }
-	}
+        unsafe {
+            match source {
+                atom!("sint64") => &mut types::sint64,
+                atom!("sint32") => &mut types::sint32,
+                atom!("sint16") => &mut types::sint16,
+                atom!("sint8") => &mut types::sint8,
+                atom!("uint64") => &mut types::uint64,
+                atom!("uint32") => &mut types::uint32,
+                atom!("uint16") => &mut types::uint16,
+                atom!("uint8") => &mut types::uint8,
+                atom!("bool") => &mut types::sint8,
+                atom!("void") => &mut types::void,
+                atom!("cstr") => &mut types::pointer,
+                atom!("ptr") => &mut types::pointer,
+                atom!("f32") => &mut types::float,
+                atom!("f64") => &mut types::double,
+                struct_name => match self.structs.get_mut(&*struct_name.as_str()) {
+                    Some(ref mut struct_type) => &mut struct_type.ffi_type,
+                    None => unreachable!(),
+                },
+            }
+        }
     }
 
-    pub(crate) fn load_library(&mut self, library_name: &str, functions: &Vec<FunctionDefinition>) -> Result<(), Box<dyn Error>> {
-	let mut ff_table: ForeignFunctionTable = Default::default();
-	unsafe {
-	    let library = Library::new(library_name)?;
-	    for function in functions {
-		let symbol_name: CString = CString::new(function.name.clone())?;
-		let code_ptr: Symbol<*mut c_void> = library.get(&symbol_name.into_bytes_with_nul())?;
-		let mut args: Vec<_> = function.args.iter().map(|x| self.map_type_ffi(&x)).collect();
-		let mut cif: ffi_cif = Default::default();
-		prep_cif(
-		    &mut cif,
-		    ffi_abi_FFI_DEFAULT_ABI,
-		    args.len(),
-		    self.map_type_ffi(&function.return_value),
-		    args.as_mut_ptr()
-		).unwrap();
+    pub(crate) fn load_library(
+        &mut self,
+        library_name: &str,
+        functions: &Vec<FunctionDefinition>,
+    ) -> Result<(), Box<dyn Error>> {
+        let mut ff_table: ForeignFunctionTable = Default::default();
+        unsafe {
+            let library = Library::new(library_name)?;
+            for function in functions {
+                let symbol_name: CString = CString::new(function.name.clone())?;
+                let code_ptr: Symbol<*mut c_void> =
+                    library.get(&symbol_name.into_bytes_with_nul())?;
+                let mut args: Vec<_> = function
+                    .args
+                    .iter()
+                    .map(|x| self.map_type_ffi(&x))
+                    .collect();
+                let mut cif: ffi_cif = Default::default();
+                prep_cif(
+                    &mut cif,
+                    ffi_abi_FFI_DEFAULT_ABI,
+                    args.len(),
+                    self.map_type_ffi(&function.return_value),
+                    args.as_mut_ptr(),
+                )
+                .unwrap();
 
-		let return_struct_name = if (*self.map_type_ffi(&function.return_value)).type_ as u32 == libffi::raw::FFI_TYPE_STRUCT {
-		    Some(function.return_value.as_str().to_string())
-		} else {
-		    None
-		};
+                let return_struct_name = if (*self.map_type_ffi(&function.return_value)).type_
+                    as u32
+                    == libffi::raw::FFI_TYPE_STRUCT
+                {
+                    Some(function.return_value.as_str().to_string())
+                } else {
+                    None
+                };
 
-		ff_table.table.insert(function.name.clone(), FunctionImpl {
-		    cif,
-		    args,
-		    code_ptr: CodePtr(code_ptr.into_raw().into_raw() as *mut _),
-		    return_struct_name,
-		});
-	    }
-	    std::mem::forget(library);
-	}
-	self.merge(ff_table);
-	Ok(())
+                ff_table.table.insert(
+                    function.name.clone(),
+                    FunctionImpl {
+                        cif,
+                        args,
+                        code_ptr: CodePtr(code_ptr.into_raw().into_raw() as *mut _),
+                        return_struct_name,
+                    },
+                );
+            }
+            std::mem::forget(library);
+        }
+        self.merge(ff_table);
+        Ok(())
     }
 
-    fn build_pointer_args(args: &mut Vec<Value>, type_args: &Vec<*mut ffi_type>, structs_table: &mut HashMap<String, StructImpl>) -> Result<PointerArgs, FFIError> {
-	let mut pointers = Vec::with_capacity(args.len());
-	let mut _memory = Vec::new();
-	for i in 0..args.len() {
-	    let field_type = type_args[i];
-	    unsafe {
-		macro_rules! push_int {
-		    ($type:ty) => {
-			{
-			    let n: $type = <$type>::try_from(args[i].as_int()?).map_err(|_| FFIError::ValueDontFit)?;
-			    let mut box_value = Box::new(n) as Box<dyn Any>;
-			    pointers.push(&mut *box_value as *mut _ as *mut c_void);
-			    _memory.push(box_value);
-			}
-		    }
-		}
-		
-		match (*field_type).type_ as u32 {
-		    libffi::raw::FFI_TYPE_UINT8 => push_int!(u8),
-		    libffi::raw::FFI_TYPE_SINT8 => push_int!(i8),
-		    libffi::raw::FFI_TYPE_UINT16 => push_int!(u16),
-		    libffi::raw::FFI_TYPE_SINT16 => push_int!(i16),
-		    libffi::raw::FFI_TYPE_UINT32 => push_int!(u32),
-		    libffi::raw::FFI_TYPE_SINT32 => push_int!(i32),
-		    libffi::raw::FFI_TYPE_UINT64 => push_int!(u64),
-		    libffi::raw::FFI_TYPE_SINT64 => push_int!(i64),
-		    libffi::raw::FFI_TYPE_FLOAT => {
-			let n: f32 = args[i].as_float()? as f32;
-			let mut box_value = Box::new(n) as Box<dyn Any>;
-			pointers.push(&mut *box_value as *mut _ as *mut c_void);
-			_memory.push(box_value);
-		    },
-		    libffi::raw::FFI_TYPE_DOUBLE => {
-			let n: f64 = args[i].as_float()?;
-			let mut box_value = Box::new(n) as Box<dyn Any>;
-			pointers.push(&mut *box_value as *mut _ as *mut c_void);
-			_memory.push(box_value);
-		    },
-		    libffi::raw::FFI_TYPE_POINTER => {
-			let ptr: *mut c_void = args[i].as_ptr()?;
-			pointers.push(ptr);
-		    },
-		    libffi::raw::FFI_TYPE_STRUCT => {
-			let (mut ptr, _size, _align) = Self::build_struct(&mut args[i], structs_table)?;
-			pointers.push(&mut *ptr as *mut _ as *mut c_void);
-			_memory.push(ptr);
-		    },
-		    _ => return Err(FFIError::InvalidFFIType)
-		}
-	    }
-	}
-	Ok(PointerArgs {
-	    pointers,
-	    _memory
-	})
+    fn build_pointer_args(
+        args: &mut Vec<Value>,
+        type_args: &Vec<*mut ffi_type>,
+        structs_table: &mut HashMap<String, StructImpl>,
+    ) -> Result<PointerArgs, FFIError> {
+        let mut pointers = Vec::with_capacity(args.len());
+        let mut _memory = Vec::new();
+        for i in 0..args.len() {
+            let field_type = type_args[i];
+            unsafe {
+                macro_rules! push_int {
+                    ($type:ty) => {{
+                        let n: $type = <$type>::try_from(args[i].as_int()?)
+                            .map_err(|_| FFIError::ValueDontFit)?;
+                        let mut box_value = Box::new(n) as Box<dyn Any>;
+                        pointers.push(&mut *box_value as *mut _ as *mut c_void);
+                        _memory.push(box_value);
+                    }};
+                }
+
+                match (*field_type).type_ as u32 {
+                    libffi::raw::FFI_TYPE_UINT8 => push_int!(u8),
+                    libffi::raw::FFI_TYPE_SINT8 => push_int!(i8),
+                    libffi::raw::FFI_TYPE_UINT16 => push_int!(u16),
+                    libffi::raw::FFI_TYPE_SINT16 => push_int!(i16),
+                    libffi::raw::FFI_TYPE_UINT32 => push_int!(u32),
+                    libffi::raw::FFI_TYPE_SINT32 => push_int!(i32),
+                    libffi::raw::FFI_TYPE_UINT64 => push_int!(u64),
+                    libffi::raw::FFI_TYPE_SINT64 => push_int!(i64),
+                    libffi::raw::FFI_TYPE_FLOAT => {
+                        let n: f32 = args[i].as_float()? as f32;
+                        let mut box_value = Box::new(n) as Box<dyn Any>;
+                        pointers.push(&mut *box_value as *mut _ as *mut c_void);
+                        _memory.push(box_value);
+                    }
+                    libffi::raw::FFI_TYPE_DOUBLE => {
+                        let n: f64 = args[i].as_float()?;
+                        let mut box_value = Box::new(n) as Box<dyn Any>;
+                        pointers.push(&mut *box_value as *mut _ as *mut c_void);
+                        _memory.push(box_value);
+                    }
+                    libffi::raw::FFI_TYPE_POINTER => {
+                        let ptr: *mut c_void = args[i].as_ptr()?;
+                        pointers.push(ptr);
+                    }
+                    libffi::raw::FFI_TYPE_STRUCT => {
+                        let (mut ptr, _size, _align) =
+                            Self::build_struct(&mut args[i], structs_table)?;
+                        pointers.push(&mut *ptr as *mut _ as *mut c_void);
+                        _memory.push(ptr);
+                    }
+                    _ => return Err(FFIError::InvalidFFIType),
+                }
+            }
+        }
+        Ok(PointerArgs { pointers, _memory })
     }
 
-    fn build_struct(arg: &mut Value, structs_table: &mut HashMap<String, StructImpl>) -> Result<(Box<dyn Any>, usize, usize), FFIError> {
-	unsafe {
-        match arg {
-	    Value::Struct(ref name, ref mut struct_args) => {
-		if let Some(ref mut struct_type) = structs_table.clone().get_mut(name) {
-		    let layout = Layout::from_size_align(struct_type.ffi_type.size, struct_type.ffi_type.alignment.into()).unwrap();
-		    let align = struct_type.ffi_type.alignment as usize;
-		    let size = struct_type.ffi_type.size;
-		    let ptr = alloc(layout) as *mut c_void;
-		    let mut field_ptr = ptr;
+    fn build_struct(
+        arg: &mut Value,
+        structs_table: &mut HashMap<String, StructImpl>,
+    ) -> Result<(Box<dyn Any>, usize, usize), FFIError> {
+        unsafe {
+            match arg {
+                Value::Struct(ref name, ref mut struct_args) => {
+                    if let Some(ref mut struct_type) = structs_table.clone().get_mut(name) {
+                        let layout = Layout::from_size_align(
+                            struct_type.ffi_type.size,
+                            struct_type.ffi_type.alignment.into(),
+                        )
+                        .unwrap();
+                        let align = struct_type.ffi_type.alignment as usize;
+                        let size = struct_type.ffi_type.size;
+                        let ptr = alloc(layout) as *mut c_void;
+                        let mut field_ptr = ptr;
 
-		    for i in 0..(struct_type.fields.len()-1) {
-			macro_rules! try_write_int {
-			    ($type:ty) => {
-				{
-				    field_ptr = field_ptr.add(field_ptr.align_offset(std::mem::align_of::<$type>()));
-				    let n: $type = <$type>::try_from(struct_args[i].as_int()?).map_err(|_| FFIError::ValueDontFit)?;
-				    std::ptr::write(field_ptr as *mut $type, n);
-				    field_ptr = field_ptr.add(std::mem::size_of::<$type>());
-				}
-			    }
-			}
+                        for i in 0..(struct_type.fields.len() - 1) {
+                            macro_rules! try_write_int {
+                                ($type:ty) => {{
+                                    field_ptr = field_ptr
+                                        .add(field_ptr.align_offset(std::mem::align_of::<$type>()));
+                                    let n: $type = <$type>::try_from(struct_args[i].as_int()?)
+                                        .map_err(|_| FFIError::ValueDontFit)?;
+                                    std::ptr::write(field_ptr as *mut $type, n);
+                                    field_ptr = field_ptr.add(std::mem::size_of::<$type>());
+                                }};
+                            }
 
-			macro_rules! write {
-			    ($type:ty, $value:expr) => {
-				{
-				    let data: $type = $value;
-				    std::ptr::write(field_ptr as *mut $type, data);
-				    field_ptr = field_ptr.add(align);
-				}
-			    }
-			}
+                            macro_rules! write {
+                                ($type:ty, $value:expr) => {{
+                                    let data: $type = $value;
+                                    std::ptr::write(field_ptr as *mut $type, data);
+                                    field_ptr = field_ptr.add(align);
+                                }};
+                            }
 
-			let field = struct_type.fields[i];
-			match (*field).type_ as u32 {
-			    libffi::raw::FFI_TYPE_UINT8 => try_write_int!(u8),
-			    libffi::raw::FFI_TYPE_SINT8 => try_write_int!(i8),
-			    libffi::raw::FFI_TYPE_UINT16 => try_write_int!(u16),
-			    libffi::raw::FFI_TYPE_SINT16 => try_write_int!(i16),
-			    libffi::raw::FFI_TYPE_UINT32 => try_write_int!(u32),
-			    libffi::raw::FFI_TYPE_SINT32 => try_write_int!(i32),
-			    libffi::raw::FFI_TYPE_UINT64 => try_write_int!(u64),
-			    libffi::raw::FFI_TYPE_SINT64 => try_write_int!(i64),
-			    libffi::raw::FFI_TYPE_POINTER => write!(*mut c_void, struct_args[i].as_ptr()?),
-			    libffi::raw::FFI_TYPE_FLOAT => write!(f32, struct_args[i].as_float()? as f32),
-			    libffi::raw::FFI_TYPE_DOUBLE => write!(f64, struct_args[i].as_float()?),
-			    libffi::raw::FFI_TYPE_STRUCT => {
-				let (struct_ptr, struct_size, struct_align) = Self::build_struct(&mut struct_args[i], structs_table)?;
-				field_ptr = field_ptr.add(field_ptr.align_offset(struct_align));
-				
-				std::ptr::copy(& *struct_ptr as *const _ as *const c_void, field_ptr as *mut c_void, struct_size);
-				field_ptr = field_ptr.add(struct_size);
-			    },
-			    _ => {
-				unreachable!()
-			    }
-			}
-		    }
-		    return Ok((Box::from_raw(ptr), size, align));
-		} else {
-		    return Err(FFIError::InvalidStructName);
-		}
-	    }
-	    _ => return Err(FFIError::ValueCast)
-	}
-	}
+                            let field = struct_type.fields[i];
+                            match (*field).type_ as u32 {
+                                libffi::raw::FFI_TYPE_UINT8 => try_write_int!(u8),
+                                libffi::raw::FFI_TYPE_SINT8 => try_write_int!(i8),
+                                libffi::raw::FFI_TYPE_UINT16 => try_write_int!(u16),
+                                libffi::raw::FFI_TYPE_SINT16 => try_write_int!(i16),
+                                libffi::raw::FFI_TYPE_UINT32 => try_write_int!(u32),
+                                libffi::raw::FFI_TYPE_SINT32 => try_write_int!(i32),
+                                libffi::raw::FFI_TYPE_UINT64 => try_write_int!(u64),
+                                libffi::raw::FFI_TYPE_SINT64 => try_write_int!(i64),
+                                libffi::raw::FFI_TYPE_POINTER => {
+                                    write!(*mut c_void, struct_args[i].as_ptr()?)
+                                }
+                                libffi::raw::FFI_TYPE_FLOAT => {
+                                    write!(f32, struct_args[i].as_float()? as f32)
+                                }
+                                libffi::raw::FFI_TYPE_DOUBLE => {
+                                    write!(f64, struct_args[i].as_float()?)
+                                }
+                                libffi::raw::FFI_TYPE_STRUCT => {
+                                    let (struct_ptr, struct_size, struct_align) =
+                                        Self::build_struct(&mut struct_args[i], structs_table)?;
+                                    field_ptr = field_ptr.add(field_ptr.align_offset(struct_align));
+
+                                    std::ptr::copy(
+                                        &*struct_ptr as *const _ as *const c_void,
+                                        field_ptr as *mut c_void,
+                                        struct_size,
+                                    );
+                                    field_ptr = field_ptr.add(struct_size);
+                                }
+                                _ => {
+                                    unreachable!()
+                                }
+                            }
+                        }
+                        return Ok((Box::from_raw(ptr), size, align));
+                    } else {
+                        return Err(FFIError::InvalidStructName);
+                    }
+                }
+                _ => return Err(FFIError::ValueCast),
+            }
+        }
     }
 
     pub fn exec(&mut self, name: &str, mut args: Vec<Value>) -> Result<Value, FFIError> {
-	let function_impl = self.table.get_mut(name).ok_or(FFIError::FunctionNotFound)?;
-	let mut pointer_args = Self::build_pointer_args(&mut args, &function_impl.args, &mut self.structs)?;
-	
-	return unsafe {
-	    macro_rules! call_and_return {
-		($type:ty) => {
-		    {
-			let mut n: Box<u8> = Box::new(0);
-			libffi::raw::ffi_call(
-			    &mut function_impl.cif,
-			    Some(*function_impl.code_ptr.as_safe_fun()),
-			    &mut *n as *mut _ as *mut c_void,
-			    pointer_args.pointers.as_mut_ptr() as *mut *mut c_void
-			);
-			Ok(Value::Int(i64::from(*n)))
-		    }
-		}
-	    }
-	    
-	    match (*function_impl.cif.rtype).type_ as u32 {
-		libffi::raw::FFI_TYPE_VOID => call_and_return!(i32),
-		libffi::raw::FFI_TYPE_UINT8 => call_and_return!(u8),
-		libffi::raw::FFI_TYPE_SINT8 => call_and_return!(i8),
-		libffi::raw::FFI_TYPE_UINT16 => call_and_return!(u16),
-		libffi::raw::FFI_TYPE_SINT16 => call_and_return!(i16),
-		libffi::raw::FFI_TYPE_UINT32 => call_and_return!(u32),
-		libffi::raw::FFI_TYPE_SINT32 => call_and_return!(i32),
-		libffi::raw::FFI_TYPE_UINT64 => {
-		    let mut n: Box<u64> = Box::new(0);
-		    libffi::raw::ffi_call(
-			&mut function_impl.cif,
-			Some(*function_impl.code_ptr.as_safe_fun()),
-			&mut *n as *mut _ as *mut c_void,
-			pointer_args.pointers.as_mut_ptr() as *mut *mut c_void
-		    );
-		    Ok(Value::Int(i64::try_from(*n).map_err(|_| FFIError::ValueDontFit)?))
-		},
-		libffi::raw::FFI_TYPE_SINT64 => call_and_return!(i64),
-		libffi::raw::FFI_TYPE_POINTER => call_and_return!(*mut c_void),
-		libffi::raw::FFI_TYPE_FLOAT => {
-		    let mut n: Box<f32> = Box::new(0.0);
-		    libffi::raw::ffi_call(
-			&mut function_impl.cif,
-			Some(*function_impl.code_ptr.as_safe_fun()),
-			&mut *n as *mut _ as *mut c_void,
-			pointer_args.pointers.as_mut_ptr() as *mut *mut c_void
-		    );
-		    Ok(Value::Float((*n).into()))
-		},
-		libffi::raw::FFI_TYPE_DOUBLE => {
-		    let mut n: Box<f64> = Box::new(0.0);
-		    libffi::raw::ffi_call(
-			&mut function_impl.cif,
-			Some(*function_impl.code_ptr.as_safe_fun()),
-			&mut *n as *mut _ as *mut c_void,
-			pointer_args.pointers.as_mut_ptr() as *mut *mut c_void
-		    );
-		    Ok(Value::Float(*n))
-		},
-		libffi::raw::FFI_TYPE_STRUCT => {
-		    let name = &function_impl.return_struct_name.clone().ok_or(FFIError::StructNotFound)?;
-		    let struct_type = self.structs.get(name).ok_or(FFIError::StructNotFound)?;
-		    let layout = Layout::from_size_align(struct_type.ffi_type.size, struct_type.ffi_type.alignment.into()).unwrap();
-		    let ptr = alloc(layout) as *mut c_void;
+        let function_impl = self.table.get_mut(name).ok_or(FFIError::FunctionNotFound)?;
+        let mut pointer_args =
+            Self::build_pointer_args(&mut args, &function_impl.args, &mut self.structs)?;
 
-		    libffi::raw::ffi_call(
-			&mut function_impl.cif,
-			Some(*function_impl.code_ptr.as_safe_fun()),
-			&mut *ptr as *mut _ as *mut c_void,
-			pointer_args.pointers.as_mut_ptr() as *mut *mut c_void
-		    );
-		    let struct_val = self.read_struct(ptr, name, struct_type);
-		    drop(Box::from_raw(ptr));
-		    struct_val
-		}
-	    _ => unreachable!()
-	    }
-	};
+        return unsafe {
+            macro_rules! call_and_return {
+                ($type:ty) => {{
+                    let mut n: Box<u8> = Box::new(0);
+                    libffi::raw::ffi_call(
+                        &mut function_impl.cif,
+                        Some(*function_impl.code_ptr.as_safe_fun()),
+                        &mut *n as *mut _ as *mut c_void,
+                        pointer_args.pointers.as_mut_ptr() as *mut *mut c_void,
+                    );
+                    Ok(Value::Int(i64::from(*n)))
+                }};
+            }
+
+            match (*function_impl.cif.rtype).type_ as u32 {
+                libffi::raw::FFI_TYPE_VOID => call_and_return!(i32),
+                libffi::raw::FFI_TYPE_UINT8 => call_and_return!(u8),
+                libffi::raw::FFI_TYPE_SINT8 => call_and_return!(i8),
+                libffi::raw::FFI_TYPE_UINT16 => call_and_return!(u16),
+                libffi::raw::FFI_TYPE_SINT16 => call_and_return!(i16),
+                libffi::raw::FFI_TYPE_UINT32 => call_and_return!(u32),
+                libffi::raw::FFI_TYPE_SINT32 => call_and_return!(i32),
+                libffi::raw::FFI_TYPE_UINT64 => {
+                    let mut n: Box<u64> = Box::new(0);
+                    libffi::raw::ffi_call(
+                        &mut function_impl.cif,
+                        Some(*function_impl.code_ptr.as_safe_fun()),
+                        &mut *n as *mut _ as *mut c_void,
+                        pointer_args.pointers.as_mut_ptr() as *mut *mut c_void,
+                    );
+                    Ok(Value::Int(
+                        i64::try_from(*n).map_err(|_| FFIError::ValueDontFit)?,
+                    ))
+                }
+                libffi::raw::FFI_TYPE_SINT64 => call_and_return!(i64),
+                libffi::raw::FFI_TYPE_POINTER => call_and_return!(*mut c_void),
+                libffi::raw::FFI_TYPE_FLOAT => {
+                    let mut n: Box<f32> = Box::new(0.0);
+                    libffi::raw::ffi_call(
+                        &mut function_impl.cif,
+                        Some(*function_impl.code_ptr.as_safe_fun()),
+                        &mut *n as *mut _ as *mut c_void,
+                        pointer_args.pointers.as_mut_ptr() as *mut *mut c_void,
+                    );
+                    Ok(Value::Float((*n).into()))
+                }
+                libffi::raw::FFI_TYPE_DOUBLE => {
+                    let mut n: Box<f64> = Box::new(0.0);
+                    libffi::raw::ffi_call(
+                        &mut function_impl.cif,
+                        Some(*function_impl.code_ptr.as_safe_fun()),
+                        &mut *n as *mut _ as *mut c_void,
+                        pointer_args.pointers.as_mut_ptr() as *mut *mut c_void,
+                    );
+                    Ok(Value::Float(*n))
+                }
+                libffi::raw::FFI_TYPE_STRUCT => {
+                    let name = &function_impl
+                        .return_struct_name
+                        .clone()
+                        .ok_or(FFIError::StructNotFound)?;
+                    let struct_type = self.structs.get(name).ok_or(FFIError::StructNotFound)?;
+                    let layout = Layout::from_size_align(
+                        struct_type.ffi_type.size,
+                        struct_type.ffi_type.alignment.into(),
+                    )
+                    .unwrap();
+                    let ptr = alloc(layout) as *mut c_void;
+
+                    libffi::raw::ffi_call(
+                        &mut function_impl.cif,
+                        Some(*function_impl.code_ptr.as_safe_fun()),
+                        &mut *ptr as *mut _ as *mut c_void,
+                        pointer_args.pointers.as_mut_ptr() as *mut *mut c_void,
+                    );
+                    let struct_val = self.read_struct(ptr, name, struct_type);
+                    drop(Box::from_raw(ptr));
+                    struct_val
+                }
+                _ => unreachable!(),
+            }
+        };
     }
 
-    fn read_struct(&self, ptr: *mut c_void, name: &str, struct_type: &StructImpl) -> Result<Value, FFIError> {
-	unsafe {
-	    let mut returns = Vec::new();
-	    let mut field_ptr = ptr;
+    fn read_struct(
+        &self,
+        ptr: *mut c_void,
+        name: &str,
+        struct_type: &StructImpl,
+    ) -> Result<Value, FFIError> {
+        unsafe {
+            let mut returns = Vec::new();
+            let mut field_ptr = ptr;
 
-	    for i in 0..(struct_type.fields.len()-1) {
-		let field = struct_type.fields[i];
+            for i in 0..(struct_type.fields.len() - 1) {
+                let field = struct_type.fields[i];
 
-		macro_rules! read_and_push_int {
-		    ($type:ty) => {
-			{
-			    field_ptr = field_ptr.add(field_ptr.align_offset(std::mem::align_of::<$type>()));
-			    let n = std::ptr::read(field_ptr as *mut $type);
-			    returns.push(Value::Int(i64::from(n)));
-			    field_ptr = field_ptr.add(std::mem::size_of::<$type>());
-			}
-		    }
-		}
+                macro_rules! read_and_push_int {
+                    ($type:ty) => {{
+                        field_ptr =
+                            field_ptr.add(field_ptr.align_offset(std::mem::align_of::<$type>()));
+                        let n = std::ptr::read(field_ptr as *mut $type);
+                        returns.push(Value::Int(i64::from(n)));
+                        field_ptr = field_ptr.add(std::mem::size_of::<$type>());
+                    }};
+                }
 
-		match (*field).type_ as u32 {
-		    libffi::raw::FFI_TYPE_UINT8 => read_and_push_int!(u8),
-		    libffi::raw::FFI_TYPE_SINT8 => read_and_push_int!(i8),
-		    libffi::raw::FFI_TYPE_UINT16 => read_and_push_int!(u16),
-		    libffi::raw::FFI_TYPE_SINT16 => read_and_push_int!(i16),
-		    libffi::raw::FFI_TYPE_UINT32 => read_and_push_int!(u32),
-		    libffi::raw::FFI_TYPE_SINT32 => read_and_push_int!(i32),
-		    libffi::raw::FFI_TYPE_UINT64 => {
-			field_ptr = field_ptr.add(field_ptr.align_offset(std::mem::align_of::<u64>()));
-			let n = std::ptr::read(field_ptr as *mut u64);
-			returns.push(Value::Int(i64::try_from(n).map_err(|_| FFIError::ValueDontFit)?));
-			field_ptr = field_ptr.add(std::mem::size_of::<u64>());
-		    },
-		    libffi::raw::FFI_TYPE_SINT64 => read_and_push_int!(i64),
-		    libffi::raw::FFI_TYPE_POINTER => read_and_push_int!(i64),
-		    libffi::raw::FFI_TYPE_STRUCT => {
-			let substruct = struct_type.atom_fields[i].as_str();
-			let struct_type = self.structs.get(substruct).ok_or(FFIError::StructNotFound)?;
-			field_ptr = field_ptr.add(field_ptr.align_offset(struct_type.ffi_type.alignment as usize));
-			let struct_val = self.read_struct(field_ptr, substruct, struct_type);
-			returns.push(struct_val?);
-			field_ptr = field_ptr.add(struct_type.ffi_type.size);
-		    },
-		    _ => {
-			unreachable!()
-		    }
-		}
-	    }
-	    Ok(Value::Struct(name.into(), returns))
-	}
+                match (*field).type_ as u32 {
+                    libffi::raw::FFI_TYPE_UINT8 => read_and_push_int!(u8),
+                    libffi::raw::FFI_TYPE_SINT8 => read_and_push_int!(i8),
+                    libffi::raw::FFI_TYPE_UINT16 => read_and_push_int!(u16),
+                    libffi::raw::FFI_TYPE_SINT16 => read_and_push_int!(i16),
+                    libffi::raw::FFI_TYPE_UINT32 => read_and_push_int!(u32),
+                    libffi::raw::FFI_TYPE_SINT32 => read_and_push_int!(i32),
+                    libffi::raw::FFI_TYPE_UINT64 => {
+                        field_ptr =
+                            field_ptr.add(field_ptr.align_offset(std::mem::align_of::<u64>()));
+                        let n = std::ptr::read(field_ptr as *mut u64);
+                        returns.push(Value::Int(
+                            i64::try_from(n).map_err(|_| FFIError::ValueDontFit)?,
+                        ));
+                        field_ptr = field_ptr.add(std::mem::size_of::<u64>());
+                    }
+                    libffi::raw::FFI_TYPE_SINT64 => read_and_push_int!(i64),
+                    libffi::raw::FFI_TYPE_POINTER => read_and_push_int!(i64),
+                    libffi::raw::FFI_TYPE_STRUCT => {
+                        let substruct = struct_type.atom_fields[i].as_str();
+                        let struct_type = self
+                            .structs
+                            .get(&*substruct)
+                            .ok_or(FFIError::StructNotFound)?;
+                        field_ptr = field_ptr
+                            .add(field_ptr.align_offset(struct_type.ffi_type.alignment as usize));
+                        let struct_val = self.read_struct(field_ptr, &*substruct, struct_type);
+                        returns.push(struct_val?);
+                        field_ptr = field_ptr.add(struct_type.ffi_type.size);
+                    }
+                    _ => {
+                        unreachable!()
+                    }
+                }
+            }
+            Ok(Value::Struct(name.into(), returns))
+        }
     }
 }
 
@@ -410,26 +465,26 @@ pub enum Value {
 
 impl Value {
     fn as_int(&self) -> Result<i64, FFIError> {
-	match self {
-	    Value::Int(n) => Ok(*n),
-	    _ => Err(FFIError::ValueCast),
-	}
+        match self {
+            Value::Int(n) => Ok(*n),
+            _ => Err(FFIError::ValueCast),
+        }
     }
 
     fn as_float(&self) -> Result<f64, FFIError> {
-	match self {
-	    Value::Float(n) => Ok(*n),
-	    Value::Int(n) => Ok(*n as f64),
-	    _ => Err(FFIError::ValueCast),
-	}
+        match self {
+            Value::Float(n) => Ok(*n),
+            Value::Int(n) => Ok(*n as f64),
+            _ => Err(FFIError::ValueCast),
+        }
     }
 
     fn as_ptr(&mut self) -> Result<*mut c_void, FFIError> {
-	match self {
-	    Value::CString(ref mut cstr) => Ok(&mut *cstr as *mut _ as *mut c_void),
-	    Value::Int(n) => Ok(*n as *mut c_void),
-	    _ => Err(FFIError::ValueCast)
-	}
+        match self {
+            Value::CString(ref mut cstr) => Ok(&mut *cstr as *mut _ as *mut c_void),
+            Value::Int(n) => Ok(*n as *mut c_void),
+            _ => Err(FFIError::ValueCast),
+        }
     }
 }
 

src/forms.rs

@@ -7,8 +7,8 @@ use crate::machine::loader::PredicateQueue;
 use crate::machine::machine_errors::*;
 use crate::machine::machine_indices::*;
 use crate::parser::ast::*;
-use crate::parser::parser::CompositeOpDesc;
 use crate::parser::dashu::{Integer, Rational};
+use crate::parser::parser::CompositeOpDesc;
 use crate::types::*;
 
 use fxhash::FxBuildHasher;
@@ -58,7 +58,7 @@ impl AppendOrPrepend {
 #[derive(Debug, Clone, Copy)]
 pub enum VarComparison {
     Indistinct,
-    Distinct
+    Distinct,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -153,11 +153,14 @@ impl DerefMut for ChunkedTermVec {
 impl ChunkedTermVec {
     #[inline]
     pub fn new() -> Self {
-        Self { chunk_vec: VecDeque::new() }
+        Self {
+            chunk_vec: VecDeque::new(),
+        }
     }
 
     pub fn reserve_branch(&mut self, capacity: usize) {
-        self.chunk_vec.push_back(ChunkedTerms::Branch(Vec::with_capacity(capacity)));
+        self.chunk_vec
+            .push_back(ChunkedTerms::Branch(Vec::with_capacity(capacity)));
     }
 
     pub fn push_branch_arm(&mut self, branch: VecDeque<ChunkedTerms>) {
@@ -173,19 +176,22 @@ impl ChunkedTermVec {
 
     #[inline]
     pub fn add_chunk(&mut self) {
-        self.chunk_vec.push_back(ChunkedTerms::Chunk(VecDeque::from(vec![])));
+        self.chunk_vec
+            .push_back(ChunkedTerms::Chunk(VecDeque::from(vec![])));
     }
 
     pub fn push_chunk_term(&mut self, term: QueryTerm) {
         match self.chunk_vec.back_mut() {
             Some(ChunkedTerms::Branch(_)) => {
-                self.chunk_vec.push_back(ChunkedTerms::Chunk(VecDeque::from(vec![term])));
+                self.chunk_vec
+                    .push_back(ChunkedTerms::Chunk(VecDeque::from(vec![term])));
             }
             Some(ChunkedTerms::Chunk(chunk)) => {
                 chunk.push_back(term);
             }
             None => {
-                self.chunk_vec.push_back(ChunkedTerms::Chunk(VecDeque::from(vec![term])));
+                self.chunk_vec
+                    .push_back(ChunkedTerms::Chunk(VecDeque::from(vec![term])));
             }
         }
     }
@@ -196,7 +202,7 @@ pub enum QueryTerm {
     // register, clause type, subterms, clause call policy.
     Clause(Cell<RegType>, ClauseType, Vec<Term>, CallPolicy),
     Fail,
-    LocalCut(usize), // var_num
+    LocalCut { var_num: usize, cut_prev: bool },  // var_num
     GlobalCut(usize), // var_num
     GetCutPoint { var_num: usize, prev_b: bool },
     GetLevel(usize), // var_num
@@ -266,11 +272,10 @@ impl ClauseInfo for Term {
     fn name(&self) -> Option<Atom> {
         match self {
             Term::Clause(_, name, terms) => {
-
                 match name {
                     atom!(":-") => {
                         match terms.len() {
-                            1 => None,            // a declaration.
+                            1 => None, // a declaration.
                             2 => terms[0].name(),
                             _ => Some(*name),
                         }
@@ -285,7 +290,7 @@ impl ClauseInfo for Term {
 
     fn arity(&self) -> usize {
         match self {
-            Term::Clause(_, name, terms) => match name.as_str() {
+            Term::Clause(_, name, terms) => match &*name.as_str() {
                 ":-" => match terms.len() {
                     1 => 0,
                     2 => terms[0].arity(),
@@ -410,7 +415,6 @@ pub(crate) fn fixity(spec: u32) -> Fixity {
     }
 }
 
-
 impl OpDecl {
     #[inline]
     pub(crate) fn new(op_desc: OpDesc, name: Atom) -> Self {
@@ -477,35 +481,27 @@ pub enum AtomOrString {
 
 impl AtomOrString {
     #[inline]
-    pub fn as_atom(&self, atom_tbl: &mut AtomTable) -> Atom {
+    pub fn as_atom(&self, atom_tbl: &AtomTable) -> Atom {
         match self {
-            &AtomOrString::Atom(atom) => {
-                atom
-            }
-            AtomOrString::String(string) => {
-                atom_tbl.build_with(&string)
-            }
+            &AtomOrString::Atom(atom) => atom,
+            AtomOrString::String(string) => AtomTable::build_with(atom_tbl, &string),
         }
     }
 
     #[inline]
-    pub fn as_str(&self) -> &str {
+    pub fn as_str(&self) -> AtomString<'_> {
         match self {
-            AtomOrString::Atom(atom) if atom == &atom!("[]") => "",
+            AtomOrString::Atom(atom) if atom == &atom!("[]") => AtomString::Static(""),
             AtomOrString::Atom(atom) => atom.as_str(),
-            AtomOrString::String(string) => string.as_str(),
+            AtomOrString::String(string) => AtomString::Static(string.as_str()),
         }
     }
 
     #[inline]
     pub fn to_string(self) -> String {
         match self {
-            AtomOrString::Atom(atom) => {
-                atom.as_str().to_owned()
-            }
-            AtomOrString::String(string) => {
-                string
-            }
+            AtomOrString::Atom(atom) => atom.as_str().to_owned(),
+            AtomOrString::String(string) => string,
         }
     }
 }
@@ -561,9 +557,7 @@ pub(crate) fn fetch_op_spec(name: Atom, arity: usize, op_dir: &OpDir) -> Option<
                 }
             })
         }
-        0 => {
-            fetch_atom_op_spec(name, None, op_dir)
-        }
+        0 => fetch_atom_op_spec(name, None, op_dir),
         _ => None,
     }
 }
@@ -595,10 +589,7 @@ pub struct Module {
 
 // Module's and related types are defined in forms.
 impl Module {
-    pub(crate) fn new(
-        module_decl: ModuleDecl,
-        listing_src: ListingSource,
-    ) -> Self {
+    pub(crate) fn new(module_decl: ModuleDecl, listing_src: ListingSource) -> Self {
         Module {
             module_decl,
             code_dir: CodeDir::with_hasher(FxBuildHasher::default()),
@@ -620,7 +611,7 @@ impl Module {
             meta_predicates: MetaPredicateDir::with_hasher(FxBuildHasher::default()),
             extensible_predicates: ExtensiblePredicates::with_hasher(FxBuildHasher::default()),
             local_extensible_predicates: LocalExtensiblePredicates::with_hasher(
-                FxBuildHasher::default()
+                FxBuildHasher::default(),
             ),
             listing_src: ListingSource::DynamicallyGenerated,
         }
@@ -923,8 +914,10 @@ impl PredicateInfo {
 
     #[inline]
     pub(crate) fn must_retract_local_clauses(&self, is_cross_module_clause: bool) -> bool {
-        self.is_extensible && self.has_clauses && !self.is_discontiguous &&
-            !(self.is_multifile && is_cross_module_clause)
+        self.is_extensible
+            && self.has_clauses
+            && !self.is_discontiguous
+            && !(self.is_multifile && is_cross_module_clause)
     }
 }
 
@@ -1013,19 +1006,17 @@ impl PredicateSkeleton {
         &mut self,
         clause_clause_loc: usize,
     ) -> Option<usize> {
-        let search_result = self.core.clause_clause_locs
-            .make_contiguous()[0..self.core.clause_assert_margin]
+        let search_result = self.core.clause_clause_locs.make_contiguous()
+            [0..self.core.clause_assert_margin]
             .binary_search_by(|loc| clause_clause_loc.cmp(&loc));
 
         match search_result {
             Ok(loc) => Some(loc),
-            Err(_) => {
-                self.core.clause_clause_locs
-                    .make_contiguous()[self.core.clause_assert_margin..]
-                    .binary_search_by(|loc| loc.cmp(&clause_clause_loc))
-                    .map(|loc| loc + self.core.clause_assert_margin)
-                    .ok()
-            }
+            Err(_) => self.core.clause_clause_locs.make_contiguous()
+                [self.core.clause_assert_margin..]
+                .binary_search_by(|loc| loc.cmp(&clause_clause_loc))
+                .map(|loc| loc + self.core.clause_assert_margin)
+                .ok(),
         }
     }
 }

src/heap_print.rs

@@ -1,7 +1,9 @@
 use crate::arena::*;
 use crate::atom_table::*;
 use crate::parser::ast::*;
-use crate::parser::dashu::{Integer, Rational};
+use crate::parser::dashu::{ibig, Integer, Rational};
+use crate::parser::dashu::base::RemEuclid;
+use crate::parser::dashu::integer::Sign;
 use crate::{
     alpha_numeric_char, capital_letter_char, cut_char, decimal_digit_char, graphic_token_char,
     is_fx, is_infix, is_postfix, is_prefix, is_xf, is_xfx, is_xfy, is_yfx, semicolon_char,
@@ -18,8 +20,6 @@ use crate::machine::stack::*;
 use crate::machine::streams::*;
 use crate::types::*;
 
-use dashu::base::DivRem;
-use dashu::base::DivRemEuclid;
 use ordered_float::OrderedFloat;
 
 use indexmap::IndexMap;
@@ -29,6 +29,7 @@ use std::convert::TryFrom;
 use std::iter::once;
 use std::net::{IpAddr, TcpListener};
 use std::rc::Rc;
+use std::sync::Arc;
 
 /* contains the location, name, precision and Specifier of the parent op. */
 #[derive(Debug, Copy, Clone)]
@@ -46,7 +47,7 @@ impl DirectedOp {
     }
 
     #[inline]
-    fn is_prefix(&self )-> bool {
+    fn is_prefix(&self) -> bool {
         match self {
             &DirectedOp::Left(_name, cell) | &DirectedOp::Right(_name, cell) => {
                 is_prefix!(cell.get_spec() as u32)
@@ -74,7 +75,7 @@ fn needs_bracketing(child_desc: OpDesc, op: &DirectedOp) -> bool {
         DirectedOp::Left(name, cell) => {
             let (priority, spec) = cell.get();
 
-            if name.as_str() == "-" {
+            if &*name.as_str() == "-" {
                 let child_assoc = child_desc.get_spec();
                 if is_prefix!(spec) && (is_postfix!(child_assoc) || is_infix!(child_assoc)) {
                     return true;
@@ -103,7 +104,7 @@ fn needs_bracketing(child_desc: OpDesc, op: &DirectedOp) -> bool {
     }
 }
 
-impl<'a> StackfulPreOrderHeapIter<'a> {
+impl<'a, ElideLists> StackfulPreOrderHeapIter<'a, ElideLists> {
     /*
      * descend into the subtree where the iterator is currently parked
      * and check that the leftmost leaf is a number, with every node
@@ -178,16 +179,16 @@ fn char_to_string(is_quoted: bool, c: char) -> String {
         '\u{08}' if is_quoted => "\\b".to_string(), // UTF-8 backspace
         '\u{07}' if is_quoted => "\\a".to_string(), // UTF-8 alert
         '\\' if is_quoted => "\\\\".to_string(),
-        ' ' | '\'' | '\n' | '\r' | '\t' | '\u{0b}' | '\u{0c}' | '\u{08}' | '\u{07}' | '"' | '\\' => {
-            c.to_string()
-        }
-        _ =>
+        ' ' | '\'' | '\n' | '\r' | '\t' | '\u{0b}' | '\u{0c}' | '\u{08}' | '\u{07}' | '"'
+        | '\\' => c.to_string(),
+        _ => {
             if c.is_whitespace() || c.is_control() {
                 // print all other control and whitespace characters in hex.
                 format!("\\x{:x}\\", c as u32)
             } else {
                 c.to_string()
             }
+        }
     }
 }
 
@@ -207,6 +208,15 @@ impl NumberFocus {
     }
 }
 
+#[derive(Debug, Clone, Copy)]
+struct CommaSeparatedCharList {
+    pstr: PartialString,
+    offset: usize,
+    max_depth: usize,
+    end_cell: HeapCellValue,
+    end_h: Option<usize>,
+}
+
 #[derive(Debug, Clone)]
 enum TokenOrRedirect {
     Atom(Atom),
@@ -217,7 +227,8 @@ enum TokenOrRedirect {
     CompositeRedirect(usize, DirectedOp),
     CurlyBracketRedirect(usize),
     FunctorRedirect(usize),
-    #[allow(unused)] IpAddr(IpAddr),
+    #[allow(unused)]
+    IpAddr(IpAddr),
     NumberFocus(usize, NumberFocus, Option<DirectedOp>),
     Open,
     Close,
@@ -231,6 +242,8 @@ enum TokenOrRedirect {
     OpenList(Rc<Cell<(bool, usize)>>),
     CloseList(Rc<Cell<(bool, usize)>>),
     HeadTailSeparator,
+    StackPop,
+    CommaSeparatedCharList(CommaSeparatedCharList),
 }
 
 pub(crate) fn requires_space(atom: &str, op: &str) -> bool {
@@ -394,7 +407,7 @@ fn is_numbered_var(name: Atom, arity: usize) -> bool {
 
 #[inline]
 fn negated_op_needs_bracketing(
-    iter: &StackfulPreOrderHeapIter,
+    iter: &StackfulPreOrderHeapIter<ListElider>,
     op_dir: &OpDir,
     op: &Option<DirectedOp>,
 ) -> bool {
@@ -467,8 +480,8 @@ pub fn fmt_float(mut fl: f64) -> String {
      */
 
     if let Some(e_index) = fl_str.find('e') {
-        if !fl_str[0 .. e_index].contains('.') {
-            return fl_str[0 .. e_index].to_string() + ".0" + &fl_str[e_index ..];
+        if !fl_str[0..e_index].contains('.') {
+            return fl_str[0..e_index].to_string() + ".0" + &fl_str[e_index..];
         }
     }
 
@@ -478,8 +491,8 @@ pub fn fmt_float(mut fl: f64) -> String {
 #[derive(Debug)]
 pub struct HCPrinter<'a, Outputter> {
     outputter: Outputter,
-    iter: StackfulPreOrderHeapIter<'a>,
-    atom_tbl: &'a mut AtomTable,
+    iter: StackfulPreOrderHeapIter<'a, ListElider>,
+    atom_tbl: Arc<AtomTable>,
     op_dir: &'a OpDir,
     state_stack: Vec<TokenOrRedirect>,
     toplevel_spec: Option<DirectedOp>,
@@ -513,13 +526,10 @@ pub(crate) fn numbervar(offset: &Integer, addr: HeapCellValue) -> Option<String>
             'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
         ];
 
-        let n_clone: Integer = n.clone();
+        let i: usize = (&n).rem_euclid(ibig!(26)).try_into().unwrap();
+        let j = n / ibig!(26);
 
-        let i = n.div_rem_euclid(Integer::from(26)).1.to_f32().value() as usize;
-        let j = n_clone.div_rem(Integer::from(26));
-        let j = <(Integer, Integer)>::from(j).0;
-
-        if j == Integer::from(0) {
+        if j.is_zero() {
             CHAR_CODES[i].to_string()
         } else {
             format!("{}{}", CHAR_CODES[i], j)
@@ -548,7 +558,7 @@ pub(crate) fn numbervar(offset: &Integer, addr: HeapCellValue) -> Option<String>
 impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
     pub fn new(
         heap: &'a mut Heap,
-        atom_tbl: &'a mut AtomTable,
+        atom_tbl: Arc<AtomTable>,
         stack: &'a mut Stack,
         op_dir: &'a OpDir,
         output: Outputter,
@@ -578,7 +588,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
     fn ambiguity_check(&self, atom: &str) -> bool {
         let tail = &self.outputter.as_str()[self.last_item_idx..];
 
-        if !self.quoted || non_quoted_token(atom.chars()) {
+        if atom == "," || !self.quoted || non_quoted_token(atom.chars()) {
             requires_space(tail, atom)
         } else {
             requires_space(tail, "'")
@@ -625,11 +635,12 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
             } else {
                 let op = DirectedOp::Left(name, spec);
 
-                self.state_stack.push(TokenOrRedirect::CompositeRedirect(max_depth, op));
+                self.state_stack
+                    .push(TokenOrRedirect::CompositeRedirect(max_depth, op));
                 self.state_stack.push(TokenOrRedirect::Op(name, spec));
             }
         } else {
-            match name.as_str() {
+            match &*name.as_str() {
                 "|" => {
                     self.format_bar_separator_op(max_depth, name, spec);
                     return;
@@ -643,19 +654,40 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
 
                 self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
             } else if self.check_max_depth(&mut max_depth) {
-                self.iter.pop_stack();
-                self.iter.pop_stack();
+                if is_xfy!(spec.get_spec()) {
+                    let left_directed_op = DirectedOp::Left(name, spec);
 
-                self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
-                self.state_stack.push(TokenOrRedirect::Op(name, spec));
-                self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
+                    self.state_stack.push(TokenOrRedirect::CompositeRedirect(
+                        0,
+                        left_directed_op,
+                    ));
+
+                    self.state_stack.push(TokenOrRedirect::Op(name, spec));
+                    self.state_stack.push(TokenOrRedirect::StackPop);
+                } else { // is_yfx!
+                    let right_directed_op = DirectedOp::Right(name, spec);
+
+                    self.state_stack.push(TokenOrRedirect::StackPop);
+                    self.state_stack.push(TokenOrRedirect::Op(name, spec));
+                    self.state_stack.push(TokenOrRedirect::CompositeRedirect(
+                        0,
+                        right_directed_op,
+                    ));
+                }
             } else {
                 let left_directed_op = DirectedOp::Left(name, spec);
                 let right_directed_op = DirectedOp::Right(name, spec);
 
-                self.state_stack.push(TokenOrRedirect::CompositeRedirect(max_depth, left_directed_op));
+                self.state_stack.push(TokenOrRedirect::CompositeRedirect(
+                    max_depth,
+                    left_directed_op,
+                ));
+
                 self.state_stack.push(TokenOrRedirect::Op(name, spec));
-                self.state_stack.push(TokenOrRedirect::CompositeRedirect(max_depth, right_directed_op));
+                self.state_stack.push(TokenOrRedirect::CompositeRedirect(
+                    max_depth,
+                    right_directed_op,
+                ));
             }
         }
     }
@@ -681,7 +713,8 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
             self.state_stack.push(TokenOrRedirect::Close);
 
             for _ in 0..arity {
-                self.state_stack.push(TokenOrRedirect::FunctorRedirect(max_depth));
+                self.state_stack
+                    .push(TokenOrRedirect::FunctorRedirect(max_depth));
                 self.state_stack.push(TokenOrRedirect::Comma);
             }
 
@@ -738,9 +771,9 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
             return false;
         }
 
-
         self.state_stack.push(TokenOrRedirect::RightCurly);
-        self.state_stack.push(TokenOrRedirect::CurlyBracketRedirect(max_depth));
+        self.state_stack
+            .push(TokenOrRedirect::CurlyBracketRedirect(max_depth));
         self.state_stack.push(TokenOrRedirect::LeftCurly);
 
         true
@@ -750,10 +783,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
         let h = self.iter.stack_last().unwrap();
 
         let cell = self.iter.read_cell(h);
-        let cell = heap_bound_store(
-            &self.iter.heap,
-            heap_bound_deref(&self.iter.heap, cell),
-        );
+        let cell = heap_bound_store(&self.iter.heap, heap_bound_deref(&self.iter.heap, cell));
 
         // 7.10.4
         if let Some(var) = numbervar(&self.numbervars_offset, cell) {
@@ -831,57 +861,93 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
         )
     }
 
-    fn check_for_seen(&mut self) -> Option<HeapCellValue> {
-        if let Some(cell) = self.iter.next() {
-            let is_cyclic = cell.get_forwarding_bit();
+    fn check_for_seen(&mut self, max_depth: &mut usize) -> Option<HeapCellValue> {
+        if let Some(mut orig_cell) = self.iter.next() {
+            loop {
+                let is_cyclic = orig_cell.get_forwarding_bit();
 
-            let cell = heap_bound_store(
-                self.iter.heap,
-                heap_bound_deref(self.iter.heap, cell),
-            );
-            let cell = unmark_cell_bits!(cell);
+                let cell = heap_bound_store(self.iter.heap, heap_bound_deref(self.iter.heap, orig_cell));
+                let cell = unmark_cell_bits!(cell);
 
-            match self.var_names.get(&cell).cloned() {
-                Some(var) if cell.is_var() => {
-                    // If cell is an unbound variable and maps to
-                    // a name via heap_locs, append the name to
-                    // the current output, and return None. None
-                    // short-circuits handle_heap_term.
-                    // self.iter.pop_stack();
+                match self.var_names.get(&cell).cloned() {
+                    Some(var) if cell.is_var() => {
+                        // If cell is an unbound variable and maps to
+                        // a name via heap_locs, append the name to
+                        // the current output, and return None. None
+                        // short-circuits handle_heap_term.
+                        // self.iter.pop_stack();
 
-                    let var_str = var.borrow().to_string();
+                        let var_str = var.borrow().to_string();
 
-                    push_space_if_amb!(self, &var_str, {
-                        append_str!(self, &var_str);
-                    });
-
-                    None
-                }
-                var_opt => {
-                    if is_cyclic && cell.is_compound(self.iter.heap) {
-                        // self-referential variables are marked "cyclic".
-                        match var_opt {
-                            Some(var) => {
-                                // If the term is bound to a named variable,
-                                // print the variable's name to output.
-                                let var_str = var.borrow().to_string();
-
-                                push_space_if_amb!(self, &var_str, {
-                                    append_str!(self, &var_str);
-                                });
-                            }
-                            None => {
-                                // otherwise, contract it to an ellipsis.
-                                push_space_if_amb!(self, "...", {
-                                    append_str!(self, "...");
-                                });
-                            }
-                        }
+                        push_space_if_amb!(self, &var_str, {
+                            append_str!(self, &var_str);
+                        });
 
                         return None;
                     }
+                    var_opt => {
+                        if is_cyclic && cell.is_compound(self.iter.heap) {
+                            // self-referential variables are marked "cyclic".
+                            read_heap_cell!(cell,
+                                (HeapCellValueTag::Lis, vh) => {
+                                    if self.iter.heap[vh].get_forwarding_bit() {
+                                        self.iter.pop_stack();
+                                    }
 
-                    Some(cell)
+                                    if self.iter.heap[vh+1].get_forwarding_bit() {
+                                        self.iter.pop_stack();
+                                    }
+                                }
+                                _ => {}
+                            );
+
+                            match var_opt {
+                                Some(var) => {
+                                    // If the term is bound to a named variable,
+                                    // print the variable's name to output.
+                                    let var_str = var.borrow().to_string();
+
+                                    push_space_if_amb!(self, &var_str, {
+                                        append_str!(self, &var_str);
+                                    });
+                                }
+                                None => {
+                                    if self.max_depth == 0 || *max_depth == 0 {
+                                        // otherwise, contract it to an ellipsis.
+                                        push_space_if_amb!(self, "...", {
+                                            append_str!(self, "...");
+                                        });
+                                    } else {
+                                        debug_assert!(cell.is_ref());
+
+                                        // as usual, the WAM's
+                                        // optimization of the Lis tag
+                                        // (conflating the location of
+                                        // the list and that of its
+                                        // first element) needs
+                                        // special consideration here
+                                        // lest we find ourselves in
+                                        // an infinite loop.
+                                        if cell.get_tag() == HeapCellValueTag::Lis {
+                                            *max_depth -= 1;
+                                        }
+
+                                        let h = cell.get_value() as usize;
+                                        self.iter.push_stack(IterStackLoc::iterable_loc(h, HeapOrStackTag::Heap));
+
+                                        if let Some(cell) = self.iter.next() {
+                                            orig_cell = cell;
+                                            continue;
+                                        }
+                                    }
+                                }
+                            }
+
+                            return None;
+                        }
+
+                        return Some(cell);
+                    }
                 }
             }
         } else {
@@ -891,7 +957,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
     }
 
     fn print_impromptu_atom(&mut self, atom: Atom) {
-        let result = self.print_op_addendum(atom.as_str());
+        let result = self.print_op_addendum(&*atom.as_str());
 
         push_space_if_amb!(self, result.as_str(), {
             append_str!(self, &result);
@@ -1020,7 +1086,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
 
         match self.op_dir.get(&(atom!("rdiv"), Fixity::In)) {
             Some(op_desc) => {
-                if r.is_integer() {
+                if r.is_int() {
                     let output_str = format!("{}", r);
 
                     push_space_if_amb!(self, &output_str, {
@@ -1050,7 +1116,8 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                         NumberFocus::Denominator(r),
                         left_directed_op,
                     ));
-                    self.state_stack.push(TokenOrRedirect::Op(rdiv_ct, *op_desc));
+                    self.state_stack
+                        .push(TokenOrRedirect::Op(rdiv_ct, *op_desc));
                     self.state_stack.push(TokenOrRedirect::NumberFocus(
                         max_depth,
                         NumberFocus::Numerator(r),
@@ -1088,10 +1155,19 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
     }
 
     // returns true if max_depth limit is reached and ellipsis is printed.
-    fn print_string_as_functor(&mut self, focus: usize, max_depth: usize) -> bool {
+    fn print_string_as_functor(&mut self, focus: usize, max_depth: &mut usize) -> bool {
         let iter = HeapPStrIter::new(self.iter.heap, focus);
 
         for (char_count, c) in iter.chars().enumerate() {
+            if self.check_max_depth(max_depth) {
+                if char_count > 0 {
+                    self.state_stack.push(TokenOrRedirect::Close);
+                }
+
+                self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
+                return true;
+            }
+
             append_str!(self, "'.'");
             push_char!(self, '(');
 
@@ -1099,16 +1175,13 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
             push_char!(self, ',');
 
             self.state_stack.push(TokenOrRedirect::Close);
-
-            if max_depth >= char_count + 1 {
-                self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
-                return true;
-            }
         }
 
         false
     }
 
+    // proper strings are terminal so there's no need for max_depth to
+    // be a mutable ref here.
     fn print_proper_string(&mut self, focus: usize, max_depth: usize) {
         push_char!(self, '"');
 
@@ -1157,8 +1230,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
             HeapCellValueTag::PStr | HeapCellValueTag::PStrOffset => {
                 self.iter.pop_stack();
             }
-            HeapCellValueTag::CStr => {
-            }
+            HeapCellValueTag::CStr => {}
             _ => {
                 unreachable!();
             }
@@ -1197,7 +1269,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
             self.at_cdr(",");
             self.remove_list_children(focus.value() as usize);
 
-            if !self.print_string_as_functor(focus.value() as usize, max_depth) {
+            if !self.print_string_as_functor(focus.value() as usize, &mut max_depth) {
                 if end_cell == empty_list_as_cell!() {
                     if !self.at_cdr("") {
                         append_str!(self, "[]");
@@ -1222,49 +1294,27 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                     let switch = self.close_list(switch);
 
                     let (h, offset) = pstr_loc_and_offset(self.iter.heap, focus.value() as usize);
-                    let pstr = cell_as_string!(self.iter.heap[h]);
 
-                    let pstr = pstr.as_str_from(offset.get_num() as usize);
+                    let offset = offset.get_num() as usize;
                     let tag = value.get_tag();
 
-                    if tag == HeapCellValueTag::PStrOffset {
+                    let end_h = if tag == HeapCellValueTag::PStrOffset {
                         // remove the fixnum offset from the iterator stack so we don't
                         // print an extraneous number. pstr offset value cells are never
                         // used by the iterator to mark cyclic terms so the removal is safe.
                         self.iter.pop_stack();
-                    }
-
-                    if max_depth > 0 && pstr.chars().count() + 1 >= max_depth {
-                        if tag != HeapCellValueTag::PStrOffset && tag != HeapCellValueTag::CStr {
-                            self.iter.pop_stack();
-                        }
+                        Some(end_h)
+                    } else {
+                        None
+                    };
 
+                    if !self.max_depth_exhausted(max_depth) {
+                        let pstr = cell_as_string!(self.iter.heap[h]);
+                        self.state_stack.push(TokenOrRedirect::CommaSeparatedCharList(CommaSeparatedCharList {
+                            pstr, offset, max_depth, end_cell, end_h,
+                        }));
+                    } else {
                         self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
-                        self.state_stack.push(TokenOrRedirect::HeadTailSeparator);
-                    } else if end_cell != empty_list_as_cell!() {
-                        if tag == HeapCellValueTag::PStrOffset {
-                            self.iter.push_stack(IterStackLoc::iterable_loc(end_h, HeapOrStackTag::Heap));
-                        }
-
-                        self.state_stack.push(TokenOrRedirect::FunctorRedirect(max_depth));
-                        self.state_stack.push(TokenOrRedirect::HeadTailSeparator);
-                    }
-
-                    let state_stack_len = self.state_stack.len();
-
-                    for (char_count, c) in pstr.chars().enumerate() {
-                        if max_depth > 0 && char_count + 1 >= max_depth {
-                            break;
-                        }
-
-                        self.state_stack.push(TokenOrRedirect::Comma);
-                        self.state_stack.push(TokenOrRedirect::Char(c));
-                    }
-
-                    self.state_stack[state_stack_len ..].reverse();
-
-                    if let Some(TokenOrRedirect::Comma) = self.state_stack.last() {
-                        self.state_stack.pop();
                     }
 
                     self.open_list(switch);
@@ -1298,7 +1348,8 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
             }
         }
 
-        self.state_stack.push(TokenOrRedirect::CloseList(switch.clone()));
+        self.state_stack
+            .push(TokenOrRedirect::CloseList(switch.clone()));
         Some(switch)
     }
 
@@ -1337,7 +1388,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
 
         self.state_stack.push(TokenOrRedirect::FunctorRedirect(max_depth));
         self.state_stack.push(TokenOrRedirect::HeadTailSeparator); // bar
-        self.state_stack.push(TokenOrRedirect::FunctorRedirect(max_depth+1));
+        self.state_stack.push(TokenOrRedirect::FunctorRedirect(max_depth + 1));
 
         self.open_list(switch);
     }
@@ -1353,15 +1404,15 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
         max_depth: usize,
     ) {
         let add_brackets = if !self.ignore_ops {
-            negated_operand ||
-                if let Some(ref op) = op {
+            negated_operand
+                || if let Some(ref op) = op {
                     if self.numbervars && arity == 1 && name == atom!("$VAR") {
                         !self.iter.immediate_leaf_has_property(|addr| {
                             match Number::try_from(addr) {
-                                Ok(Number::Integer(n)) => &*n >= &Integer::from(0),
+                                Ok(Number::Integer(n)) => (*n).sign() == Sign::Positive,
                                 Ok(Number::Fixnum(n)) => n.get_num() >= 0,
                                 Ok(Number::Float(f)) => f >= OrderedFloat(0f64),
-                                Ok(Number::Rational(r)) => &*r >= &Integer::from(0),
+                                Ok(Number::Rational(r)) => (*r).sign() == Sign::Positive,
                                 _ => false,
                             }
                         }) && needs_bracketing(op_desc, op)
@@ -1381,7 +1432,8 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
             self.state_stack.push(TokenOrRedirect::Open);
 
             if !self.outputter.ends_with(" ") {
-                let parent_op = self.parent_of_first_op
+                let parent_op = self
+                    .parent_of_first_op
                     .and_then(|(parent_op, last_item_idx)| {
                         // if parent_op isn't printed to the output string
                         // already, then it doesn't border the present op
@@ -1395,7 +1447,9 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
 
                 for op in &[op, parent_op] {
                     if let Some(ref op) = &op {
-                        if op.is_left() && (op.is_prefix() || requires_space(op.as_atom().as_str(), "(")) {
+                        if op.is_left()
+                            && (op.is_prefix() || requires_space(&*op.as_atom().as_str(), "("))
+                        {
                             self.state_stack.push(TokenOrRedirect::Space);
                             return;
                         }
@@ -1490,20 +1544,68 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
         }
     }
 
+    fn print_comma_separated_char_list(&mut self, char_list: CommaSeparatedCharList) {
+        let CommaSeparatedCharList { pstr, offset, max_depth, end_cell, end_h } = char_list;
+        let pstr_str = pstr.as_str_from(offset);
+
+        if let Some(c) = pstr_str.chars().next() {
+            let offset = offset + c.len_utf8();
+
+            if !self.max_depth_exhausted(max_depth) {
+                self.state_stack.push(TokenOrRedirect::CommaSeparatedCharList(CommaSeparatedCharList {
+                    pstr,
+                    offset,
+                    max_depth: max_depth.saturating_sub(1),
+                    end_cell,
+                    end_h,
+                }));
+
+                let max_depth_allows = self.max_depth == 0 || max_depth > 1;
+
+                if max_depth_allows && pstr_str.chars().skip(1).next().is_some() {
+                    self.state_stack.push(TokenOrRedirect::Comma);
+                }
+
+                self.state_stack.push(TokenOrRedirect::Char(c));
+            } else {
+                self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
+                self.state_stack.push(TokenOrRedirect::HeadTailSeparator);
+            }
+        } else if self.max_depth_exhausted(max_depth) {
+            self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
+            self.state_stack.push(TokenOrRedirect::HeadTailSeparator);
+        } else if end_cell != empty_list_as_cell!() {
+            if let Some(end_h) = end_h {
+                self.iter.push_stack(IterStackLoc::iterable_loc(end_h, HeapOrStackTag::Heap));
+            }
+
+            self.state_stack.push(TokenOrRedirect::FunctorRedirect(max_depth + 1));
+            self.state_stack.push(TokenOrRedirect::HeadTailSeparator);
+        }
+    }
+
     fn handle_heap_term(
         &mut self,
         op: Option<DirectedOp>,
         is_functor_redirect: bool,
-        max_depth: usize,
+        mut max_depth: usize,
     ) {
         let negated_operand = negated_op_needs_bracketing(&self.iter, self.op_dir, &op);
 
+        let addr = match self.check_for_seen(&mut max_depth) {
+            Some(addr) => addr,
+            None => return,
+        };
+
         let print_struct = |printer: &mut Self, name: Atom, arity: usize| {
             if name == atom!("[]") && arity == 0 {
-                if let Some(TokenOrRedirect::CloseList(_)) = printer.state_stack.last() {
-                    if printer.at_cdr("") {
-                        return;
+                match printer.state_stack.last() {
+                    Some(TokenOrRedirect::CloseList(_) | TokenOrRedirect::ChildCloseList) => {
+                        if printer.at_cdr("") {
+                            return;
+                        }
                     }
+                    _ => {}
                 }
 
                 append_str!(printer, "[]");
@@ -1519,7 +1621,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                         max_depth,
                     );
                 } else {
-                    push_space_if_amb!(printer, name.as_str(), {
+                    push_space_if_amb!(printer, &*name.as_str(), {
                         printer.format_clause(max_depth, arity, name, None);
                     });
                 }
@@ -1529,14 +1631,18 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                 if let Some(ref op) = op {
                     let op_is_prefix = op.is_prefix() && op.is_left();
 
-                    if op_is_prefix || printer.outputter.ends_with(&format!(" {}", op.as_atom().as_str())) {
+                    if op_is_prefix
+                        || printer
+                            .outputter
+                            .ends_with(&format!(" {}", op.as_atom().as_str()))
+                    {
                         result.push(' ');
                     }
 
                     result.push('(');
                 }
 
-                result += &printer.print_op_addendum(name.as_str());
+                result += &printer.print_op_addendum(&*name.as_str());
 
                 if op.is_some() {
                     result.push(')');
@@ -1546,19 +1652,20 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                     append_str!(printer, &result);
                 });
             } else {
-                push_space_if_amb!(printer, name.as_str(), {
+                push_space_if_amb!(printer, &*name.as_str(), {
                     printer.print_impromptu_atom(name);
                 });
             }
         };
 
-        let addr = match self.check_for_seen() {
-            Some(addr) => addr,
-            None => return,
-        };
+        if !addr.is_var()
+            && !addr.is_compound(&self.iter.heap)
+            && self.max_depth_exhausted(max_depth)
+        {
+            if !(addr == atom_as_cell!(atom!("[]")) && self.at_cdr("")) {
+                self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
+            }
 
-        if !addr.is_var() && !addr.is_compound(&self.iter.heap) && self.max_depth_exhausted(max_depth) {
-            self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
             return;
         }
 
@@ -1567,7 +1674,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                 print_struct(self, name, arity);
             }
             (HeapCellValueTag::Char, c) => {
-                let name = self.atom_tbl.build_with(&String::from(c));
+                let name = AtomTable::build_with(&self.atom_tbl, &String::from(c));
                 print_struct(self, name, 0);
             }
             (HeapCellValueTag::Str, s) => {
@@ -1585,7 +1692,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                         max_depth,
                     );
                 } else {
-                    push_space_if_amb!(self, name.as_str(), {
+                    push_space_if_amb!(self, &*name.as_str(), {
                         self.format_clause(max_depth, arity, name, None);
                     });
                 }
@@ -1627,9 +1734,6 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                    (ArenaHeaderTag::Stream, stream) => {
                        self.print_stream(stream, max_depth);
                    }
-                   (ArenaHeaderTag::OssifiedOpDir, _op_dir) => {
-                       self.print_impromptu_atom(atom!("$ossified_op_dir"));
-                   }
                    (ArenaHeaderTag::Dropped, _value) => {
                        self.print_impromptu_atom(atom!("$dropped_value"));
                    }
@@ -1668,7 +1772,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                 TokenOrRedirect::BarAsOp => append_str!(self, " | "),
                 TokenOrRedirect::Char(c) => print_char!(self, self.quoted, c),
                 TokenOrRedirect::Op(atom, op) => {
-                    self.print_op(atom.as_str());
+                    self.print_op(&*atom.as_str());
 
                     if is_prefix!(op.get_spec()) {
                         self.set_parent_of_first_op(Some(DirectedOp::Left(atom, op)));
@@ -1715,6 +1819,13 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                 TokenOrRedirect::Space => push_char!(self, ' '),
                 TokenOrRedirect::LeftCurly => push_char!(self, '{'),
                 TokenOrRedirect::RightCurly => push_char!(self, '}'),
+                TokenOrRedirect::StackPop => {
+                    self.iter.pop_stack();
+                    self.state_stack.push(TokenOrRedirect::Atom(atom!("...")));
+                }
+                TokenOrRedirect::CommaSeparatedCharList(char_list) => {
+                    self.print_comma_separated_char_list(char_list);
+                }
             }
         }
 
@@ -1737,16 +1848,18 @@ mod tests {
         let b_atom = atom!("b");
         let c_atom = atom!("c");
 
-        wam.machine_st.heap.extend(functor!(f_atom, [atom(a_atom), atom(b_atom)]));
+        wam.machine_st
+            .heap
+            .extend(functor!(f_atom, [atom(a_atom), atom(b_atom)]));
 
         {
             let printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                &mut wam.machine_st.atom_tbl,
+                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0)
+                heap_loc_as_cell!(0),
             );
 
             let output = printer.print();
@@ -1771,11 +1884,11 @@ mod tests {
         {
             let printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                &mut wam.machine_st.atom_tbl,
+                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0)
+                heap_loc_as_cell!(0),
             );
 
             let output = printer.print();
@@ -1795,11 +1908,11 @@ mod tests {
         {
             let printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                &mut wam.machine_st.atom_tbl,
+                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0)
+                heap_loc_as_cell!(0),
             );
 
             let output = printer.print();
@@ -1808,14 +1921,16 @@ mod tests {
 
             let mut printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                &mut wam.machine_st.atom_tbl,
+                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0)
+                heap_loc_as_cell!(0),
             );
 
-            printer.var_names.insert(list_loc_as_cell!(1), VarPtr::from("L"));
+            printer
+                .var_names
+                .insert(list_loc_as_cell!(1), VarPtr::from("L"));
 
             let output = printer.print();
 
@@ -1839,7 +1954,7 @@ mod tests {
         {
             let printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                &mut wam.machine_st.atom_tbl,
+                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
                 &wam.op_dir,
                 PrinterOutputter::new(),
@@ -1858,7 +1973,7 @@ mod tests {
         {
             let printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                &mut wam.machine_st.atom_tbl,
+                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
                 &wam.op_dir,
                 PrinterOutputter::new(),
@@ -1875,14 +1990,16 @@ mod tests {
         {
             let mut printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                &mut wam.machine_st.atom_tbl,
+                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0)
+                heap_loc_as_cell!(0),
             );
 
-            printer.var_names.insert(list_loc_as_cell!(1), VarPtr::from("L"));
+            printer
+                .var_names
+                .insert(list_loc_as_cell!(1), VarPtr::from("L"));
 
             let output = printer.print();
 
@@ -1905,11 +2022,11 @@ mod tests {
         {
             let mut printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                &mut wam.machine_st.atom_tbl,
+                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                heap_loc_as_cell!(0)
+                heap_loc_as_cell!(0),
             );
 
             printer.max_depth = 5;
@@ -1923,16 +2040,16 @@ mod tests {
 
         wam.machine_st.heap.clear();
 
-        put_partial_string(&mut wam.machine_st.heap, "abc", &mut wam.machine_st.atom_tbl);
+        put_partial_string(&mut wam.machine_st.heap, "abc", &wam.machine_st.atom_tbl);
 
         {
             let printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                &mut wam.machine_st.atom_tbl,
+                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
                 &wam.op_dir,
                 PrinterOutputter::new(),
-                pstr_loc_as_cell!(0)
+                pstr_loc_as_cell!(0),
             );
 
             let output = printer.print();
@@ -1956,7 +2073,7 @@ mod tests {
         {
             let mut printer = HCPrinter::new(
                 &mut wam.machine_st.heap,
-                &mut wam.machine_st.atom_tbl,
+                Arc::clone(&wam.machine_st.atom_tbl),
                 &mut wam.machine_st.stack,
                 &wam.op_dir,
                 PrinterOutputter::new(),
@@ -2000,35 +2117,39 @@ mod tests {
 
         all_cells_unmarked(&wam.machine_st.heap);
 
-        wam.op_dir.insert(
-            (atom!("+"), Fixity::In),
-            OpDesc::build_with(500, YFX as u8),
-        );
-        wam.op_dir.insert(
-            (atom!("*"), Fixity::In),
-            OpDesc::build_with(400, YFX as u8),
-        );
+        wam.op_dir
+            .insert((atom!("+"), Fixity::In), OpDesc::build_with(500, YFX as u8));
+        wam.op_dir
+            .insert((atom!("*"), Fixity::In), OpDesc::build_with(400, YFX as u8));
 
-        assert_eq!(&wam.parse_and_print_term("[a|[] + b].").unwrap(), "[a|[]+b]");
+        assert_eq!(
+            &wam.parse_and_print_term("[a|[] + b].").unwrap(),
+            "[a|[]+b]"
+        );
 
         all_cells_unmarked(&wam.machine_st.heap);
 
-        assert_eq!(&wam.parse_and_print_term("[a|[b|c]*d].").unwrap(), "[a|[b|c]*d]");
+        assert_eq!(
+            &wam.parse_and_print_term("[a|[b|c]*d].").unwrap(),
+            "[a|[b|c]*d]"
+        );
 
         all_cells_unmarked(&wam.machine_st.heap);
 
-        wam.op_dir.insert(
-            (atom!("fy"), Fixity::Pre),
-            OpDesc::build_with(9, FY as u8),
+        wam.op_dir
+            .insert((atom!("fy"), Fixity::Pre), OpDesc::build_with(9, FY as u8));
+
+        wam.op_dir
+            .insert((atom!("yf"), Fixity::Post), OpDesc::build_with(9, YF as u8));
+
+        assert_eq!(
+            &wam.parse_and_print_term("(fy (fy 1)yf)yf.").unwrap(),
+            "(fy (fy 1)yf)yf"
         );
 
-        wam.op_dir.insert(
-            (atom!("yf"), Fixity::Post),
-            OpDesc::build_with(9, YF as u8),
+        assert_eq!(
+            &wam.parse_and_print_term("fy(fy(yf(fy(1)))).").unwrap(),
+            "fy fy (fy 1)yf"
         );
-
-        assert_eq!(&wam.parse_and_print_term("(fy (fy 1)yf)yf.").unwrap(), "(fy (fy 1)yf)yf");
-
-        assert_eq!(&wam.parse_and_print_term("fy(fy(yf(fy(1)))).").unwrap(), "fy fy (fy 1)yf");
     }
 }

src/http.rs

@@ -1,54 +1,23 @@
 use std::sync::{Arc, Mutex, Condvar};
-use std::future::Future;
-use std::pin::Pin;
-use http_body_util::Full;
-use bytes::Bytes;
-use hyper::service::Service;
-use hyper::{body::Incoming as IncomingBody, Request, Response};
+use std::io::BufRead;
+
+use warp::http;
 
 pub struct HttpListener {
-    pub incoming: std::sync::mpsc::Receiver<HttpRequest>
+    pub incoming: std::sync::mpsc::Receiver<HttpRequest>,
 }
 
-#[derive(Debug)]
 pub struct HttpRequest {
-    pub request: Request<IncomingBody>,
+    pub request_data: HttpRequestData,
     pub response: HttpResponse,
 }
 
-pub type HttpResponse = Arc<(Mutex<bool>, Mutex<Option<Response<Full<Bytes>>>>, Condvar)>;
+pub type HttpResponse = Arc<(Mutex<bool>, Mutex<Option<warp::reply::Response>>, Condvar)>;
 
-pub struct HttpService {
-    pub tx: std::sync::mpsc::SyncSender<HttpRequest>,
-}
-
-impl Service<Request<IncomingBody>> for HttpService {
-    type Response = Response<Full<Bytes>>;
-    type Error = hyper::Error;
-    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
-
-    fn call(&mut self, req: Request<IncomingBody>) -> Self::Future {
-	// new connection!
-	// we send the Request info to Prolog
-	let response = Arc::new((Mutex::new(false), Mutex::new(None), Condvar::new()));
-	let http_request = HttpRequest { request: req, response: Arc::clone(&response) };
-	self.tx.send(http_request).unwrap();
-
-	// we wait for the Response info from Prolog
-	{
-	    let (ready, _response, cvar) = &*response;
-	    let mut ready = ready.lock().unwrap();
-	    while !*ready {
-		ready = cvar.wait(ready).unwrap();
-	    }
-	}
-	{
-	    let (_, response, _) = &*response;
-	    let response = response.lock().unwrap().take();
-	    let res = response.expect("Data race error in HTTP Server");
-	    Box::pin(async move {
-		Ok(res)
-	    })
-	}
-    }
+pub struct HttpRequestData {
+    pub method: http::Method,
+    pub headers: http::HeaderMap,
+    pub path: String,
+    pub query: String,
+    pub body: Box<dyn BufRead + Send>,
 }

src/indexing.rs

@@ -150,17 +150,20 @@ impl<'a> IndexingCodeMergingPtr<'a> {
         let third_level_index = if self.append_or_prepend.is_append() {
             vec![
                 IndexedChoiceInstruction::Try(external),
-                IndexedChoiceInstruction::Trust(index)
-            ].into()
+                IndexedChoiceInstruction::Trust(index),
+            ]
+            .into()
         } else {
             vec![
                 IndexedChoiceInstruction::Try(index),
-                IndexedChoiceInstruction::Trust(external)
-            ].into()
+                IndexedChoiceInstruction::Trust(external),
+            ]
+            .into()
         };
 
         let indexing_code_len = self.indexing_code.len();
-        self.indexing_code.push(IndexingLine::IndexedChoice(third_level_index));
+        self.indexing_code
+            .push(IndexingLine::IndexedChoice(third_level_index));
 
         match &mut self.indexing_code[self.offset] {
             IndexingLine::Indexing(IndexingInstruction::SwitchOnConstant(ref mut constants)) => {
@@ -188,7 +191,8 @@ impl<'a> IndexingCodeMergingPtr<'a> {
         };
 
         let indexing_code_len = self.indexing_code.len();
-        self.indexing_code.push(IndexingLine::DynamicIndexedChoice(third_level_index));
+        self.indexing_code
+            .push(IndexingLine::DynamicIndexedChoice(third_level_index));
 
         match &mut self.indexing_code[self.offset] {
             IndexingLine::Indexing(IndexingInstruction::SwitchOnConstant(ref mut constants)) => {
@@ -275,10 +279,8 @@ impl<'a> IndexingCodeMergingPtr<'a> {
                             );
                         }
                         None | Some(IndexingCodePtr::Fail) => {
-                            constants.insert(
-                                overlapping_constant,
-                                IndexingCodePtr::External(index),
-                            );
+                            constants
+                                .insert(overlapping_constant, IndexingCodePtr::External(index));
                         }
                         Some(IndexingCodePtr::DynamicExternal(o)) => {
                             self.add_dynamic_indexed_choice_for_constant(
@@ -345,16 +347,10 @@ impl<'a> IndexingCodeMergingPtr<'a> {
                 IndexingLine::Indexing(IndexingInstruction::SwitchOnConstant(constants)) => {
                     match constants.get(&constant).cloned() {
                         None | Some(IndexingCodePtr::Fail) if self.is_dynamic => {
-                            constants.insert(
-                                constant,
-                                IndexingCodePtr::DynamicExternal(index),
-                            );
+                            constants.insert(constant, IndexingCodePtr::DynamicExternal(index));
                         }
                         None | Some(IndexingCodePtr::Fail) => {
-                            constants.insert(
-                                constant,
-                                IndexingCodePtr::External(index),
-                            );
+                            constants.insert(constant, IndexingCodePtr::External(index));
                         }
                         Some(IndexingCodePtr::DynamicExternal(o)) => {
                             self.add_dynamic_indexed_choice_for_constant(o, constant, index);
@@ -432,17 +428,20 @@ impl<'a> IndexingCodeMergingPtr<'a> {
         let third_level_index = if self.append_or_prepend.is_append() {
             vec![
                 IndexedChoiceInstruction::Try(external),
-                IndexedChoiceInstruction::Trust(index)
-            ].into()
+                IndexedChoiceInstruction::Trust(index),
+            ]
+            .into()
         } else {
             vec![
                 IndexedChoiceInstruction::Try(index),
-                IndexedChoiceInstruction::Trust(external)
-            ].into()
+                IndexedChoiceInstruction::Trust(external),
+            ]
+            .into()
         };
 
         let indexing_code_len = self.indexing_code.len();
-        self.indexing_code.push(IndexingLine::IndexedChoice(third_level_index));
+        self.indexing_code
+            .push(IndexingLine::IndexedChoice(third_level_index));
 
         match &mut self.indexing_code[self.offset] {
             IndexingLine::Indexing(IndexingInstruction::SwitchOnStructure(ref mut structures)) => {
@@ -470,7 +469,8 @@ impl<'a> IndexingCodeMergingPtr<'a> {
         };
 
         let indexing_code_len = self.indexing_code.len();
-        self.indexing_code.push(IndexingLine::DynamicIndexedChoice(third_level_index));
+        self.indexing_code
+            .push(IndexingLine::DynamicIndexedChoice(third_level_index));
 
         match &mut self.indexing_code[self.offset] {
             IndexingLine::Indexing(IndexingInstruction::SwitchOnStructure(ref mut structures)) => {
@@ -584,13 +584,15 @@ impl<'a> IndexingCodeMergingPtr<'a> {
                         let third_level_index = if self.append_or_prepend.is_append() {
                             vec![
                                 IndexedChoiceInstruction::Try(o),
-                                IndexedChoiceInstruction::Trust(index)
-                            ].into()
+                                IndexedChoiceInstruction::Trust(index),
+                            ]
+                            .into()
                         } else {
                             vec![
                                 IndexedChoiceInstruction::Try(index),
-                                IndexedChoiceInstruction::Trust(o)
-                            ].into()
+                                IndexedChoiceInstruction::Trust(o),
+                            ]
+                            .into()
                         };
 
                         self.indexing_code
@@ -613,7 +615,7 @@ pub(crate) fn merge_clause_index(
     target_indexing_code: &mut Vec<IndexingLine>,
     skeleton: &mut [ClauseIndexInfo], // the clause to be merged is the last element in the skeleton.
     retracted_clauses: &Option<Vec<ClauseIndexInfo>>,
-    new_clause_loc: usize,            // the absolute location of the new clause in the code vector.
+    new_clause_loc: usize, // the absolute location of the new clause in the code vector.
     append_or_prepend: AppendOrPrepend,
 ) {
     let opt_arg_index_key = match append_or_prepend {
@@ -636,11 +638,7 @@ pub(crate) fn merge_clause_index(
             for overlapping_constant in overlapping_constants {
                 merging_ptr.offset = 0;
 
-                merging_ptr.index_overlapping_constant(
-                    *constant,
-                    *overlapping_constant,
-                    offset,
-                );
+                merging_ptr.index_overlapping_constant(*constant, *overlapping_constant, offset);
             }
         }
         OptArgIndexKey::Structure(_, index_loc, name, arity) => {
@@ -1060,19 +1058,27 @@ fn cap_choice_seq(prelude: &mut [IndexedChoiceInstruction]) {
 
 #[inline]
 fn cap_choice_seq_with_trust(prelude: &mut [IndexedChoiceInstruction]) {
-    prelude.last_mut().map(|instr| {
-        if let IndexedChoiceInstruction::Retry(i) = instr {
+    prelude.last_mut().map(|instr| match instr {
+        IndexedChoiceInstruction::Retry(i) => {
             *instr = IndexedChoiceInstruction::Trust(*i);
         }
+        IndexedChoiceInstruction::DefaultRetry(i) => {
+            *instr = IndexedChoiceInstruction::DefaultTrust(*i);
+        }
+        _ => {}
     });
 }
 
 #[inline]
 fn uncap_choice_seq_with_trust(prelude: &mut [IndexedChoiceInstruction]) {
-    prelude.last_mut().map(|instr| {
-        if let IndexedChoiceInstruction::Trust(i) = instr {
+    prelude.last_mut().map(|instr| match instr {
+        IndexedChoiceInstruction::Trust(i) => {
             *instr = IndexedChoiceInstruction::Retry(*i);
         }
+        IndexedChoiceInstruction::DefaultTrust(i) => {
+            *instr = IndexedChoiceInstruction::DefaultRetry(*i);
+        }
+        _ => {}
     });
 }
 
@@ -1087,7 +1093,7 @@ fn uncap_choice_seq_with_try(prelude: &mut [IndexedChoiceInstruction]) {
 
 pub(crate) fn constant_key_alternatives(
     constant: Literal,
-    atom_tbl: &mut AtomTable,
+    atom_tbl: &AtomTable,
     // arena: &mut Arena,
 ) -> Vec<Literal> {
     let mut constants = vec![];
@@ -1099,7 +1105,7 @@ pub(crate) fn constant_key_alternatives(
             }
         }
         Literal::Char(c) => {
-            let atom = atom_tbl.build_with(&c.to_string());
+            let atom = AtomTable::build_with(&atom_tbl, &c.to_string());
             constants.push(Literal::Atom(atom));
         }
         /*
@@ -1116,8 +1122,9 @@ pub(crate) fn constant_key_alternatives(
         }
         */
         Literal::Integer(ref n) => {
-            if let Some(n) = n.to_isize() {
-                Fixnum::build_with_checked(n as i64).map(|n| {
+            let result = (&**n).try_into();
+            if let Ok(value) = result {
+                Fixnum::build_with_checked(value).map(|n| {
                     constants.push(Literal::Fixnum(n));
                 }).unwrap();
             }
@@ -1147,11 +1154,19 @@ pub(crate) trait Indexer {
 
     fn new() -> Self;
 
-    fn constants(&mut self) -> &mut IndexMap<Literal, VecDeque<Self::ThirdLevelIndex>, FxBuildHasher>;
+    fn constants(
+        &mut self,
+    ) -> &mut IndexMap<Literal, VecDeque<Self::ThirdLevelIndex>, FxBuildHasher>;
     fn lists(&mut self) -> &mut VecDeque<Self::ThirdLevelIndex>;
-    fn structures(&mut self) -> &mut IndexMap<(Atom, usize), VecDeque<Self::ThirdLevelIndex>, FxBuildHasher>;
+    fn structures(
+        &mut self,
+    ) -> &mut IndexMap<(Atom, usize), VecDeque<Self::ThirdLevelIndex>, FxBuildHasher>;
 
-    fn compute_index(is_initial_index: bool, index: usize) -> Self::ThirdLevelIndex;
+    fn compute_index(
+        is_initial_index: bool,
+        index: usize,
+        non_counted_bt: bool,
+    ) -> Self::ThirdLevelIndex;
 
     fn second_level_index<IndexKey: Eq + Hash>(
         indices: IndexMap<IndexKey, VecDeque<Self::ThirdLevelIndex>, FxBuildHasher>,
@@ -1187,7 +1202,9 @@ impl Indexer for StaticCodeIndices {
     }
 
     #[inline]
-    fn constants(&mut self) -> &mut IndexMap<Literal, VecDeque<IndexedChoiceInstruction>, FxBuildHasher> {
+    fn constants(
+        &mut self,
+    ) -> &mut IndexMap<Literal, VecDeque<IndexedChoiceInstruction>, FxBuildHasher> {
         &mut self.constants
     }
 
@@ -1197,13 +1214,21 @@ impl Indexer for StaticCodeIndices {
     }
 
     #[inline]
-    fn structures(&mut self) -> &mut IndexMap<(Atom, usize), VecDeque<IndexedChoiceInstruction>, FxBuildHasher> {
+    fn structures(
+        &mut self,
+    ) -> &mut IndexMap<(Atom, usize), VecDeque<IndexedChoiceInstruction>, FxBuildHasher> {
         &mut self.structures
     }
 
-    fn compute_index(is_initial_index: bool, index: usize) -> IndexedChoiceInstruction {
+    fn compute_index(
+        is_initial_index: bool,
+        index: usize,
+        non_counted_bt: bool,
+    ) -> IndexedChoiceInstruction {
         if is_initial_index {
             IndexedChoiceInstruction::Try(index + 1)
+        } else if non_counted_bt {
+            IndexedChoiceInstruction::DefaultRetry(index + 1)
         } else {
             IndexedChoiceInstruction::Retry(index + 1)
         }
@@ -1231,7 +1256,9 @@ impl Indexer for StaticCodeIndices {
     }
 
     fn switch_on<IndexKey: Eq + Hash>(
-        mut instr_fn: impl FnMut(IndexMap<IndexKey, IndexingCodePtr, FxBuildHasher>) -> IndexingInstruction,
+        mut instr_fn: impl FnMut(
+            IndexMap<IndexKey, IndexingCodePtr, FxBuildHasher>,
+        ) -> IndexingInstruction,
         index: &mut IndexMap<IndexKey, VecDeque<IndexedChoiceInstruction>, FxBuildHasher>,
         prelude: &mut VecDeque<IndexingLine>,
     ) -> IndexingCodePtr {
@@ -1318,7 +1345,7 @@ impl Indexer for DynamicCodeIndices {
     }
 
     #[inline]
-    fn compute_index(_: bool, index: usize) -> usize {
+    fn compute_index(_: bool, index: usize, _: bool) -> usize {
         index + 1
     }
 
@@ -1331,7 +1358,9 @@ impl Indexer for DynamicCodeIndices {
         for (key, code) in indices.into_iter() {
             if code.len() > 1 {
                 index_locs.insert(key, IndexingCodePtr::Internal(prelude.len() + 1));
-                prelude.push_back(IndexingLine::DynamicIndexedChoice(code.into_iter().collect()));
+                prelude.push_back(IndexingLine::DynamicIndexedChoice(
+                    code.into_iter().collect(),
+                ));
             } else {
                 code.front().map(|i| {
                     index_locs.insert(key, IndexingCodePtr::DynamicExternal(*i));
@@ -1343,7 +1372,9 @@ impl Indexer for DynamicCodeIndices {
     }
 
     fn switch_on<IndexKey: Eq + Hash>(
-        mut instr_fn: impl FnMut(IndexMap<IndexKey, IndexingCodePtr, FxBuildHasher>) -> IndexingInstruction,
+        mut instr_fn: impl FnMut(
+            IndexMap<IndexKey, IndexingCodePtr, FxBuildHasher>,
+        ) -> IndexingInstruction,
         index: &mut IndexMap<IndexKey, VecDeque<usize>, FxBuildHasher>,
         prelude: &mut VecDeque<IndexingLine>,
     ) -> IndexingCodePtr {
@@ -1370,7 +1401,9 @@ impl Indexer for DynamicCodeIndices {
     ) -> IndexingCodePtr {
         if lists.len() > 1 {
             let lists = mem::replace(lists, VecDeque::new());
-            prelude.push_back(IndexingLine::DynamicIndexedChoice(lists.into_iter().collect()));
+            prelude.push_back(IndexingLine::DynamicIndexedChoice(
+                lists.into_iter().collect(),
+            ));
             IndexingCodePtr::Internal(1)
         } else {
             lists
@@ -1400,33 +1433,43 @@ impl Indexer for DynamicCodeIndices {
 pub(crate) struct CodeOffsets<I: Indexer> {
     indices: I,
     optimal_index: usize,
+    non_counted_bt: bool,
 }
 
 impl<I: Indexer> CodeOffsets<I> {
-    pub(crate) fn new(indices: I, optimal_index: usize) -> Self {
+    pub(crate) fn new(indices: I, optimal_index: usize, non_counted_bt: bool) -> Self {
         CodeOffsets {
             indices,
             optimal_index,
+            non_counted_bt,
         }
     }
 
     fn index_list(&mut self, index: usize) {
         let is_initial_index = self.indices.lists().is_empty();
-        let index = I::compute_index(is_initial_index, index);
+        let index = I::compute_index(is_initial_index, index, self.non_counted_bt);
         self.indices.lists().push_back(index);
     }
 
     fn index_constant(
         &mut self,
-        atom_tbl: &mut AtomTable,
+        atom_tbl: &AtomTable,
         constant: Literal,
         index: usize,
     ) -> Vec<Literal> {
         let overlapping_constants = constant_key_alternatives(constant, atom_tbl);
-        let code = self.indices.constants().entry(constant).or_insert(VecDeque::new());
+        let code = self
+            .indices
+            .constants()
+            .entry(constant)
+            .or_insert(VecDeque::new());
 
         let is_initial_index = code.is_empty();
-        code.push_back(I::compute_index(is_initial_index, index));
+        code.push_back(I::compute_index(
+            is_initial_index,
+            index,
+            self.non_counted_bt,
+        ));
 
         for constant in &overlapping_constants {
             let code = self
@@ -1436,7 +1479,7 @@ impl<I: Indexer> CodeOffsets<I> {
                 .or_insert(VecDeque::new());
 
             let is_initial_index = code.is_empty();
-            let index = I::compute_index(is_initial_index, index);
+            let index = I::compute_index(is_initial_index, index, self.non_counted_bt);
 
             code.push_back(index);
         }
@@ -1454,7 +1497,11 @@ impl<I: Indexer> CodeOffsets<I> {
         let code_len = code.len();
         let is_initial_index = code.is_empty();
 
-        code.push_back(I::compute_index(is_initial_index, index));
+        code.push_back(I::compute_index(
+            is_initial_index,
+            index,
+            self.non_counted_bt,
+        ));
         code_len
     }
 
@@ -1463,7 +1510,7 @@ impl<I: Indexer> CodeOffsets<I> {
         optimal_arg: &Term,
         index: usize,
         clause_index_info: &mut ClauseIndexInfo,
-        atom_tbl: &mut AtomTable,
+        atom_tbl: &AtomTable,
     ) {
         match optimal_arg {
             &Term::Clause(_, atom!("."), ref terms) if terms.len() == 2 => {

src/iterators.rs

@@ -62,9 +62,7 @@ impl<'a> TermIterState<'a> {
             Term::PartialString(cell, string_buf, tail) => {
                 TermIterState::InitialPartialString(lvl, cell, string_buf, tail)
             }
-            Term::CompleteString(cell, atom) => {
-                TermIterState::CompleteString(lvl, cell, *atom)
-            }
+            Term::CompleteString(cell, atom) => TermIterState::CompleteString(lvl, cell, *atom),
             Term::Var(cell, var_ptr) => TermIterState::Var(lvl, cell, var_ptr.clone()),
         }
     }
@@ -77,7 +75,8 @@ pub(crate) struct QueryIterator<'a> {
 
 impl<'a> QueryIterator<'a> {
     fn push_subterm(&mut self, lvl: Level, term: &'a Term) {
-        self.state_stack.push(TermIterState::subterm_to_state(lvl, term));
+        self.state_stack
+            .push(TermIterState::subterm_to_state(lvl, term));
     }
 
     /*
@@ -94,19 +93,16 @@ impl<'a> QueryIterator<'a> {
 
     fn from_term(term: &'a Term) -> Self {
         let state = match term {
-            Term::AnonVar | Term::Cons(..) | Term::Literal(..) |
-            Term::PartialString(..) | Term::CompleteString(..) => {
+            Term::AnonVar
+            | Term::Cons(..)
+            | Term::Literal(..)
+            | Term::PartialString(..)
+            | Term::CompleteString(..) => {
                 return QueryIterator {
                     state_stack: vec![],
                 }
             }
-            Term::Clause(r, name, terms) => TermIterState::Clause(
-                Level::Root,
-                0,
-                r,
-                *name,
-                terms,
-            ),
+            Term::Clause(r, name, terms) => TermIterState::Clause(Level::Root, 0, r, *name, terms),
             Term::Var(cell, var_ptr) => TermIterState::Var(Level::Root, cell, var_ptr.clone()),
         };
 
@@ -118,18 +114,21 @@ impl<'a> QueryIterator<'a> {
     fn extend_state(&mut self, lvl: Level, term: &'a QueryTerm) {
         match term {
             &QueryTerm::Clause(ref cell, ClauseType::CallN(_), ref terms, _) => {
-                self.state_stack.push(TermIterState::Clause(lvl, 1, cell, atom!("$call"), terms));
+                self.state_stack
+                    .push(TermIterState::Clause(lvl, 1, cell, atom!("$call"), terms));
             }
             &QueryTerm::Clause(ref cell, ref ct, ref terms, _) => {
-                self.state_stack.push(TermIterState::Clause(lvl, 0, cell, ct.name(), terms));
-            }
-            _ => {
+                self.state_stack
+                    .push(TermIterState::Clause(lvl, 0, cell, ct.name(), terms));
             }
+            _ => {}
         }
     }
 
     pub fn new(term: &'a QueryTerm) -> Self {
-        let mut iter = QueryIterator { state_stack: vec![] };
+        let mut iter = QueryIterator {
+            state_stack: vec![],
+        };
         iter.extend_state(Level::Root, term);
         iter
     }
@@ -170,13 +169,15 @@ impl<'a> Iterator for QueryIterator<'a> {
                     }
                 }
                 TermIterState::InitialCons(lvl, cell, head, tail) => {
-                    self.state_stack.push(TermIterState::FinalCons(lvl, cell, head, tail));
+                    self.state_stack
+                        .push(TermIterState::FinalCons(lvl, cell, head, tail));
 
                     self.push_subterm(lvl.child_level(), tail);
                     self.push_subterm(lvl.child_level(), head);
                 }
                 TermIterState::InitialPartialString(lvl, cell, string, tail) => {
-                    self.state_stack.push(TermIterState::FinalPartialString(lvl, cell, string, tail));
+                    self.state_stack
+                        .push(TermIterState::FinalPartialString(lvl, cell, string, tail));
                     self.push_subterm(lvl.child_level(), tail);
                 }
                 TermIterState::FinalPartialString(lvl, cell, atom, tail) => {
@@ -248,11 +249,7 @@ impl<'a> FactIterator<'a> {
                 )]
             }
             Term::CompleteString(cell, atom) => {
-                vec![TermIterState::CompleteString(
-                    Level::Root,
-                    cell,
-                    *atom,
-                )]
+                vec![TermIterState::CompleteString(Level::Root, cell, *atom)]
             }
             Term::Literal(cell, constant) => {
                 vec![TermIterState::Literal(Level::Root, cell, constant)]
@@ -319,7 +316,10 @@ pub(crate) fn post_order_iter<'a>(term: &'a Term) -> QueryIterator<'a> {
     QueryIterator::from_term(term)
 }
 
-pub(crate) fn breadth_first_iter<'a>(term: &'a Term, iterable_root: RootIterationPolicy) -> FactIterator<'a> {
+pub(crate) fn breadth_first_iter<'a>(
+    term: &'a Term,
+    iterable_root: RootIterationPolicy,
+) -> FactIterator<'a> {
     FactIterator::new(term, iterable_root)
 }
 
@@ -356,18 +356,14 @@ fn state_from_chunked_terms<'a>(chunk_vec: &'a VecDeque<ChunkedTerms>) -> Clause
 impl<'a> ClauseIterator<'a> {
     pub fn new(clauses: &'a ChunkedTermVec) -> Self {
         match state_from_chunked_terms(&clauses.chunk_vec) {
-            state @ ClauseIteratorState::RemainingBranches(..) => {
-                Self {
-                    state_stack: vec![state],
-                    remaining_chunks_on_stack: 0,
-                }
-            }
-            state @ ClauseIteratorState::RemainingChunks(..) => {
-                Self {
-                    state_stack: vec![state],
-                    remaining_chunks_on_stack: 1,
-                }
-            }
+            state @ ClauseIteratorState::RemainingBranches(..) => Self {
+                state_stack: vec![state],
+                remaining_chunks_on_stack: 0,
+            },
+            state @ ClauseIteratorState::RemainingChunks(..) => Self {
+                state_stack: vec![state],
+                remaining_chunks_on_stack: 1,
+            },
         }
     }
 
@@ -403,14 +399,16 @@ impl<'a> Iterator for ClauseIterator<'a> {
             match state {
                 ClauseIteratorState::RemainingChunks(chunks, focus) if focus < chunks.len() => {
                     if focus + 1 < chunks.len() {
-                        self.state_stack.push(ClauseIteratorState::RemainingChunks(chunks, focus + 1));
+                        self.state_stack
+                            .push(ClauseIteratorState::RemainingChunks(chunks, focus + 1));
                     } else {
                         self.remaining_chunks_on_stack -= 1;
                     }
 
                     match &chunks[focus] {
                         ChunkedTerms::Branch(branches) => {
-                            self.state_stack.push(ClauseIteratorState::RemainingBranches(branches, 0));
+                            self.state_stack
+                                .push(ClauseIteratorState::RemainingBranches(branches, 0));
                         }
                         ChunkedTerms::Chunk(chunk) => {
                             return Some(ClauseItem::Chunk(chunk));
@@ -420,8 +418,11 @@ impl<'a> Iterator for ClauseIterator<'a> {
                 ClauseIteratorState::RemainingChunks(chunks, focus) => {
                     debug_assert_eq!(chunks.len(), focus);
                 }
-                ClauseIteratorState::RemainingBranches(branches, focus) if focus < branches.len() => {
-                    self.state_stack.push(ClauseIteratorState::RemainingBranches(&branches, focus + 1));
+                ClauseIteratorState::RemainingBranches(branches, focus)
+                    if focus < branches.len() =>
+                {
+                    self.state_stack
+                        .push(ClauseIteratorState::RemainingBranches(&branches, focus + 1));
                     let state = state_from_chunked_terms(&branches[focus]);
 
                     if let ClauseIteratorState::RemainingChunks(..) = &state {

src/lib.rs

@@ -2,6 +2,8 @@
 
 #[macro_use]
 extern crate static_assertions;
+#[cfg(test)]
+#[macro_use] extern crate maplit;
 
 #[macro_use]
 pub mod macros;
@@ -17,13 +19,13 @@ pub mod codegen;
 mod debray_allocator;
 #[cfg(feature = "ffi")]
 mod ffi;
-mod variable_records;
 mod forms;
 mod heap_iter;
 pub mod heap_print;
 #[cfg(feature = "http")]
 mod http;
 mod indexing;
+mod variable_records;
 #[macro_use]
 pub mod instructions {
     include!(concat!(env!("OUT_DIR"), "/instructions.rs"));
@@ -38,3 +40,18 @@ mod targets;
 pub mod types;
 
 use instructions::instr;
+
+mod rcu;
+
+#[cfg(target_arch = "wasm32")]
+use wasm_bindgen::prelude::*;
+
+#[cfg(target_arch = "wasm32")]
+#[wasm_bindgen]
+pub fn eval_code(s: &str) -> String {
+    use machine::mock_wam::*;
+
+    let mut wam = Machine::with_test_streams();
+    let bytes = wam.test_load_string(s);
+    String::from_utf8_lossy(&bytes).to_string()
+}

src/lib/builtins.pl

@@ -124,7 +124,7 @@ call(_, _, _, _, _, _, _, _, _).
 % while others can be set with `set_prolog_flag/2`.
 %
 % The flags that Scryer Prolog support are:
-% 
+%
 %  * `max_arity`: The max arity a predicate can have in Prolog. On Scryer is set to 1023. Read only.
 %  * `bounded`: `true` if integer arithmethic is bounded between some min/max values. On Scryer is always set
 %    to `false` since it supports unbounded integer arithmethic. Read only.
@@ -143,6 +143,7 @@ call(_, _, _, _, _, _, _, _, _).
 %    enabled) and `error` which throws an exception when a cylic term is created. Read and write.
 %  * `unknown`: How undefined predicates are handled when called. Possible values are `error` (the default, an error is thrown),
 %    `fail` (the call silently fails) and `warn` (the call fails and a warning about the undefined predicate is printed).
+%  * `answer_write_options`: Additional write options used by the top level for writing answers.
 %
 current_prolog_flag(Flag, Value) :- Flag == max_arity, !, Value = 1023.
 current_prolog_flag(max_arity, 1023).
@@ -160,6 +161,14 @@ current_prolog_flag(Flag, OccursCheckEnabled) :-
     Flag == occurs_check,
     !,
     '$is_sto_enabled'(OccursCheckEnabled).
+current_prolog_flag(occurs_check, OccursCheckEnabled) :-
+    '$is_sto_enabled'(OccursCheckEnabled).
+current_prolog_flag(Flag, Value) :-
+    Flag == answer_write_options,
+    !,
+    answer_write_options(Value).
+current_prolog_flag(answer_write_options, Value) :-
+    answer_write_options(Value).
 current_prolog_flag(Flag, _) :-
     atom(Flag),
     throw(error(domain_error(prolog_flag, Flag), current_prolog_flag/2)). % 8.17.2.3 b
@@ -167,10 +176,15 @@ current_prolog_flag(Flag, _) :-
     nonvar(Flag),
     throw(error(type_error(atom, Flag), current_prolog_flag/2)). % 8.17.2.3 a
 
+answer_write_options(Value) :-
+    (   iso_ext:bb_get('$answer_write_options', Value) -> true
+    ;   Value = []
+    ).
+
 %% set_prolog_flag(Flag, Value).
 %
 % Sets the internal value of the flag. To see the list of flags supported by Scryer Prolog,
-% check `current_prolog_flag/2`. The flags that are read only will fail if you try to change their values 
+% check `current_prolog_flag/2`. The flags that are read only will fail if you try to change their values
 set_prolog_flag(Flag, Value) :-
     (var(Flag) ; var(Value)),
     throw(error(instantiation_error, set_prolog_flag/2)). % 8.17.1.3 a, b
@@ -207,14 +221,25 @@ set_prolog_flag(occurs_check, false) :-
 set_prolog_flag(occurs_check, error) :-
     !, '$set_sto_with_error_as_unify'.
 set_prolog_flag(double_quotes, Value) :-
-    throw(error(domain_error(flag_value, double_quotes + Value),
-                set_prolog_flag/2)). % 8.17.1.3 e
+    flag_domain_error(double_quotes, Value).
+set_prolog_flag(answer_write_options, Options) :-
+    !,
+    catch(catch(builtins:parse_write_options(Options, _, set_prolog_flag/2),
+                error(domain_error(_,_), _),
+                throw(error(type_error(_,_), _))), % convert domain error to type error ....
+          error(type_error(_,_), _),               % ... to catch type and domain errors.
+          flag_domain_error(answer_write_options, Options)),
+    iso_ext:bb_put('$answer_write_options', Options).
 set_prolog_flag(Flag, _) :-
     atom(Flag),
     throw(error(domain_error(prolog_flag, Flag), set_prolog_flag/2)). % 8.17.1.3 d
 set_prolog_flag(Flag, _) :-
     throw(error(type_error(atom, Flag), set_prolog_flag/2)). % 8.17.1.3 c
 
+flag_domain_error(Flag, Value) :-
+    % domain error via 8.17.1.3 e: Value is inappropriate for Flag
+    throw(error(domain_error(flag_value, Flag + Value), set_prolog_flag/2)).
+
 % control operators.
 
 %% fail.
@@ -262,6 +287,9 @@ repeat :- repeat.
 %% ->(G1, G2)
 %
 % If-then and if-then-else constructs
+
+:- non_counted_backtracking (->)/2.
+
 G1 -> G2 :- control_entry_point((G1 -> G2)).
 
 
@@ -275,6 +303,9 @@ staggered_if_then(G1, G2) :-
 %% ;(G1, G2)
 %
 % Disjunction (or)
+
+:- non_counted_backtracking (;)/2.
+
 G1 ; G2 :- control_entry_point((G1 ; G2)).
 
 
@@ -297,6 +328,9 @@ staggered_sc(_, G) :- call(G).
 % to reason about the programs. Also restricts the ability to run the program with alternative execution strategies
 !.
 
+:- non_counted_backtracking get_cp/1.
+get_cp(B) :- '$get_cp'(B).
+
 :- non_counted_backtracking set_cp/1.
 
 set_cp(B) :- '$set_cp'(B).
@@ -304,6 +338,9 @@ set_cp(B) :- '$set_cp'(B).
 %% ,(G1, G2)
 %
 % Conjuction (and)
+
+:- non_counted_backtracking (',')/2.
+
 ','(G1, G2) :- control_entry_point((G1, G2)).
 
 
@@ -325,24 +362,21 @@ cont_list_goal(Conts, '$call'(builtins:dispatch_call_list(Conts))).
 
 :- non_counted_backtracking dispatch_prep/3.
 
-dispatch_prep(Gs, B, [Cont|Conts]) :-
+dispatch_prep(Gs, B, Conts) :-
     (  callable(Gs) ->
        strip_module(Gs, M, Gs0),
        (  nonvar(Gs0),
-          dispatch_prep_(Gs0, B, [Cont|Conts]) ->
+          dispatch_prep_(Gs0, B, Conts) ->
           true
        ;  Gs0 == ! ->
-          Cont = '$call'(builtins:set_cp(B)),
-          Conts = []
+          Conts = ['$call'(builtins:set_cp(B))]
        ;  nonvar(Gs0),
           \+ callable(Gs0) ->
           throw(dispatch_prep_error)
-       ;  Cont = Gs,
-          Conts = []
+       ;  Conts = [Gs]
        )
     ;  var(Gs) ->
-       Cont = Gs,
-       Conts = []
+       Conts = [Gs]
     ;  throw(dispatch_prep_error)
     ).
 
@@ -353,20 +387,32 @@ dispatch_prep_((G1, G2), B, [Cont|Conts]) :-
     dispatch_prep(G1, B, IConts1),
     cont_list_goal(IConts1, Cont),
     dispatch_prep(G2, B, Conts).
-dispatch_prep_((G1 ; G2), B, [Cont|Conts]) :-
-    dispatch_prep(G1, B, IConts0),
+dispatch_prep_((G1 ; G2), B, Conts) :-
+    (  nonvar(G1) ->
+       (  G1 = (G11 -> G12) ->
+          dispatch_prep(G11, B, IConts2),
+          dispatch_prep(G12, B, IConts3),
+          cont_list_goal(IConts2, Cont2),
+          cont_list_goal(IConts3, Cont3),
+          Cont0 = '$call'(builtins:staggered_if_then(Cont2, Cont3))
+       ;  dispatch_prep(G1, B, IConts0),
+          dispatch_prep(G2, B, IConts1),
+          cont_list_goal(IConts0, Cont0)
+       )
+    ;  dispatch_prep(G1, B1, IConts0),
+       cont_list_goal(IConts0, Cont0)
+    ),
     dispatch_prep(G2, B, IConts1),
     cont_list_goal(IConts0, Cont0),
     cont_list_goal(IConts1, Cont1),
-    Cont = '$call'(builtins:staggered_sc(Cont0, Cont1)),
-    Conts = [].
-dispatch_prep_((G1 -> G2), B, [Cont|Conts]) :-
-    dispatch_prep(G1, B, IConts1),
+    Conts = ['$call'(builtins:staggered_sc(Cont0, Cont1))].
+dispatch_prep_((G1 -> G2), B, Conts) :-
+    dispatch_prep(G1, B1, IConts1),
     dispatch_prep(G2, B, IConts2),
     cont_list_goal(IConts1, Cont1),
     cont_list_goal(IConts2, Cont2),
-    Cont = '$call'(builtins:staggered_if_then(Cont1, Cont2)),
-    Conts = [].
+    Conts = ['$call'(builtins:get_cp(B1)),
+             '$call'(builtins:staggered_if_then(Cont1, Cont2))].
 
 
 :- non_counted_backtracking dispatch_call_list/1.
@@ -540,26 +586,30 @@ parse_write_options(Options, OptionValues, Stub) :-
 
 
 parse_write_options_(double_quotes(DoubleQuotes), double_quotes-DoubleQuotes) :-
-    (  nonvar(DoubleQuotes),
-       lists:member(DoubleQuotes, [true, false]),
+    (  var(DoubleQuotes) ->
+       throw(error(instantiation_error, _))
+    ;  lists:member(DoubleQuotes, [true, false]),
        !
     ;  throw(error(domain_error(write_option, double_quotes(DoubleQuotes)), _))
     ).
 parse_write_options_(ignore_ops(IgnoreOps), ignore_ops-IgnoreOps) :-
-    (  nonvar(IgnoreOps),
-       lists:member(IgnoreOps, [true, false]),
+    (  var(IgnoreOps) ->
+       throw(error(instantiation_error, _))
+    ;  lists:member(IgnoreOps, [true, false]),
        !
     ;  throw(error(domain_error(write_option, ignore_ops(IgnoreOps)), _))
     ).
 parse_write_options_(quoted(Quoted), quoted-Quoted) :-
-    (  nonvar(Quoted),
-       lists:member(Quoted, [true, false]),
+    (  var(Quoted) ->
+       throw(error(instantiation_error, _))
+    ;  lists:member(Quoted, [true, false]),
        !
     ;  throw(error(domain_error(write_option, quoted(Quoted)), _))
     ).
 parse_write_options_(numbervars(NumberVars), numbervars-NumberVars) :-
-    (  nonvar(NumberVars),
-       lists:member(NumberVars, [true, false]),
+    (  var(NumberVars) ->
+       throw(error(instantiation_error, _))
+    ;  lists:member(NumberVars, [true, false]),
        !
     ;  throw(error(domain_error(write_option, numbervars(NumberVars)), _))
     ).
@@ -567,7 +617,9 @@ parse_write_options_(variable_names(VNNames), variable_names-VNNames) :-
     must_be_var_names_list(VNNames),
     !.
 parse_write_options_(max_depth(MaxDepth), max_depth-MaxDepth) :-
-    (  integer(MaxDepth),
+    (  var(MaxDepth) ->
+       throw(error(instantiation_error, _))
+    ;  integer(MaxDepth),
        MaxDepth >= 0,
        !
     ;  throw(error(domain_error(write_option, max_depth(MaxDepth)), _))
@@ -681,30 +733,9 @@ parse_read_term_options(Options, OptionValues, Stub) :-
     parse_options_list(Options, builtins:parse_read_term_options_, DefaultOptions, OptionValues, Stub).
 
 
-parse_read_term_options_(singletons(Vars), singletons-Vars) :-
-    (  ( var(Vars)
-       ; '$skip_max_list'(_, _, Vars, Rs),
-         Rs == []
-       ) ->
-       !
-    ;  throw(error(domain_error(read_option, singletons(Vars)), read_term/2))
-    ).
-parse_read_term_options_(variables(Vars), variables-Vars) :-
-    (  ( var(Vars)
-       ; '$skip_max_list'(_, _, Vars, Rs),
-         Rs == []
-       ) ->
-       !
-    ;  throw(error(domain_error(read_option, variables(Vars)), read_term/2))
-    ).
-parse_read_term_options_(variable_names(Vars), variable_names-Vars) :-
-    (  ( var(Vars)
-       ; '$skip_max_list'(_, _, Vars, Rs),
-         Rs == []
-       ) ->
-       !
-    ;  throw(error(domain_error(read_option, variable_names(Vars)), read_term/2))
-    ).
+parse_read_term_options_(singletons(Vars), singletons-Vars) :- !.
+parse_read_term_options_(variables(Vars), variables-Vars) :- !.
+parse_read_term_options_(variable_names(Vars), variable_names-Vars) :- !.
 parse_read_term_options_(E,_) :-
     throw(error(domain_error(read_option, E), _)).
 
@@ -714,7 +745,7 @@ parse_read_term_options_(E,_) :-
 % Read Term from the stream Stream. It supports several options:
 %  * `variables(-Vars)` unifies Vars with a list of variables in the term. Similar to do `term_variables/2` with the new term.
 %  * `variable_names(-Vars)` unifies Vars with a list `Name=Var` with Name describing the variable name and Var the variable itself that appears in Term.
-%  * `singletons` similar to `variable_names` but only reports variables occurring only once in Term. 
+%  * `singletons` similar to `variable_names` but only reports variables occurring only once in Term.
 read_term(Stream, Term, Options) :-
     parse_read_term_options(Options, [Singletons, VariableNames, Variables], read_term/3),
     '$read_term'(Stream, Term, Singletons, Variables, VariableNames).
@@ -788,7 +819,7 @@ catch(G,C,R) :-
 
 catch(G,C,R,Bb) :-
     '$install_new_block'(NBb),
-    '$call_with_inference_counting'(call(G)),
+    call(G),
     end_block(Bb, NBb).
 catch(G,C,R,Bb) :-
     '$reset_block'(Bb),
@@ -1342,11 +1373,6 @@ current_predicate(Pred) :-
     ;  throw(error(type_error(predicate_indicator, Pred), current_predicate/1))
     ).
 
-'$iterate_op_db_refs'(RPriority, RSpec, ROp, _, RPriority, RSpec, ROp).
-'$iterate_op_db_refs'(RPriority, RSpec, ROp, OssifiedOpDir, Priority, Spec, Op) :-
-    '$get_next_op_db_ref'(RPriority, RSpec, ROp, OssifiedOpDir, RRPriority, RRSpec, RROp),
-    '$iterate_op_db_refs'(RRPriority, RRSpec, RROp, OssifiedOpDir, Priority, Spec, Op).
-
 can_be_op_priority(Priority) :- var(Priority).
 can_be_op_priority(Priority) :- op_priority(Priority).
 
@@ -1362,8 +1388,8 @@ current_op(Priority, Spec, Op) :-
     (  can_be_op_priority(Priority),
        can_be_op_specifier(Spec),
        error:can_be(atom, Op) ->
-       '$get_next_op_db_ref'(RPriority, RSpec, ROp, OssifiedOpDir, _, _, Op),
-       '$iterate_op_db_refs'(RPriority, RSpec, ROp, OssifiedOpDir, Priority, Spec, Op)
+       '$get_next_op_db_ref'(Priority, Spec, Op, ListOfOps),
+       lists:member(op(Priority, Spec, Op), ListOfOps)
     ).
 
 list_of_op_atoms(Var) :-
@@ -1587,7 +1613,7 @@ atom_concat(Atom_1, Atom_2, Atom_12) :-
 %% sub_atom(+Atom, ?Before, ?Length, ?After, ?SubAtom).
 %
 % Relates an atom to a subatom inside with some key properties:
-% 
+%
 %  * SubAtom starts at Before characters (0-based) from Atom
 %  * SubAtom has Length characters
 %  * After SubAtom there are After characters in Atom
@@ -2186,6 +2212,9 @@ set_stream_position(S_or_a, Position) :-
 %% callable(X).
 %
 % True iff X is bound o an atom or a compund term.
+
+:- non_counted_backtracking callable/1.
+
 callable(X) :-
     (  nonvar(X), functor(X, F, _), atom(F) ->
        true
@@ -2209,4 +2238,7 @@ nl(Stream) :-
 %
 % Throws an exception of the following structure: `error(ErrorTerm, ImpDef)`.
 error(Error_term, Imp_def) :-
-   throw(error(Error_term, Imp_def)).
+    (  var(Error_term) ->
+       throw(error(instantiation_error, error/2))
+    ;  throw(error(Error_term, Imp_def))
+    ).

src/lib/charsio.pl

@@ -105,8 +105,8 @@ extend_var_list_([V|Vs], N, VarList, NewVarList, VarType) :-
 % - `symbolic_control`
 % - `symbolic_hexadecimal`
 % - `upper`
-% - `to_lower(Lower)`
-% - `to_upper(Upper)`
+% - `lower(Lower)`
+% - `upper(Upper)`
 % - `whitespace`
 %
 % An example:
@@ -124,8 +124,8 @@ extend_var_list_([V|Vs], N, VarList, NewVarList, VarType) :-
 % ;  Type = octet
 % ;  Type = prolog
 % ;  Type = symbolic_control
-% ;  Type = to_lower("a")
-% ;  Type = to_upper("A")
+% ;  Type = lower("a")
+% ;  Type = upper("A")
 % ;  false.
 % ```
 %
@@ -168,8 +168,8 @@ ctype(sign).
 ctype(solo).
 ctype(symbolic_control).
 ctype(symbolic_hexadecimal).
-ctype(to_lower(_)).
-ctype(to_upper(_)).
+ctype(lower(_)).
+ctype(upper(_)).
 ctype(upper).
 ctype(whitespace).
 

src/lib/clpb.pl

@@ -1,10 +1,29 @@
 /*  CLP(B): Constraint Logic Programming over Boolean Variables
 
-    Copyright (C): 2019-2023 Markus Triska
-    All rights reserved.
-
+    Author:        Markus Triska
     E-mail:        triska@metalevel.at
-    WWW:           http://www.metalevel.at
+    WWW:           https://www.metalevel.at
+    Copyright (C): 2019-2023 Markus Triska
+
+    Permission is hereby granted, free of charge, to any person
+    obtaining a copy of this software and associated documentation
+    files (the "Software"), to deal in the Software without
+    restriction, including without limitation the rights to use, copy,
+    modify, merge, publish, distribute, sublicense, and/or sell copies
+    of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be
+    included in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+    HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+    WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
 
 */
 
@@ -17,8 +36,8 @@
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
 :- module(clpb, [op(300, fy, ~),
-		         op(500, yfx, #),
-		         sat/1,
+                 op(500, yfx, #),
+                 sat/1,
                  taut/2,
                  labeling/1,
                  sat_count/2,
@@ -91,6 +110,46 @@ domain_error(Expectation, Term) :-
 type_error(Expectation, Term) :-
         type_error(Expectation, Term, unknown(Term)-1).
 
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+Compatibility predicates.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- meta_predicate(include(1, ?, ?)).
+
+include(_, [], []).
+include(Goal, [L|Ls0], Ls) :-
+        (   call(Goal, L) ->
+            Ls = [L|Rest]
+        ;   Ls = Rest
+        ),
+        include(Goal, Ls0, Rest).
+
+:- meta_predicate(exclude(1, ?, ?)).
+
+exclude(_, [], []).
+exclude(Goal, [L|Ls0], Ls) :-
+        (   call(Goal, L) ->
+            Ls = Rest
+        ;   Ls = [L|Rest]
+        ),
+        exclude(Goal, Ls0, Rest).
+
+:- meta_predicate(partition(2,?,?,?,?)).
+
+partition(_, [], [], [], []).
+partition(Pred, [H|T], L, E, G) :-
+    call(Pred, H, Diff),
+    partition_(Diff, H, Pred, T, L, E, G).
+
+partition_(<, H, Pred, T, [H|Rest], E, G) :-
+    partition(Pred, T, Rest, E, G).
+partition_(=, H, Pred, T, L, [H|Rest], G) :-
+    partition(Pred, T, L, Rest, G).
+partition_(>, H, Pred, T, L, E, [H|Rest]) :-
+    partition(Pred, T, L, E, Rest).
+
+:- meta_predicate(partition(1,?,?,?)).
+
 partition(Pred, Ls0, As, Bs) :-
         include(Pred, Ls0, As),
         exclude(Pred, Ls0, Bs).
@@ -447,6 +506,10 @@ non_monotonic(X) :-
         ;   true
         ).
 
+:- meta_predicate(bdd_nodes(1, ?, ?)).
+:- meta_predicate(bdd_nodes_(1, ?, ?, ?)).
+:- meta_predicate(with_aux(1, ?)).
+
 /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Rewriting to canonical expressions.
    Atoms are converted to variables with a special attribute.
@@ -1513,8 +1576,7 @@ random_bindings(VNum, Node) -->
 %
 % ```
 % ?- sat(A#B), weighted_maximum([1,2,1], [A,B,C], Maximum).
-%    A = 0, B = 1, C = 1, Maximum = 3
-% ;  false.
+%    A = 0, B = 1, C = 1, Maximum = 3.
 % ```
 
 weighted_maximum(Ws, Vars, Max) :-
@@ -1635,8 +1697,7 @@ attribute_goals(Var) -->
                 { bdd_nodes(BDD, Nodes),
                   phrase(nodes(Nodes), Ns) },
                 [clpb:'$clpb_bdd'(Ns)]
-            ;   { prepare_global_variables(BDD),
-                  phrase(sat_ands(Formula), Ands0),
+            ;   { phrase(sat_ands(Formula), Ands0),
                   ands_fusion(Ands0, Ands),
                   maplist(formula_anf, Ands, ANFs0),
                   sort(ANFs0, ANFs1),
@@ -1656,6 +1717,10 @@ attribute_goals(Var) -->
             booleans(RestVs)
         ;   boolean(Var)  % the variable may have occurred only in taut/2
         ).
+attribute_goals(Var) -->
+        { get_atts(Var, clpb_max(_)),
+          !,
+          put_atts(Var, -clpb_max(_)) }.
 attribute_goals(Var) -->
         { get_atts(Var, clpb_bdd(BDD)),
           ground(BDD),
@@ -1663,36 +1728,13 @@ attribute_goals(Var) -->
 
 del_clpb(Var) :-
         del_attr(Var, clpb),
-        del_attr(Var, clpb_hash).
-
-/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-   To make residual projection work with recorded constraints, the
-   global counters must be adjusted so that new variables and nodes
-   also get new IDs. Also, clpb_next_id/2 is used to actually create
-   these counters, because creating them with b_setval/2 would make
-   them [] on backtracking, which is quite unfortunate in itself.
-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+        del_attr(Var, clpb_hash),
+        del_attr(Var, clpb_atom).
 
 b_setval(K, T) :- bb_b_put(K, T).
 nb_setval(K, T) :- bb_put(K, T).
 b_getval(K, T) :- bb_get(K, T).
 
-prepare_global_variables(BDD) :-
-        clpb_next_id('$clpb_next_var', V0),
-        clpb_next_id('$clpb_next_node', N0),
-        bdd_nodes(BDD, Nodes),
-        foldl(max_variable_node, Nodes, V0-N0, MaxV0-MaxN0),
-        MaxV is MaxV0 + 1,
-        MaxN is MaxN0 + 1,
-        b_setval('$clpb_next_var', MaxV),
-        b_setval('$clpb_next_node', MaxN).
-
-max_variable_node(Node, V0-N0, V-N) :-
-        node_id(Node, N1),
-        node_varindex(Node, V1),
-        N is max(N0,N1),
-        V is max(V0,V1).
-
 /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Fuse formulas that share the same variables into single conjunctions.
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
@@ -1817,7 +1859,8 @@ booleans([B|Bs]) --> boolean(B), booleans(Bs).
 
 boolean(Var) -->
         { del_clpb(Var) },
-        (   { get_attr(Var, clpb_omit_boolean, true) } -> []
+        (   { get_attr(Var, clpb_omit_boolean, true) } ->
+            { put_atts(Var, -clpb_omit_boolean(_)) }
         ;   [clpb:sat(Var =:= Var)]
         ).
 
@@ -1919,49 +1962,3 @@ clpb_atom_var(Atom, Var) :-
             put_assoc(Atom, A0, Var, A),
             b_setval('$clpb_atoms', A)
         ).
-
-
-
-/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-Compatibility predicates.
-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
-
-
-include(Goal, List, Is) :-
-        include_(List, Goal, Is).
-
-include_([], _, []).
-include_([X1|Xs1], P, Is) :-
-        (   call(P, X1)
-        ->  Is = [X1|Is1]
-        ;   Is = Is1
-        ),
-        include_(Xs1, P, Is1).
-
-
-exclude(Goal, List, Is) :-
-        exclude_(List, Goal, Is).
-
-exclude_([], _, []).
-exclude_([X1|Xs1], P, Is) :-
-        (   call(P, X1)
-        ->  Is = Is1
-        ;   Is = [X1|Is1]
-        ),
-        exclude_(Xs1, P, Is1).
-
-
-partition(Pred, List, Less, Equal, Greater) :-
-    partition_(List, Pred, Less, Equal, Greater).
-
-partition_([], _, [], [], []).
-partition_([H|T], Pred, L, E, G) :-
-    call(Pred, H, Diff),
-    partition_(Diff, H, Pred, T, L, E, G).
-
-partition_(<, H, Pred, T, [H|Rest], E, G) :-
-    partition_(T, Pred, Rest, E, G).
-partition_(=, H, Pred, T, L, [H|Rest], G) :-
-    partition_(T, Pred, L, Rest, G).
-partition_(>, H, Pred, T, L, E, [H|Rest]) :-
-    partition_(T, Pred, L, E, Rest).

src/lib/clpz.pl

@@ -1030,8 +1030,8 @@ term_expansion(Term0, Term) :-
         once(duodcg_body(Body0, Body, As0, As, Bs0, Bs)).
 
 duodcg_body([], (As0=As,Bs0=Bs), As0, As, Bs0, Bs).
-duodcg_body(Xs+Ys, (phrase(list(Xs), As0, As),
-                       phrase(list(Ys), Bs0, Bs)), As0, As, Bs0, Bs).
+duodcg_body(Xs+Ys, (phrase(seq(Xs), As0, As),
+                       phrase(seq(Ys), Bs0, Bs)), As0, As, Bs0, Bs).
 duodcg_body({Goal}, call(Goal), As, As, Bs, Bs).
 duodcg_body((A0,B0), (A,B), As0, As, Bs0, Bs) :-
         duodcg_body(A0, A, As0, As1, Bs0, Bs1),
@@ -1957,7 +1957,6 @@ choice_order_variable(step, Order, Var, Vars, Vars0, Selection, Consistency) :-
         (   Var = Next,
             label(Vars, Selection, Order, step, Consistency)
         ;   neq_num(Var, Next),
-            do_queue,
             label(Vars0, Selection, Order, step, Consistency)
         ).
 choice_order_variable(enum, Order, Var, Vars, _, Selection, Consistency) :-
@@ -2142,16 +2141,17 @@ fds_sespsize([V|Vs], S0, S) :-
         fds_sespsize(Vs, S2, S).
 
 /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-   Optimisation uses destructive assignment to save the computed
-   extremum over backtracking. Failure is used to get rid of copies of
-   attributed variables that are created in intermediate steps. At
-   least that's the intention - it currently doesn't work in SWI:
+   Optimisation uses the clause database to save the computed extremum
+   over backtracking. Failure is used to get rid of copies of
+   attributed variables that are created in intermediate steps.
 
-   %?- X in 0..3, call_residue_vars(labeling([min(X)], [X]), Vs).
-   %@ X = 0,
-   %@ Vs = [_G6174, _G6177],
-   %@ _G6174 in 0..3
+   Example:
 
+     ?- X in 1..3, call_residue_vars(labeling([min(X)], [X]), Vs).
+     %@    X = 1, Vs = []
+     %@ ;  X = 2, Vs = []
+     %@ ;  X = 3, Vs = []
+     %@ ;  false.
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
 :- dynamic(extremum/1).
@@ -2565,13 +2565,13 @@ parse_clpz(E, R,
              g(power_var_num(E, V, N)) => [p(pexp(V, N, R))],
              m(A*B)            => [p(ptimes(A, B, R))],
              m(A-B)            => [p(pplus(R,B,A))],
-             m(-A)             => [p(ptimes(-1,A,R))],
+             m(-A)             => [p(pplus(A,R,0))],
              m(max(A,B))       => [g(A #=< #R), g(B #=< R), p(pmax(A, B, R))],
              m(min(A,B))       => [g(A #>= #R), g(B #>= R), p(pmin(A, B, R))],
              m(A mod B)        => [g(B #\= 0), p(pmod(A, B, R))],
              m(A rem B)        => [g(B #\= 0), p(prem(A, B, R))],
              m(abs(A))         => [g(#R #>= 0), p(pabs(A, R))],
-             m(A/B)            => [g(B #\= 0), p(prdiv(A, B, R))],
+             m(A/B)            => [g(B #\= 0), p(ptimes(R, B, A))],
              m(A//B)           => [g(B #\= 0), p(ptzdiv(A, B, R))],
              m(A div B)        => [g(#R #= (A - (A mod B)) // B)],
              m(A^B)            => [p(pexp(A, B, R))],
@@ -2635,14 +2635,37 @@ parse_goals([]) --> [].
 parse_goals([G|Gs]) --> parse_goal(G), parse_goals(Gs).
 
 parse_goal(g(Goal)) --> [Goal].
-parse_goal(p(Prop)) -->
-        { term_variables(Prop, Vs) },
+parse_goal(p(Prop0)) -->
+        { term_variables(Prop0, Vs),
+          morphing_propagator(Prop0, Prop, _) },
         [make_propagator(Prop, P),
          new_queue(Q0),
          phrase(init_propagator_(Vs, P), [Q0], [Q]),
          variables_same_queue(Vs),
          trigger_once_(P, Q)].
 
+morphing(pplus).
+morphing(ptimes).
+morphing(pexp).
+morphing(ptzdiv).
+
+morphing_propagator(P0, P, Target) :-
+        P0 =.. [F|Args0],
+        (   morphing(F) ->
+            append(Args0, [Last], Args),
+            Target = p(Last)
+        ;   Args = Args0,
+            Target = none
+        ),
+        P =.. [F|Args].
+
+morph_into_propagator(MState, Vs, P0, Morph) -->
+        kill(MState),
+        { morphing_propagator(P0, P, _),
+          make_propagator(P, Morph) },
+        init_propagator_(Vs, Morph),
+        trigger_prop(Morph).
+
 /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 ?- use_module(library(lists)),
    use_module(library(format)),
@@ -2733,14 +2756,12 @@ geq(A, B) :-
                 )
             ;   (   AI cis_geq n(B) -> true
                 ;   domain_remove_smaller_than(AD, B, AD1),
-                    fd_put(A, AD1, APs),
-                    do_queue
+                    fd_put(A, AD1, APs)
                 )
             )
         ;   fd_get(B, BD, BPs) ->
             domain_remove_greater_than(BD, A, BD1),
-            fd_put(B, BD1, BPs),
-            do_queue
+            fd_put(B, BD1, BPs)
         ;   A >= B
         ).
 
@@ -2810,7 +2831,7 @@ matches([
          m(var(X) #= var(Y)+var(Z)) => [p(pplus(Y,Z,X))],
          m(var(X) #= var(Y)-var(Z)) => [p(pplus(X,Z,Y))],
          m(var(X) #= var(Y)*var(Z)) => [p(ptimes(Y,Z,X))],
-         m(var(X) #= -var(Z))       => [p(ptimes(-1, Z, X))],
+         m(var(X) #= -var(Y))       => [p(pplus(X,Y,0))],
          m_c(any(X) #= any(Y), left_right_linsum_const(X, Y, Cs, Vs, S)) =>
             [g(scalar_product_(#=, Cs, Vs, S))],
          m_c(var(X) #= abs(var(Y)) + any(V0), X == Y) => [d(V0,V),p(x_eq_abs_plus_v(X,V))],
@@ -2906,8 +2927,9 @@ match_goals([G|Gs], F) --> match_goal(G, F), match_goals(Gs, F).
 match_goal(r(X,Y), F)  --> { G =.. [F,X,Y] }, [G].
 match_goal(d(X,Y), _)  --> [parse_clpz(X, Y)].
 match_goal(g(Goal), _) --> [Goal].
-match_goal(p(Prop), _) -->
-        { term_variables(Prop, Vs) },
+match_goal(p(Prop0), _) -->
+        { term_variables(Prop0, Vs),
+          morphing_propagator(Prop0, Prop, _) },
         [make_propagator(Prop, P),
          new_queue(Q0),
          phrase(init_propagator_(Vs, P), [Q0], [Q]),
@@ -3295,7 +3317,7 @@ integer_kroot_leq(L, U, N, K, R) :-
 % When reasoning over integers, replace (=\=)/2 by (#\=)/2 to obtain more
 % general relations.
 
-X #\= Y :- clpz_neq(X, Y), do_queue.
+X #\= Y :- clpz_neq(X, Y).
 
 % X #\= Y + Z
 
@@ -3358,7 +3380,7 @@ X #< Y  :- Y #> X.
 % X in inf.. -4\/1..9\/81..sup.
 % ```
 
-#\ Q       :- reify(Q, 0), do_queue.
+#\ Q       :- reify(Q, 0).
 
 %% #<==>(?P, ?Q)
 %
@@ -3396,7 +3418,7 @@ X #< Y  :- Y #> X.
 % Z = 2.
 % ```
 
-L #<==> R  :- reify(L, B), reify(R, B), do_queue.
+L #<==> R  :- reify(L, B), reify(R, B).
 
 %% #==>(?P, ?Q)
 %
@@ -3431,7 +3453,7 @@ L #<== R   :- R #==> L.
 %
 % P and Q hold.
 
-L #/\ R    :- reify(L, 1), reify(R, 1), do_queue.
+L #/\ R    :- reify(L, 1), reify(R, 1).
 
 conjunctive_neqs_var_drep(Eqs, Var, Drep) :-
         conjunctive_neqs_var(Eqs, Var),
@@ -3519,16 +3541,17 @@ L #\ R :- (L #\/ R) #/\ #\ (L #/\ R).
    d(D) that states D is 1 iff all subexpressions are defined. a(V)
    means that V is an auxiliary variable that was introduced while
    parsing a compound expression. a(X,V) means V is auxiliary unless
-   it is ==/2 X, and a(X,Y,V) means V is auxiliary unless it is ==/2 X
-   or Y. l(L) means the literal L occurs in the described list.
+   it is (==)/2 X, and a(X,Y,V) means V is auxiliary unless it is
+   (==)/2 X or Y. l(L) means the literal L occurs in the described
+   list, and ls(Ls) means the literals Ls occur in the described list.
 
    When a constraint becomes entailed or subexpressions become
    undefined, created auxiliary constraints are killed, and the
    "clpz" attribute is removed from auxiliary variables.
 
-   For mod/2, div/2, rem/2 etc. we create a skeleton propagator and
-   remember it as an auxiliary constraint. The pskeleton propagator
-   can use the skeleton when the constraint is defined.
+   For (//)/2, (mod)/2 and (rem)/2, we create a skeleton propagator
+   and remember it as an auxiliary constraint. The pskeleton
+   propagator can use the skeleton when the constraint is defined.
 
    We cannot use a skeleton propagator for (/)/2, since (/)/2 can
    fail in cases such as 0 #==> X #= 1/2, where we expect success.
@@ -3544,27 +3567,32 @@ parse_reified(E, R, D,
                m(A+B)        => [d(D), p(pplus(A,B,R)), a(A,B,R)],
                m(A*B)        => [d(D), p(ptimes(A,B,R)), a(A,B,R)],
                m(A-B)        => [d(D), p(pplus(R,B,A)), a(A,B,R)],
-               m(-A)         => [d(D), p(ptimes(-1,A,R)), a(R)],
+               m(-A)         => [d(D), p(pplus(A,R,0)), a(R)],
                m(max(A,B))   => [d(D), p(pgeq(R, A)), p(pgeq(R, B)), p(pmax(A,B,R)), a(A,B,R)],
                m(min(A,B))   => [d(D), p(pgeq(A, R)), p(pgeq(B, R)), p(pmin(A,B,R)), a(A,B,R)],
-               m(abs(A))     => [g(#R#>=0), d(D), p(pabs(A, R)), a(A,R)],
-               m(A/B)        => [p(preified_slash(A,B,D,R)), a(A,B,R)],
+               m(abs(A))     => [d(D), g(#R#>=0), p(pabs(A, R)), a(A,R)],
+               m(A^B)        => [d(D1), p(preified_exp(A,B,D2,R)),
+                                 p(reified_and(D1,[],D2,[],D)),a(D2),a(A,B,R)],
+               m(A/B)        => [d(D1), p(preified_slash(A,B,D2,R)),
+                                 p(reified_and(D1,[],D2,[],D)),a(D2),a(A,B,R)],
+               m(A div B)    => [d(D1),
+                                 g(phrase(parse_reified_clpz(((A-(A mod B)) // B), R, D2), Ps)),
+                                 ls(Ps),
+                                 p(reified_and(D1,[],D2,[],D)),a(D2),a(A,B,R)],
                m(A//B)       => [skeleton(A,B,D,R,ptzdiv)],
-               m(A div B)    => [skeleton(A,B,D,R,pdiv)],
                m(A mod B)    => [skeleton(A,B,D,R,pmod)],
                m(A rem B)    => [skeleton(A,B,D,R,prem)],
-               m(A^B)        => [d(D), p(pexp(A,B,R)), a(A,B,R)],
                % bitwise operations
                m(\A)         => [function(D,\,A,R)],
                m(msb(A))     => [g(#A#>0) ,function(D,msb,A,R)],
                m(lsb(A))     => [g(#A#>0), function(D,lsb,A,R)],
-               m(popcount(A)) => [function(D,popcount,A,R)],
-               m(sign(A))    => [function(D,sign,A,R)],
+               m(popcount(A)) => [d(D), p(ppopcount(A, R)), a(A,R)],
+               m(sign(A))    => [d(D), p(psign(A, R)), a(A,R)],
                m(A<<B)       => [function(D,<<,A,B,R)],
                m(A>>B)       => [function(D,>>,A,B,R)],
                m(A/\B)       => [function(D,/\,A,B,R)],
                m(A\/B)       => [function(D,\/,A,B,R)],
-               m(xor(A, B))  => [function(D,xor,A,B,R)],
+               m(xor(A, B))  => [skeleton(A,B,D,R,pxor)],
                g(true)       => [g(domain_error(clpz_expression, E))]]
              ).
 
@@ -3620,10 +3648,13 @@ reified_goal(d(D), Ds) -->
         ;   { domain_error(one_or_two_element_list, Ds) }
         ).
 reified_goal(g(Goal), _) --> [{Goal}].
-reified_goal(p(Vs, Prop), _) -->
+reified_goal(p(Vs, Prop0), _) -->
+        { morphing_propagator(Prop0, Prop, Target) },
         [{make_propagator(Prop, P)}],
+        target_propagator(Target),
         parse_init_dcg(Vs, P),
-        [{trigger_once(P)}],
+        [{variables_same_queue(Vs),
+          trigger_once(P)}],
         [( { propagator_state(P, S), S == dead } -> [] ; [p(P)])].
 reified_goal(p(Prop), Ds) -->
         { term_variables(Prop, Vs) },
@@ -3633,7 +3664,9 @@ reified_goal(function(D,Op,A,B,R), Ds) -->
 reified_goal(function(D,Op,A,R), Ds) -->
         reified_goals([d(D),p(pfunction(Op,A,R)),a(A,R)], Ds).
 reified_goal(skeleton(A,B,D,R,F), Ds) -->
-        { Prop =.. [F,X,Y,Z] },
+        { Prop0 =.. [F,X,Y,Z],
+          morphing_propagator(Prop0, Prop, Target) },
+        target_propagator(Target),
         reified_goals([d(D1),l(p(P)),g(make_propagator(Prop, P)),
                        p([A,B,D2,R], pskeleton(A,B,D2,[X,Y,Z]-P,R,F)),
                        p(reified_and(D1,[],D2,[],D)),a(D2),a(A,B,R)], Ds).
@@ -3641,12 +3674,20 @@ reified_goal(a(V), _)     --> [a(V)].
 reified_goal(a(X,V), _)   --> [a(X,V)].
 reified_goal(a(X,Y,V), _) --> [a(X,Y,V)].
 reified_goal(l(L), _)     --> [[L]].
+reified_goal(ls(Ls), _)   --> [Ls].
+
+target_propagator(p(Prop)) --> [[p(Prop)]].
+target_propagator(none)    --> [].
 
 parse_init_dcg([], _)     --> [].
 parse_init_dcg([V|Vs], P) --> [{init_propagator(V, P)}], parse_init_dcg(Vs, P).
 
-%?- set_prolog_flag(answer_write_options, [portray(true)]),
-%   clpz:parse_reified_clauses(Cs), maplist(portray_clause, Cs).
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+?- use_module(library(lists)),
+   use_module(library(format)),
+   clpz:parse_reified_clauses(Cs),
+   maplist(portray_clause, Cs).
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
 reify(E, B) :- reify(E, B, _).
 
@@ -3691,7 +3732,7 @@ reify_(tuples_in(Tuples, Relation), B) -->
           #B #<==> And },
         propagator_init_trigger([B], tuples_not_in(Tuples, Relation, B)),
         kill_reified_tuples(Bs, Ps, Bs),
-        list(Ps),
+        seq(Ps),
         as([B|Bs]).
 reify_(finite_domain(V), B) -->
         propagator_init_trigger(reified_fd(V,B)),
@@ -3723,20 +3764,17 @@ arithmetic(L, R, B, Functor) -->
         { phrase((parse_reified_clpz(L, LR, LD),
                   parse_reified_clpz(R, RR, RD)), Ps),
           Prop =.. [Functor,LD,LR,RD,RR,Ps,B] },
-        list(Ps),
+        seq(Ps),
         propagator_init_trigger([LD,LR,RD,RR,B], Prop),
         a(B).
 
 boolean(L, R, B, Functor) -->
         { reify(L, LR, Ps1), reify(R, RR, Ps2),
           Prop =.. [Functor,LR,Ps1,RR,Ps2,B] },
-        list(Ps1), list(Ps2),
+        seq(Ps1), seq(Ps2),
         propagator_init_trigger([LR,RR,B], Prop),
         a(LR, RR, B).
 
-list([])     --> [].
-list([L|Ls]) --> [L], list(Ls).
-
 a(X,Y,B) -->
         (   nonvar(X) -> a(Y, B)
         ;   nonvar(Y) -> a(X, B)
@@ -3871,7 +3909,6 @@ domain(V, Dom) :-
             domains_intersection(Dom, Dom0, Dom1),
             %format("intersected\n: ~w\n ~w\n==> ~w\n\n", [Dom,Dom0,Dom1]),
             fd_put(V, Dom1, VPs),
-            do_queue,
             reinforce(V)
         ;   domain_contains(Dom, V)
         ).
@@ -4186,7 +4223,6 @@ activate_propagator(propagator(P,State)) -->
 
 enable_queue  :- true. % NOP
 disable_queue :- true. % NOP
-do_queue.              % NOP
 
 %do_queue --> print_queue, { false }.
 do_queue -->
@@ -4768,7 +4804,7 @@ run_propagator(scalar_product_eq(Cs0,Vs0,P0), MState) -->
           ) }.
 
 % X + Y = Z
-run_propagator(pplus(X,Y,Z), MState) -->
+run_propagator(pplus(X,Y,Z,Morph), MState) -->
         (   nonvar(X) ->
             (   X =:= 0 -> kill(MState), Y = Z
             ;   Y == Z -> kill(MState), X =:= 0
@@ -4787,7 +4823,7 @@ run_propagator(pplus(X,Y,Z), MState) -->
                 ;   []
                 )
             )
-        ;   nonvar(Y) -> run_propagator(pplus(Y,X,Z), MState)
+        ;   nonvar(Y) -> run_propagator(pplus(Y,X,Z,Morph), MState)
         ;   nonvar(Z) ->
             (   X == Y -> kill(MState), { even(Z), X is Z // 2 }
             ;   { fd_get(X, XD, _),
@@ -4804,7 +4840,8 @@ run_propagator(pplus(X,Y,Z), MState) -->
                 ;   []
                 )
             )
-        ;   (   X == Y -> { kill(MState), 2*X #= Z }
+        ;   (   X == Y ->
+                morph_into_propagator(MState, [X,Z], ptimes(2,X,Z), Morph)
             ;   X == Z -> kill(MState), Y = 0
             ;   Y == Z -> kill(MState), X = 0
             ;   { fd_get(X, XD, XL, XU, XPs),
@@ -4830,7 +4867,7 @@ run_propagator(pplus(X,Y,Z), MState) -->
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
-run_propagator(ptimes(X,Y,Z), MState) -->
+run_propagator(ptimes(X,Y,Z,Morph), MState) -->
         (   nonvar(X) ->
             (   nonvar(Y) -> kill(MState), Z is X * Y
             ;   X =:= 0 -> kill(MState), Z = 0
@@ -4850,7 +4887,7 @@ run_propagator(ptimes(X,Y,Z), MState) -->
                     )
                 )
             )
-        ;   nonvar(Y) -> run_propagator(ptimes(Y,X,Z), MState)
+        ;   nonvar(Y) -> run_propagator(ptimes(Y,X,Z,Morph), MState)
         ;   nonvar(Z) ->
             (   X == Y ->
                 kill(MState),
@@ -4876,7 +4913,8 @@ run_propagator(ptimes(X,Y,Z), MState) -->
                 ;  neq_num(X, 0), neq_num(Y, 0)
                 )
             )
-        ;   (   X == Y -> kill(MState), { X^2 #= Z }
+        ;   (   X == Y ->
+                morph_into_propagator(MState, [X,Z], pexp(X,2,Z), Morph)
             ;   { fd_get(X, XD, XL, XU, XPs),
                   fd_get(Y, _, YL, YU, _),
                   fd_get(Z, ZD, ZL, ZU, _) },
@@ -4907,17 +4945,8 @@ run_propagator(ptimes(X,Y,Z), MState) -->
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
-% X div Y = Z
-run_propagator(pdiv(X,Y,Z), MState) -->
-        { kill(MState), Z #= (X-(X mod Y)) // Y }.
-
-% X rdiv Y = Z
-run_propagator(prdiv(X,Y,Z), MState) -->
-        { kill(MState), Z*Y #= X }.
-
-
 % X // Y = Z (round towards zero)
-run_propagator(ptzdiv(X,Y,Z), MState) -->
+run_propagator(ptzdiv(X,Y,Z,Morph), MState) -->
         (   nonvar(X) ->
             (   nonvar(Y) -> kill(MState), Y =\= 0, Z is X // Y
             ;   { fd_get(Y, YD, YL, YU, YPs) },
@@ -4961,7 +4990,8 @@ run_propagator(ptzdiv(X,Y,Z), MState) -->
         ;   nonvar(Y) ->
             Y =\= 0,
             (   Y =:= 1 -> kill(MState), X = Z
-            ;   Y =:= -1 -> kill(MState), { Z #= -X }
+            ;   Y =:= -1 ->
+                morph_into_propagator(MState, [X,Z], pplus(X,Z,0), Morph)
             ;   { fd_get(X, XD, XL, XU, XPs) },
                 (   nonvar(Z) ->
                     kill(MState),
@@ -5411,9 +5441,11 @@ run_propagator(pmin(X,Y,Z), MState) -->
 %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %% % Z = X ^ Y
 
-run_propagator(pexp(X,Y,Z), MState) -->
+run_propagator(pexp(X,Y,Z,Morph), MState) -->
         (   X == 1 -> kill(MState), Z = 1
-        ;   X == 0 -> kill(MState), queue_goal((Z in 0..1, Y #>= 0, Z #<==> Y #= 0))
+        ;   X == 0 ->
+            queue_goal((Z in 0..1, Y #>= 0)),
+            morph_into_propagator(MState, [Y,Z], reified_eq(1,Y,1,0,[],Z), Morph)
         ;   Y == 0 -> kill(MState), Z = 1
         ;   Y == 1 -> kill(MState), Z = X
         ;   nonvar(X) ->
@@ -5473,7 +5505,9 @@ run_propagator(pexp(X,Y,Z), MState) -->
             )
         ;   nonvar(Y), Y > 0 ->
             (   { even(Y) } ->
-                { geq(Z, 0) }
+                { fd_get(Z, ZD0, ZPs0),
+                  domain_remove_smaller_than(ZD0, 0, ZDG0) },
+                fd_put(Z, ZDG0, ZPs0)
             ;   true
             ),
             (   { fd_get(X, XD, XL, XU, _), fd_get(Z, ZD, ZL, ZU, ZPs) } ->
@@ -5906,6 +5940,35 @@ run_propagator(preified_slash(X, Y, D, R), MState) -->
         ;   []
         ).
 
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+run_propagator(preified_exp(X, Y, D, R), MState) -->
+        (   X == 1 ->
+            kill(MState),
+            D = 1,
+            R = 1
+        ;   Y == 0 ->
+            kill(MState),
+            D = 1,
+            R = 1
+        ;   Y == 1 ->
+            kill(MState),
+            D = 1,
+            R = X
+        ;   nonvar(X),
+            nonvar(Y) ->
+            kill(MState),
+            (   ( abs(X) =:= 1 ; Y >= 0 ) ->
+                D = 1,
+                R is X^Y
+            ;   D = 0
+            )
+        ;   D == 1 ->
+            kill(MState),
+            queue_goal(X^Y #= R)
+        ;   []
+        ).
+
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
@@ -6054,7 +6117,7 @@ domain_to_list(Domain, List) :- phrase(domain_to_list(Domain), List).
 domain_to_list(split(_, Left, Right)) -->
         domain_to_list(Left), domain_to_list(Right).
 domain_to_list(empty)                 --> [].
-domain_to_list(from_to(n(F),n(T)))    --> { numlist(F, T, Ns) }, list(Ns).
+domain_to_list(from_to(n(F),n(T)))    --> { numlist(F, T, Ns) }, seq(Ns).
 
 difference_arcs([], []) --> [].
 difference_arcs([V|Vs], FL0) -->
@@ -6414,8 +6477,7 @@ num_infinite(Var, N0, N) :-
 weak_arc_all_distinct(Ls) :-
         must_be(list, Ls),
         Orig = original_goal(_, weak_arc_all_distinct(Ls)),
-        all_distinct(Ls, [], Orig),
-        do_queue.
+        all_distinct(Ls, [], Orig).
 
 all_distinct([], _, _).
 all_distinct([X|Right], Left, Orig) :-
@@ -6728,8 +6790,10 @@ gcc_pairs([Key-Num0|KNs], Vs, [Key-Num|Rest]) :-
 
 gcc_global(Vs, KNs) :-
         gcc_check(KNs),
-        % reach fix-point: all elements of clpz_gcc_vs must be variables
-        do_queue,
+        % previously: call do_queue/0 (now a NOP) here to reach a
+        % fix-point: all elements of clpz_gcc_vs must be variables. We
+        % must ensure this holds if gcc_check/1 is later rewritten to
+        % actually disable the queue.
         with_local_attributes(Vs,
               (gcc_arcs(KNs, S, Vals),
                variables_with_num_occurrences(Vs, VNs),
@@ -7752,7 +7816,7 @@ attributes_goals([propagator(P, State)|As]) -->
               ;   maplist(unwrap_with(=), Gs, Gs1)
               ),
               maplist(with_clpz, Gs1, Gs2) },
-            list(Gs2)
+            seq(Gs2)
         ;   [P] % possibly user-defined constraint
         ),
         attributes_goals(As).
@@ -7770,17 +7834,15 @@ bare_integer(V0, V)    :- ( integer(V0) -> V = V0 ; V = #V0 ).
 
 attribute_goal_(presidual(Goal))       --> [Goal].
 attribute_goal_(pgeq(A,B))             --> [#A #>= #B].
-attribute_goal_(pplus(X,Y,Z))          --> [#X + #Y #= #Z].
+attribute_goal_(pplus(X,Y,Z,_))        --> [#X + #Y #= #Z].
 attribute_goal_(pneq(A,B))             --> [#A #\= #B].
-attribute_goal_(ptimes(X,Y,Z))         --> [#X * #Y #= #Z].
+attribute_goal_(ptimes(X,Y,Z,_))       --> [#X * #Y #= #Z].
 attribute_goal_(absdiff_neq(X,Y,C))    --> [abs(#X - #Y) #\= C].
 attribute_goal_(x_eq_abs_plus_v(X,V))  --> [#X #= abs(#X) + #V].
 attribute_goal_(x_neq_y_plus_z(X,Y,Z)) --> [#X #\= #Y + #Z].
 attribute_goal_(x_leq_y_plus_c(X,Y,C)) --> [#X #=< #Y + C].
-attribute_goal_(ptzdiv(X,Y,Z))         --> [#X // #Y #= #Z].
-attribute_goal_(pdiv(X,Y,Z))           --> [#X div #Y #= #Z].
-attribute_goal_(prdiv(X,Y,Z))          --> [#X / #Y #= #Z].
-attribute_goal_(pexp(X,Y,Z))           --> [#X ^ #Y #= #Z].
+attribute_goal_(ptzdiv(X,Y,Z,_))       --> [#X // #Y #= #Z].
+attribute_goal_(pexp(X,Y,Z,_))         --> [#X ^ #Y #= #Z].
 attribute_goal_(psign(X,Y))            --> [#Y #= sign(#X)].
 attribute_goal_(pabs(X,Y))             --> [#Y #= abs(#X)].
 attribute_goal_(pmod(X,M,K))           --> [#X mod #M #= #K].
@@ -7840,6 +7902,7 @@ attribute_goal_(reified_and(X,_,Y,_,B))    --> [#X #/\ #Y #<==> #B].
 attribute_goal_(reified_or(X, _, Y, _, B)) --> [#X #\/ #Y #<==> #B].
 attribute_goal_(reified_not(X, Y))         --> [#\ #X #<==> #Y].
 attribute_goal_(preified_slash(X, Y, _, R)) --> [#X/ #Y #= R].
+attribute_goal_(preified_exp(X, Y, _, R))  --> [#X^ #Y #= R].
 attribute_goal_(pimpl(X, Y, _))            --> [#X #==> #Y].
 attribute_goal_(pfunction(Op, A, B, R)) -->
         { Expr =.. [Op,#A,#B] },

src/lib/dif.pl

@@ -7,7 +7,7 @@ arguments are different terms.
 
 :- use_module(library(atts)).
 :- use_module(library(dcgs)).
-:- use_module(library(lists), [append/3]).
+:- use_module(library(lists), [append/3, maplist/3]).
 
 :- attribute dif/1.
 
@@ -23,6 +23,32 @@ dif_set_variables([Var|Vars], X, Y) :-
     put_dif_att(Var, X, Y),
     dif_set_variables(Vars, X, Y).
 
+remove_goal([], _, []).
+remove_goal([G0|G0s], Goal0, Goals) :-
+    (   G0 == Goal0 ->
+        remove_goal(G0s, Goal0, Goals)
+    ;   Goals = [G0|Goals1],
+        remove_goal(G0s, Goal0, Goals1)
+    ).
+
+vars_remove_goal([], _).
+vars_remove_goal([Var|Vars], Goal0) :-
+    get_atts(Var, +dif(Goals0)),
+    remove_goal(Goals0, Goal0, Goals),
+    (   Goals = [] ->
+        put_atts(Var, -dif(_))
+    ;   put_atts(Var, +dif(Goals))
+    ),
+    vars_remove_goal(Vars, Goal0).
+
+reinforce_goal(Goal0, Goal) :-
+    Goal = (
+        term_variables(Goal0, Vars),
+        dif:vars_remove_goal(Vars, Goal0),
+        Goal0 = (L \== R),
+        dif:dif(L, R)
+    ).
+
 append_goals([], _).
 append_goals([Var|Vars], Goals) :-
     (   get_atts(Var, +dif(VarGoals)) ->
@@ -34,9 +60,10 @@ append_goals([Var|Vars], Goals) :-
     append_goals(Vars, Goals).
 
 verify_attributes(Var, Value, Goals) :-
-    (   get_atts(Var, +dif(Goals)) ->
+    (   get_atts(Var, +dif(Goals0)) ->
 	    term_variables(Value, ValueVars),
-	    append_goals(ValueVars, Goals)
+	    append_goals(ValueVars, Goals0),
+        maplist(reinforce_goal, Goals0, Goals)
     ;   Goals = []
     ).
 

src/lib/http/http_server.pl

@@ -6,8 +6,8 @@
 */
 
 /** This library provides an starting point to build HTTP server based applications.
-It is based on [Hyper](https://hyper.rs/), which allows for HTTP/1.0, HTTP/1.1 and HTTP/2. However,
-some advanced features that Hyper provides are still not accesible.
+It is based on [Warp](https://github.com/seanmonstar/warp), which allows for HTTP/1.0, HTTP/1.1 and HTTP/2. However,
+some advanced features that Warp provides are still not accesible.
 
 ## Usage
 
@@ -46,7 +46,6 @@ recommeded to use the helper predicates, which are easier to understand and clea
 Some things that are still missing:
 
    - Read forms in multipart format
-   - HTTP Basic Auth
    - Session handling via cookies
    - HTML Templating (but you can use [Teruel](https://github.com/aarroyoc/teruel/), [Marquete](https://github.com/aarroyoc/marquete/) or [Djota](https://github.com/aarroyoc/djota) for that)
 */
@@ -54,14 +53,19 @@ Some things that are still missing:
 
 :- module(http_server, [
 	      http_listen/2,
+	      http_listen/3,
 	      http_headers/2,
 	      http_status_code/2,
 	      http_body/2,
 	      http_redirect/2,
-	      http_query/3
+	      http_query/3,
+	      http_basic_auth/4
 ]).
 
 :- meta_predicate http_listen(?, :).
+:- meta_predicate http_listen(?, :, ?).
+
+:- meta_predicate http_basic_auth(:, :, ?, ?).
 
 :- use_module(library(charsio)).
 :- use_module(library(crypto)).
@@ -74,25 +78,58 @@ Some things that are still missing:
 
 %% http_listen(+Port, +Handlers).
 %
-% Listens for HTTP connections on port Port. Each handler on the list Handlers should be of the form: `HttpVerb(PathUnification, Predicate)`.
-% For example: `get(user/User, get_info(User))` will match an HTTP request that is a GET, the path unifies with /user/User (where User is a variable)
-% and it will call `get_info` with three arguments: an `http_request` term, an `http_response` term and User. 
+% Equivalent to `http_listen(Port, Handlers, [])`.
 http_listen(Port, Module:Handlers0) :-
     must_be(integer, Port),
     must_be(list, Handlers0),
     maplist(module_qualification(Module), Handlers0, Handlers),
-    http_listen_(Port, Handlers).
+    http_listen_(Port, Handlers, []).
+
+%% http_listen(+Port, +Handlers, +Options).
+%
+% Listens for HTTP connections on port Port. Each handler on the list Handlers should be of the form: `HttpVerb(PathUnification, Predicate)`.
+% For example: `get(user/User, get_info(User))` will match an HTTP request that is a GET, the path unifies with /user/User (where User is a variable)
+% and it will call `get_info` with three arguments: an `http_request` term, an `http_response` term and User.
+%
+% The following options are supported:
+%
+% - `tls_key(+Key)` - a TLS key for HTTPS (string)
+% - `tls_cert(+Cert)` - a TLS cert for HTTPS (string)
+% - `content_length_limit(+Limit)` - maximum length (in bytes) for the incoming bodies. By default, 32KB.
+%
+% In order to have a HTTPS server (instead of plain HTTP), both `tls_key` and `tls_cert` options must be provided.
+http_listen(Port, Module:Handlers0, Options) :-
+    must_be(integer, Port),
+    must_be(list, Handlers0),
+    must_be(list, Options),
+    maplist(module_qualification(Module), Handlers0, Handlers),
+    http_listen_(Port, Handlers, Options).
 
 module_qualification(M, H0, H) :-
     H0 =.. [Method, Path, Goal],
     H =.. [Method, Path, M:Goal].
 
-http_listen_(Port, Handlers) :-
+http_listen_(Port, Handlers, Options) :-
+    parse_options(Options, TLSKey, TLSCert, ContentLengthLimit),
     phrase(format_("0.0.0.0:~d", [Port]), Addr),
-    '$http_listen'(Addr, HttpListener),!,
+    '$http_listen'(Addr, HttpListener, TLSKey, TLSCert, ContentLengthLimit),!,
     format("Listening at ~s\n", [Addr]),
     http_loop(HttpListener, Handlers).
 
+parse_options(Options, TLSKey, TLSCert, ContentLengthLimit) :-
+    member_option_default(tls_key, Options, "", TLSKey),
+    member_option_default(tls_cert, Options, "", TLSCert),
+    member_option_default(content_length_limit, Options, 32768, ContentLengthLimit),
+    must_be(integer, ContentLengthLimit).
+
+member_option_default(Key, List, _Default, Value) :-
+    X =.. [Key, Value],
+    member(X, List).
+member_option_default(Key, List, Default, Default) :-
+    X =.. [Key, _],
+    \+ member(X, List).
+	
+
 http_loop(HttpListener, Handlers) :-
     '$http_accept'(HttpListener, RequestMethod, RequestPath, RequestHeaders, RequestQuery, RequestStream, ResponseHandle),
     current_time(Time),
@@ -114,7 +151,7 @@ http_loop(HttpListener, Handlers) :-
 	)
     ; (
 	'$http_answer'(ResponseHandle, 404, [], ResponseStream),
-	call_cleanup(format(ResponseStream, "Not Found"), close(ResponseStream)))
+	call_cleanup(format(ResponseStream, "Not Found", []), close(ResponseStream)))
     ),
     http_loop(HttpListener, Handlers).
 
@@ -263,25 +300,21 @@ http_query(http_request(_, _, Queries), Key, Value) :- member(Key-Value, Queries
 
 parse_queries([Key-Value|Queries]) -->
     string_without("=", Key0),
-    {
-        phrase(url_decode(Key), Key0)
-    },
     "=",
     string_without("&", Value0),
-    {
-        phrase(url_decode(Value), Value0)
-    },
     "&",
-    parse_queries(Queries).
+    parse_queries(Queries),
+    {
+	phrase(url_decode(Key), Key0),
+	phrase(url_decode(Value), Value0)
+    }.
 
 parse_queries([Key-Value]) -->
     string_without("=", Key0),
-    {
-        phrase(url_decode(Key), Key0)
-    },
     "=",
     string_without(" ", Value0),
     {
+	phrase(url_decode(Key), Key0),
         phrase(url_decode(Value), Value0)  
     }.
 
@@ -292,9 +325,13 @@ parse_queries([]) -->
 url_decode([Char|Chars]) -->
     [Char],
     {
-        Char \= '%'
+        Char \= '%',
+	Char \= (+)
     },
     url_decode(Chars).
+url_decode([' '|Chars]) -->
+    "+",
+    url_decode(Chars).
 url_decode([Char|Chars]) -->
     "%",
     [A],
@@ -352,3 +389,49 @@ url_decode([Char|Chars]) -->
     url_decode(Chars).
 
 url_decode([]) --> [].
+
+%% http_basic_auth(+LoginPredicate, +Handler, +Request, -Response)
+%
+% Metapredicate that wraps an existing Handler with an HTTP Basic Auth flow.
+% Checks if a given user + password is authorized to execute that handler, returning 401
+% if it's not satisfied.
+% 
+% `LoginPredicate` must be a predicate of arity 2 that takes a User and a Password.
+% `Handler` will have, in addition to the Request and Response arguments, a User argument
+% containing the User given in the authentication.
+%
+% Example:
+%
+% ```
+% main :-
+%    http_listen(8800,[get('/', http_basic_auth(login, inside_handler("data")))]).
+%
+% login(User, Pass) :-
+%    User = "aarroyoc",
+%    Pass = "123456".
+%
+% inside_handler(Data, User, Request, Response) :-
+%    http_body(Response, text(User)).
+% ```
+http_basic_auth(LoginPredicate, Handler, Request, Response) :-
+    http_headers(Request, Headers),
+    member("authorization"-AuthorizationStr, Headers),
+    append("Basic ", Coded, AuthorizationStr),
+    chars_base64(UserPass, Coded, []),
+    append(User, [':'|Password], UserPass),
+    (
+	call(LoginPredicate, User, Password) ->
+	call(Handler, User, Request, Response)
+    ;   http_basic_auth_unauthorized_response(Response)
+    ).
+
+http_basic_auth(_LoginPredicate, _Handler, Request, Response) :-
+    http_headers(Request, Headers),
+    \+ member("authorization"-_, Headers),
+    http_basic_auth_unauthorized_response(Response).
+
+http_basic_auth_unauthorized_response(Response) :-
+    http_status_code(Response, 401),
+    http_headers(Response, ["www-authenticate"-"Basic realm=\"Scryer Prolog\", charset=\"UTF-8\""]),
+    http_body(Response, text("Unauthorized")).
+	

src/lib/iso_ext.pl

@@ -214,26 +214,6 @@ run_cleaners_without_handling(Cp) :-
 
 % call_with_inference_limit
 
-:- non_counted_backtracking end_block/4.
-
-end_block(_, Bb, NBb, _L) :-
-    '$clean_up_block'(NBb),
-    '$reset_block'(Bb).
-end_block(B, _Bb, NBb, L) :-
-    '$install_inference_counter'(B, L, _),
-    '$reset_block'(NBb),
-    '$fail'.
-
-:- non_counted_backtracking handle_ile/3.
-
-handle_ile(B, inference_limit_exceeded(B), inference_limit_exceeded) :-
-    !,
-    '$pop_ball_stack'.
-handle_ile(B, _, _) :-
-    '$remove_call_policy_check'(B),
-    '$pop_from_ball_stack',
-    '$unwind_stack'.
-
 :- meta_predicate(call_with_inference_limit(0, ?, ?)).
 
 :- non_counted_backtracking call_with_inference_limit/3.
@@ -256,8 +236,6 @@ call_with_inference_limit(G, L, R) :-
     call_with_inference_limit(G, L, R, Bb, B),
     '$remove_call_policy_check'(B).
 
-install_inference_counter(B, L, Count0) :-
-    '$install_inference_counter'(B, L, Count0).
 
 :- meta_predicate(call_with_inference_limit(0,?,?,?,?)).
 
@@ -265,23 +243,34 @@ install_inference_counter(B, L, Count0) :-
 
 call_with_inference_limit(G, L, R, Bb, B) :-
     '$install_new_block'(NBb),
-    '$install_inference_counter'(B, L, Count0),
+    '$install_inference_counter'(NBb, L, Count0),
     '$call_with_inference_counting'(call(G)),
     '$inference_level'(R, B),
-    '$remove_inference_counter'(B, Count1),
+    '$remove_inference_counter'(NBb, Count1),
     Diff is L - (Count1 - Count0),
-    end_block(B, Bb, NBb, Diff).
+    (  '$clean_up_block'(NBb),
+       '$reset_block'(Bb)
+    ;  '$install_inference_counter'(NBb, Diff, _),
+       '$reset_block'(NBb),
+       '$fail'
+    ).
 call_with_inference_limit(_, _, R, Bb, B) :-
+    (  '$inference_limit_exceeded' ->
+       R = inference_limit_exceeded
+    ;  true
+    ),
+    '$get_current_block'(NBb),
+    '$remove_inference_counter'(NBb, _),
     '$reset_block'(Bb),
-    '$remove_inference_counter'(B, _),
-    (  '$get_ball'(Ball),
+    '$remove_call_policy_check'(B),
+    (  '$get_ball'(_),
        '$push_ball_stack',
        '$get_cp'(Cp),
-       '$set_cp_by_default'(Cp)
-    ;  '$remove_call_policy_check'(B),
-       '$fail'
-    ),
-    handle_ile(B, Ball, R).
+       '$set_cp_by_default'(Cp),
+       '$pop_from_ball_stack',
+       '$unwind_stack'
+    ;  nonvar(R)
+    ).
 
 %% partial_string(String, L, L0)
 %
@@ -358,10 +347,10 @@ call_nth_nesting(C, ID) :-
     bb_put(ID, 0),
     bb_put(i_call_nth_counter, C).
 
-%% countall(Goal, N).
+%% countall(G_0, N).
 %
-% countall(Goal, N) counts all solutions of Goal and unifies N with
-% this number of solutions. This predicate always succeeds once.
+% countall(G_0, N) is true iff N unifies with the total number of
+% answers of call(G_0).
 
 :- meta_predicate(countall(0, ?)).
 
@@ -370,7 +359,7 @@ countall(Goal, N) :-
     (   integer(N) ->
         (   N < 0 ->
             domain_error(not_less_than_zero, N, countall/2)
-        ;   N > 0
+        ;   true
         )
     ;   true
     ),

src/lib/pio.pl

@@ -9,6 +9,7 @@
 
 :- module(pio, [phrase_from_file/2,
                 phrase_from_file/3,
+                phrase_from_stream/2,
                 phrase_to_file/2,
                 phrase_to_file/3,
                 phrase_to_stream/2
@@ -17,16 +18,30 @@
 :- use_module(library(dcgs)).
 :- use_module(library(error)).
 :- use_module(library(freeze)).
-:- use_module(library(iso_ext), [setup_call_cleanup/3, partial_string/3]).
-:- use_module(library(lists), [member/2, maplist/2]).
+:- use_module(library(gensym)).
+:- use_module(library(iso_ext), [
+    bb_get/2, bb_put/2, setup_call_cleanup/3, partial_string/3, partial_string_tail/2
+]).
+:- use_module(library(lists), [append/3, length/2, member/2, maplist/2]).
 :- use_module(library(charsio), [get_n_chars/3]).
 
 :- meta_predicate(phrase_from_file(2, ?)).
 :- meta_predicate(phrase_from_file(2, ?, ?)).
+:- meta_predicate(phrase_from_stream(2, ?)).
 :- meta_predicate(phrase_to_file(2, ?)).
 :- meta_predicate(phrase_to_file(2, ?, ?)).
 :- meta_predicate(phrase_to_stream(2, ?)).
 
+
+%% phrase_from_stream(+GRBody, +Stream)
+%
+%  True if grammar rule body GRBody covers the contents of the stream,
+%  represented as a list of characters.
+
+phrase_from_stream(GRBody, Stream) :-
+    stream_to_lazy_list(Stream, Ls),
+    phrase(GRBody, Ls).
+
 %% phrase_from_file(+GRBody, +File)
 %
 %  True if grammar rule body GRBody covers the contents of File,
@@ -48,25 +63,121 @@ phrase_from_file(NT, File, Options) :-
             member(Type, [text,binary])
         ;   Type = text
         ),
-        setup_call_cleanup(open(File, read, Stream, [reposition(true)|Options]),
-                           (   stream_to_lazy_list(Stream, Xs),
-                               phrase(NT, Xs) ),
-                           close(Stream))
-   ).
+        setup_call_cleanup(
+            open(File, read, Stream, Options),
+            phrase_from_stream(NT, Stream),
+            close(Stream)
+        )
+    ).
 
+% How many chars to read from stream and buffer in each step
+chars_to_read(4096).
 
-stream_to_lazy_list(Stream, Xs) :-
-        stream_property(Stream, position(Pos)),
-        freeze(Xs, reader_step(Stream, Pos, Xs)).
+stream_to_lazy_list(Stream, Ls) :-
+    get_stream_buffer_position(Stream, Pos),
+    freeze(Ls, render_step(Stream, Pos, Ls)).
 
-reader_step(Stream, Pos, Xs0) :-
-        set_stream_position(Stream, Pos),
-        (   at_end_of_stream(Stream)
-        ->  Xs0 = []
-        ;   get_n_chars(Stream, 4096, Cs),
-            partial_string(Cs, Xs0, Xs),
-            stream_to_lazy_list(Stream, Xs)
-        ).
+render_step(Stream, Pos, Ls) :-
+    set_stream_buffer_position(Stream, Pos),
+    (   buffer_at_end_of_stream(Stream) ->
+        Ls = []
+    ;   chars_to_read(CharsToRead),
+        buffer_get_n_chars(Stream, CharsToRead, Chars),
+        partial_string(Chars, Ls, Ls0),
+        stream_to_lazy_list(Stream, Ls0)
+    ).
+
+buffer_at_end_of_stream(Stream) :-
+    stream_bufferids(Stream, _, BufferPosId, _),
+    bb_get(BufferPosId, Pos),
+    Pos = eof.
+
+get_stream_buffer_position(Stream, Pos) :-
+    stream_bufferids(Stream, _, BufferPosId, _),
+    bb_get(BufferPosId, Pos).
+
+set_stream_buffer_position(Stream, Pos) :-
+    stream_bufferids(Stream, _, BufferPosId, _),
+    bb_put(BufferPosId, Pos).
+
+buffer_get_n_chars(Stream, N, Chars) :-
+    stream_bufferids(Stream, BufferId, BufferPosId, BufferLenId),
+    buffer_prepare_for_n(Stream, BufferId, BufferPosId, BufferLenId, N),
+    bb_get(BufferId, Buffer),
+    bb_get(BufferPosId, BufferPos),
+    (   BufferPos = eof ->
+        Chars = []
+    ;   string_get_n_chars(Buffer, BufferPos, N, Chars),
+        length(Chars, NChars),
+        (   NChars = 0 ->
+            BufferPos1 = eof
+        ;   BufferPos1 is BufferPos + NChars
+        ),
+        bb_put(BufferPosId, BufferPos1)
+    ).
+
+buffer_prepare_for_n(Stream, BufferId, BufferPosId, BufferLenId, N) :-
+    bb_get(BufferPosId, BufferPos),
+    bb_get(BufferLenId, BufferLen),
+    (   BufferLen < BufferPos + N ->
+        bb_get(BufferId, Buffer),
+        (
+            (   var(Buffer) ->
+                BufferTail = Buffer
+            ;   partial_string_last_tail(Buffer, BufferTail)
+            ) ->
+            (   at_end_of_stream(Stream) ->
+                BufferTail = [],
+                bb_put(BufferId, Buffer)
+            ;   chars_to_read(CharsToRead),
+                get_n_chars(Stream, CharsToRead, Chars),
+                length(Chars, NChars),
+                partial_string(Chars, BufferTail, _),
+                bb_put(BufferId, Buffer),
+                BufferLen1 is BufferLen + NChars,
+                bb_put(BufferLenId, BufferLen1),
+                buffer_prepare_for_n(Stream, BufferId, BufferPosId, BufferLenId, N)
+            )
+        ;   true
+        )
+    ;   true
+    ).
+
+partial_string_last_tail(PartialString, PartialStringTail) :-
+    partial_string_tail(PartialString, PartialStringTail0),
+    (   var(PartialStringTail0) ->
+        PartialStringTail = PartialStringTail0
+    ;   partial_string_last_tail(PartialStringTail0, PartialStringTail)
+    ).
+
+string_get_n_chars(String, Pos, N, Chars) :-
+    '$skip_max_list'(_, Pos, String, String1),
+    '$skip_max_list'(N1, N, String1, _),
+    length(Chars, N1),
+    append(Chars, _, String1).
+
+stream_bufferids(Stream, BufferId, BufferPosId, BufferLenId) :-
+    (   bb_get(streams_buffers, _) ->
+        true
+    ;   bb_put(streams_buffers, [])
+    ),
+    bb_get(streams_buffers, StreamsBuffers),
+    (   member(
+            stream_buffer(Stream, BufferId, BufferPosId, BufferLenId),
+            StreamsBuffers
+        ) ->
+        true
+    ;   gensym(buffer, BufferId),
+        gensym(buffer_pos, BufferPosId),
+        gensym(buffer_len, BufferLenId),
+        bb_put(
+            streams_buffers,
+            [stream_buffer(Stream, BufferId, BufferPosId, BufferLenId)|StreamsBuffers]
+        ),
+        bb_put(BufferId, _),
+        bb_put(BufferPosId, 0),
+        bb_put(BufferLenId, 0)
+    ).
 
 %% phrase_to_stream(+GRBody, +Stream)
 %

src/loader.pl

@@ -35,9 +35,9 @@ write_error(Error) :-
     ),
     write('.').
 
-% '$print_message_and_fail'(inference_limit_exceeded(B)) :-
-%     integer(B),
-%     throw(inference_limit_exceeded(B)).
+
+:- non_counted_backtracking '$print_message_and_fail'/1.
+
 '$print_message_and_fail'(Error) :-
     write_error(Error),
     nl,
@@ -70,6 +70,8 @@ term_expansion_list([Term|Terms], ExpandedTermsHead, ExpandedTermsTail) :-
     ).
 
 
+:- non_counted_backtracking goal_expansion/3.
+
 goal_expansion(Goal, Module, ExpandedGoal) :-
     (  atom(Module),
        '$predicate_defined'(Module, goal_expansion, 2),
@@ -84,7 +86,6 @@ goal_expansion(Goal, Module, ExpandedGoal) :-
     ).
 
 
-
 create_file_load_context(Stream, Path, Evacuable) :-
     '$push_load_context'(Stream, Path),
     '$push_load_state_payload'(Evacuable).
@@ -134,9 +135,15 @@ file_load_init(Stream, Evacuable) :-
     run_initialization_goals.
 
 file_load_cleanup(Evacuable, Error) :-
+    load_context(Module),
+    abolish(Module:'$initialization_goals'/1),
     unload_evacuable(Evacuable),
-    '$print_message_and_fail'(Error),
-	throw(Error).
+    (  clause('$toplevel':argv(_), _) ->
+       % let the toplevel call loader:write_error/1
+       throw(Error)
+    ;  '$print_message_and_fail'(Error)
+    ;  throw(file_load_error)
+    ).
 
 file_load(Stream, Path, Evacuable) :-
     create_file_load_context(Stream, Path, Evacuable),
@@ -373,6 +380,59 @@ remove_module(Module, Evacuable) :-
     ).
 
 
+predicate_indicator(PI) :-
+    (  var(PI) ->
+       throw(error(instantiation_error, _))
+    ;  PI = Name/Arity,
+       must_be(atom, Name),
+       must_be(integer, Arity),
+       Arity >= 0
+    ).
+
+predicate_indicator_sequence(PI_Seq) :-
+    (  var(PI_Seq) ->
+       throw(error(instantiation_error, load/1))
+    ;  PI_Seq = (PI, PIs),
+       predicate_indicator(PI),
+       (  predicate_indicator(PIs) ->
+          true
+       ;  predicate_indicator_sequence(PIs)
+       )
+    ).
+
+:- meta_predicate add_predicate_declaration(3, ?).
+
+add_predicate_declaration(Handler, Name/Arity) :-
+    predicate_indicator(Name/Arity),
+    prolog_load_context(module, Module),
+    call(Handler, Module, Name, Arity).
+add_predicate_declaration(Handler, Module:Name/Arity) :-
+    must_be(atom, Module),
+    predicate_indicator(Name/Arity),
+    call(Handler, Module, Name, Arity).
+add_predicate_declaration(Handler, [PI|PIs]) :-
+    '$skip_max_list'(_, _, PIs, Tail),
+    (  Tail == [],
+       maplist(loader:predicate_indicator, PIs) ->
+       maplist(loader:add_predicate_declaration(Handler), [PI|PIs])
+    ;  throw(error(type_error(predicate_indicator_list, [PI|PIs]), load/1))
+    ).
+add_predicate_declaration(Handler, (PI, PIs)) :-
+    (  predicate_indicator_sequence((PI, PIs)) ->
+       add_predicate_declaration(Handler, PI),
+       add_predicate_declaration(Handler, PIs)
+    ;  throw(error(type_error(predicate_indicator_sequence, (PI, PIs)), load/1))
+    ).
+
+add_dynamic_predicate(Evacuable, Module, Name, Arity) :-
+    '$add_dynamic_predicate'(Module, Name, Arity, Evacuable).
+
+add_multifile_predicate(Evacuable, Module, Name, Arity) :-
+    '$add_multifile_predicate'(Module, Name, Arity, Evacuable).
+
+add_discontiguous_predicate(Evacuable, Module, Name, Arity) :-
+    '$add_discontiguous_predicate'(Module, Name, Arity, Evacuable).
+
 compile_declaration(use_module(Module), Evacuable) :-
     use_module(Module, [], Evacuable).
 compile_declaration(use_module(Module, Exports), Evacuable) :-
@@ -385,39 +445,12 @@ compile_declaration(module(Module, Exports), Evacuable) :-
        '$declare_module'(Module, Exports, Evacuable)
     ;  type_error(atom, Module, load/1)
     ).
-compile_declaration(dynamic(Module:Name/Arity), Evacuable) :-
-    !,
-    must_be(atom, Module),
-    must_be(atom, Name),
-    must_be(integer, Arity),
-    '$add_dynamic_predicate'(Module, Name, Arity, Evacuable).
-compile_declaration(dynamic(Name/Arity), Evacuable) :-
-    must_be(atom, Name),
-    must_be(integer, Arity),
-    prolog_load_context(module, Module),
-    '$add_dynamic_predicate'(Module, Name, Arity, Evacuable).
-compile_declaration(multifile(Module:Name/Arity), Evacuable) :-
-    !,
-    must_be(atom, Module),
-    must_be(atom, Name),
-    must_be(integer, Arity),
-    '$add_multifile_predicate'(Module, Name, Arity, Evacuable).
-compile_declaration(multifile(Name/Arity), Evacuable) :-
-    must_be(atom, Name),
-    must_be(integer, Arity),
-    prolog_load_context(module, Module),
-    '$add_multifile_predicate'(Module, Name, Arity, Evacuable).
-compile_declaration(discontiguous(Module:Name/Arity), Evacuable) :-
-    !,
-    must_be(atom, Module),
-    must_be(atom, Name),
-    must_be(integer, Arity),
-    '$add_discontiguous_predicate'(Module, Name, Arity, Evacuable).
-compile_declaration(discontiguous(Name/Arity), Evacuable) :-
-    must_be(atom, Name),
-    must_be(integer, Arity),
-    prolog_load_context(module, Module),
-    '$add_discontiguous_predicate'(Module, Name, Arity, Evacuable).
+compile_declaration(dynamic(PIs), Evacuable) :-
+    add_predicate_declaration(loader:add_dynamic_predicate(Evacuable), PIs).
+compile_declaration(multifile(PIs), Evacuable) :-
+    add_predicate_declaration(loader:add_multifile_predicate(Evacuable), PIs).
+compile_declaration(discontiguous(PIs), Evacuable) :-
+    add_predicate_declaration(loader:add_discontiguous_predicate(Evacuable), PIs).
 compile_declaration(initialization(Goal), Evacuable) :-
     prolog_load_context(module, Module),
     assertz(Module:'$initialization_goals'(Goal)).
@@ -504,7 +537,9 @@ consult(Item) :-
 
 use_module(Module) :-
     '$push_load_state_payload'(Evacuable),
-    use_module(Module, [], Evacuable).
+    catch('$call'(loader:use_module(Module, [], Evacuable)),
+          file_load_error,
+          '$call'(builtins:false)).
 
 use_module(Module, Exports) :-
     '$push_load_state_payload'(Evacuable),
@@ -586,6 +621,12 @@ use_module(Module, Exports, Evacuable) :-
        )
     ).
 
+consult_stream(Stream, PathFileName) :-
+   '$push_load_state_payload'(Evacuable),
+    file_load(Stream, PathFileName, Subevacuable),
+    '$use_module'(Evacuable, Subevacuable, _).
+
+:- non_counted_backtracking check_predicate_property/5.
 
 check_predicate_property(meta_predicate, Module, Name, Arity, MetaPredicateTerm) :-
     '$meta_predicate_property'(Module, Name, Arity, MetaPredicateTerm).
@@ -599,6 +640,7 @@ check_predicate_property(discontiguous, Module, Name, Arity, discontiguous) :-
     '$discontiguous_property'(Module, Name, Arity).
 
 
+:- non_counted_backtracking extract_predicate_property/2.
 
 extract_predicate_property(Property, PropertyType) :-
     (  var(Property) ->
@@ -606,12 +648,16 @@ extract_predicate_property(Property, PropertyType) :-
     ;  functor(Property, PropertyType, _)
     ).
 
+:- non_counted_backtracking load_context/1.
+
 load_context(Module) :-
     (  prolog_load_context(module, Module) ->
        true
     ;  Module = user
     ).
 
+:- non_counted_backtracking predicate_property/2.
+
 predicate_property(Callable, Property) :-
     (  var(Callable) ->
        instantiation_error(predicate_property/2)
@@ -648,8 +694,6 @@ strip_subst_module(Goal, M1, M2, G) :-
     ;  true
     ).
 
-:- non_counted_backtracking subgoal_expansion/3.
-
 /*
  * subgoal_expansion differs from goal_expansion only in that it fails
  * unconditionally after catching an(y) exception, aborting the
@@ -657,10 +701,14 @@ strip_subst_module(Goal, M1, M2, G) :-
  * when expand_goal is later invoked at runtime.
  */
 
+:- non_counted_backtracking subgoal_expansion_fail/1.
+
 subgoal_expansion_fail(B) :-
     builtins:set_cp(B),
     fail.
 
+:- non_counted_backtracking subgoal_expansion/3.
+
 subgoal_expansion(Goal, Module, ExpandedGoal) :-
     '$get_cp'(B),
     (  atom(Module),
@@ -695,7 +743,7 @@ expand_subgoal(UnexpandedGoals, MS, M, ExpandedGoals, HeadVars) :-
        expand_module_names(UnexpandedGoals4, MetaSpecs, Module1, ExpandedGoals0, HeadVars)
     ;  ExpandedGoals0 = UnexpandedGoals4
     ),
-    '$compile_inline_or_expanded_goal'(ExpandedGoals0, SuppArgs, ExpandedGoals1, Module1),
+    '$compile_inline_or_expanded_goal'(ExpandedGoals0, SuppArgs, ExpandedGoals1, Module1, UnexpandedGoals0),
     expand_module_name(ExpandedGoals1, MS, Module1, ExpandedGoals).
 
 
@@ -890,7 +938,6 @@ thread_goals(Goals0, Goals1, Hole, Functor) :-
 % n_call_clause(N, Clauses) :-
 %     length(Args, N),
 %     Head =.. [call, G | Args],
-%     CallNHead =.. [call, '$call'(G) | Args],
 %     N1 is N + 1,
 %     StripModule =.. ['$strip_module', G, M1, G1],
 %     FastCall =.. ['$fast_call', G | Args],
@@ -903,7 +950,7 @@ thread_goals(Goals0, Goals1, Hole, Functor) :-
 %                         PrepareCallClause,
 %                         expand_call_goal(G2, M1, G3),
 %                         strip_subst_module(G3, M1, M2, G4),
-%                         '$call_with_inference_counting'(ModuleCall))].
+%                         ModuleCall)].
 %
 % generate_call_forms :-
 %     between(1, 64, N),
@@ -930,7 +977,7 @@ call(G0) :-
     '$strip_module'(G0, M0, G1),
     expand_call_goal(G1, M0, G2),
     strip_subst_module(G2, M0, M1, G3),
-    '$call_with_inference_counting'('$module_call'(M1, G3)).
+    '$module_call'(M1, G3).
 
 :-non_counted_backtracking call/2.
 call(A,B) :-
@@ -943,7 +990,7 @@ call(A,B) :-
    '$prepare_call_clause'(E,D,B),
    expand_call_goal(E,C,F),
    strip_subst_module(F,C,G,H),
-   '$call_with_inference_counting'('$module_call'(G,H)).
+   '$module_call'(G,H).
 
 :-non_counted_backtracking call/3.
 call(A,B,C) :-
@@ -956,7 +1003,7 @@ call(A,B,C) :-
    '$prepare_call_clause'(F,E,B,C),
    expand_call_goal(F,D,G),
    strip_subst_module(G,D,H,I),
-   '$call_with_inference_counting'('$module_call'(H,I)).
+   '$module_call'(H,I).
 
 :-non_counted_backtracking call/4.
 call(A,B,C,D) :-
@@ -969,7 +1016,7 @@ call(A,B,C,D) :-
    '$prepare_call_clause'(G,F,B,C,D),
    expand_call_goal(G,E,H),
    strip_subst_module(H,E,I,J),
-   '$call_with_inference_counting'('$module_call'(I,J)).
+   '$module_call'(I,J).
 
 :-non_counted_backtracking call/5.
 call(A,B,C,D,E) :-
@@ -982,7 +1029,7 @@ call(A,B,C,D,E) :-
    '$prepare_call_clause'(H,G,B,C,D,E),
    expand_call_goal(H,F,I),
    strip_subst_module(I,F,J,K),
-   '$call_with_inference_counting'('$module_call'(J,K)).
+   '$module_call'(J,K).
 
 :-non_counted_backtracking call/6.
 call(A,B,C,D,E,F) :-
@@ -995,7 +1042,7 @@ call(A,B,C,D,E,F) :-
    '$prepare_call_clause'(I,H,B,C,D,E,F),
    expand_call_goal(I,G,J),
    strip_subst_module(J,G,K,L),
-   '$call_with_inference_counting'('$module_call'(K,L)).
+   '$module_call'(K,L).
 
 :-non_counted_backtracking call/7.
 call(A,B,C,D,E,F,G) :-
@@ -1008,7 +1055,7 @@ call(A,B,C,D,E,F,G) :-
    '$prepare_call_clause'(J,I,B,C,D,E,F,G),
    expand_call_goal(J,H,K),
    strip_subst_module(K,H,L,M),
-   '$call_with_inference_counting'('$module_call'(L,M)).
+   '$module_call'(L,M).
 
 :-non_counted_backtracking call/8.
 call(A,B,C,D,E,F,G,H) :-
@@ -1021,7 +1068,7 @@ call(A,B,C,D,E,F,G,H) :-
    '$prepare_call_clause'(K,J,B,C,D,E,F,G,H),
    expand_call_goal(K,I,L),
    strip_subst_module(L,I,M,N),
-   '$call_with_inference_counting'('$module_call'(M,N)).
+   '$module_call'(M,N).
 
 :-non_counted_backtracking call/9.
 call(A,B,C,D,E,F,G,H,I) :-
@@ -1034,7 +1081,7 @@ call(A,B,C,D,E,F,G,H,I) :-
    '$prepare_call_clause'(L,K,B,C,D,E,F,G,H,I),
    expand_call_goal(L,J,M),
    strip_subst_module(M,J,N,O),
-   '$call_with_inference_counting'('$module_call'(N,O)).
+   '$module_call'(N,O).
 
 :-non_counted_backtracking call/10.
 call(A,B,C,D,E,F,G,H,I,J) :-
@@ -1047,7 +1094,7 @@ call(A,B,C,D,E,F,G,H,I,J) :-
    '$prepare_call_clause'(M,L,B,C,D,E,F,G,H,I,J),
    expand_call_goal(M,K,N),
    strip_subst_module(N,K,O,P),
-   '$call_with_inference_counting'('$module_call'(O,P)).
+   '$module_call'(O,P).
 
 :-non_counted_backtracking call/11.
 call(A,B,C,D,E,F,G,H,I,J,K) :-
@@ -1060,7 +1107,7 @@ call(A,B,C,D,E,F,G,H,I,J,K) :-
    '$prepare_call_clause'(N,M,B,C,D,E,F,G,H,I,J,K),
    expand_call_goal(N,L,O),
    strip_subst_module(O,L,P,Q),
-   '$call_with_inference_counting'('$module_call'(P,Q)).
+   '$module_call'(P,Q).
 
 :-non_counted_backtracking call/12.
 call(A,B,C,D,E,F,G,H,I,J,K,L) :-
@@ -1073,7 +1120,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L) :-
    '$prepare_call_clause'(O,N,B,C,D,E,F,G,H,I,J,K,L),
    expand_call_goal(O,M,P),
    strip_subst_module(P,M,Q,R),
-   '$call_with_inference_counting'('$module_call'(Q,R)).
+   '$module_call'(Q,R).
 
 :-non_counted_backtracking call/13.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M) :-
@@ -1086,7 +1133,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M) :-
    '$prepare_call_clause'(P,O,B,C,D,E,F,G,H,I,J,K,L,M),
    expand_call_goal(P,N,Q),
    strip_subst_module(Q,N,R,S),
-   '$call_with_inference_counting'('$module_call'(R,S)).
+   '$module_call'(R,S).
 
 :-non_counted_backtracking call/14.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N) :-
@@ -1099,7 +1146,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N) :-
    '$prepare_call_clause'(Q,P,B,C,D,E,F,G,H,I,J,K,L,M,N),
    expand_call_goal(Q,O,R),
    strip_subst_module(R,O,S,T),
-   '$call_with_inference_counting'('$module_call'(S,T)).
+   '$module_call'(S,T).
 
 :-non_counted_backtracking call/15.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O) :-
@@ -1112,7 +1159,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O) :-
    '$prepare_call_clause'(R,Q,B,C,D,E,F,G,H,I,J,K,L,M,N,O),
    expand_call_goal(R,P,S),
    strip_subst_module(S,P,T,U),
-   '$call_with_inference_counting'('$module_call'(T,U)).
+   '$module_call'(T,U).
 
 :-non_counted_backtracking call/16.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P) :-
@@ -1125,7 +1172,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P) :-
    '$prepare_call_clause'(S,R,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P),
    expand_call_goal(S,Q,T),
    strip_subst_module(T,Q,U,V),
-   '$call_with_inference_counting'('$module_call'(U,V)).
+   '$module_call'(U,V).
 
 :-non_counted_backtracking call/17.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q) :-
@@ -1138,7 +1185,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q) :-
    '$prepare_call_clause'(T,S,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q),
    expand_call_goal(T,R,U),
    strip_subst_module(U,R,V,W),
-   '$call_with_inference_counting'('$module_call'(V,W)).
+   '$module_call'(V,W).
 
 :-non_counted_backtracking call/18.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R) :-
@@ -1151,7 +1198,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R) :-
    '$prepare_call_clause'(U,T,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R),
    expand_call_goal(U,S,V),
    strip_subst_module(V,S,W,X),
-   '$call_with_inference_counting'('$module_call'(W,X)).
+   '$module_call'(W,X).
 
 :-non_counted_backtracking call/19.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S) :-
@@ -1164,7 +1211,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S) :-
    '$prepare_call_clause'(V,U,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S),
    expand_call_goal(V,T,W),
    strip_subst_module(W,T,X,Y),
-   '$call_with_inference_counting'('$module_call'(X,Y)).
+   '$module_call'(X,Y).
 
 :-non_counted_backtracking call/20.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T) :-
@@ -1177,7 +1224,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T) :-
    '$prepare_call_clause'(W,V,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T),
    expand_call_goal(W,U,X),
    strip_subst_module(X,U,Y,Z),
-   '$call_with_inference_counting'('$module_call'(Y,Z)).
+   '$module_call'(Y,Z).
 
 :-non_counted_backtracking call/21.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U) :-
@@ -1190,7 +1237,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U) :-
    '$prepare_call_clause'(X,W,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U),
    expand_call_goal(X,V,Y),
    strip_subst_module(Y,V,Z,A1),
-   '$call_with_inference_counting'('$module_call'(Z,A1)).
+   '$module_call'(Z,A1).
 
 :-non_counted_backtracking call/22.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V) :-
@@ -1203,7 +1250,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V) :-
    '$prepare_call_clause'(Y,X,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V),
    expand_call_goal(Y,W,Z),
    strip_subst_module(Z,W,A1,B1),
-   '$call_with_inference_counting'('$module_call'(A1,B1)).
+   '$module_call'(A1,B1).
 
 :-non_counted_backtracking call/23.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W) :-
@@ -1216,7 +1263,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W) :-
    '$prepare_call_clause'(Z,Y,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W),
    expand_call_goal(Z,X,A1),
    strip_subst_module(A1,X,B1,C1),
-   '$call_with_inference_counting'('$module_call'(B1,C1)).
+   '$module_call'(B1,C1).
 
 :-non_counted_backtracking call/24.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X) :-
@@ -1229,7 +1276,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X) :-
    '$prepare_call_clause'(A1,Z,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X),
    expand_call_goal(A1,Y,B1),
    strip_subst_module(B1,Y,C1,D1),
-   '$call_with_inference_counting'('$module_call'(C1,D1)).
+   '$module_call'(C1,D1).
 
 :-non_counted_backtracking call/25.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y) :-
@@ -1242,7 +1289,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y) :-
    '$prepare_call_clause'(B1,A1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y),
    expand_call_goal(B1,Z,C1),
    strip_subst_module(C1,Z,D1,E1),
-   '$call_with_inference_counting'('$module_call'(D1,E1)).
+   '$module_call'(D1,E1).
 
 :-non_counted_backtracking call/26.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z) :-
@@ -1255,7 +1302,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z) :-
    '$prepare_call_clause'(C1,B1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z),
    expand_call_goal(C1,A1,D1),
    strip_subst_module(D1,A1,E1,F1),
-   '$call_with_inference_counting'('$module_call'(E1,F1)).
+   '$module_call'(E1,F1).
 
 :-non_counted_backtracking call/27.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1) :-
@@ -1268,7 +1315,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1) :-
    '$prepare_call_clause'(D1,C1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1),
    expand_call_goal(D1,B1,E1),
    strip_subst_module(E1,B1,F1,G1),
-   '$call_with_inference_counting'('$module_call'(F1,G1)).
+   '$module_call'(F1,G1).
 
 :-non_counted_backtracking call/28.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1) :-
@@ -1281,7 +1328,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1) :-
    '$prepare_call_clause'(E1,D1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1),
    expand_call_goal(E1,C1,F1),
    strip_subst_module(F1,C1,G1,H1),
-   '$call_with_inference_counting'('$module_call'(G1,H1)).
+   '$module_call'(G1,H1).
 
 :-non_counted_backtracking call/29.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1) :-
@@ -1294,7 +1341,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1) :-
    '$prepare_call_clause'(F1,E1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1),
    expand_call_goal(F1,D1,G1),
    strip_subst_module(G1,D1,H1,I1),
-   '$call_with_inference_counting'('$module_call'(H1,I1)).
+   '$module_call'(H1,I1).
 
 :-non_counted_backtracking call/30.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1) :-
@@ -1307,7 +1354,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1) :-
    '$prepare_call_clause'(G1,F1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1),
    expand_call_goal(G1,E1,H1),
    strip_subst_module(H1,E1,I1,J1),
-   '$call_with_inference_counting'('$module_call'(I1,J1)).
+   '$module_call'(I1,J1).
 
 :-non_counted_backtracking call/31.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1) :-
@@ -1320,7 +1367,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1) :-
    '$prepare_call_clause'(H1,G1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1),
    expand_call_goal(H1,F1,I1),
    strip_subst_module(I1,F1,J1,K1),
-   '$call_with_inference_counting'('$module_call'(J1,K1)).
+   '$module_call'(J1,K1).
 
 :-non_counted_backtracking call/32.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1) :-
@@ -1333,7 +1380,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1) :-
    '$prepare_call_clause'(I1,H1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1),
    expand_call_goal(I1,G1,J1),
    strip_subst_module(J1,G1,K1,L1),
-   '$call_with_inference_counting'('$module_call'(K1,L1)).
+   '$module_call'(K1,L1).
 
 :-non_counted_backtracking call/33.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1) :-
@@ -1346,7 +1393,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1) :
    '$prepare_call_clause'(J1,I1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1),
    expand_call_goal(J1,H1,K1),
    strip_subst_module(K1,H1,L1,M1),
-   '$call_with_inference_counting'('$module_call'(L1,M1)).
+   '$module_call'(L1,M1).
 
 :-non_counted_backtracking call/34.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1) :-
@@ -1359,7 +1406,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(K1,J1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1),
    expand_call_goal(K1,I1,L1),
    strip_subst_module(L1,I1,M1,N1),
-   '$call_with_inference_counting'('$module_call'(M1,N1)).
+   '$module_call'(M1,N1).
 
 :-non_counted_backtracking call/35.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1) :-
@@ -1372,7 +1419,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(L1,K1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1),
    expand_call_goal(L1,J1,M1),
    strip_subst_module(M1,J1,N1,O1),
-   '$call_with_inference_counting'('$module_call'(N1,O1)).
+   '$module_call'(N1,O1).
 
 :-non_counted_backtracking call/36.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1) :-
@@ -1385,7 +1432,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(M1,L1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1),
    expand_call_goal(M1,K1,N1),
    strip_subst_module(N1,K1,O1,P1),
-   '$call_with_inference_counting'('$module_call'(O1,P1)).
+   '$module_call'(O1,P1).
 
 :-non_counted_backtracking call/37.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1) :-
@@ -1398,7 +1445,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(N1,M1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1),
    expand_call_goal(N1,L1,O1),
    strip_subst_module(O1,L1,P1,Q1),
-   '$call_with_inference_counting'('$module_call'(P1,Q1)).
+   '$module_call'(P1,Q1).
 
 :-non_counted_backtracking call/38.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1) :-
@@ -1411,7 +1458,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(O1,N1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1),
    expand_call_goal(O1,M1,P1),
    strip_subst_module(P1,M1,Q1,R1),
-   '$call_with_inference_counting'('$module_call'(Q1,R1)).
+   '$module_call'(Q1,R1).
 
 :-non_counted_backtracking call/39.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1) :-
@@ -1424,7 +1471,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(P1,O1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1),
    expand_call_goal(P1,N1,Q1),
    strip_subst_module(Q1,N1,R1,S1),
-   '$call_with_inference_counting'('$module_call'(R1,S1)).
+   '$module_call'(R1,S1).
 
 :-non_counted_backtracking call/40.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1) :-
@@ -1437,7 +1484,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(Q1,P1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1),
    expand_call_goal(Q1,O1,R1),
    strip_subst_module(R1,O1,S1,T1),
-   '$call_with_inference_counting'('$module_call'(S1,T1)).
+   '$module_call'(S1,T1).
 
 :-non_counted_backtracking call/41.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1) :-
@@ -1450,7 +1497,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(R1,Q1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1),
    expand_call_goal(R1,P1,S1),
    strip_subst_module(S1,P1,T1,U1),
-   '$call_with_inference_counting'('$module_call'(T1,U1)).
+   '$module_call'(T1,U1).
 
 :-non_counted_backtracking call/42.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1) :-
@@ -1463,7 +1510,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(S1,R1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1),
    expand_call_goal(S1,Q1,T1),
    strip_subst_module(T1,Q1,U1,V1),
-   '$call_with_inference_counting'('$module_call'(U1,V1)).
+   '$module_call'(U1,V1).
 
 :-non_counted_backtracking call/43.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1) :-
@@ -1476,7 +1523,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(T1,S1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1),
    expand_call_goal(T1,R1,U1),
    strip_subst_module(U1,R1,V1,W1),
-   '$call_with_inference_counting'('$module_call'(V1,W1)).
+   '$module_call'(V1,W1).
 
 :-non_counted_backtracking call/44.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1) :-
@@ -1489,7 +1536,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(U1,T1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1),
    expand_call_goal(U1,S1,V1),
    strip_subst_module(V1,S1,W1,X1),
-   '$call_with_inference_counting'('$module_call'(W1,X1)).
+   '$module_call'(W1,X1).
 
 :-non_counted_backtracking call/45.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1) :-
@@ -1502,7 +1549,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(V1,U1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1),
    expand_call_goal(V1,T1,W1),
    strip_subst_module(W1,T1,X1,Y1),
-   '$call_with_inference_counting'('$module_call'(X1,Y1)).
+   '$module_call'(X1,Y1).
 
 :-non_counted_backtracking call/46.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1) :-
@@ -1515,7 +1562,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(W1,V1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1),
    expand_call_goal(W1,U1,X1),
    strip_subst_module(X1,U1,Y1,Z1),
-   '$call_with_inference_counting'('$module_call'(Y1,Z1)).
+   '$module_call'(Y1,Z1).
 
 :-non_counted_backtracking call/47.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1) :-
@@ -1528,7 +1575,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(X1,W1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1),
    expand_call_goal(X1,V1,Y1),
    strip_subst_module(Y1,V1,Z1,A2),
-   '$call_with_inference_counting'('$module_call'(Z1,A2)).
+   '$module_call'(Z1,A2).
 
 :-non_counted_backtracking call/48.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1) :-
@@ -1541,7 +1588,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(Y1,X1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1),
    expand_call_goal(Y1,W1,Z1),
    strip_subst_module(Z1,W1,A2,B2),
-   '$call_with_inference_counting'('$module_call'(A2,B2)).
+   '$module_call'(A2,B2).
 
 :-non_counted_backtracking call/49.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1) :-
@@ -1554,7 +1601,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(Z1,Y1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1),
    expand_call_goal(Z1,X1,A2),
    strip_subst_module(A2,X1,B2,C2),
-   '$call_with_inference_counting'('$module_call'(B2,C2)).
+   '$module_call'(B2,C2).
 
 :-non_counted_backtracking call/50.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1) :-
@@ -1567,7 +1614,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(A2,Z1,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1),
    expand_call_goal(A2,Y1,B2),
    strip_subst_module(B2,Y1,C2,D2),
-   '$call_with_inference_counting'('$module_call'(C2,D2)).
+   '$module_call'(C2,D2).
 
 :-non_counted_backtracking call/51.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1) :-
@@ -1580,7 +1627,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(B2,A2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1),
    expand_call_goal(B2,Z1,C2),
    strip_subst_module(C2,Z1,D2,E2),
-   '$call_with_inference_counting'('$module_call'(D2,E2)).
+   '$module_call'(D2,E2).
 
 :-non_counted_backtracking call/52.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1) :-
@@ -1593,7 +1640,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(C2,B2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1),
    expand_call_goal(C2,A2,D2),
    strip_subst_module(D2,A2,E2,F2),
-   '$call_with_inference_counting'('$module_call'(E2,F2)).
+   '$module_call'(E2,F2).
 
 :-non_counted_backtracking call/53.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2) :-
@@ -1606,7 +1653,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(D2,C2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2),
    expand_call_goal(D2,B2,E2),
    strip_subst_module(E2,B2,F2,G2),
-   '$call_with_inference_counting'('$module_call'(F2,G2)).
+   '$module_call'(F2,G2).
 
 :-non_counted_backtracking call/54.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2) :-
@@ -1619,7 +1666,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(E2,D2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2),
    expand_call_goal(E2,C2,F2),
    strip_subst_module(F2,C2,G2,H2),
-   '$call_with_inference_counting'('$module_call'(G2,H2)).
+   '$module_call'(G2,H2).
 
 :-non_counted_backtracking call/55.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2) :-
@@ -1632,7 +1679,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(F2,E2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2),
    expand_call_goal(F2,D2,G2),
    strip_subst_module(G2,D2,H2,I2),
-   '$call_with_inference_counting'('$module_call'(H2,I2)).
+   '$module_call'(H2,I2).
 
 :-non_counted_backtracking call/56.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2) :-
@@ -1645,7 +1692,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(G2,F2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2),
    expand_call_goal(G2,E2,H2),
    strip_subst_module(H2,E2,I2,J2),
-   '$call_with_inference_counting'('$module_call'(I2,J2)).
+   '$module_call'(I2,J2).
 
 :-non_counted_backtracking call/57.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2) :-
@@ -1658,7 +1705,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(H2,G2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2),
    expand_call_goal(H2,F2,I2),
    strip_subst_module(I2,F2,J2,K2),
-   '$call_with_inference_counting'('$module_call'(J2,K2)).
+   '$module_call'(J2,K2).
 
 :-non_counted_backtracking call/58.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2) :-
@@ -1671,7 +1718,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(I2,H2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2),
    expand_call_goal(I2,G2,J2),
    strip_subst_module(J2,G2,K2,L2),
-   '$call_with_inference_counting'('$module_call'(K2,L2)).
+   '$module_call'(K2,L2).
 
 :-non_counted_backtracking call/59.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2) :-
@@ -1684,7 +1731,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(J2,I2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2),
    expand_call_goal(J2,H2,K2),
    strip_subst_module(K2,H2,L2,M2),
-   '$call_with_inference_counting'('$module_call'(L2,M2)).
+   '$module_call'(L2,M2).
 
 :-non_counted_backtracking call/60.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2,H2) :-
@@ -1697,7 +1744,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(K2,J2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2,H2),
    expand_call_goal(K2,I2,L2),
    strip_subst_module(L2,I2,M2,N2),
-   '$call_with_inference_counting'('$module_call'(M2,N2)).
+   '$module_call'(M2,N2).
 
 :-non_counted_backtracking call/61.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2,H2,I2) :-
@@ -1710,7 +1757,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(L2,K2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2,H2,I2),
    expand_call_goal(L2,J2,M2),
    strip_subst_module(M2,J2,N2,O2),
-   '$call_with_inference_counting'('$module_call'(N2,O2)).
+   '$module_call'(N2,O2).
 
 :-non_counted_backtracking call/62.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2,H2,I2,J2) :-
@@ -1723,7 +1770,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(M2,L2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2,H2,I2,J2),
    expand_call_goal(M2,K2,N2),
    strip_subst_module(N2,K2,O2,P2),
-   '$call_with_inference_counting'('$module_call'(O2,P2)).
+   '$module_call'(O2,P2).
 
 :-non_counted_backtracking call/63.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2,H2,I2,J2,K2) :-
@@ -1736,7 +1783,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(N2,M2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2,H2,I2,J2,K2),
    expand_call_goal(N2,L2,O2),
    strip_subst_module(O2,L2,P2,Q2),
-   '$call_with_inference_counting'('$module_call'(P2,Q2)).
+   '$module_call'(P2,Q2).
 
 :-non_counted_backtracking call/64.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2,H2,I2,J2,K2,L2) :-
@@ -1749,7 +1796,7 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(O2,N2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2,H2,I2,J2,K2,L2),
    expand_call_goal(O2,M2,P2),
    strip_subst_module(P2,M2,Q2,R2),
-   '$call_with_inference_counting'('$module_call'(Q2,R2)).
+   '$module_call'(Q2,R2).
 
 :-non_counted_backtracking call/65.
 call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2,H2,I2,J2,K2,L2,M2) :-
@@ -1762,4 +1809,4 @@ call(A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1
    '$prepare_call_clause'(P2,O2,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A1,B1,C1,D1,E1,F1,G1,H1,I1,J1,K1,L1,M1,N1,O1,P1,Q1,R1,S1,T1,U1,V1,W1,X1,Y1,Z1,A2,B2,C2,D2,E2,F2,G2,H2,I2,J2,K2,L2,M2),
    expand_call_goal(P2,N2,Q2),
    strip_subst_module(Q2,N2,R2,S2),
-   '$call_with_inference_counting'('$module_call'(R2,S2)).
+   '$module_call'(R2,S2).

src/machine/arithmetic_ops.rs

@@ -1,7 +1,8 @@
-use dashu::base::Abs;
-use dashu::base::Gcd;
+use dashu::base::{Abs, Gcd, Signed, UnsignedAbs};
 use dashu::integer::IBig;
+use dashu::integer::fast_div::ConstDivisor;
 use divrem::*;
+use num_order::NumOrd;
 
 use crate::arena::*;
 use crate::arithmetic::*;
@@ -50,9 +51,7 @@ macro_rules! drop_iter_on_err {
     };
 }
 
-fn zero_divisor_eval_error(
-    stub_gen: impl Fn() -> FunctorStub + 'static,
-) -> MachineStubGen {
+fn zero_divisor_eval_error(stub_gen: impl Fn() -> FunctorStub + 'static) -> MachineStubGen {
     Box::new(move |machine_st| {
         let eval_error = machine_st.evaluation_error(EvalError::ZeroDivisor);
         let stub = stub_gen();
@@ -61,9 +60,7 @@ fn zero_divisor_eval_error(
     })
 }
 
-fn undefined_eval_error(
-    stub_gen: impl Fn() -> FunctorStub + 'static,
-) -> MachineStubGen {
+fn undefined_eval_error(stub_gen: impl Fn() -> FunctorStub + 'static) -> MachineStubGen {
     Box::new(move |machine_st| {
         let eval_error = machine_st.evaluation_error(EvalError::Undefined);
         let stub = stub_gen();
@@ -169,9 +166,7 @@ pub(crate) fn add(lhs: Number, rhs: Number, arena: &mut Arena) -> Result<Number,
             Ok(Number::Float(add_f(float_i_to_f(&n1)?, n2)?))
         }
         (Number::Integer(n1), Number::Rational(n2))
-        | (Number::Rational(n2), Number::Integer(n1)) => {
-            Ok(Number::arena_from(&*n1 + &*n2, arena))
-        }
+        | (Number::Rational(n2), Number::Integer(n1)) => Ok(Number::arena_from(&*n1 + &*n2, arena)),
         (Number::Rational(n1), Number::Float(OrderedFloat(n2)))
         | (Number::Float(OrderedFloat(n2)), Number::Rational(n1)) => {
             Ok(Number::Float(add_f(float_r_to_f(&n1)?, n2)?))
@@ -179,9 +174,7 @@ pub(crate) fn add(lhs: Number, rhs: Number, arena: &mut Arena) -> Result<Number,
         (Number::Float(OrderedFloat(f1)), Number::Float(OrderedFloat(f2))) => {
             Ok(Number::Float(add_f(f1, f2)?))
         }
-        (Number::Rational(r1), Number::Rational(r2)) => {
-            Ok(Number::arena_from(&*r1 + &*r2, arena))
-        }
+        (Number::Rational(r1), Number::Rational(r2)) => Ok(Number::arena_from(&*r1 + &*r2, arena)),
     }
 }
 
@@ -197,12 +190,12 @@ pub(crate) fn neg(n: Number, arena: &mut Arena) -> Number {
         Number::Integer(n) => {
             let n_clone: Integer = (*n).clone();
             Number::arena_from(-Integer::from(n_clone), arena)
-        },
+        }
         Number::Float(OrderedFloat(f)) => Number::Float(OrderedFloat(-f)),
         Number::Rational(r) => {
             let r_clone: Rational = (*r).clone();
             Number::arena_from(-Rational::from(r_clone), arena)
-        },
+        }
     }
 }
 
@@ -219,12 +212,12 @@ pub(crate) fn abs(n: Number, arena: &mut Arena) -> Number {
         Number::Integer(n) => {
             let n_clone: Integer = (*n).clone();
             Number::arena_from(Integer::from(n_clone.abs()), arena)
-        },
+        }
         Number::Float(f) => Number::Float(f.abs()),
         Number::Rational(r) => {
             let r_clone: Rational = (*r).clone();
             Number::arena_from(Rational::from(r_clone.abs()), arena)
-        },
+        }
     }
 }
 
@@ -368,7 +361,11 @@ pub(crate) fn int_pow(n1: Number, n2: Number, arena: &mut Arena) -> Result<Numbe
         (Number::Integer(n1), Number::Fixnum(n2)) => {
             let n2_i = n2.get_num();
 
-            if !(&*n1 == &Integer::from(1) || &*n1 == &Integer::from(0) || &*n1 == &Integer::from(-1)) && n2_i < 0 {
+            if !(&*n1 == &Integer::from(1)
+                || &*n1 == &Integer::from(0)
+                || &*n1 == &Integer::from(-1))
+                && n2_i < 0
+            {
                 let n = Number::Integer(n1);
                 Err(numerical_type_error(ValidType::Float, n, stub_gen))
             } else {
@@ -377,7 +374,11 @@ pub(crate) fn int_pow(n1: Number, n2: Number, arena: &mut Arena) -> Result<Numbe
             }
         }
         (Number::Integer(n1), Number::Integer(n2)) => {
-            if !(&*n1 == &Integer::from(1) || &*n1 == &Integer::from(0) || &*n1 == &Integer::from(-1)) && &*n2 < &Integer::from(0) {
+            if !(&*n1 == &Integer::from(1)
+                || &*n1 == &Integer::from(0)
+                || &*n1 == &Integer::from(-1))
+                && &*n2 < &Integer::from(0)
+            {
                 let n = Number::Integer(n1);
                 Err(numerical_type_error(ValidType::Float, n, stub_gen))
             } else {
@@ -454,14 +455,14 @@ pub(crate) fn max(n1: Number, n2: Number) -> Result<Number, MachineStubGen> {
             }
         }
         (Number::Fixnum(n1), Number::Integer(n2)) => {
-            if &*n2 > &n1.get_num() {
+            if (&*n2).num_gt(&n1.get_num()) {
                 Ok(Number::Integer(n2))
             } else {
                 Ok(Number::Fixnum(n1))
             }
         }
         (Number::Integer(n1), Number::Fixnum(n2)) => {
-            if &*n1 > &n2.get_num() {
+            if (&*n1).num_gt(&n2.get_num()) {
                 Ok(Number::Integer(n1))
             } else {
                 Ok(Number::Fixnum(n2))
@@ -498,14 +499,14 @@ pub(crate) fn min(n1: Number, n2: Number) -> Result<Number, MachineStubGen> {
             }
         }
         (Number::Fixnum(n1), Number::Integer(n2)) => {
-            if &*n2 < &n1.get_num() {
+            if (&*n2).num_lt(&n1.get_num()) {
                 Ok(Number::Integer(n2))
             } else {
                 Ok(Number::Fixnum(n1))
             }
         }
         (Number::Integer(n1), Number::Fixnum(n2)) => {
-            if &*n1 < &n2.get_num() {
+            if (&*n1).num_lt(&n2.get_num()) {
                 Ok(Number::Integer(n1))
             } else {
                 Ok(Number::Fixnum(n2))
@@ -552,7 +553,7 @@ pub fn rational_from_number(
         Number::Integer(n) => {
             let n_clone: Integer = (*n).clone();
             Ok(arena_alloc!(Rational::from(n_clone), arena))
-        },
+        }
     }
 }
 
@@ -560,7 +561,7 @@ pub(crate) fn rdiv(
     r1: TypedArenaPtr<Rational>,
     r2: TypedArenaPtr<Rational>,
 ) -> Result<Rational, MachineStubGen> {
-    if &*r2 == &0 {
+    if r2.is_zero() {
         let stub_gen = || {
             let rdiv_atom = atom!("rdiv");
             functor_stub(rdiv_atom, 2)
@@ -594,7 +595,7 @@ pub(crate) fn idiv(n1: Number, n2: Number, arena: &mut Arena) -> Result<Number,
             }
         }
         (Number::Fixnum(n1), Number::Integer(n2)) => {
-            if &*n2 == &0 {
+            if n2.is_zero() {
                 Err(zero_divisor_eval_error(stub_gen))
             } else {
                 Ok(Number::arena_from(Integer::from(n1) / &*n2, arena))
@@ -608,13 +609,10 @@ pub(crate) fn idiv(n1: Number, n2: Number, arena: &mut Arena) -> Result<Number,
             }
         }
         (Number::Integer(n1), Number::Integer(n2)) => {
-            if &*n2 == &0 {
+            if n2.is_zero() {
                 Err(zero_divisor_eval_error(stub_gen))
             } else {
-                Ok(Number::arena_from(
-                    <(Integer, Integer)>::from(n1.div_rem_floor_ref(&*n2)).0,
-                    arena,
-                ))
+                Ok(Number::arena_from(&*n1 / &*n2, arena))
             }
         }
         (Number::Fixnum(_), n2) | (Number::Integer(_), n2) => {
@@ -659,31 +657,42 @@ pub(crate) fn shr(n1: Number, n2: Number, arena: &mut Arena) -> Result<Number, M
 
             if let Ok(n2) = usize::try_from(n2_i) {
                 return Ok(Number::arena_from(n1 >> n2, arena));
-	        } else {
+            } else {
                 return Ok(Number::arena_from(n1 >> usize::max_value(), arena));
             }
         }
         (Number::Fixnum(n1), Number::Integer(n2)) => {
             let n1 = Integer::from(n1.get_num());
 
-            match n2.to_usize() {
-                Some(n2) => Ok(Number::arena_from(n1 >> n2, arena)),
-                _ => {
-			        Ok(Number::arena_from(n1 >> usize::max_value(), arena))
-		        },
+            let result: Result<usize, _> = (&*n2).try_into();
+
+            match result {
+                Ok(n2) => {
+                    Ok(Number::arena_from(n1 >> n2, arena))
+                }
+                Err(_) => {
+                    Ok(Number::arena_from(n1 >> usize::max_value(), arena))
+                }
             }
         }
         (Number::Integer(n1), Number::Fixnum(n2)) => match usize::try_from(n2.get_num()) {
             Ok(n2) => Ok(Number::arena_from(Integer::from(&*n1 >> n2), arena)),
-            _ => {
-		        Ok(Number::arena_from(Integer::from(&*n1 >> usize::max_value()),arena))
-	        },
+            _ => Ok(Number::arena_from(
+                Integer::from(&*n1 >> usize::max_value()),
+                arena,
+            )),
         },
-        (Number::Integer(n1), Number::Integer(n2)) => match n2.to_usize() {
-            Some(n2) => Ok(Number::arena_from(Integer::from(&*n1 >> n2), arena)),
-            _ => {
-		        Ok(Number::arena_from(Integer::from(&*n1 >> usize::max_value()), arena))
-            },
+        (Number::Integer(n1), Number::Integer(n2)) => {
+            let result: Result<usize, _> = (&*n2).try_into();
+
+            match result {
+                Ok(n2) => {
+                    Ok(Number::arena_from(Integer::from(&*n1 >> n2), arena))
+                }
+                Err(_) => {
+                    Ok(Number::arena_from(Integer::from(&*n1 >> usize::max_value()), arena))
+                }
+            }
         },
         (Number::Integer(_), n2) => Err(numerical_type_error(ValidType::Integer, n2, stub_gen)),
         (Number::Fixnum(_), n2) => Err(numerical_type_error(ValidType::Integer, n2, stub_gen)),
@@ -710,15 +719,18 @@ pub(crate) fn shl(n1: Number, n2: Number, arena: &mut Arena) -> Result<Number, M
 
             if let Ok(n2) = usize::try_from(n2_i) {
                 return Ok(Number::arena_from(n1 << n2, arena));
-	        } else {
+            } else {
                 return Ok(Number::arena_from(n1 << usize::max_value(), arena));
             }
         }
         (Number::Fixnum(n1), Number::Integer(n2)) => {
             let n1 = Integer::from(n1.get_num());
 
-            match n2.to_u32() {
-                Some(n2) => Ok(Number::arena_from(n1.to_u64().unwrap() << n2, arena)),
+            match (&*n2).try_into() as Result<u32, _> {
+                Ok(n2) => {
+                    let n1: u64 = n1.try_into().unwrap();
+                    Ok(Number::arena_from(n1 << n2, arena))
+                },
                 _ => {
 			        Ok(Number::arena_from(n1 << usize::max_value(), arena))
 		        }
@@ -726,12 +738,16 @@ pub(crate) fn shl(n1: Number, n2: Number, arena: &mut Arena) -> Result<Number, M
         }
         (Number::Integer(n1), Number::Fixnum(n2)) => match usize::try_from(n2.get_num()) {
             Ok(n2) => Ok(Number::arena_from(Integer::from(&*n1 << n2), arena)),
-            _ => {
-		        Ok(Number::arena_from(Integer::from(&*n1 << usize::max_value()),arena))
-		    }
+            _ => Ok(Number::arena_from(
+                Integer::from(&*n1 << usize::max_value()),
+                arena,
+            )),
         },
-        (Number::Integer(n1), Number::Integer(n2)) => match n2.to_u32() {
-            Some(n2) => Ok(Number::arena_from(Integer::from(n1.to_u64().unwrap() << n2), arena)),
+        (Number::Integer(n1), Number::Integer(n2)) => match (&*n2).try_into() as Result<u32, _> {
+            Ok(n2) => {
+                let n1: u64 = (&*n1).try_into().unwrap();
+                Ok(Number::arena_from(Integer::from(n1 << n2), arena))
+            },
             _ => {
 		        Ok(Number::arena_from(Integer::from(&*n1 << usize::max_value()),arena))
 	        }
@@ -833,6 +849,23 @@ pub(crate) fn modulus(x: Number, y: Number, arena: &mut Arena) -> Result<Number,
         functor_stub(mod_atom, 2)
     };
 
+    fn ibig_rem_floor(n1: &Integer, n2: &Integer) -> Integer {
+        let ring = ConstDivisor::new(n2.unsigned_abs());
+        let n1 = n1.clone();
+
+        if n2.is_negative() {
+            let unsigned_result = IBig::from(ring.reduce(n1).residue());
+
+            if unsigned_result.is_zero() {
+                unsigned_result
+            } else {
+                unsigned_result + n2
+            }
+        } else {
+            IBig::from(ring.reduce(n1).residue())
+        }
+    }
+
     match (x, y) {
         (Number::Fixnum(n1), Number::Fixnum(n2)) => {
             let n2_i = n2.get_num();
@@ -845,14 +878,11 @@ pub(crate) fn modulus(x: Number, y: Number, arena: &mut Arena) -> Result<Number,
             }
         }
         (Number::Fixnum(n1), Number::Integer(n2)) => {
-            if &*n2 == &0 {
+            if n2.is_zero() {
                 Err(zero_divisor_eval_error(stub_gen))
             } else {
                 let n1 = Integer::from(n1.get_num());
-                Ok(Number::arena_from(
-                    <(Integer, Integer)>::from(n1.div_rem_floor_ref(&*n2)).1,
-                    arena,
-                ))
+                Ok(Number::arena_from(ibig_rem_floor(&n1, &*n2), arena))
             }
         }
         (Number::Integer(n1), Number::Fixnum(n2)) => {
@@ -862,20 +892,14 @@ pub(crate) fn modulus(x: Number, y: Number, arena: &mut Arena) -> Result<Number,
                 Err(zero_divisor_eval_error(stub_gen))
             } else {
                 let n2 = Integer::from(n2_i);
-                Ok(Number::arena_from(
-                    <(Integer, Integer)>::from(n1.div_rem_floor_ref(&n2)).1,
-                    arena,
-                ))
+                Ok(Number::arena_from(ibig_rem_floor(&*n1, &n2), arena))
             }
         }
-        (Number::Integer(x), Number::Integer(y)) => {
-            if &*y == &0 {
+        (Number::Integer(n1), Number::Integer(n2)) => {
+            if n2.is_zero() {
                 Err(zero_divisor_eval_error(stub_gen))
             } else {
-                Ok(Number::arena_from(
-                    <(Integer, Integer)>::from(x.div_rem_floor_ref(&*y)).1,
-                    arena,
-                ))
+                Ok(Number::arena_from(ibig_rem_floor(&*n1, &*n2), arena))
             }
         }
         (Number::Integer(_), n2) | (Number::Fixnum(_), n2) => {
@@ -903,7 +927,7 @@ pub(crate) fn remainder(x: Number, y: Number, arena: &mut Arena) -> Result<Numbe
             }
         }
         (Number::Fixnum(n1), Number::Integer(n2)) => {
-            if &*n2 == &0 {
+            if n2.is_zero() {
                 Err(zero_divisor_eval_error(stub_gen))
             } else {
                 let n1 = Integer::from(n1.get_num());
@@ -921,7 +945,7 @@ pub(crate) fn remainder(x: Number, y: Number, arena: &mut Arena) -> Result<Numbe
             }
         }
         (Number::Integer(n1), Number::Integer(n2)) => {
-            if &*n2 == &0 {
+            if n2.is_zero() {
                 Err(zero_divisor_eval_error(stub_gen))
             } else {
                 Ok(Number::arena_from(Integer::from(&*n1 % &*n2), arena))
@@ -948,11 +972,8 @@ pub(crate) fn gcd(n1: Number, n2: Number, arena: &mut Arena) -> Result<Number, M
             if let Some(result) = isize_gcd(n1_i, n2_i) {
                 Ok(Number::arena_from(result, arena))
             } else {
-                let value: IBig = Integer::from(n1_i).gcd(&Integer::from(n2_i)).into();
-                Ok(Number::arena_from(
-                    value,
-                    arena,
-                ))
+                let value: Integer = Integer::from(n1_i).gcd(&Integer::from(n2_i)).into();
+                Ok(Number::arena_from(value, arena))
             }
         }
         (Number::Fixnum(n1), Number::Integer(n2)) | (Number::Integer(n2), Number::Fixnum(n1)) => {
@@ -961,8 +982,9 @@ pub(crate) fn gcd(n1: Number, n2: Number, arena: &mut Arena) -> Result<Number, M
             Ok(Number::arena_from(Integer::from(n2_clone.gcd(&n1)), arena))
         }
         (Number::Integer(n1), Number::Integer(n2)) => {
-            let n1_clone: Integer = (*n1).clone();
-            Ok(Number::arena_from(Integer::from(n1_clone.gcd(&Integer::from(n2.to_isize().unwrap()))) as IBig, arena))
+            let n2: isize = (&*n2).try_into().unwrap();
+            let value: Integer = (&*n1).gcd(&Integer::from(n2)).into();
+            Ok(Number::arena_from(value, arena))
         }
         (Number::Float(f), _) | (_, Number::Float(f)) => {
             let n = Number::Float(f);
@@ -1031,53 +1053,6 @@ pub(crate) fn atan(n1: Number) -> Result<f64, MachineStubGen> {
     unary_float_fn_template(n1, |f| f.atan())
 }
 
-#[inline]
-pub(crate) fn asinh(n1: Number) -> Result<f64, MachineStubGen> {
-    unary_float_fn_template(n1, |f| f.asinh())
-}
-
-#[inline]
-pub(crate) fn acosh(n1: Number) -> Result<f64, MachineStubGen> {
-    unary_float_fn_template(n1, |f| f.acosh())
-}
-
-#[inline]
-pub(crate) fn atanh(n1: Number) -> Result<f64, MachineStubGen> {
-    let stub_gen = || {
-        let is_atom = atom!("is");
-        functor_stub(is_atom, 2)
-    };
-
-    let f1 = try_numeric_result!(result_f(&n1), stub_gen)?;
-
-    try_numeric_result!(if f1 == 1.0 || f1 == -1.0 {
-        Err(EvalError::Undefined)
-    } else {
-        result_f(&Number::Float(OrderedFloat(f1.atanh())))
-    },
-    stub_gen)
-}
-
-#[inline]
-pub(crate) fn sinh(n1: Number) -> Result<f64, MachineStubGen> {
-    unary_float_fn_template(n1, |f| f.sinh())
-}
-
-#[inline]
-pub(crate) fn cosh(n1: Number) -> Result<f64, MachineStubGen> {
-    unary_float_fn_template(n1, |f| f.cosh())
-}
-
-#[inline]
-pub(crate) fn tanh(n1: Number) -> Result<f64, MachineStubGen> {
-    unary_float_fn_template(n1, |f| f.tanh())
-}
-
-#[inline]
-pub(crate) fn log10(n1: Number) -> Result<f64, MachineStubGen> {
-    unary_float_fn_template(n1, |f| f.log(10f64))
-}
-
 #[inline]
 pub(crate) fn float_fractional_part(n1: Number) -> Result<f64, MachineStubGen> {
     unary_float_fn_template(n1, |f| f.fract())
@@ -1107,7 +1082,6 @@ pub(crate) fn floor(n1: Number, arena: &mut Arena) -> Number {
     rnd_i(&n1, arena)
 }
 
-
 #[inline]
 pub(crate) fn ceiling(n1: Number, arena: &mut Arena) -> Number {
     let n1 = neg(n1, arena);
@@ -1160,16 +1134,17 @@ impl MachineState {
     pub fn get_number(&mut self, at: &ArithmeticTerm) -> Result<Number, MachineStub> {
         match at {
             &ArithmeticTerm::Reg(r) => {
-		        let value = self.store(self.deref(self[r]));
+                let value = self.store(self.deref(self[r]));
 
                 match Number::try_from(value) {
                     Ok(n) => Ok(n),
                     Err(_) => self.arith_eval_by_metacall(value),
                 }
             }
-            &ArithmeticTerm::Interm(i) => {
-                Ok(mem::replace(&mut self.interms[i - 1], Number::Fixnum(Fixnum::build_with(0))))
-            }
+            &ArithmeticTerm::Interm(i) => Ok(mem::replace(
+                &mut self.interms[i - 1],
+                Number::Fixnum(Fixnum::build_with(0)),
+            )),
             &ArithmeticTerm::Number(n) => Ok(n),
         }
     }
@@ -1183,13 +1158,17 @@ impl MachineState {
 
         match rational_from_number(n, caller, &mut self.arena) {
             Ok(r) => Ok(r),
-            Err(e_gen) => Err(e_gen(self))
+            Err(e_gen) => Err(e_gen(self)),
         }
     }
 
-    pub(crate) fn arith_eval_by_metacall(&mut self, value: HeapCellValue) -> Result<Number, MachineStub> {
+    pub(crate) fn arith_eval_by_metacall(
+        &mut self,
+        value: HeapCellValue,
+    ) -> Result<Number, MachineStub> {
         let stub_gen = || functor_stub(atom!("is"), 2);
-        let mut iter = stackful_post_order_iter(&mut self.heap, &mut self.stack, value);
+        let mut iter = stackful_post_order_iter::<NonListElider>
+            (&mut self.heap, &mut self.stack, value);
 
         while let Some(value) = iter.next() {
             if value.get_forwarding_bit() {
@@ -1338,27 +1317,6 @@ impl MachineState {
                             atom!("tan") => self.interms.push(Number::Float(OrderedFloat(
                                 drop_iter_on_err!(self, iter, tan(a1))
                             ))),
-                            atom!("cosh") => self.interms.push(Number::Float(OrderedFloat(
-                                drop_iter_on_err!(self, iter, cosh(a1))
-                            ))),
-                            atom!("sinh") => self.interms.push(Number::Float(OrderedFloat(
-                                drop_iter_on_err!(self, iter, sinh(a1))
-                            ))),
-                            atom!("tanh") => self.interms.push(Number::Float(OrderedFloat(
-                                drop_iter_on_err!(self, iter, tanh(a1))
-                            ))),
-                            atom!("acosh") => self.interms.push(Number::Float(OrderedFloat(
-                                drop_iter_on_err!(self, iter, acosh(a1))
-                            ))),
-                            atom!("asinh") => self.interms.push(Number::Float(OrderedFloat(
-                                drop_iter_on_err!(self, iter, asinh(a1))
-                            ))),
-                            atom!("atanh") => self.interms.push(Number::Float(OrderedFloat(
-                                drop_iter_on_err!(self, iter, atanh(a1))
-                            ))),
-                            atom!("log10") => self.interms.push(Number::Float(OrderedFloat(
-                                drop_iter_on_err!(self, iter, log10(a1))
-                            ))),
                             atom!("float_fractional_part") => self.interms.push(Number::Float(OrderedFloat(
                                 drop_iter_on_err!(self, iter, float_fractional_part(a1))
                             ))),
@@ -1493,26 +1451,11 @@ mod tests {
         let mut wam = MachineState::new();
         let mut op_dir = default_op_dir();
 
-        op_dir.insert(
-            (atom!("+"), Fixity::In),
-            OpDesc::build_with(500, YFX as u8),
-        );
-        op_dir.insert(
-            (atom!("-"), Fixity::In),
-            OpDesc::build_with(500, YFX as u8),
-        );
-        op_dir.insert(
-            (atom!("-"), Fixity::Pre),
-            OpDesc::build_with(200, FY as u8),
-        );
-        op_dir.insert(
-            (atom!("*"), Fixity::In),
-            OpDesc::build_with(400, YFX as u8),
-        );
-        op_dir.insert(
-            (atom!("/"), Fixity::In),
-            OpDesc::build_with(400, YFX as u8),
-        );
+        op_dir.insert((atom!("+"), Fixity::In), OpDesc::build_with(500, YFX as u8));
+        op_dir.insert((atom!("-"), Fixity::In), OpDesc::build_with(500, YFX as u8));
+        op_dir.insert((atom!("-"), Fixity::Pre), OpDesc::build_with(200, FY as u8));
+        op_dir.insert((atom!("*"), Fixity::In), OpDesc::build_with(400, YFX as u8));
+        op_dir.insert((atom!("/"), Fixity::In), OpDesc::build_with(400, YFX as u8));
 
         let term_write_result =
             parse_and_write_parsed_term_to_heap(&mut wam, "3 + 4 - 1 + 2.", &op_dir).unwrap();

src/machine/attributed_variables.rs

@@ -118,12 +118,9 @@ impl MachineState {
             and_frame[i] = self.registers[i];
         }
 
-        and_frame[arity + 1] =
-            fixnum_as_cell!(Fixnum::build_with(self.b0 as i64));
-        and_frame[arity + 2] =
-            fixnum_as_cell!(Fixnum::build_with(self.num_of_args as i64));
-        and_frame[arity + 3] =
-            fixnum_as_cell!(Fixnum::build_with(self.attr_var_init.cp as i64));
+        and_frame[arity + 1] = fixnum_as_cell!(Fixnum::build_with(self.b0 as i64));
+        and_frame[arity + 2] = fixnum_as_cell!(Fixnum::build_with(self.num_of_args as i64));
+        and_frame[arity + 3] = fixnum_as_cell!(Fixnum::build_with(self.attr_var_init.cp as i64));
 
         self.verify_attributes();
 
@@ -136,7 +133,8 @@ impl MachineState {
         let mut seen_set = IndexSet::new();
         let mut seen_vars = vec![];
 
-        let mut iter = stackful_preorder_iter(&mut self.heap, &mut self.stack, cell);
+        let mut iter = stackful_preorder_iter::<NonListElider>
+            (&mut self.heap, &mut self.stack, cell);
 
         while let Some(value) = iter.next() {
             read_heap_cell!(value,

src/machine/code_walker.rs

@@ -8,7 +8,9 @@ fn capture_offset(line: &Instruction, index: usize, stack: &mut Vec<usize>) -> b
         &Instruction::TryMeElse(offset) if offset > 0 => {
             stack.push(index + offset);
         }
-        &Instruction::DefaultRetryMeElse(offset) | &Instruction::RetryMeElse(offset) if offset > 0 => {
+        &Instruction::DefaultRetryMeElse(offset) | &Instruction::RetryMeElse(offset)
+            if offset > 0 =>
+        {
             stack.push(index + offset);
         }
         &Instruction::DynamicElse(_, _, NextOrFail::Next(offset)) if offset > 0 => {

src/machine/compile.rs

@@ -28,17 +28,15 @@ pub(super) fn bootstrapping_compile(
 ) -> Result<(), SessionError> {
     let (wam_prelude, machine_st) = wam.prelude_view_and_machine_st();
 
-    let term_stream = BootstrappingTermStream::from_char_reader(
-        stream,
-        machine_st,
-        listing_src,
-    );
+    let term_stream = BootstrappingTermStream::from_char_reader(stream, machine_st, listing_src);
 
-    let payload = BootstrappingLoadState(
-        LoadStatePayload::new(wam_prelude.code.len(), term_stream)
-    );
+    let payload =
+        BootstrappingLoadState(LoadStatePayload::new(wam_prelude.code.len(), term_stream));
 
-    let loader: Loader<'_, BootstrappingLoadState> = Loader { payload, wam_prelude };
+    let loader: Loader<'_, BootstrappingLoadState> = Loader {
+        payload,
+        wam_prelude,
+    };
 
     loader.load()?;
     Ok(())
@@ -98,8 +96,8 @@ fn derelictize_try_me_else(
             retraction_info.push_record(RetractionRecord::ReplacedDynamicElseOffset(index, *o));
             Some(mem::replace(o, 0))
         }
-        Instruction::DynamicElse(_, _, NextOrFail::Fail(_)) |
-        Instruction::DynamicInternalElse(_, _, NextOrFail::Fail(_)) => None,
+        Instruction::DynamicElse(_, _, NextOrFail::Fail(_))
+        | Instruction::DynamicInternalElse(_, _, NextOrFail::Fail(_)) => None,
         Instruction::TryMeElse(0) => None,
         Instruction::TryMeElse(ref mut o) => {
             retraction_info.push_record(RetractionRecord::ModifiedTryMeElse(index, *o));
@@ -154,8 +152,8 @@ fn merge_indices(
 fn find_outer_choice_instr(code: &Code, mut index: usize) -> usize {
     loop {
         match &code[index] {
-            Instruction::DynamicElse(_, _, NextOrFail::Next(i)) |
-            Instruction::DynamicInternalElse(_, _, NextOrFail::Next(i))
+            Instruction::DynamicElse(_, _, NextOrFail::Next(i))
+            | Instruction::DynamicInternalElse(_, _, NextOrFail::Next(i))
                 if *i > 0 =>
             {
                 index += i;
@@ -170,42 +168,37 @@ fn find_outer_choice_instr(code: &Code, mut index: usize) -> usize {
 fn find_inner_choice_instr(code: &Code, mut index: usize, index_loc: usize) -> usize {
     loop {
         match &code[index] {
-            Instruction::TryMeElse(o) |
-            Instruction::RetryMeElse(o) => {
+            Instruction::TryMeElse(o) | Instruction::RetryMeElse(o) => {
                 if *o > 0 {
                     return index;
                 } else {
                     index = index_loc;
                 }
             }
-            &Instruction::DynamicElse(_, _, next_or_fail) => {
-                match next_or_fail {
-                    NextOrFail::Next(i) => {
-                        if i == 0 {
-                            index = index_loc;
-                        } else {
-                            return index;
-                        }
-                    }
-                    NextOrFail::Fail(_) => {
+            &Instruction::DynamicElse(_, _, next_or_fail) => match next_or_fail {
+                NextOrFail::Next(i) => {
+                    if i == 0 {
                         index = index_loc;
-                    }
-                }
-            }
-            &Instruction::DynamicInternalElse(_, _, next_or_fail) => {
-                match next_or_fail {
-                    NextOrFail::Next(i) => {
-                        if i == 0 {
-                            index = index_loc;
-                        } else {
-                            return index;
-                        }
-                    }
-                    NextOrFail::Fail(_) => {
+                    } else {
                         return index;
                     }
                 }
-            }
+                NextOrFail::Fail(_) => {
+                    index = index_loc;
+                }
+            },
+            &Instruction::DynamicInternalElse(_, _, next_or_fail) => match next_or_fail {
+                NextOrFail::Next(i) => {
+                    if i == 0 {
+                        index = index_loc;
+                    } else {
+                        return index;
+                    }
+                }
+                NextOrFail::Fail(_) => {
+                    return index;
+                }
+            },
             Instruction::TrustMe(_) => {
                 return index;
             }
@@ -215,11 +208,7 @@ fn find_inner_choice_instr(code: &Code, mut index: usize, index_loc: usize) -> u
                         index += v;
                     }
                     IndexingCodePtr::DynamicExternal(v) => match &code[index + v] {
-                        &Instruction::DynamicInternalElse(
-                            _,
-                            _,
-                            NextOrFail::Next(0),
-                        ) => {
+                        &Instruction::DynamicInternalElse(_, _, NextOrFail::Next(0)) => {
                             return index + v;
                         }
                         _ => {
@@ -309,8 +298,7 @@ fn merge_indexed_subsequences(
                         code[inner_try_me_else_loc] = Instruction::TrustMe(o);
                     }
                     _ => {
-                        code[inner_try_me_else_loc] =
-                            Instruction::RetryMeElse(o);
+                        code[inner_try_me_else_loc] = Instruction::RetryMeElse(o);
                     }
                 },
             }
@@ -376,7 +364,9 @@ fn delete_from_skeleton(
     }
 
     if skeleton.core.is_dynamic {
-        skeleton.core.add_retracted_dynamic_clause_info(clause_index_info);
+        skeleton
+            .core
+            .add_retracted_dynamic_clause_info(clause_index_info);
 
         retraction_info.push_record(RetractionRecord::RemovedDynamicSkeletonClause(
             compilation_target,
@@ -409,8 +399,8 @@ fn blunt_leading_choice_instr(
                 code[instr_loc] = Instruction::TryMeElse(*o);
                 return instr_loc;
             }
-            Instruction::DynamicElse(_, _, NextOrFail::Next(_)) |
-            Instruction::DynamicInternalElse(_, _, NextOrFail::Next(_)) => {
+            Instruction::DynamicElse(_, _, NextOrFail::Next(_))
+            | Instruction::DynamicInternalElse(_, _, NextOrFail::Next(_)) => {
                 return instr_loc;
             }
             &mut Instruction::DynamicElse(b, d, NextOrFail::Fail(o)) => {
@@ -422,26 +412,19 @@ fn blunt_leading_choice_instr(
                 code[instr_loc] = Instruction::DynamicElse(b, d, NextOrFail::Next(0));
                 return instr_loc;
             }
-            &mut Instruction::DynamicInternalElse(
-                b,
-                d,
-                NextOrFail::Fail(o),
-            ) => {
+            &mut Instruction::DynamicInternalElse(b, d, NextOrFail::Fail(o)) => {
                 retraction_info.push_record(RetractionRecord::AppendedNextOrFail(
                     instr_loc,
                     NextOrFail::Fail(o),
                 ));
 
-                code[instr_loc] = Instruction::DynamicInternalElse(
-                    b,
-                    d,
-                    NextOrFail::Next(0),
-                );
+                code[instr_loc] = Instruction::DynamicInternalElse(b, d, NextOrFail::Next(0));
 
                 return instr_loc;
             }
             Instruction::TrustMe(o) => {
-                retraction_info.push_record(RetractionRecord::AppendedTrustMe(instr_loc, *o, false));
+                retraction_info
+                    .push_record(RetractionRecord::AppendedTrustMe(instr_loc, *o, false));
 
                 code[instr_loc] = Instruction::TryMeElse(0);
                 return instr_loc + 1;
@@ -481,9 +464,9 @@ fn set_switch_var_offset_to_choice_instr(
     };
 
     match &code[index_loc + v] {
-        Instruction::TryMeElse(_) |
-        Instruction::DynamicElse(..) |
-        Instruction::DynamicInternalElse(..) => {}
+        Instruction::TryMeElse(_)
+        | Instruction::DynamicElse(..)
+        | Instruction::DynamicInternalElse(..) => {}
         _ => {
             set_switch_var_offset(code, index_loc, offset, retraction_info);
         }
@@ -523,9 +506,8 @@ fn internalize_choice_instr_at(
     retraction_info: &mut RetractionInfo,
 ) {
     match &mut code[instr_loc] {
-        Instruction::DynamicElse(_, _, NextOrFail::Fail(_)) |
-        Instruction::DynamicInternalElse(_, _, NextOrFail::Fail(_)) => {
-        }
+        Instruction::DynamicElse(_, _, NextOrFail::Fail(_))
+        | Instruction::DynamicInternalElse(_, _, NextOrFail::Fail(_)) => {}
         Instruction::DynamicElse(_, _, ref mut o @ NextOrFail::Next(0)) => {
             retraction_info.push_record(RetractionRecord::ReplacedDynamicElseOffset(instr_loc, 0));
             *o = NextOrFail::Fail(0);
@@ -554,18 +536,10 @@ fn internalize_choice_instr_at(
 
             match &mut code[instr_loc + o] {
                 Instruction::RevJmpBy(p) if *p == 0 => {
-                    code[instr_loc] = Instruction::DynamicInternalElse(
-                        b,
-                        d,
-                        NextOrFail::Fail(o),
-                    );
+                    code[instr_loc] = Instruction::DynamicInternalElse(b, d, NextOrFail::Fail(o));
                 }
                 _ => {
-                    code[instr_loc] = Instruction::DynamicInternalElse(
-                        b,
-                        d,
-                        NextOrFail::Next(o),
-                    );
+                    code[instr_loc] = Instruction::DynamicInternalElse(b, d, NextOrFail::Next(o));
                 }
             }
         }
@@ -609,23 +583,20 @@ fn thread_choice_instr_at_to(
                 *o = target_loc - instr_loc;
                 return;
             }
-            Instruction::DynamicElse(_, _, NextOrFail::Next(ref mut o)) |
-            Instruction::DynamicInternalElse(
-                _,
-                _,
-                NextOrFail::Next(ref mut o),
-            ) if target_loc >= instr_loc => {
+            Instruction::DynamicElse(_, _, NextOrFail::Next(ref mut o))
+            | Instruction::DynamicInternalElse(_, _, NextOrFail::Next(ref mut o))
+                if target_loc >= instr_loc =>
+            {
                 retraction_info
                     .push_record(RetractionRecord::ReplacedDynamicElseOffset(instr_loc, *o));
                 *o = target_loc - instr_loc;
                 return;
             }
-            Instruction::DynamicElse(_, _, NextOrFail::Next(o)) |
-            Instruction::DynamicInternalElse(_, _, NextOrFail::Next(o)) => {
+            Instruction::DynamicElse(_, _, NextOrFail::Next(o))
+            | Instruction::DynamicInternalElse(_, _, NextOrFail::Next(o)) => {
                 instr_loc += *o;
             }
-            Instruction::TryMeElse(o)
-            | Instruction::RetryMeElse(o) => {
+            Instruction::TryMeElse(o) | Instruction::RetryMeElse(o) => {
                 instr_loc += *o;
             }
             Instruction::RevJmpBy(ref mut o) if instr_loc >= target_loc => {
@@ -642,7 +613,8 @@ fn thread_choice_instr_at_to(
             {
                 retraction_info.push_record(RetractionRecord::AppendedNextOrFail(instr_loc, *fail));
 
-                code[instr_loc] = instr!("dynamic_else",
+                code[instr_loc] = instr!(
+                    "dynamic_else",
                     birth,
                     death,
                     NextOrFail::Next(target_loc - instr_loc)
@@ -653,14 +625,13 @@ fn thread_choice_instr_at_to(
             Instruction::DynamicElse(_, _, NextOrFail::Fail(o)) if *o > 0 => {
                 instr_loc += *o;
             }
-            &mut Instruction::DynamicInternalElse(
-                birth,
-                death,
-                ref mut fail,
-            ) if target_loc >= instr_loc => {
+            &mut Instruction::DynamicInternalElse(birth, death, ref mut fail)
+                if target_loc >= instr_loc =>
+            {
                 retraction_info.push_record(RetractionRecord::AppendedNextOrFail(instr_loc, *fail));
 
-                code[instr_loc] = instr!("dynamic_internal_else",
+                code[instr_loc] = instr!(
+                    "dynamic_internal_else",
                     birth,
                     death,
                     NextOrFail::Next(target_loc - instr_loc)
@@ -668,9 +639,7 @@ fn thread_choice_instr_at_to(
 
                 return;
             }
-            Instruction::DynamicInternalElse(_, _, NextOrFail::Fail(o))
-                if *o > 0 =>
-            {
+            Instruction::DynamicInternalElse(_, _, NextOrFail::Fail(o)) if *o > 0 => {
                 instr_loc += *o;
             }
             Instruction::TrustMe(ref mut o) if target_loc >= instr_loc => {
@@ -711,33 +680,31 @@ fn remove_non_leading_clause(
 
             None
         }
-        Instruction::TrustMe(_) => {
-            match &mut code[preceding_choice_instr_loc] {
-                Instruction::RetryMeElse(o) => {
-                    retraction_info.push_record(RetractionRecord::ModifiedRetryMeElse(
-                        preceding_choice_instr_loc,
-                        *o,
-                    ));
+        Instruction::TrustMe(_) => match &mut code[preceding_choice_instr_loc] {
+            Instruction::RetryMeElse(o) => {
+                retraction_info.push_record(RetractionRecord::ModifiedRetryMeElse(
+                    preceding_choice_instr_loc,
+                    *o,
+                ));
 
-                    code[preceding_choice_instr_loc] = Instruction::TrustMe(0);
+                code[preceding_choice_instr_loc] = Instruction::TrustMe(0);
 
-                    None
-                }
-                Instruction::TryMeElse(ref mut o) => {
-                    retraction_info.push_record(RetractionRecord::ModifiedTryMeElse(
-                        preceding_choice_instr_loc,
-                        *o,
-                    ));
-
-                    *o = 0;
-
-                    Some(IndexPtr::index(preceding_choice_instr_loc + 1))
-                }
-                _ => {
-                    unreachable!();
-                }
+                None
             }
-        }
+            Instruction::TryMeElse(ref mut o) => {
+                retraction_info.push_record(RetractionRecord::ModifiedTryMeElse(
+                    preceding_choice_instr_loc,
+                    *o,
+                ));
+
+                *o = 0;
+
+                Some(IndexPtr::index(preceding_choice_instr_loc + 1))
+            }
+            _ => {
+                unreachable!();
+            }
+        },
         _ => {
             unreachable!();
         }
@@ -988,11 +955,7 @@ fn prepend_compiled_clause(
                     Instruction::TryMeElse(ref mut o) if *o == 0 => {
                         *o = prepend_queue_len - 2;
                     }
-                    Instruction::DynamicInternalElse(
-                        _,
-                        _,
-                        ref mut o @ NextOrFail::Next(0),
-                    ) => {
+                    Instruction::DynamicInternalElse(_, _, ref mut o @ NextOrFail::Next(0)) => {
                         *o = NextOrFail::Fail(prepend_queue_len - 2);
                     }
                     _ => {
@@ -1258,7 +1221,11 @@ fn print_overwrite_warning(
         _ => {}
     }
 
-    println!("Warning: overwriting {}/{} because the clauses are discontiguous", key.0.as_str(), key.1);
+    println!(
+        "Warning: overwriting {}/{} because the clauses are discontiguous",
+        key.0.as_str(),
+        key.1
+    );
 }
 
 impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
@@ -1270,8 +1237,9 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
 
             if let Some(path_str) = load_context.path.to_str() {
                 if !path_str.is_empty() {
-                    return Some(LS::machine_st(&mut self.payload).atom_tbl.build_with(
-                        path_str
+                    return Some(AtomTable::build_with(
+                        &LS::machine_st(&mut self.payload).atom_tbl,
+                        path_str,
                     ));
                 }
             }
@@ -1290,10 +1258,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         let clause = self.try_term_to_tl(term, &mut preprocessor)?;
         // let queue = preprocessor.parse_queue(self)?;
 
-        let mut cg = CodeGenerator::new(
-            &mut LS::machine_st(&mut self.payload).atom_tbl,
-            settings,
-        );
+        let mut cg = CodeGenerator::new(&LS::machine_st(&mut self.payload).atom_tbl, settings);
 
         let clause_code = cg.compile_predicate(vec![clause])?;
 
@@ -1323,10 +1288,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             clauses.push(self.try_term_to_tl(term, &mut preprocessor)?);
         }
 
-        let mut cg = CodeGenerator::new(
-            &mut LS::machine_st(&mut self.payload).atom_tbl,
-            settings,
-        );
+        let mut cg = CodeGenerator::new(&LS::machine_st(&mut self.payload).atom_tbl, settings);
 
         let mut code = cg.compile_predicate(clauses)?;
 
@@ -1361,26 +1323,23 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                         .clause_clause_locs
                         .extend(&clause_clause_locs.make_contiguous()[0..]);
 
-                    self.payload.retraction_info
-                        .push_record(RetractionRecord::SkeletonClauseTruncateBack(
+                    self.payload.retraction_info.push_record(
+                        RetractionRecord::SkeletonClauseTruncateBack(
                             predicates.compilation_target,
                             key,
                             skeleton_clause_len,
-                        ));
+                        ),
+                    );
                 }
                 None => {
                     cg.skeleton
-                      .core
-                      .clause_clause_locs
-                      .extend(&clause_clause_locs.make_contiguous()[0..]);
+                        .core
+                        .clause_clause_locs
+                        .extend(&clause_clause_locs.make_contiguous()[0..]);
 
                     let skeleton = cg.skeleton;
 
-                    self.add_extensible_predicate(
-                        key,
-                        skeleton,
-                        predicates.compilation_target,
-                    );
+                    self.add_extensible_predicate(key, skeleton, predicates.compilation_target);
                 }
             };
 
@@ -1450,11 +1409,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                 let mut skeleton = LocalPredicateSkeleton::new();
                 skeleton.clause_clause_locs = clause_clause_locs;
 
-                self.add_local_extensible_predicate(
-                    *compilation_target,
-                    *key,
-                    skeleton,
-                );
+                self.add_local_extensible_predicate(*compilation_target, *key, skeleton);
             }
         }
     }
@@ -1490,11 +1445,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                 let mut skeleton = LocalPredicateSkeleton::new();
                 skeleton.clause_clause_locs.push_front(code_len);
 
-                self.add_local_extensible_predicate(
-                    *compilation_target,
-                    *key,
-                    skeleton,
-                );
+                self.add_local_extensible_predicate(*compilation_target, *key, skeleton);
             }
         }
     }
@@ -1530,11 +1481,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                 let mut skeleton = LocalPredicateSkeleton::new();
                 skeleton.clause_clause_locs.push_back(code_len);
 
-                self.add_local_extensible_predicate(
-                    *compilation_target,
-                    *key,
-                    skeleton,
-                );
+                self.add_local_extensible_predicate(*compilation_target, *key, skeleton);
             }
         }
     }
@@ -1606,7 +1553,8 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
 
                 skeleton.core.clause_clause_locs.push_back(code_len);
 
-                self.payload.retraction_info
+                self.payload
+                    .retraction_info
                     .push_record(RetractionRecord::SkeletonClausePopBack(
                         compilation_target,
                         key,
@@ -1624,8 +1572,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
 
                 self.push_back_to_local_predicate_skeleton(&compilation_target, &key, code_len);
 
-                let code_index =
-                    self.get_or_insert_code_index(key, compilation_target);
+                let code_index = self.get_or_insert_code_index(key, compilation_target);
 
                 if let Some(new_code_ptr) = result {
                     set_code_index(
@@ -1646,7 +1593,8 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                 skeleton.core.clause_clause_locs.push_front(code_len);
                 skeleton.core.clause_assert_margin += 1;
 
-                self.payload.retraction_info
+                self.payload
+                    .retraction_info
                     .push_record(RetractionRecord::SkeletonClausePopFront(
                         compilation_target,
                         key,
@@ -1666,8 +1614,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
 
                 self.push_front_to_local_predicate_skeleton(&compilation_target, &key, code_len);
 
-                let code_index =
-                    self.get_or_insert_code_index(key, compilation_target);
+                let code_index = self.get_or_insert_code_index(key, compilation_target);
 
                 set_code_index(
                     &mut self.payload.retraction_info,
@@ -1698,19 +1645,17 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             .opt_arg_index_key
             .switch_on_term_loc()
         {
-            Some(index_loc) => {
-                find_inner_choice_instr(
-                    &self.wam_prelude.code,
-                    skeleton.clauses[target_pos].clause_start,
-                    index_loc,
-                )
-            }
+            Some(index_loc) => find_inner_choice_instr(
+                &self.wam_prelude.code,
+                skeleton.clauses[target_pos].clause_start,
+                index_loc,
+            ),
             None => skeleton.clauses[target_pos].clause_start,
         };
 
         match &mut self.wam_prelude.code[clause_loc] {
-            Instruction::DynamicElse(_, ref mut d, _) |
-            Instruction::DynamicInternalElse(_, ref mut d, _) => {
+            Instruction::DynamicElse(_, ref mut d, _)
+            | Instruction::DynamicInternalElse(_, ref mut d, _) => {
                 *d = Death::Finite(LS::machine_st(&mut self.payload).global_clock);
             }
             _ => unreachable!(),
@@ -1797,11 +1742,11 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                             skeleton.clauses[target_pos + 1].clause_start =
                                 skeleton.clauses[target_pos].clause_start;
 
-                            let update_code_index = target_pos == 0 &&
-                                skeleton.clauses[target_pos + 1]
-                                  .opt_arg_index_key
-                                  .switch_on_term_loc()
-                                  .is_none();
+                            let update_code_index = target_pos == 0
+                                && skeleton.clauses[target_pos + 1]
+                                    .opt_arg_index_key
+                                    .switch_on_term_loc()
+                                    .is_none();
 
                             let index_ptr_opt = if update_code_index {
                                 Some(IndexPtr::index(clause_loc))
@@ -1964,7 +1909,8 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                                 index_loc,
                             );
 
-                            let lower_bound_clause_start = skeleton.clauses[lower_bound].clause_start;
+                            let lower_bound_clause_start =
+                                skeleton.clauses[lower_bound].clause_start;
                             let preceding_choice_instr_loc;
 
                             match &mut code[clause_start] {
@@ -2093,13 +2039,8 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         clause_clauses: ClauseIter,
         append_or_prepend: AppendOrPrepend,
     ) -> Result<(), SessionError> {
-        let clause_predicates = clause_clauses.map(|(head, body)| {
-            Term::Clause(
-                Cell::default(),
-                atom!("$clause"),
-                vec![head, body],
-            )
-        });
+        let clause_predicates = clause_clauses
+            .map(|(head, body)| Term::Clause(Cell::default(), atom!("$clause"), vec![head, body]));
 
         let clause_clause_compilation_target = match compilation_target {
             CompilationTarget::User => CompilationTarget::Module(atom!("builtins")),
@@ -2132,21 +2073,21 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                     .cloned()
                     .collect()
             }
-            Some(skeleton) => {
-                skeleton.core.clause_clause_locs.make_contiguous()[0..num_clause_predicates]
-                    .iter()
-                    .cloned()
-                    .collect()
-            }
+            Some(skeleton) => skeleton.core.clause_clause_locs.make_contiguous()
+                [0..num_clause_predicates]
+                .iter()
+                .cloned()
+                .collect(),
             None => {
                 unreachable!()
             }
         };
 
-        match self.wam_prelude.indices.get_predicate_skeleton_mut(
-            &clause_clause_compilation_target,
-            &(atom!("$clause"), 2),
-        ) {
+        match self
+            .wam_prelude
+            .indices
+            .get_predicate_skeleton_mut(&clause_clause_compilation_target, &(atom!("$clause"), 2))
+        {
             Some(skeleton) if append_or_prepend.is_append() => {
                 for _ in 0..num_clause_predicates {
                     skeleton.core.clause_clause_locs.pop_back();
@@ -2270,25 +2211,25 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                         println!(
                             "Warning: overwriting multifile predicate {}:{}/{} because \
                                   it was not locally declared multifile.",
-                            self.payload.predicates.compilation_target, key.0.as_str(), key.1
+                            self.payload.predicates.compilation_target,
+                            key.0.as_str(),
+                            key.1
                         );
                     }
 
-                    if let Some(skeleton) = self
-                        .wam_prelude
-                        .indices
-                        .remove_predicate_skeleton(&self.payload.predicates.compilation_target, &key)
-                    {
+                    if let Some(skeleton) = self.wam_prelude.indices.remove_predicate_skeleton(
+                        &self.payload.predicates.compilation_target,
+                        &key,
+                    ) {
                         let compilation_target = self.payload.predicates.compilation_target;
 
                         if predicate_info.is_dynamic {
-                            let clause_clause_compilation_target =
-                                match compilation_target {
-                                    CompilationTarget::User => {
-                                        CompilationTarget::Module(atom!("builtins"))
-                                    }
-                                    module => module,
-                                };
+                            let clause_clause_compilation_target = match compilation_target {
+                                CompilationTarget::User => {
+                                    CompilationTarget::Module(atom!("builtins"))
+                                }
+                                module => module,
+                            };
 
                             self.retract_local_clauses_by_locs(
                                 clause_clause_compilation_target,
@@ -2301,11 +2242,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                         }
 
                         self.payload.retraction_info.push_record(
-                            RetractionRecord::RemovedSkeleton(
-                                compilation_target,
-                                key,
-                                skeleton,
-                            ),
+                            RetractionRecord::RemovedSkeleton(compilation_target, key, skeleton),
                         );
                     }
                 }
@@ -2328,9 +2265,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                 match self.wam_prelude.indices.modules.get_mut(&filename) {
                     Some(ref mut module) => {
                         let index_ptr = code_index.get();
-                        let code_index = module.code_dir.entry(key)
-                            .or_insert(code_index)
-                            .clone();
+                        let code_index = module.code_dir.entry(key).or_insert(code_index).clone();
 
                         set_code_index(
                             &mut self.payload.retraction_info,
@@ -2349,8 +2284,10 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             LS::machine_st(&mut self.payload).global_clock += 1;
 
             let clause_clauses_len = self.payload.clause_clauses.len();
-            let clauses_vec: Vec<_> = self.payload
-                .clause_clauses.drain(0..std::cmp::min(predicates_len, clause_clauses_len))
+            let clauses_vec: Vec<_> = self
+                .payload
+                .clause_clauses
+                .drain(0..std::cmp::min(predicates_len, clause_clauses_len))
                 .collect();
 
             let compilation_target = self.payload.predicates.compilation_target;
@@ -2374,10 +2311,7 @@ impl Machine {
         module_name: HeapCellValue,
         key: PredicateKey,
     ) -> CodeIndex {
-        let mut loader: Loader<'_, InlineLoadState<'_>> = Loader::new(
-            self,
-            InlineTermStream {},
-        );
+        let mut loader: Loader<'_, InlineLoadState<'_>> = Loader::new(self, InlineTermStream {});
 
         let module_name = if module_name.get_tag() == HeapCellValueTag::Atom {
             cell_as_atom!(module_name)
@@ -2394,12 +2328,10 @@ impl Machine {
         vars: &[Term],
     ) -> Result<(), SessionError> {
         let mut compile = || {
-            let mut loader: Loader<'_, InlineLoadState<'_>> = Loader::new(
-                self,
-                InlineTermStream {},
-            );
+            let mut loader: Loader<'_, InlineLoadState<'_>> =
+                Loader::new(self, InlineTermStream {});
 
-            let term = loader.read_term_from_heap(term_loc)?;
+            let term = loader.read_term_from_heap(term_loc);
             let clause = build_rule_body(vars, term);
 
             let settings = CodeGenSettings {

src/machine/config.rs

@@ -0,0 +1,32 @@
+pub struct MachineConfig {
+    pub streams: StreamConfig,
+    pub toplevel: &'static str,
+}
+
+pub enum StreamConfig {
+    Stdio,
+    Memory,
+}
+
+impl Default for MachineConfig {
+    fn default() -> Self {
+        MachineConfig {
+            streams: StreamConfig::Stdio,
+            toplevel: include_str!("../toplevel.pl"),
+        }
+    }
+}
+
+impl MachineConfig {
+    pub fn in_memory() -> Self {
+        MachineConfig {
+            streams: StreamConfig::Memory,
+            ..Default::default()
+        }
+    }
+
+    pub fn with_toplevel(mut self, toplevel: &'static str) -> Self {
+        self.toplevel = toplevel;
+        self
+    }
+}

src/machine/copier.rs

@@ -91,12 +91,16 @@ impl<T: CopierTarget> CopyTermState<T> {
             self.target.push(hcv);
         }
 
-        let cdr = self.target.store(self.target.deref(heap_loc_as_cell!(addr + 1)));
+        let cdr = self
+            .target
+            .store(self.target.deref(heap_loc_as_cell!(addr + 1)));
 
         if !cdr.is_var() {
             self.trail_list_cell(addr + 1, threshold);
         } else {
-            let car = self.target.store(self.target.deref(heap_loc_as_cell!(addr)));
+            let car = self
+                .target
+                .store(self.target.deref(heap_loc_as_cell!(addr)));
 
             if !car.is_var() {
                 self.trail_list_cell(addr, threshold);
@@ -188,10 +192,10 @@ impl<T: CopierTarget> CopyTermState<T> {
         while let HeapCellValueTag::Lis = list_addr.get_tag() {
             let threshold = self.target.threshold();
             let heap_loc = list_addr.get_value() as usize;
-            let str_loc  = self.target[heap_loc].get_value() as usize;
+            let str_loc = self.target[heap_loc].get_value() as usize;
 
-            self.target.push(heap_loc_as_cell!(threshold+2));
-            self.target.push(heap_loc_as_cell!(threshold+1));
+            self.target.push(heap_loc_as_cell!(threshold + 2));
+            self.target.push(heap_loc_as_cell!(threshold + 1));
 
             read_heap_cell!(self.target[str_loc],
                 (HeapCellValueTag::Atom) => {
@@ -377,8 +381,9 @@ mod tests {
         let a_atom = atom!("a");
         let b_atom = atom!("b");
 
-        wam.machine_st.heap
-           .extend(functor!(f_atom, [atom(a_atom), atom(b_atom)]));
+        wam.machine_st
+            .heap
+            .extend(functor!(f_atom, [atom(a_atom), atom(b_atom)]));
 
         assert_eq!(wam.machine_st.heap[0], atom_as_cell!(f_atom, 2));
         assert_eq!(wam.machine_st.heap[1], atom_as_cell!(a_atom));
@@ -401,20 +406,26 @@ mod tests {
 
         wam.machine_st.heap.clear();
 
-        let pstr_var_cell = put_partial_string(&mut wam.machine_st.heap, "abc ", &mut wam.machine_st.atom_tbl);
+        let pstr_var_cell =
+            put_partial_string(&mut wam.machine_st.heap, "abc ", &wam.machine_st.atom_tbl);
         let pstr_cell = wam.machine_st.heap[pstr_var_cell.get_value() as usize];
 
         wam.machine_st.heap.pop();
         wam.machine_st.heap.push(pstr_loc_as_cell!(2));
 
-        let pstr_second_var_cell = put_partial_string(&mut wam.machine_st.heap, "def", &mut wam.machine_st.atom_tbl);
+        let pstr_second_var_cell =
+            put_partial_string(&mut wam.machine_st.heap, "def", &wam.machine_st.atom_tbl);
         let pstr_second_cell = wam.machine_st.heap[pstr_second_var_cell.get_value() as usize];
 
         wam.machine_st.heap.pop();
-        wam.machine_st.heap.push(pstr_loc_as_cell!(wam.machine_st.heap.len() + 1));
+        wam.machine_st
+            .heap
+            .push(pstr_loc_as_cell!(wam.machine_st.heap.len() + 1));
 
         wam.machine_st.heap.push(pstr_offset_as_cell!(0));
-        wam.machine_st.heap.push(fixnum_as_cell!(Fixnum::build_with(0i64)));
+        wam.machine_st
+            .heap
+            .push(fixnum_as_cell!(Fixnum::build_with(0i64)));
 
         {
             let wam = TermCopyingMockWAM { wam: &mut wam };
@@ -428,14 +439,20 @@ mod tests {
         assert_eq!(wam.machine_st.heap[2], pstr_second_cell);
         assert_eq!(wam.machine_st.heap[3], pstr_loc_as_cell!(4));
         assert_eq!(wam.machine_st.heap[4], pstr_offset_as_cell!(0));
-        assert_eq!(wam.machine_st.heap[5], fixnum_as_cell!(Fixnum::build_with(0i64)));
+        assert_eq!(
+            wam.machine_st.heap[5],
+            fixnum_as_cell!(Fixnum::build_with(0i64))
+        );
 
         assert_eq!(wam.machine_st.heap[7], pstr_cell);
         assert_eq!(wam.machine_st.heap[8], pstr_loc_as_cell!(9));
         assert_eq!(wam.machine_st.heap[9], pstr_second_cell);
         assert_eq!(wam.machine_st.heap[10], pstr_loc_as_cell!(11));
         assert_eq!(wam.machine_st.heap[11], pstr_offset_as_cell!(7));
-        assert_eq!(wam.machine_st.heap[12], fixnum_as_cell!(Fixnum::build_with(0i64)));
+        assert_eq!(
+            wam.machine_st.heap[12],
+            fixnum_as_cell!(Fixnum::build_with(0i64))
+        );
 
         wam.machine_st.heap.clear();
 

src/machine/cycle_detection.rs

@@ -0,0 +1,429 @@
+use crate::atom_table::*;
+use crate::types::*;
+
+/* Use the pointer reversal technique of the Deutsch-Schorr-Waite
+ * algorithm to detect cycles in Prolog terms.
+ *
+ * Much of the structure and nomenclature of the GC marking algorithm
+ * is adapted here but there are a few significant changes:
+ *
+ * - Forwarded cells now form a trail of bread crumbs leading back to self.start
+ * - Cells are only marked during the backward phase
+ * - Visiting subterms of a visited compound does not immediately shift to the backward phase
+ * - The heads of LIS structures are both marked and forwarded rather
+ *   than just forwarded to distinguish them from tails;
+ *   continue_forwarding() checks for this before entering the forward
+ *   phase
+ *
+ * Commonalities with the GC marking algorithm:
+ * - The contents of forwarded cells are modified only when they are unforwarded
+ * - Marked (but unforwarded!) cells immediately shift to the backward phase
+ */
+
+#[derive(Debug)]
+pub(crate) struct CycleDetectingIter<'a, const STOP_AT_CYCLES: bool> {
+    pub(crate) heap: &'a mut [HeapCellValue],
+    start: usize,
+    current: usize,
+    next: u64,
+    cycle_found: bool,
+    mark_phase: bool,
+}
+
+impl<'a, const STOP_AT_CYCLES: bool> CycleDetectingIter<'a, STOP_AT_CYCLES> {
+    pub(crate) fn new(heap: &'a mut [HeapCellValue], start: usize) -> Self {
+        heap[start].set_forwarding_bit(true);
+        let next = heap[start].get_value();
+
+        Self {
+            heap,
+            start,
+            current: start,
+            next,
+            cycle_found: false,
+            mark_phase: true,
+        }
+    }
+
+    #[inline]
+    pub(crate) fn cycle_found(&self) -> bool {
+        self.cycle_found
+    }
+
+    #[inline]
+    fn cycle_detection_active(&self) -> bool {
+        STOP_AT_CYCLES && self.mark_phase && !self.cycle_found
+    }
+
+    fn backward_and_return(&mut self) -> HeapCellValue {
+        let mut current = self.heap[self.current];
+        current.set_value(self.next);
+
+        if self.backward() {
+            // set the f and m bits on the heap cell at start
+            // so we invoke backward() and return None next call.
+
+            self.heap[self.current].set_forwarding_bit(false);
+            self.heap[self.current].set_mark_bit(self.mark_phase);
+        }
+
+        current
+    }
+
+    fn traverse_subterm(&mut self, h: usize, arity: usize) -> Option<usize> {
+        let mut last_cell_loc = h + arity - 1;
+
+        for idx in (h .. h + arity).rev() {
+            if self.heap[idx].get_forwarding_bit() {
+                if self.cycle_detection_active() {
+                    self.cycle_found = true;
+                    return None;
+                }
+
+                last_cell_loc -= 1;
+            } else if self.heap[idx].get_mark_bit() == self.mark_phase {
+                last_cell_loc -= 1;
+            } else {
+                break;
+            }
+        }
+
+        Some(last_cell_loc)
+    }
+
+    #[inline]
+    fn continue_forwarding(&self) -> bool {
+        self.heap[self.current].get_mark_bit() != self.mark_phase ||
+            self.heap[self.current].get_forwarding_bit()
+    }
+
+    fn forward(&mut self) -> Option<HeapCellValue> {
+        loop {
+            if self.continue_forwarding() {
+                match self.heap[self.current].get_tag() {
+                    tag @ HeapCellValueTag::AttrVar | tag @ HeapCellValueTag::Var => {
+                        let next = self.next as usize;
+
+                        if self.heap[next].get_forwarding_bit() {
+                            return if self.current != next {
+                                if self.cycle_detection_active() {
+                                    self.cycle_found = true;
+                                    None
+                                } else {
+                                    Some(self.backward_and_return())
+                                }
+                            } else {
+                                Some(self.backward_and_return())
+                            };
+                        } else if self.heap[next].get_mark_bit() == self.mark_phase {
+                            return Some(self.backward_and_return());
+                        }
+
+                        self.heap[next].set_forwarding_bit(true);
+
+                        let temp = self.heap[next].get_value();
+
+                        self.heap[next].set_value(self.current as u64);
+                        self.current = next;
+                        self.next = temp;
+
+                        if self.next < self.heap.len() as u64 {
+                            return Some(HeapCellValue::build_with(tag, next as u64));
+                        }
+                    }
+                    HeapCellValueTag::Str => {
+                        let h = self.next as usize;
+                        let cell = self.heap[h];
+                        let arity = cell_as_atom_cell!(self.heap[h]).get_arity();
+
+                        let last_cell_loc = match self.traverse_subterm(h + 1, arity) {
+                            Some(last_cell_loc) => last_cell_loc,
+                            None => return None,
+                        };
+
+                        if last_cell_loc == h {
+                            if self.backward() {
+                                return None;
+                            }
+
+                            continue;
+                        }
+
+                        if self.cycle_detection_active() {
+                            for idx in (h + 1 .. last_cell_loc).rev() {
+                                if self.heap[idx].get_forwarding_bit() {
+                                    self.cycle_found = true;
+                                    return None;
+                                }
+                            }
+                        }
+
+                        self.heap[last_cell_loc].set_forwarding_bit(true);
+
+                        self.next = self.heap[last_cell_loc].get_value();
+                        self.heap[last_cell_loc].set_value(self.current as u64);
+                        self.current = last_cell_loc;
+
+                        return Some(cell);
+                    }
+                    HeapCellValueTag::Lis => {
+                        let mut cell = self.heap[self.current];
+                        cell.set_value(self.next);
+
+                        let last_cell_loc = match self.traverse_subterm(self.next as usize, 2) {
+                            Some(last_cell_loc) => last_cell_loc,
+                            None => return None,
+                        };
+
+                        if self.cycle_detection_active() {
+                            for idx in (self.next as usize .. last_cell_loc).rev() {
+                                if self.heap[idx].get_forwarding_bit() {
+                                    self.cycle_found = true;
+                                    return None;
+                                }
+                            }
+                        }
+
+                        if (last_cell_loc + 1) as u64 == self.next {
+                            if self.backward() {
+                                return None;
+                            }
+
+                            continue;
+                        } else if last_cell_loc as u64 == self.next {
+                            // car cells of lists are both marked and forwarded.
+                            self.heap[last_cell_loc].set_mark_bit(self.mark_phase);
+                        }
+
+                        self.heap[last_cell_loc].set_forwarding_bit(true);
+
+                        self.next = self.heap[last_cell_loc].get_value();
+                        self.heap[last_cell_loc].set_value(self.current as u64);
+                        self.current = last_cell_loc;
+
+                        return Some(cell);
+                    }
+                    HeapCellValueTag::PStrLoc => {
+                        let h = self.next as usize;
+                        let cell = self.heap[h];
+                        let last_cell_loc = h + 1;
+
+                        if self.heap[last_cell_loc].get_forwarding_bit() {
+                            if self.cycle_detection_active() {
+                                self.cycle_found = true;
+                                return None;
+                            } else if self.backward() {
+                                return None;
+                            }
+
+                            continue;
+                        }
+
+                        self.heap[last_cell_loc].set_forwarding_bit(true);
+
+                        self.next = self.heap[last_cell_loc].get_value();
+                        self.heap[last_cell_loc].set_value(self.current as u64);
+                        self.current = last_cell_loc;
+
+                        return Some(cell);
+                    }
+                    HeapCellValueTag::PStrOffset => {
+                        let h = self.next as usize;
+                        let cell = self.heap[h];
+                        let last_cell_loc = h + 1;
+
+                        if self.heap[h].get_tag() == HeapCellValueTag::PStr {
+                            if self.heap[last_cell_loc].get_forwarding_bit() {
+                                if self.cycle_detection_active() {
+                                    self.cycle_found = true;
+                                    return None;
+                                } else if self.backward() {
+                                    return None;
+                                }
+
+                                continue;
+                            }
+
+                            self.heap[last_cell_loc].set_forwarding_bit(true);
+
+                            self.next = self.heap[last_cell_loc].get_value();
+                            self.heap[last_cell_loc].set_value(self.current as u64);
+                            self.current = last_cell_loc;
+                        } else {
+                            debug_assert!(self.heap[h].get_tag() == HeapCellValueTag::CStr);
+
+                            self.next = self.heap[h].get_value();
+                            self.heap[h].set_value(self.current as u64);
+                            self.current = h;
+                        }
+
+                        return Some(cell);
+                    }
+                    tag @ HeapCellValueTag::Atom => {
+                        let cell = HeapCellValue::build_with(tag, self.next);
+                        let arity = AtomCell::from_bytes(cell.into_bytes()).get_arity();
+
+                        if arity == 0 {
+                            return Some(self.backward_and_return());
+                        } else if self.backward() {
+                            return None;
+                        }
+                    }
+                    HeapCellValueTag::PStr => {
+                        if self.backward() {
+                            return None;
+                        }
+                    }
+                    _ => {
+                        return Some(self.backward_and_return());
+                    }
+                }
+            } else if self.backward() {
+                return None;
+            }
+        }
+    }
+
+    fn pivot_subterm(&mut self) {
+        self.current -= 1;
+
+        let temp = self.heap[self.current + 1].get_value();
+
+        self.heap[self.current + 1].set_value(self.next);
+        self.next = self.heap[self.current].get_value();
+        self.heap[self.current].set_value(temp);
+
+        self.heap[self.current].set_forwarding_bit(true);
+    }
+
+    fn continue_backward(&mut self) -> bool {
+        self.heap[self.current].set_forwarding_bit(false);
+
+        if self.current == self.start {
+            return false;
+        }
+
+        let temp = self.heap[self.current].get_value();
+
+        match self.heap[temp as usize].get_tag() {
+            HeapCellValueTag::Str => {
+                let mut new_str_back_link = self.current;
+
+                for idx in (0 .. self.current).rev() {
+                    if self.heap[idx].get_tag() == HeapCellValueTag::Atom {
+                        if cell_as_atom_cell!(self.heap[idx]).get_arity() > 0 {
+                            new_str_back_link = idx;
+                            break;
+                        }
+                    }
+
+                    if self.heap[idx].get_mark_bit() != self.mark_phase {
+                        if !self.heap[idx].get_forwarding_bit() {
+                            new_str_back_link = idx;
+                            break;
+                        }
+                    }
+                }
+
+                self.heap[self.current].set_mark_bit(self.mark_phase);
+                self.heap[self.current].set_value(self.next);
+
+                let back_link_cell = self.heap[new_str_back_link];
+
+                self.next = back_link_cell.get_value();
+                self.heap[new_str_back_link].set_value(temp);
+                self.current = new_str_back_link;
+
+                read_heap_cell!(back_link_cell,
+                    (HeapCellValueTag::Atom, (_name, arity)) => {
+                        if arity > 0 {
+                            self.heap[self.current].set_mark_bit(self.mark_phase);
+                            return true;
+                        }
+                    }
+                    _ => {}
+                );
+
+                self.heap[self.current].set_forwarding_bit(true);
+                false
+            }
+            HeapCellValueTag::Lis => {
+                if self.heap[self.current].get_mark_bit() == self.mark_phase {
+                    true
+                } else {
+                    self.heap[self.current - 1].set_mark_bit(self.mark_phase);
+                    self.heap[self.current].set_mark_bit(self.mark_phase);
+
+                    if self.heap[self.current - 1].get_forwarding_bit() {
+                        self.heap[self.current].set_value(self.next);
+                        self.next = self.current as u64 - 1;
+                        self.current = temp as usize;
+
+                        true
+                    } else {
+                        self.pivot_subterm();
+                        false
+                    }
+                }
+            }
+            _ => {
+                self.heap[self.current].set_mark_bit(self.mark_phase);
+                true
+            }
+        }
+    }
+
+    fn backward(&mut self) -> bool {
+        while self.continue_backward() {
+            let temp = self.heap[self.current].get_value();
+
+            self.heap[self.current].set_value(self.next);
+            self.next = self.current as u64;
+            self.current = temp as usize;
+        }
+
+        if self.current == self.start {
+            return true;
+        }
+
+        false
+    }
+
+    fn invert_marker(&mut self) {
+        self.cycle_found = false;
+
+        if self.heap[self.start].get_forwarding_bit() {
+            while !self.backward() {}
+        }
+
+        self.mark_phase = false;
+        self.heap[self.start].set_forwarding_bit(true);
+
+        self.next = self.heap[self.start].get_value();
+        self.current = self.start;
+
+        while let Some(_) = self.forward() {}
+    }
+}
+
+impl<'a, const STOP_AT_CYCLES: bool> Iterator for CycleDetectingIter<'a, STOP_AT_CYCLES> {
+    type Item = HeapCellValue;
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        self.forward()
+    }
+}
+
+
+impl<'a, const STOP_AT_CYCLES: bool> Drop for CycleDetectingIter<'a, STOP_AT_CYCLES> {
+    fn drop(&mut self) {
+        self.invert_marker();
+
+        if self.current == self.start {
+            return;
+        }
+
+        while !self.backward() {}
+    }
+}

src/machine/disjuncts.rs

@@ -74,7 +74,7 @@ impl BranchNumber {
     fn halve_delta(&self) -> BranchNumber {
         BranchNumber {
             branch_num: self.branch_num.clone(),
-            delta : &self.delta / Rational::from(2),
+            delta: &self.delta / Rational::from(2),
         }
     }
 }
@@ -108,7 +108,10 @@ pub struct BranchInfo {
 
 impl BranchInfo {
     fn new(branch_num: BranchNumber) -> Self {
-        Self { branch_num, chunks: vec![] }
+        Self {
+            branch_num,
+            chunks: vec![],
+        }
     }
 }
 
@@ -149,11 +152,14 @@ enum TraversalState {
     // where it leaves off.
     BuildFinalDisjunct(usize),
     Fail,
-    GetCutPoint{ var_num: usize, prev_b: bool },
+    GetCutPoint { var_num: usize, prev_b: bool },
     Cut { var_num: usize, is_global: bool },
+    CutPrev(usize),
     ResetCallPolicy(CallPolicy),
     Term(Term),
-    RemoveBranchNum, // pop the current_branch_num and from the root set.
+    OverrideGlobalCutVar(usize),
+    ResetGlobalCutVarOverride(Option<usize>),
+    RemoveBranchNum,            // pop the current_branch_num and from the root set.
     AddBranchNum(BranchNumber), // set current_branch_num, add it to the root set
     RepBranchNum(BranchNumber), // replace current_branch_num and the latest in the root set
 }
@@ -168,6 +174,7 @@ pub struct VariableClassifier {
     var_num: usize,
     root_set: RootSet,
     global_cut_var_num: Option<usize>,
+    global_cut_var_num_override: Option<usize>,
 }
 
 #[derive(Debug, Default)]
@@ -179,22 +186,22 @@ pub struct VarData {
 
 impl VarData {
     fn emit_initial_get_level(&mut self, build_stack: &mut ChunkedTermVec) {
-        let global_cut_var_num =
-            if let &Some(global_cut_var_num) = &self.global_cut_var_num {
-                match &self.records[global_cut_var_num].allocation {
-                    VarAlloc::Perm(..) => Some(global_cut_var_num),
-                    VarAlloc::Temp { term_loc, .. } if term_loc.chunk_num() > 0 => {
-                        Some(global_cut_var_num)
-                    }
-                    _ => None
+        let global_cut_var_num = if let &Some(global_cut_var_num) = &self.global_cut_var_num {
+            match &self.records[global_cut_var_num].allocation {
+                VarAlloc::Perm(..) => Some(global_cut_var_num),
+                VarAlloc::Temp { term_loc, .. } if term_loc.chunk_num() > 0 => {
+                    Some(global_cut_var_num)
                 }
-            } else {
-                None
-            };
+                _ => None,
+            }
+        } else {
+            None
+        };
 
         if let Some(global_cut_var_num) = global_cut_var_num {
             let term = QueryTerm::GetLevel(global_cut_var_num);
-            self.records[global_cut_var_num].allocation = VarAlloc::Perm(0, PermVarAllocation::Pending);
+            self.records[global_cut_var_num].allocation =
+                VarAlloc::Perm(0, PermVarAllocation::Pending);
 
             match build_stack.front_mut() {
                 Some(ChunkedTerms::Branch(_)) => {
@@ -229,7 +236,7 @@ fn merge_branch_seq(branches: impl Iterator<Item = BranchInfo>) -> BranchInfo {
 }
 
 fn flatten_into_disjunct(build_stack: &mut ChunkedTermVec, preceding_len: usize) {
-    let branch_vec = build_stack.drain(preceding_len + 1 ..).collect();
+    let branch_vec = build_stack.drain(preceding_len + 1..).collect();
 
     if let ChunkedTerms::Branch(ref mut disjuncts) = &mut build_stack[preceding_len] {
         disjuncts.push(branch_vec);
@@ -249,16 +256,20 @@ impl VariableClassifier {
             root_set: RootSet::new(),
             var_num: 0,
             global_cut_var_num: None,
+            global_cut_var_num_override: None,
         }
     }
 
     pub fn classify_fact(mut self, term: Term) -> Result<ClassifyFactResult, CompilationError> {
         self.classify_head_variables(&term)?;
-        Ok((term, self.branch_map.separate_and_classify_variables(
-            self.var_num,
-            self.global_cut_var_num,
-            self.current_chunk_num,
-        )))
+        Ok((
+            term,
+            self.branch_map.separate_and_classify_variables(
+                self.var_num,
+                self.global_cut_var_num,
+                self.current_chunk_num,
+            ),
+        ))
     }
 
     pub fn classify_rule<'a, LS: LoadState<'a>>(
@@ -298,7 +309,7 @@ impl VariableClassifier {
                     }
                 }
 
-                let iter = old_branches.drain(old_branches_len - 1 ..);
+                let iter = old_branches.drain(old_branches_len - 1..);
                 branches.push(merge_branch_seq(iter));
             }
 
@@ -346,9 +357,13 @@ impl VariableClassifier {
     }
 
     fn probe_body_var(&mut self, var_info: VarInfo) {
-        let term_loc = self.current_chunk_type.to_gen_context(self.current_chunk_num);
+        let term_loc = self
+            .current_chunk_type
+            .to_gen_context(self.current_chunk_num);
 
-        let branch_info_v = self.branch_map.entry(var_info.var_ptr.clone())
+        let branch_info_v = self
+            .branch_map
+            .entry(var_info.var_ptr.clone())
             .or_insert_with(|| vec![]);
 
         let needs_new_branch = if let Some(last_bi) = branch_info_v.last() {
@@ -396,12 +411,14 @@ impl VariableClassifier {
 
     fn classify_head_variables(&mut self, term: &Term) -> Result<(), CompilationError> {
         match term {
-            Term::Clause(..) | Term::Literal(_, Literal::Atom(_)) => {
-            }
+            Term::Clause(..) | Term::Literal(_, Literal::Atom(_)) => {}
             _ => return Err(CompilationError::InvalidRuleHead),
         }
 
-        let mut classify_info = ClassifyInfo { arg_c: 1, arity: term.arity() };
+        let mut classify_info = ClassifyInfo {
+            arg_c: 1,
+            arity: term.arity(),
+        };
 
         match term {
             Term::Clause(_, _, terms) => {
@@ -414,13 +431,16 @@ impl VariableClassifier {
                             // the body of the if let here is an inlined
                             // "probe_head_var". note the difference between it
                             // and "probe_body_var".
-                            let branch_info_v = self.branch_map.entry(var_ptr.clone())
+                            let branch_info_v = self
+                                .branch_map
+                                .entry(var_ptr.clone())
                                 .or_insert_with(|| vec![]);
 
                             let needs_new_branch = branch_info_v.is_empty();
 
                             if needs_new_branch {
-                                branch_info_v.push(BranchInfo::new(self.current_branch_num.clone()));
+                                branch_info_v
+                                    .push(BranchInfo::new(self.current_branch_num.clone()));
                             }
 
                             let branch_info = branch_info_v.last_mut().unwrap();
@@ -502,6 +522,12 @@ impl VariableClassifier {
                     self.probe_in_situ_var(var_num);
                     build_stack.push_chunk_term(QueryTerm::GetCutPoint { var_num, prev_b });
                 }
+                TraversalState::OverrideGlobalCutVar(var_num) => {
+                    self.global_cut_var_num_override = Some(var_num);
+                }
+                TraversalState::ResetGlobalCutVarOverride(old_override) => {
+                    self.global_cut_var_num_override = old_override;
+                }
                 TraversalState::Cut { var_num, is_global } => {
                     if self.try_set_chunk_at_inlined_boundary() {
                         build_stack.add_chunk();
@@ -509,13 +535,20 @@ impl VariableClassifier {
 
                     self.probe_in_situ_var(var_num);
 
-                    build_stack.push_chunk_term(
-                        if is_global {
-                            QueryTerm::GlobalCut(var_num)
-                        } else {
-                            QueryTerm::LocalCut(var_num)
-                        }
-                    );
+                    build_stack.push_chunk_term(if is_global {
+                        QueryTerm::GlobalCut(var_num)
+                    } else {
+                        QueryTerm::LocalCut { var_num, cut_prev: false }
+                    });
+                }
+                TraversalState::CutPrev(var_num) => {
+                    if self.try_set_chunk_at_inlined_boundary() {
+                        build_stack.add_chunk();
+                    }
+
+                    self.probe_in_situ_var(var_num);
+
+                    build_stack.push_chunk_term(QueryTerm::LocalCut { var_num, cut_prev: true });
                 }
                 TraversalState::Fail => {
                     build_stack.push_chunk_term(QueryTerm::Fail);
@@ -539,22 +572,28 @@ impl VariableClassifier {
                             classifier.probe_body_term(arg_c + 1, terms.len(), term);
                         }
 
-                        build_stack.push_chunk_term(
-                            clause_to_query_term(
-                                loader,
-                                name,
-                                terms,
-                                classifier.call_policy,
-                            ),
-                        );
+                        build_stack.push_chunk_term(clause_to_query_term(
+                            loader,
+                            name,
+                            terms,
+                            classifier.call_policy,
+                        ));
                     };
 
                     match term {
-                        Term::Clause(_, name @ (atom!("->") | atom!(";") | atom!(",")), mut terms) if terms.len() == 3 => {
+                        Term::Clause(
+                            _,
+                            name @ (atom!("->") | atom!(";") | atom!(",")),
+                            mut terms,
+                        ) if terms.len() == 3 => {
                             if let Some(last_arg) = terms.last() {
                                 if let Term::Literal(_, Literal::CodeIndex(_)) = last_arg {
                                     terms.pop();
-                                    state_stack.push(TraversalState::Term(Term::Clause(Cell::default(), name, terms)));
+                                    state_stack.push(TraversalState::Term(Term::Clause(
+                                        Cell::default(),
+                                        name,
+                                        terms,
+                                    )));
                                 } else {
                                     add_chunk(self, name, terms);
                                 }
@@ -583,7 +622,7 @@ impl VariableClassifier {
 
                             let mut branch_numbers = vec![first_branch_num];
 
-                            for idx in 1 .. branches.len() {
+                            for idx in 1..branches.len() {
                                 let succ_branch_number = branch_numbers[idx - 1].incr_by_delta();
 
                                 branch_numbers.push(if idx + 1 < branches.len() {
@@ -610,8 +649,11 @@ impl VariableClassifier {
                                 state_stack.push(TraversalState::AddBranchNum(branch_num));
                             }
 
-                            if let TraversalState::BuildDisjunct(build_stack_len) = state_stack[final_disjunct_loc] {
-                                state_stack[final_disjunct_loc] = TraversalState::BuildFinalDisjunct(build_stack_len);
+                            if let TraversalState::BuildDisjunct(build_stack_len) =
+                                state_stack[final_disjunct_loc]
+                            {
+                                state_stack[final_disjunct_loc] =
+                                    TraversalState::BuildFinalDisjunct(build_stack_len);
                             }
 
                             self.current_chunk_type = ChunkType::Mid;
@@ -621,18 +663,30 @@ impl VariableClassifier {
                             let then_term = terms.pop().unwrap();
                             let if_term = terms.pop().unwrap();
 
-                            let prev_b = if matches!(state_stack.last(), Some(TraversalState::RemoveBranchNum)) {
+                            let prev_b = if matches!(
+                                state_stack.last(),
+                                Some(TraversalState::RemoveBranchNum)
+                            ) {
                                 // check if the second-to-last element is a regular BuildDisjunct, as we don't
                                 // want to add GetPrevLevel in case of a TrustMe.
-                                matches!(state_stack.iter().rev().nth(1), Some(TraversalState::BuildDisjunct(..)))
+                                matches!(
+                                    state_stack.iter().rev().nth(1),
+                                    Some(TraversalState::BuildDisjunct(..))
+                                )
                             } else {
                                 false
                             };
 
                             state_stack.push(TraversalState::Term(then_term));
-                            state_stack.push(TraversalState::Cut { var_num: self.var_num, is_global: false });
+                            state_stack.push(TraversalState::Cut {
+                                var_num: self.var_num,
+                                is_global: false,
+                            });
                             state_stack.push(TraversalState::Term(if_term));
-                            state_stack.push(TraversalState::GetCutPoint { var_num: self.var_num, prev_b });
+                            state_stack.push(TraversalState::GetCutPoint {
+                                var_num: self.var_num,
+                                prev_b,
+                            });
 
                             self.var_num += 1;
                         }
@@ -643,12 +697,21 @@ impl VariableClassifier {
                             build_stack.reserve_branch(2);
 
                             state_stack.push(TraversalState::BuildFinalDisjunct(build_stack_len));
-                            state_stack.push(TraversalState::Term(Term::Clause(Cell::default(), atom!("$succeed"), vec![])));
+                            state_stack.push(TraversalState::Term(Term::Clause(
+                                Cell::default(),
+                                atom!("$succeed"),
+                                vec![],
+                            )));
                             state_stack.push(TraversalState::BuildDisjunct(build_stack_len));
                             state_stack.push(TraversalState::Fail);
-                            state_stack.push(TraversalState::Cut { var_num: self.var_num, is_global: false });
+                            state_stack.push(TraversalState::CutPrev(self.var_num));
+                            state_stack.push(TraversalState::ResetGlobalCutVarOverride(self.global_cut_var_num_override));
                             state_stack.push(TraversalState::Term(not_term));
-                            state_stack.push(TraversalState::GetCutPoint { var_num: self.var_num, prev_b: true });
+                            state_stack.push(TraversalState::OverrideGlobalCutVar(self.var_num));
+                            state_stack.push(TraversalState::GetCutPoint {
+                                var_num: self.var_num,
+                                prev_b: false,
+                            });
 
                             self.current_chunk_type = ChunkType::Mid;
                             self.current_chunk_num += 1;
@@ -668,15 +731,13 @@ impl VariableClassifier {
                                         build_stack.add_chunk();
                                     }
 
-                                    build_stack.push_chunk_term(
-                                        qualified_clause_to_query_term(
-                                            loader,
-                                            module_name,
-                                            predicate_name,
-                                            vec![],
-                                            self.call_policy,
-                                        ),
-                                    );
+                                    build_stack.push_chunk_term(qualified_clause_to_query_term(
+                                        loader,
+                                        module_name,
+                                        predicate_name,
+                                        vec![],
+                                        self.call_policy,
+                                    ));
                                 }
                                 (
                                     Term::Literal(_, Literal::Atom(module_name)),
@@ -690,15 +751,13 @@ impl VariableClassifier {
                                         self.probe_body_term(arg_c + 1, terms.len(), term);
                                     }
 
-                                    build_stack.push_chunk_term(
-                                        qualified_clause_to_query_term(
-                                            loader,
-                                            module_name,
-                                            name,
-                                            terms,
-                                            self.call_policy,
-                                        ),
-                                    );
+                                    build_stack.push_chunk_term(qualified_clause_to_query_term(
+                                        loader,
+                                        module_name,
+                                        name,
+                                        terms,
+                                        self.call_policy,
+                                    ));
                                 }
                                 (module_name, predicate_name) => {
                                     if update_chunk_data(self, atom!("call"), 2) {
@@ -711,18 +770,18 @@ impl VariableClassifier {
                                     terms.push(module_name);
                                     terms.push(predicate_name);
 
-                                    build_stack.push_chunk_term(
-                                        clause_to_query_term(
-                                            loader,
-                                            atom!("call"),
-                                            vec![Term::Clause(Cell::default(), atom!(":"), terms)],
-                                            self.call_policy,
-                                        ),
-                                    );
+                                    build_stack.push_chunk_term(clause_to_query_term(
+                                        loader,
+                                        atom!("call"),
+                                        vec![Term::Clause(Cell::default(), atom!(":"), terms)],
+                                        self.call_policy,
+                                    ));
                                 }
                             }
                         }
-                        Term::Clause(_, atom!("$call_with_inference_counting"), mut terms) if terms.len() == 1 => {
+                        Term::Clause(_, atom!("$call_with_inference_counting"), mut terms)
+                            if terms.len() == 1 =>
+                        {
                             state_stack.push(TraversalState::ResetCallPolicy(self.call_policy));
                             state_stack.push(TraversalState::Term(terms.pop().unwrap()));
 
@@ -738,41 +797,43 @@ impl VariableClassifier {
 
                             self.probe_body_term(1, 1, &var);
 
-                            build_stack.push_chunk_term(
-                                clause_to_query_term(
-                                    loader,
-                                    atom!("call"),
-                                    vec![var],
-                                    self.call_policy,
-                                ),
-                            );
+                            build_stack.push_chunk_term(clause_to_query_term(
+                                loader,
+                                atom!("call"),
+                                vec![var],
+                                self.call_policy,
+                            ));
                         }
                         Term::Literal(_, Literal::Atom(atom!("!")) | Literal::Char('!')) => {
-                            if self.global_cut_var_num.is_none() {
-                                self.global_cut_var_num = Some(self.var_num);
-                                self.var_num += 1;
-                            }
+                            let (var_num, is_global) =
+                                if let Some(var_num) = self.global_cut_var_num_override {
+                                    (var_num, false)
+                                } else if let Some(var_num) = self.global_cut_var_num {
+                                    (var_num, true)
+                                } else {
+                                    let var_num = self.var_num;
 
-                            self.probe_in_situ_var(self.global_cut_var_num.unwrap());
+                                    self.global_cut_var_num = Some(var_num);
+                                    self.var_num += 1;
 
-                            state_stack.push(TraversalState::Cut {
-                                var_num: self.global_cut_var_num.unwrap(),
-                                is_global: true,
-                            });
+                                    (var_num, true)
+                                };
+
+                            self.probe_in_situ_var(var_num);
+
+                            state_stack.push(TraversalState::Cut { var_num, is_global });
                         }
                         Term::Literal(_, Literal::Atom(name)) => {
                             if update_chunk_data(self, name, 0) {
                                 build_stack.add_chunk();
                             }
 
-                            build_stack.push_chunk_term(
-                                clause_to_query_term(
-                                    loader,
-                                    name,
-                                    vec![],
-                                    self.call_policy,
-                                ),
-                            );
+                            build_stack.push_chunk_term(clause_to_query_term(
+                                loader,
+                                name,
+                                vec![],
+                                self.call_policy,
+                            ));
                         }
                         _ => {
                             return Err(CompilationError::InadmissibleQueryTerm);
@@ -800,12 +861,11 @@ impl BranchMap {
         };
 
         for (var, branches) in self.iter_mut() {
-            let (mut var_num, var_num_incr) =
-                if let Var::InSitu(var_num) = *var.borrow() {
-                    (var_num, false)
-                } else {
-                    (var_data.records.len(), true)
-                };
+            let (mut var_num, var_num_incr) = if let Var::InSitu(var_num) = *var.borrow() {
+                (var_num, false)
+            } else {
+                (var_data.records.len(), true)
+            };
 
             for branch in branches.iter_mut() {
                 if var_num_incr {
@@ -813,7 +873,8 @@ impl BranchMap {
                     var_data.records.push(VariableRecord::default());
                 }
 
-                if branch.chunks.len() <= 1 { // true iff var is a temporary variable.
+                if branch.chunks.len() <= 1 {
+                    // true iff var is a temporary variable.
                     debug_assert_eq!(branch.chunks.len(), 1);
 
                     let chunk = &mut branch.chunks[0];
@@ -822,7 +883,9 @@ impl BranchMap {
                     for var_info in chunk.vars.iter_mut() {
                         if var_info.lvl == Level::Shallow {
                             let term_loc = var_info.chunk_type.to_gen_context(chunk.chunk_num);
-                            temp_var_data.use_set.insert((term_loc, var_info.classify_info.arg_c));
+                            temp_var_data
+                                .use_set
+                                .insert((term_loc, var_info.classify_info.arg_c));
                         }
                     }
 

src/machine/heap.rs

@@ -130,11 +130,7 @@ pub fn print_heap_terms<'a, I: Iterator<Item = &'a HeapCellValue>>(heap: I, h: u
 }
 
 #[inline]
-pub(crate) fn put_complete_string(
-    heap: &mut Heap,
-    s: &str,
-    atom_tbl: &mut AtomTable,
-) -> HeapCellValue {
+pub(crate) fn put_complete_string(heap: &mut Heap, s: &str, atom_tbl: &AtomTable) -> HeapCellValue {
     match allocate_pstr(heap, s, atom_tbl) {
         Some(h) => {
             heap.pop(); // pop the trailing variable cell from the heap planted by allocate_pstr.
@@ -157,11 +153,7 @@ pub(crate) fn put_complete_string(
 }
 
 #[inline]
-pub(crate) fn put_partial_string(
-    heap: &mut Heap,
-    s: &str,
-    atom_tbl: &mut AtomTable,
-) -> HeapCellValue {
+pub(crate) fn put_partial_string(heap: &mut Heap, s: &str, atom_tbl: &AtomTable) -> HeapCellValue {
     match allocate_pstr(heap, s, atom_tbl) {
         Some(h) => {
             pstr_loc_as_cell!(h)
@@ -173,11 +165,7 @@ pub(crate) fn put_partial_string(
 }
 
 #[inline]
-pub(crate) fn allocate_pstr(
-    heap: &mut Heap,
-    mut src: &str,
-    atom_tbl: &mut AtomTable,
-) -> Option<usize> {
+pub(crate) fn allocate_pstr(heap: &mut Heap, mut src: &str, atom_tbl: &AtomTable) -> Option<usize> {
     let orig_h = heap.len();
 
     loop {
@@ -258,7 +246,10 @@ pub(crate) fn to_local_code_ptr(heap: &Heap, addr: HeapCellValue) -> Option<usiz
     let extract_integer = |s: usize| -> Option<usize> {
         match Number::try_from(heap[s]) {
             Ok(Number::Fixnum(n)) => usize::try_from(n.get_num()).ok(),
-            Ok(Number::Integer(n)) => n.to_usize(),
+            Ok(Number::Integer(n)) => {
+                let value: usize = (&*n).try_into().unwrap();
+                Some(value)
+            },
             _ => None,
         }
     };

src/machine/lib_machine.rs

@@ -0,0 +1,484 @@
+use std::collections::BTreeMap;
+use std::sync::Arc;
+
+use crate::atom_table;
+use crate::heap_print::{HCPrinter, HCValueOutputter, PrinterOutputter};
+use crate::machine::{BREAK_FROM_DISPATCH_LOOP_LOC, LIB_QUERY_SUCCESS};
+use crate::machine::mock_wam::CompositeOpDir;
+use crate::parser::parser::{Parser, Tokens};
+use crate::read::write_term_to_heap;
+use crate::machine::machine_indices::VarKey;
+use crate::parser::ast::{Var, VarPtr};
+use indexmap::IndexMap;
+
+use super::{
+    Machine, MachineConfig, QueryResult, QueryResolutionLine,
+    Atom, AtomCell, HeapCellValue, HeapCellValueTag, Value, QueryResolution,
+    streams::Stream
+};
+
+impl Machine {
+    pub fn new_lib() -> Self {
+        Machine::new(MachineConfig::in_memory())
+    }
+
+    pub fn load_module_string(&mut self, module_name: &str, program: String) {
+        let stream = Stream::from_owned_string(program, &mut self.machine_st.arena);
+        self.load_file(module_name, stream);
+    }
+
+    pub fn consult_module_string(&mut self, module_name: &str, program: String) {
+        let stream = Stream::from_owned_string(program, &mut self.machine_st.arena);
+        self.machine_st.registers[1] = stream_as_cell!(stream);
+        self.machine_st.registers[2] = atom_as_cell!(&atom_table::AtomTable::build_with(&self.machine_st.atom_tbl, module_name));
+
+        self.run_module_predicate(atom!("loader"), (atom!("consult_stream"), 2));
+    }
+
+    fn allocate_stub_choice_point(&mut self) {
+        // NOTE: create a choice point to terminate the dispatch_loop
+        // if an exception is thrown. since the and/or stack is presumed empty,
+
+        let stub_b = self.machine_st.stack.allocate_or_frame(0);
+        let or_frame = self.machine_st.stack.index_or_frame_mut(0);
+
+        or_frame.prelude.num_cells = 0;
+        or_frame.prelude.e = 0;
+        or_frame.prelude.cp = 0;
+        or_frame.prelude.b = 0;
+        or_frame.prelude.bp = BREAK_FROM_DISPATCH_LOOP_LOC;
+        or_frame.prelude.boip = 0;
+        or_frame.prelude.biip = 0;
+        or_frame.prelude.tr = 0;
+        or_frame.prelude.h = 0;
+        or_frame.prelude.b0 = 0;
+        or_frame.prelude.attr_var_queue_len = 0;
+
+        self.machine_st.b = stub_b;
+    }
+
+    pub fn run_query(&mut self, query: String) -> QueryResult {
+        println!("Query: {}", query);
+        // Parse the query so we can analyze and then call the term
+        let mut parser = Parser::new(
+            Stream::from_owned_string(query, &mut self.machine_st.arena),
+            &mut self.machine_st
+        );
+        let op_dir = CompositeOpDir::new(&self.indices.op_dir, None);
+        let term = parser.read_term(&op_dir, Tokens::Default).expect("Failed to parse query");
+
+        // Write parsed term to heap
+        let term_write_result = write_term_to_heap(&term, &mut self.machine_st.heap, &mut self.machine_st.atom_tbl).expect("couldn't write term to heap");
+
+        // Write term to heap
+        self.machine_st.registers[1] = self.machine_st.heap[term_write_result.heap_loc];
+
+        self.machine_st.cp = LIB_QUERY_SUCCESS; // BREAK_FROM_DISPATCH_LOOP_LOC;
+        self.machine_st.p = self.indices.code_dir.get(&(atom!("call"), 1)).expect("couldn't get code index").local().unwrap();
+
+        let var_names: IndexMap<_, _> = term_write_result.var_dict.iter()
+            .map(|(var_key, cell)| match var_key {
+                // NOTE: not the intention behind Var::InSitu here but
+                // we can hijack it to store anonymous variables
+                // without creating problems.
+                VarKey::AnonVar(h) => (*cell, VarPtr::from(Var::InSitu(*h))),
+                VarKey::VarPtr(var_ptr) => (*cell, var_ptr.clone()),
+            })
+            .collect();
+
+        self.allocate_stub_choice_point();
+
+        let stub_b = self.machine_st.b;
+
+        let mut matches: Vec<QueryResolutionLine> = Vec::new();
+        // Call the term
+        loop {
+            self.dispatch_loop();
+
+            //println!("b: {}", self.machine_st.b);
+            //println!("stub_b: {}", stub_b);
+            //println!("fail: {}", self.machine_st.fail);
+
+            if self.machine_st.ball.stub.len() != 0 {
+                // NOTE: this means an exception was thrown, at which
+                // point we backtracked to the stub choice point.
+                // this should halt the search for solutions as it
+                // does in the Scryer top-level. the exception term is
+                // contained in self.machine_st.ball.
+                let error_string = self.machine_st.ball.stub
+                    .iter()
+                    .filter(|h| match h.get_tag() {
+                        HeapCellValueTag::Atom => true,
+                        HeapCellValueTag::Fixnum => true,
+                        _ => false,
+                    })
+                    .map(|h| match h.get_tag() {
+                        HeapCellValueTag::Atom => {
+                            let (name, _) = cell_as_atom_cell!(h).get_name_and_arity();
+                            name.as_str().to_string()
+                        }
+                        HeapCellValueTag::Fixnum => {
+                            h.get_value().clone().to_string()
+                        },
+                        _ => unreachable!(),
+                    })
+                    .collect::<Vec<String>>()
+                    .join(" ");
+
+                return Err(error_string);
+            }
+
+            /*
+            if self.machine_st.fail {
+                // NOTE: only print results on success
+                self.machine_st.fail = false;
+                println!("fail!");
+                matches.push(QueryResolutionLine::False);
+                break;
+            };
+            */
+
+            if term_write_result.var_dict.is_empty() {
+                if self.machine_st.p == LIB_QUERY_SUCCESS {
+                    matches.push(QueryResolutionLine::True);
+                    break;
+                } else if self.machine_st.p == BREAK_FROM_DISPATCH_LOOP_LOC {
+                    // NOTE: only print results on success
+                    // self.machine_st.fail = false;
+                    // println!("b == stub_b");
+                    matches.push(QueryResolutionLine::False);
+                    break;
+                }
+            }
+
+            let mut bindings: BTreeMap<String, Value> = BTreeMap::new();
+
+            for (var_key, term_to_be_printed) in &term_write_result.var_dict {
+                if var_key.to_string().starts_with("_") {
+                    continue;
+                }
+                let mut printer = HCPrinter::new(
+                    &mut self.machine_st.heap,
+                    Arc::clone(&self.machine_st.atom_tbl),
+                    &mut self.machine_st.stack,
+                    &self.indices.op_dir,
+                    PrinterOutputter::new(),
+                    *term_to_be_printed,
+                );
+
+                printer.ignore_ops = false;
+                printer.numbervars = true;
+                printer.quoted = true;
+                printer.max_depth = 1000; // NOTE: set this to 0 for unbounded depth
+                printer.double_quotes = true;
+                printer.var_names = var_names.clone();
+
+                let outputter = printer.print();
+
+                let output: String = outputter.result();
+                println!("Result: {} = {}", var_key.to_string(), output);
+
+                bindings.insert(var_key.to_string(), Value::try_from(output).expect("asdfs"));
+            }
+
+            matches.push(QueryResolutionLine::Match(bindings));
+
+            // NOTE: there are outstanding choicepoints, backtrack
+            // through them for further solutions. if
+            // self.machine_st.b == stub_b we've backtracked to the stub
+            // choice point, so we should break.
+            self.machine_st.backtrack();
+
+            if self.machine_st.b <= stub_b {
+                // NOTE: out of choicepoints to backtrack through, no
+                // more solutions to gather.
+                break;
+            }
+        }
+
+        // NOTE: deallocate stub choice point
+        if self.machine_st.b == stub_b {
+            self.trust_me();
+        }
+
+        Ok(QueryResolution::from(matches))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use ordered_float::OrderedFloat;
+
+    use super::*;
+    use crate::machine::{QueryMatch, Value, QueryResolution};
+
+    #[test]
+    fn programatic_query() {
+        let mut machine = Machine::new_lib();
+
+        machine.load_module_string(
+            "facts",
+            String::from(
+                r#"
+            triple("a", "p1", "b").
+            triple("a", "p2", "b").
+        "#,
+            ),
+        );
+
+        let query = String::from(r#"triple("a",P,"b")."#);
+        let output = machine.run_query(query);
+        assert_eq!(
+            output,
+            Ok(QueryResolution::Matches(vec![
+                QueryMatch::from(btreemap! {
+                    "P" => Value::from("p1"),
+                }),
+                QueryMatch::from(btreemap! {
+                    "P" => Value::from("p2"),
+                }),
+            ]))
+        );
+
+        assert_eq!(
+            machine.run_query(String::from(r#"triple("a","p1","b")."#)),
+            Ok(QueryResolution::True)
+        );
+
+        assert_eq!(
+            machine.run_query(String::from(r#"triple("x","y","z")."#)),
+            Ok(QueryResolution::False)
+        );
+    }
+
+    #[test]
+    fn failing_query() {
+        let mut machine = Machine::new_lib();
+        let query = String::from(r#"triple("a",P,"b")."#);
+        let output = machine.run_query(query);
+        assert_eq!(
+            output,
+            Err(String::from("error existence_error procedure / triple 3 / triple 3"))
+        );
+    }
+
+    #[test]
+    fn complex_results() {
+        let mut machine = Machine::new_lib();
+        machine.load_module_string(
+            "facts",
+                r#"
+                :- discontiguous(subject_class/2).
+                :- discontiguous(constructor/2).
+
+                subject_class("Todo", c).
+                constructor(c, '[{action: "addLink", source: "this", predicate: "todo://state", target: "todo://ready"}]').
+
+                subject_class("Recipe", xyz).
+                constructor(xyz, '[{action: "addLink", source: "this", predicate: "recipe://title", target: "literal://string:Meta%20Muffins"}]').
+            "#.to_string());
+
+        let result = machine.run_query(String::from("subject_class(\"Todo\", C), constructor(C, Actions)."));
+        assert_eq!(
+            result,
+            Ok(QueryResolution::Matches(vec![
+                QueryMatch::from(btreemap! {
+                    "C" => Value::from("c"),
+                    "Actions" => Value::from("[{action: \"addLink\", source: \"this\", predicate: \"todo://state\", target: \"todo://ready\"}]"),
+                }),
+            ]))
+        );
+
+        let result = machine.run_query(String::from("subject_class(\"Recipe\", C), constructor(C, Actions)."));
+        assert_eq!(
+            result,
+            Ok(QueryResolution::Matches(vec![
+                QueryMatch::from(btreemap! {
+                    "C" => Value::from("xyz"),
+                    "Actions" => Value::from("[{action: \"addLink\", source: \"this\", predicate: \"recipe://title\", target: \"literal://string:Meta%20Muffins\"}]"),
+                }),
+            ]))
+        );
+
+        let result = machine.run_query(String::from("subject_class(Class, _)."));
+        assert_eq!(
+            result,
+            Ok(QueryResolution::Matches(vec![
+                QueryMatch::from(btreemap! {
+                    "Class" => Value::from("Todo")
+                }),
+                QueryMatch::from(btreemap! {
+                    "Class" => Value::from("Recipe")
+                }),
+            ]))
+        );
+    }
+
+    #[test]
+    fn list_results() {
+        let mut machine = Machine::new_lib();
+        machine.load_module_string(
+            "facts",
+                r#"
+                list([1,2,3]).
+            "#.to_string());
+
+        let result = machine.run_query(String::from("list(X)."));
+        assert_eq!(
+            result,
+            Ok(QueryResolution::Matches(vec![
+                QueryMatch::from(btreemap! {
+                    "X" => Value::List(
+                        Vec::from([
+                            Value::Float(OrderedFloat::from(1.0)),
+                            Value::Float(OrderedFloat::from(2.0)),
+                            Value::Float(OrderedFloat::from(3.0))
+                        ])
+                    )
+                }),
+            ]))
+        );
+    }
+
+
+    #[test]
+    fn consult() {
+        let mut machine = Machine::new_lib();
+
+        machine.consult_module_string(
+            "facts",
+            String::from(
+                r#"
+            triple("a", "p1", "b").
+            triple("a", "p2", "b").
+        "#,
+            ),
+        );
+
+        let query = String::from(r#"triple("a",P,"b")."#);
+        let output = machine.run_query(query);
+        assert_eq!(
+            output,
+            Ok(QueryResolution::Matches(vec![
+                QueryMatch::from(btreemap! {
+                    "P" => Value::from("p1"),
+                }),
+                QueryMatch::from(btreemap! {
+                    "P" => Value::from("p2"),
+                }),
+            ]))
+        );
+
+        assert_eq!(
+            machine.run_query(String::from(r#"triple("a","p1","b")."#)),
+            Ok(QueryResolution::True)
+        );
+
+        assert_eq!(
+            machine.run_query(String::from(r#"triple("x","y","z")."#)),
+            Ok(QueryResolution::False)
+        );
+
+        machine.consult_module_string(
+            "facts",
+            String::from(
+                r#"
+            triple("a", "new", "b").
+        "#,
+            ),
+        );
+
+        assert_eq!(
+            machine.run_query(String::from(r#"triple("a","p1","b")."#)),
+            Ok(QueryResolution::False)
+        );
+
+        assert_eq!(
+            machine.run_query(String::from(r#"triple("a","new","b")."#)),
+            Ok(QueryResolution::True)
+        );
+
+    }
+
+    #[ignore = "fails on windows"]
+    #[test]
+    fn stress_integration_test() {
+        let mut machine = Machine::new_lib();
+
+        // File with test commands, i.e. program code to consult and queries to run
+        let code = include_str!("./lib_integration_test_commands.txt");
+
+        // Split the code into blocks
+        let blocks = code.split("=====");
+
+        let mut i = 0;
+        // Iterate over the blocks
+        for block in blocks {
+            // Trim the block to remove any leading or trailing whitespace
+            let block = block.trim();
+
+            // Skip empty blocks
+            if block.is_empty() {
+                continue;
+            }
+
+            // Check if the block is a query
+            if block.starts_with("query") {
+                // Extract the query from the block
+                let query = &block[5..];
+
+                i += 1;
+                println!("query #{}: {}", i, query);
+                // Parse and execute the query
+                let result = machine.run_query(query.to_string());
+
+                assert!(result.is_ok());
+
+                // Print the result
+                println!("{:?}", result);
+            } else if block.starts_with("consult") {
+                // Extract the code from the block
+                let code = &block[7..];
+
+                println!("load code: {}", code);
+
+                // Load the code into the machine
+                machine.consult_module_string("facts", code.to_string());
+            }
+        }
+    }
+
+    #[test]
+    fn findall() {
+        let mut machine = Machine::new_lib();
+
+        machine.consult_module_string(
+            "facts",
+            String::from(
+                r#"
+            triple("a", "p1", "b").
+            triple("a", "p2", "b").
+        "#,
+            ),
+        );
+
+        let query = String::from(r#"findall([Predicate, Target], triple(_,Predicate,Target), Result)."#);
+        let output = machine.run_query(query);
+        assert_eq!(
+            output,
+            Ok(QueryResolution::Matches(vec![
+                QueryMatch::from(btreemap! {
+                    "Predicate" => Value::from("Predicate"),
+                    "Result" => Value::List(
+                        Vec::from([
+                            Value::List([Value::from("p1"), Value::from("b")].into()),
+                            Value::List([Value::from("p2"), Value::from("b")].into()),
+                        ])
+                    ),
+                    "Target" => Value::from("Target"),
+                }),
+            ]))
+        );
+
+    }
+}

src/machine/load_state.rs

@@ -9,7 +9,7 @@ use crate::parser::ast::*;
 
 use fxhash::FxBuildHasher;
 use indexmap::IndexSet;
-use ref_thread_local::RefThreadLocal;
+pub use ref_thread_local::RefThreadLocal;
 
 use std::collections::VecDeque;
 use std::fs::File;
@@ -63,21 +63,27 @@ fn add_op_decl_as_module_export<'a, LS: LoadState<'a>>(
 
     match op_decl.insert_into_op_dir(wam_op_dir) {
         Some(op_desc) => {
-            payload.retraction_info.push_record(RetractionRecord::ReplacedUserOp(
-                *op_decl,
-                op_desc,
-            ));
+            payload
+                .retraction_info
+                .push_record(RetractionRecord::ReplacedUserOp(*op_decl, op_desc));
 
             payload.module_op_exports.push((*op_decl, Some(op_desc)));
         }
         None => {
-            payload.retraction_info.push_record(RetractionRecord::AddedUserOp(*op_decl));
+            payload
+                .retraction_info
+                .push_record(RetractionRecord::AddedUserOp(*op_decl));
             payload.module_op_exports.push((*op_decl, None));
         }
     }
 
     let compilation_target = payload.compilation_target;
-    add_op_decl(&mut payload.retraction_info, &compilation_target, module_op_dir, op_decl);
+    add_op_decl(
+        &mut payload.retraction_info,
+        &compilation_target,
+        module_op_dir,
+        op_decl,
+    );
 }
 
 pub(super) fn add_op_decl(
@@ -89,10 +95,7 @@ pub(super) fn add_op_decl(
     match op_decl.insert_into_op_dir(op_dir) {
         Some(op_desc) => match &compilation_target {
             CompilationTarget::User => {
-                retraction_info.push_record(RetractionRecord::ReplacedUserOp(
-                    *op_decl,
-                    op_desc,
-                ));
+                retraction_info.push_record(RetractionRecord::ReplacedUserOp(*op_decl, op_desc));
             }
             CompilationTarget::Module(ref module_name) => {
                 retraction_info.push_record(RetractionRecord::ReplacedModuleOp(
@@ -107,10 +110,8 @@ pub(super) fn add_op_decl(
                 retraction_info.push_record(RetractionRecord::AddedUserOp(*op_decl));
             }
             CompilationTarget::Module(ref module_name) => {
-                retraction_info.push_record(RetractionRecord::AddedModuleOp(
-                    *module_name,
-                    *op_decl,
-                ));
+                retraction_info
+                    .push_record(RetractionRecord::AddedModuleOp(*module_name, *op_decl));
             }
         },
     }
@@ -160,7 +161,12 @@ pub(super) fn import_module_exports<'a, LS: LoadState<'a>>(
                 }
             }
             ModuleExport::OpDecl(ref op_decl) => {
-                add_op_decl(&mut payload.retraction_info, compilation_target, op_dir, op_decl);
+                add_op_decl(
+                    &mut payload.retraction_info,
+                    compilation_target,
+                    op_dir,
+                    op_decl,
+                );
             }
         }
     }
@@ -209,12 +215,7 @@ fn import_module_exports_into_module<'a, LS: LoadState<'a>>(
                 }
             }
             ModuleExport::OpDecl(ref op_decl) => {
-                add_op_decl_as_module_export::<LS>(
-                    payload,
-                    op_dir,
-                    wam_op_dir,
-                    op_decl,
-                );
+                add_op_decl_as_module_export::<LS>(payload, op_dir, wam_op_dir, op_decl);
             }
         }
     }
@@ -239,13 +240,18 @@ fn import_qualified_module_exports<'a, LS: LoadState<'a>>(
                 let key = (*name, *arity);
 
                 if let Some(meta_specs) = imported_module.meta_predicates.get(&key) {
-                    wam_prelude.indices.meta_predicates.insert(key.clone(), meta_specs.clone());
+                    wam_prelude
+                        .indices
+                        .meta_predicates
+                        .insert(key.clone(), meta_specs.clone());
                 }
 
                 if let Some(src_code_index) = imported_module.code_dir.get(&key) {
                     let arena = &mut LS::machine_st(payload).arena;
 
-                    let target_code_index = wam_prelude.indices.code_dir
+                    let target_code_index = wam_prelude
+                        .indices
+                        .code_dir
                         .entry(key.clone())
                         .or_insert_with(|| CodeIndex::new(IndexPtr::undefined(), arena))
                         .clone();
@@ -325,12 +331,7 @@ fn import_qualified_module_exports_into_module<'a, LS: LoadState<'a>>(
                 }
             }
             ModuleExport::OpDecl(ref op_decl) => {
-                add_op_decl_as_module_export::<LS>(
-                    payload,
-                    op_dir,
-                    wam_op_dir,
-                    op_decl,
-                );
+                add_op_decl_as_module_export::<LS>(payload, op_dir, wam_op_dir, op_decl);
             }
         }
     }
@@ -378,10 +379,8 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         mut clause_target_poses: Vec<Option<usize>>,
         is_dynamic: bool,
     ) {
-        let old_compilation_target = mem::replace(
-            &mut self.payload.compilation_target,
-            compilation_target,
-        );
+        let old_compilation_target =
+            mem::replace(&mut self.payload.compilation_target, compilation_target);
 
         while let Some(target_pos_opt) = clause_target_poses.pop() {
             match target_pos_opt {
@@ -482,7 +481,8 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
 
             let old_index_ptr = code_index.replace(IndexPtr::undefined());
 
-            self.payload.retraction_info
+            self.payload
+                .retraction_info
                 .push_record(RetractionRecord::ReplacedModulePredicate(
                     module_name,
                     *key,
@@ -491,7 +491,8 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         }
 
         for (key, skeleton) in removed_module.extensible_predicates.drain(..) {
-            self.payload.retraction_info
+            self.payload
+                .retraction_info
                 .push_record(RetractionRecord::RemovedSkeleton(
                     CompilationTarget::Module(module_name),
                     key,
@@ -499,7 +500,10 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                 ));
         }
 
-        self.wam_prelude.indices.modules.insert(module_name, removed_module);
+        self.wam_prelude
+            .indices
+            .modules
+            .insert(module_name, removed_module);
     }
 
     pub(super) fn remove_module_exports(&mut self, module_name: Atom) {
@@ -523,15 +527,17 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                             (Some(module_code_index), Some(target_code_index))
                                 if module_code_index.get() == target_code_index.get() =>
                             {
-                                let old_index_ptr = target_code_index.replace(IndexPtr::undefined());
-                                retraction_info.push_record(predicate_retractor(*key, old_index_ptr));
+                                let old_index_ptr =
+                                    target_code_index.replace(IndexPtr::undefined());
+                                retraction_info
+                                    .push_record(predicate_retractor(*key, old_index_ptr));
                             }
                             _ => {}
                         }
                     }
                     ModuleExport::OpDecl(op_decl) => {
-                        let op_dir_value_opt =
-                            op_dir.remove(&(op_decl.name, fixity(op_decl.op_desc.get_spec() as u32)));
+                        let op_dir_value_opt = op_dir
+                            .remove(&(op_decl.name, fixity(op_decl.op_desc.get_spec() as u32)));
 
                         if let Some(op_desc) = op_dir_value_opt {
                             retraction_info.push_record(op_retractor(*op_decl, op_desc));
@@ -552,9 +558,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                     RetractionRecord::ReplacedUserOp,
                 );
             }
-            CompilationTarget::Module(target_module_name)
-                if target_module_name != module_name =>
-            {
+            CompilationTarget::Module(target_module_name) if target_module_name != module_name => {
                 let predicate_retractor = |key, index_ptr| {
                     RetractionRecord::ReplacedModulePredicate(module_name, key, index_ptr)
                 };
@@ -563,7 +567,12 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                     RetractionRecord::ReplacedModuleOp(module_name, op_decl, op_desc)
                 };
 
-                if let Some(module) = self.wam_prelude.indices.modules.get_mut(&target_module_name) {
+                if let Some(module) = self
+                    .wam_prelude
+                    .indices
+                    .modules
+                    .get_mut(&target_module_name)
+                {
                     remove_module_exports(
                         &removed_module,
                         &mut module.code_dir,
@@ -579,7 +588,10 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             CompilationTarget::Module(_) => {}
         };
 
-        self.wam_prelude.indices.modules.insert(module_name, removed_module);
+        self.wam_prelude
+            .indices
+            .modules
+            .insert(module_name, removed_module);
     }
 
     fn get_or_insert_local_code_index(
@@ -591,10 +603,12 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             Some(ref mut module) => module
                 .code_dir
                 .entry(key)
-                .or_insert_with(|| CodeIndex::new(
-                    IndexPtr::undefined(),
-                    &mut LS::machine_st(&mut self.payload).arena,
-                ))
+                .or_insert_with(|| {
+                    CodeIndex::new(
+                        IndexPtr::undefined(),
+                        &mut LS::machine_st(&mut self.payload).arena,
+                    )
+                })
                 .clone(),
             None => {
                 self.add_dynamically_generated_module(module_name);
@@ -603,10 +617,12 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                     Some(ref mut module) => module
                         .code_dir
                         .entry(key)
-                        .or_insert_with(|| CodeIndex::new(
-                            IndexPtr::undefined(),
-                            &mut LS::machine_st(&mut self.payload).arena,
-                        ))
+                        .or_insert_with(|| {
+                            CodeIndex::new(
+                                IndexPtr::undefined(),
+                                &mut LS::machine_st(&mut self.payload).arena,
+                            )
+                        })
                         .clone(),
                     None => {
                         unreachable!()
@@ -771,10 +787,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             ClauseType::Named(arity, name, _) => {
                 let payload_compilation_target = self.payload.compilation_target;
 
-                let idx = self.get_or_insert_code_index(
-                    (name, arity),
-                    payload_compilation_target,
-                );
+                let idx = self.get_or_insert_code_index((name, arity), payload_compilation_target);
 
                 ClauseType::Named(arity, name, idx)
             }
@@ -802,13 +815,11 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
     }
 
     pub(super) fn get_meta_specs(&self, name: Atom, arity: usize) -> Option<&Vec<MetaSpec>> {
-        self.wam_prelude
-            .indices
-            .get_meta_predicate_spec(
-                name,
-                arity,
-                &self.payload.compilation_target,
-            )
+        self.wam_prelude.indices.get_meta_predicate_spec(
+            name,
+            arity,
+            &self.payload.compilation_target,
+        )
     }
 
     pub(super) fn add_meta_predicate_record(
@@ -829,19 +840,18 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                     .insert(key, meta_specs)
                 {
                     Some(old_meta_specs) => {
-                        self.payload.retraction_info
-                            .push_record(RetractionRecord::ReplacedMetaPredicate(
+                        self.payload.retraction_info.push_record(
+                            RetractionRecord::ReplacedMetaPredicate(
                                 module_name,
                                 key.0,
                                 old_meta_specs,
-                            ));
+                            ),
+                        );
                     }
                     None => {
-                        self.payload.retraction_info
-                            .push_record(RetractionRecord::AddedMetaPredicate(
-                                module_name,
-                                key,
-                            ));
+                        self.payload
+                            .retraction_info
+                            .push_record(RetractionRecord::AddedMetaPredicate(module_name, key));
                     }
                 }
             }
@@ -868,17 +878,16 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                     None => {
                         self.add_dynamically_generated_module(module_name);
 
-                        if let Some(module) = self.wam_prelude.indices.modules.get_mut(&module_name) {
+                        if let Some(module) = self.wam_prelude.indices.modules.get_mut(&module_name)
+                        {
                             module.meta_predicates.insert(key.clone(), meta_specs);
                         } else {
                             unreachable!()
                         }
 
-                        self.payload.retraction_info
-                            .push_record(RetractionRecord::AddedMetaPredicate(
-                                module_name.clone(),
-                                key,
-                            ));
+                        self.payload.retraction_info.push_record(
+                            RetractionRecord::AddedMetaPredicate(module_name.clone(), key),
+                        );
                     }
                 }
             }
@@ -901,10 +910,14 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             &mut module.meta_predicates,
         );
 
-        self.payload.retraction_info
+        self.payload
+            .retraction_info
             .push_record(RetractionRecord::AddedModule(module_name.clone()));
 
-        self.wam_prelude.indices.modules.insert(module_name.clone(), module);
+        self.wam_prelude
+            .indices
+            .modules
+            .insert(module_name.clone(), module);
     }
 
     fn import_builtins_in_module(
@@ -968,9 +981,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
 
                     if is_dynamic {
                         let clause_clause_compilation_target = match compilation_target {
-                            CompilationTarget::User => {
-                                CompilationTarget::Module(atom!("builtins"))
-                            }
+                            CompilationTarget::User => CompilationTarget::Module(atom!("builtins")),
                             module => module.clone(),
                         };
 
@@ -981,7 +992,8 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                     }
                 }
 
-                self.payload.retraction_info
+                self.payload
+                    .retraction_info
                     .push_record(RetractionRecord::ReplacedModule(
                         old_module_decl,
                         listing_src.clone(),
@@ -992,10 +1004,22 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         }
     }
 
-    pub(crate) fn add_module(&mut self, module_decl: ModuleDecl, listing_src: ListingSource) {
-        self.reset_in_situ_module(module_decl.clone(), &listing_src);
+    pub(crate) fn add_module(
+        &mut self,
+        module_decl: ModuleDecl,
+        listing_src: ListingSource,
+    ) -> Result<(), SessionError> {
         let module_name = module_decl.name;
 
+        if let Some(module) = self.wam_prelude.indices.modules.get(&module_name) {
+            if let ListingSource::DynamicallyGenerated = module.listing_src {
+            } else {
+                LS::err_on_builtin_module_overwrite(module_name)?;
+            }
+        }
+
+        self.reset_in_situ_module(module_decl.clone(), &listing_src);
+
         let mut module = match self.wam_prelude.indices.modules.remove(&module_name) {
             Some(mut module) => {
                 module.listing_src = listing_src;
@@ -1033,6 +1057,8 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
         }
 
         self.wam_prelude.indices.modules.insert(module_name, module);
+
+        Ok(())
     }
 
     pub(super) fn import_module(&mut self, module_name: Atom) -> Result<(), SessionError> {
@@ -1051,7 +1077,12 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                     )?;
                 }
                 CompilationTarget::Module(ref defining_module_name) => {
-                    match self.wam_prelude.indices.modules.get_mut(defining_module_name) {
+                    match self
+                        .wam_prelude
+                        .indices
+                        .modules
+                        .get_mut(defining_module_name)
+                    {
                         Some(ref mut target_module) => {
                             import_module_exports_into_module::<LS>(
                                 &mut self.payload,
@@ -1091,17 +1122,20 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             let payload_compilation_target = self.payload.compilation_target;
 
             let result = match &payload_compilation_target {
-                CompilationTarget::User => {
-                    import_qualified_module_exports::<LS>(
-                        &mut self.payload,
-                        &payload_compilation_target,
-                        &module,
-                        &exports,
-                        &mut self.wam_prelude,
-                    )
-                }
+                CompilationTarget::User => import_qualified_module_exports::<LS>(
+                    &mut self.payload,
+                    &payload_compilation_target,
+                    &module,
+                    &exports,
+                    &mut self.wam_prelude,
+                ),
                 CompilationTarget::Module(ref defining_module_name) => {
-                    match self.wam_prelude.indices.modules.get_mut(defining_module_name) {
+                    match self
+                        .wam_prelude
+                        .indices
+                        .modules
+                        .get_mut(defining_module_name)
+                    {
                         Some(ref mut target_module) => {
                             import_qualified_module_exports_into_module::<LS>(
                                 &mut self.payload,
@@ -1113,9 +1147,7 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                                 &mut self.wam_prelude.indices.op_dir,
                             )
                         }
-                        None => {
-                            Err(SessionError::ModuleCannotImportSelf(module_name))
-                        }
+                        None => Err(SessionError::ModuleCannotImportSelf(module_name)),
                     }
                 }
             };
@@ -1123,29 +1155,38 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             self.wam_prelude.indices.modules.insert(module_name, module);
             result
         } else {
-            Err(SessionError::ExistenceError(ExistenceError::Module(module_name)))
+            Err(SessionError::ExistenceError(ExistenceError::Module(
+                module_name,
+            )))
         }
     }
 
     pub(crate) fn use_module(&mut self, module_src: ModuleSource) -> Result<(), SessionError> {
         let (stream, listing_src) = match module_src {
             ModuleSource::File(filename) => {
-                let mut path_buf = PathBuf::from(filename.as_str());
+                let mut path_buf = PathBuf::from(&*filename.as_str());
                 path_buf.set_extension("pl");
 
                 let file = File::open(&path_buf)?;
 
                 (
-                    Stream::from_file_as_input(filename, file, &mut LS::machine_st(&mut self.payload).arena),
+                    Stream::from_file_as_input(
+                        filename,
+                        file,
+                        &mut LS::machine_st(&mut self.payload).arena,
+                    ),
                     ListingSource::File(filename, path_buf),
                 )
             }
-            ModuleSource::Library(library) => match LIBRARIES.borrow().get(library.as_str()) {
+            ModuleSource::Library(library) => match LIBRARIES.borrow().get(&*library.as_str()) {
                 Some(code) => {
                     if let Some(ref module) = self.wam_prelude.indices.modules.get(&library) {
                         if let ListingSource::DynamicallyGenerated = &module.listing_src {
                             (
-                                Stream::from_static_string(*code, &mut LS::machine_st(&mut self.payload).arena),
+                                Stream::from_static_string(
+                                    *code,
+                                    &mut LS::machine_st(&mut self.payload).arena,
+                                ),
                                 ListingSource::User,
                             )
                         } else {
@@ -1153,7 +1194,10 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
                         }
                     } else {
                         (
-                            Stream::from_static_string(*code, &mut LS::machine_st(&mut self.payload).arena),
+                            Stream::from_static_string(
+                                *code,
+                                &mut LS::machine_st(&mut self.payload).arena,
+                            ),
                             ListingSource::User,
                         )
                     }
@@ -1172,9 +1216,10 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             );
 
             let subloader: Loader<'_, BootstrappingLoadState> = Loader {
-                payload: BootstrappingLoadState(
-                    LoadStatePayload::new(self.wam_prelude.code.len(), term_stream)
-                ),
+                payload: BootstrappingLoadState(LoadStatePayload::new(
+                    self.wam_prelude.code.len(),
+                    term_stream,
+                )),
                 wam_prelude: MachinePreludeView {
                     indices: self.wam_prelude.indices,
                     code: self.wam_prelude.code,
@@ -1201,22 +1246,29 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
     ) -> Result<(), SessionError> {
         let (stream, listing_src) = match module_src {
             ModuleSource::File(filename) => {
-                let mut path_buf = PathBuf::from(filename.as_str());
+                let mut path_buf = PathBuf::from(&*filename.as_str());
                 path_buf.set_extension("pl");
                 let file = File::open(&path_buf)?;
 
                 (
-                    Stream::from_file_as_input(filename, file, &mut LS::machine_st(&mut self.payload).arena),
+                    Stream::from_file_as_input(
+                        filename,
+                        file,
+                        &mut LS::machine_st(&mut self.payload).arena,
+                    ),
                     ListingSource::File(filename, path_buf),
                 )
             }
-            ModuleSource::Library(library) => match LIBRARIES.borrow().get(library.as_str()) {
+            ModuleSource::Library(library) => match LIBRARIES.borrow().get(&*library.as_str()) {
                 Some(code) => {
                     if self.wam_prelude.indices.modules.contains_key(&library) {
                         return self.import_qualified_module(library, exports);
                     } else {
                         (
-                            Stream::from_static_string(*code, &mut LS::machine_st(&mut self.payload).arena),
+                            Stream::from_static_string(
+                                *code,
+                                &mut LS::machine_st(&mut self.payload).arena,
+                            ),
                             ListingSource::User,
                         )
                     }
@@ -1235,9 +1287,10 @@ impl<'a, LS: LoadState<'a>> Loader<'a, LS> {
             );
 
             let subloader: Loader<'_, BootstrappingLoadState> = Loader {
-                payload: BootstrappingLoadState(
-                    LoadStatePayload::new(self.wam_prelude.code.len(), term_stream),
-                ),
+                payload: BootstrappingLoadState(LoadStatePayload::new(
+                    self.wam_prelude.code.len(),
+                    term_stream,
+                )),
                 wam_prelude: MachinePreludeView {
                     indices: self.wam_prelude.indices,
                     code: self.wam_prelude.code,

src/machine/machine_errors.rs

@@ -44,7 +44,8 @@ pub(crate) enum ValidType {
     InCharacter,
     Integer,
     List,
-    #[allow(unused)] Number,
+    #[allow(unused)]
+    Number,
     Pair,
     //    PredicateIndicator,
     //    Variable
@@ -76,6 +77,12 @@ impl ValidType {
     }
 }
 
+#[derive(Debug, Clone, Copy)]
+pub(crate) enum ResourceError {
+    FiniteMemory(HeapCellValue),
+    OutOfFiles
+}
+
 pub(crate) trait TypeError {
     fn type_error(self, machine_st: &mut MachineState, valid_type: ValidType) -> MachineError;
 }
@@ -154,6 +161,26 @@ pub(crate) trait PermissionError {
     ) -> MachineError;
 }
 
+impl PermissionError for Atom {
+    fn permission_error(
+        self,
+        _machine_st: &mut MachineState,
+        index_atom: Atom,
+        perm: Permission,
+    ) -> MachineError {
+        let stub = functor!(
+            atom!("permission_error"),
+            [atom(perm.as_atom()), atom(index_atom), cell(atom_as_cell!(self))]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received,
+        }
+    }
+}
+
 impl PermissionError for HeapCellValue {
     fn permission_error(
         self,
@@ -254,9 +281,11 @@ pub(super) type FunctorStub = [HeapCellValue; 3];
 
 #[inline(always)]
 pub(super) fn functor_stub(name: Atom, arity: usize) -> FunctorStub {
-    [atom_as_cell!(atom!("/"), 2),
-     atom_as_cell!(name),
-     fixnum_as_cell!(Fixnum::build_with(arity as i64))]
+    [
+        atom_as_cell!(atom!("/"), 2),
+        atom_as_cell!(name),
+        fixnum_as_cell!(Fixnum::build_with(arity as i64)),
+    ]
 }
 
 impl MachineState {
@@ -281,11 +310,21 @@ impl MachineState {
         }
     }
 
-    pub(super) fn resource_error(&mut self, value: HeapCellValue) -> MachineError {
-        let stub = functor!(
-            atom!("resource_error"),
-            [atom(atom!("finite_memory")), cell(value)]
-        );
+    pub(super) fn resource_error(&mut self, err: ResourceError) -> MachineError {
+        let stub = match err {
+            ResourceError::FiniteMemory(size_requested) => {
+                functor!(
+                    atom!("resource_error"),
+                    [atom(atom!("finite_memory")), cell(size_requested)]
+                )
+            }
+            ResourceError::OutOfFiles => {
+                functor!(
+                    atom!("resource_error"),
+                    [atom(atom!("file_descriptors"))]
+                )
+            }
+        };
 
         MachineError {
             stub,
@@ -302,26 +341,6 @@ impl MachineState {
         culprit.type_error(self, valid_type)
     }
 
-    pub(super) fn module_resolution_error(
-        &mut self,
-        mod_name: Atom,
-        name: Atom,
-        arity: usize,
-    ) -> MachineError {
-        let h = self.heap.len();
-
-        let res_stub = functor!(atom!(":"), [atom(mod_name), atom(name)]);
-        let ind_stub = functor!(atom!("/"), [str(h + 2, 0), fixnum(arity)], [res_stub]);
-
-        let stub = functor!(atom!("evaluation_error"), [str(h, 0)], [ind_stub]);
-
-        MachineError {
-            stub,
-            location: None,
-            from: ErrorProvenance::Constructed,
-        }
-    }
-
     pub(super) fn existence_error(&mut self, err: ExistenceError) -> MachineError {
         match err {
             ExistenceError::Module(name) => {
@@ -336,6 +355,20 @@ impl MachineState {
                     from: ErrorProvenance::Received,
                 }
             }
+            ExistenceError::QualifiedProcedure { module_name, name, arity } => {
+                let h = self.heap.len();
+
+                let ind_stub = functor!(atom!("/"), [atom(name), fixnum(arity)]);
+                let res_stub = functor!(atom!(":"), [atom(module_name), str(h + 3, 0)], [ind_stub]);
+
+                let stub = functor!(atom!("existence_error"), [atom(atom!("procedure")), str(h, 0)], [res_stub]);
+
+                MachineError {
+                    stub,
+                    location: None,
+                    from: ErrorProvenance::Constructed,
+                }
+            }
             ExistenceError::Procedure(name, arity) => {
                 let culprit = functor!(atom!("/"), [atom(name), fixnum(arity)]);
 
@@ -440,17 +473,22 @@ impl MachineState {
     pub(super) fn session_error(&mut self, err: SessionError) -> MachineError {
         match err {
             SessionError::CannotOverwriteBuiltIn(key) => {
-            // SessionError::CannotOverwriteImport(pred_atom) => {
                 self.permission_error(
                     Permission::Modify,
                     atom!("static_procedure"),
-                    functor_stub(key.0, key.1).into_iter().collect::<MachineStub>(),
+                    functor_stub(key.0, key.1)
+                        .into_iter()
+                        .collect::<MachineStub>(),
+                )
+            }
+            SessionError::CannotOverwriteBuiltInModule(module) => {
+                self.permission_error(
+                    Permission::Modify,
+                    atom!("static_module"),
+                    module,
                 )
             }
             SessionError::ExistenceError(err) => self.existence_error(err),
-            // SessionError::InvalidFileName(filename) => {
-            //     Self::existence_error(h, ExistenceError::Module(filename))
-            // }
             SessionError::ModuleDoesNotContainExport(..) => {
                 let error_atom = atom!("module_does_not_contain_claimed_export");
 
@@ -471,7 +509,11 @@ impl MachineState {
             }
             SessionError::NamelessEntry => {
                 let error_atom = atom!("nameless_procedure");
-                self.permission_error(Permission::Create, atom!("static_procedure"), functor!(error_atom))
+                self.permission_error(
+                    Permission::Create,
+                    atom!("static_procedure"),
+                    functor!(error_atom),
+                )
             }
             SessionError::OpIsInfixAndPostFix(op) => {
                 self.permission_error(Permission::Create, atom!("operator"), functor!(op))
@@ -541,21 +583,21 @@ impl MachineState {
 
     #[cfg(feature = "ffi")]
     pub(super) fn ffi_error(&mut self, err: FFIError) -> MachineError {
-	let error_atom = match err {
-	    FFIError::ValueCast => atom!("value_cast"),
-	    FFIError::ValueDontFit => atom!("value_dont_fit"),
-	    FFIError::InvalidFFIType => atom!("invalid_ffi_type"),
-	    FFIError::InvalidStructName => atom!("invalid_struct_name"),
-	    FFIError::FunctionNotFound => atom!("function_not_found"),
-	    FFIError::StructNotFound => atom!("struct_not_found"),
-	};
-	let stub = functor!(atom!("ffi_error"),[atom(error_atom)]);
+        let error_atom = match err {
+            FFIError::ValueCast => atom!("value_cast"),
+            FFIError::ValueDontFit => atom!("value_dont_fit"),
+            FFIError::InvalidFFIType => atom!("invalid_ffi_type"),
+            FFIError::InvalidStructName => atom!("invalid_struct_name"),
+            FFIError::FunctionNotFound => atom!("function_not_found"),
+            FFIError::StructNotFound => atom!("struct_not_found"),
+        };
+        let stub = functor!(atom!("ffi_error"), [atom(error_atom)]);
 
-	MachineError {
-	    stub,
-	    location: None,
-	    from: ErrorProvenance::Constructed,
-	}
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Constructed,
+        }
     }
 
     pub(super) fn error_form(&mut self, err: MachineError, src: FunctorStub) -> MachineStub {
@@ -682,10 +724,12 @@ impl CompilationError {
             &CompilationError::ExpectedRel => {
                 functor!(atom!("expected_relation"))
             }
-            &CompilationError::InadmissibleFact => { // TODO: type_error(callable, _).
+            &CompilationError::InadmissibleFact => {
+                // TODO: type_error(callable, _).
                 functor!(atom!("inadmissible_fact"))
             }
-            &CompilationError::InadmissibleQueryTerm => { // TODO: type_error(callable, _).
+            &CompilationError::InadmissibleQueryTerm => {
+                // TODO: type_error(callable, _).
                 functor!(atom!("inadmissible_query_term"))
             }
             &CompilationError::InconsistentEntry => {
@@ -820,10 +864,10 @@ pub enum CycleSearchResult {
     Cyclic(usize),
     EmptyList,
     NotList(usize, HeapCellValue), // the list length until the second argument in the heap
-    PartialList(usize, Ref), // the list length (up to max), and an offset into the heap.
-    ProperList(usize),       // the list length.
+    PartialList(usize, Ref),       // the list length (up to max), and an offset into the heap.
+    ProperList(usize),             // the list length.
     PStrLocation(usize, usize, usize), // list length (up to max), the heap address of the PStr, the offset
-    UntouchedList(usize, usize),   // list length (up to max), the address of an uniterated Addr::Lis(address).
+    UntouchedList(usize, usize), // list length (up to max), the address of an uniterated Addr::Lis(address).
     UntouchedCStr(Atom, usize),
 }
 
@@ -838,7 +882,7 @@ impl MachineState {
         match BrentAlgState::detect_cycles(&self.heap, list) {
             CycleSearchResult::PartialList(..) => {
                 let err = self.instantiation_error();
-                return Err(self.error_form(err, stub_gen()))
+                return Err(self.error_form(err, stub_gen()));
             }
             CycleSearchResult::NotList(..) | CycleSearchResult::Cyclic(_) => {
                 let err = self.type_error(ValidType::List, list);
@@ -942,6 +986,7 @@ pub enum ExistenceError {
     Module(Atom),
     ModuleSource(ModuleSource),
     Procedure(Atom, usize),
+    QualifiedProcedure { module_name: Atom, name: Atom, arity: usize },
     SourceSink(HeapCellValue),
     Stream(HeapCellValue),
 }
@@ -950,6 +995,7 @@ pub enum ExistenceError {
 pub enum SessionError {
     CompilationError(CompilationError),
     CannotOverwriteBuiltIn(PredicateKey),
+    CannotOverwriteBuiltInModule(Atom),
     ExistenceError(ExistenceError),
     ModuleDoesNotContainExport(Atom, PredicateKey),
     ModuleCannotImportSelf(Atom),

src/machine/machine_indices.rs

@@ -3,15 +3,15 @@ use crate::parser::ast::*;
 use crate::arena::*;
 use crate::atom_table::*;
 use crate::forms::*;
-use crate::machine::ClauseType;
 use crate::machine::loader::*;
 use crate::machine::machine_state::*;
 use crate::machine::streams::Stream;
+use crate::machine::ClauseType;
 
 use fxhash::FxBuildHasher;
 use indexmap::{IndexMap, IndexSet};
-use modular_bitfield::{BitfieldSpecifier, bitfield};
 use modular_bitfield::specifiers::*;
+use modular_bitfield::{bitfield, BitfieldSpecifier};
 
 use std::cmp::Ordering;
 use std::collections::BTreeSet;
@@ -21,14 +21,6 @@ use crate::types::*;
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub(crate) struct OrderedOpDirKey(pub(crate) Atom, pub(crate) Fixity);
 
-pub(crate) type OssifiedOpDir = IndexMap<(Atom, Fixity), (usize, Specifier)>;
-
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum DBRef {
-    NamedPred(Atom, usize),
-    Op(Atom, Fixity, TypedArenaPtr<OssifiedOpDir>),
-}
-
 // 7.2
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
 pub enum TermOrderCategory {
@@ -86,7 +78,8 @@ pub enum IndexPtrTag {
 #[derive(Debug, Clone, Copy, Eq, Hash, Ord, PartialEq, PartialOrd)]
 pub struct IndexPtr {
     pub p: B56,
-    #[allow(unused)] m: bool,
+    #[allow(unused)]
+    m: bool,
     pub tag: IndexPtrTag,
 }
 
@@ -143,10 +136,10 @@ impl IndexPtr {
 #[derive(Debug, Clone, Copy, Ord, Hash, PartialOrd, Eq, PartialEq)]
 pub struct CodeIndex(TypedArenaPtr<IndexPtr>);
 
-#[cfg(target_pointer_width="32")]
+#[cfg(target_pointer_width = "32")]
 const_assert!(std::mem::align_of::<CodeIndex>() == 4);
 
-#[cfg(target_pointer_width="64")]
+#[cfg(target_pointer_width = "64")]
 const_assert!(std::mem::align_of::<CodeIndex>() == 8);
 
 impl Deref for CodeIndex {
@@ -293,7 +286,8 @@ impl IndexStore {
         let (name, arity) = key;
 
         if !ClauseType::is_inbuilt(name, arity) {
-            self.modules.get(&(atom!("builtins")))
+            self.modules
+                .get(&(atom!("builtins")))
                 .map(|module| module.code_dir.contains_key(&(name, arity)))
                 .unwrap_or(false)
         } else {
@@ -444,11 +438,7 @@ impl IndexStore {
         }
     }
 
-    pub(crate) fn is_dynamic_predicate(
-        &self,
-        module_name: Atom,
-        key: PredicateKey,
-    ) -> bool {
+    pub(crate) fn is_dynamic_predicate(&self, module_name: Atom, key: PredicateKey) -> bool {
         match module_name {
             atom!("user") => self
                 .extensible_predicates

src/machine/machine_state.rs

@@ -3,7 +3,6 @@ use crate::atom_table::*;
 use crate::forms::*;
 use crate::heap_iter::*;
 use crate::heap_print::*;
-use crate::machine::Machine;
 use crate::machine::attributed_variables::*;
 use crate::machine::copier::*;
 use crate::machine::heap::*;
@@ -11,6 +10,7 @@ use crate::machine::machine_errors::*;
 use crate::machine::machine_indices::*;
 use crate::machine::stack::*;
 use crate::machine::streams::*;
+use crate::machine::Machine;
 use crate::parser::ast::*;
 use crate::read::TermWriteResult;
 use crate::types::*;
@@ -22,6 +22,7 @@ use indexmap::IndexMap;
 use std::convert::TryFrom;
 use std::fmt;
 use std::ops::{Index, IndexMut};
+use std::sync::Arc;
 
 pub(crate) type Registers = [HeapCellValue; MAX_ARITY + 1];
 
@@ -57,14 +58,14 @@ pub enum OnEOF {
 }
 
 pub struct MachineState {
-    pub atom_tbl: AtomTable,
+    pub atom_tbl: Arc<AtomTable>,
     pub arena: Arena,
     pub(super) pdl: Vec<HeapCellValue>,
     pub(super) s: HeapPtr,
     pub(super) s_offset: usize,
     pub(super) p: usize,
     pub(super) oip: u32, // first internal code ptr
-    pub(super) iip : u32, // second internal code ptr
+    pub(super) iip: u32, // second internal code ptr
     pub(super) b: usize,
     pub(super) b0: usize,
     pub(super) e: usize,
@@ -79,7 +80,7 @@ pub struct MachineState {
     pub(super) trail: Vec<TrailEntry>,
     pub(super) tr: usize,
     pub(super) hb: usize,
-    pub(super) block: usize, // an offset into the OR stack.
+    pub(super) block: usize,     // an offset into the OR stack.
     pub(super) scc_block: usize, // an offset into the OR stack for setup_call_cleanup/3.
     pub(super) ball: Ball,
     pub(super) ball_stack: Vec<Ball>, // save current ball before jumping via, e.g., verify_attr interrupt.
@@ -95,7 +96,7 @@ pub struct MachineState {
     pub(crate) unify_fn: fn(&mut MachineState),
     pub(crate) bind_fn: fn(&mut MachineState, Ref, HeapCellValue),
     pub(crate) run_cleaners_fn: fn(&mut Machine) -> bool,
-    pub(crate) increment_call_count_fn: fn(&mut MachineState) -> CallResult,
+    pub(crate) increment_call_count_fn: fn(&mut MachineState) -> bool,
 }
 
 impl fmt::Debug for MachineState {
@@ -203,12 +204,12 @@ pub fn pstr_loc_and_offset(heap: &[HeapCellValue], index: usize) -> (usize, Fixn
 fn push_var_eq_functors<'a>(
     heap: &mut Heap,
     iter: impl Iterator<Item = (&'a VarKey, &'a HeapCellValue)>,
-    atom_tbl: &mut AtomTable,
+    atom_tbl: &AtomTable,
 ) -> Vec<HeapCellValue> {
     let mut list_of_var_eqs = vec![];
 
     for (var, binding) in iter {
-        let var_atom = atom_tbl.build_with(&var.to_string());
+        let var_atom = AtomTable::build_with(atom_tbl, &var.to_string());
         let h = heap.len();
 
         heap.push(atom_as_cell!(atom!("="), 2));
@@ -243,9 +244,11 @@ impl Ball {
     pub(super) fn copy_and_align(&self, h: usize) -> Heap {
         let diff = self.boundary as i64 - h as i64;
 
-        self.stub.iter().cloned().map(|heap_value| {
-            heap_value - diff
-        }).collect()
+        self.stub
+            .iter()
+            .cloned()
+            .map(|heap_value| heap_value - diff)
+            .collect()
     }
 }
 
@@ -409,28 +412,31 @@ impl MachineState {
         self.fail = false;
     }
 
-    pub(crate) fn increment_call_count(&mut self) -> CallResult {
+    pub(crate) fn increment_call_count(&mut self) -> bool {
         if self.cwil.inference_limit_exceeded || self.ball.stub.len() > 0 {
-            return Ok(());
+            return true;
         }
 
-        if let Some(&(ref limit, bp)) = self.cwil.limits.last() {
+        if let Some(&(ref limit, block)) = self.cwil.limits.last() {
             if self.cwil.count == *limit {
                 self.cwil.inference_limit_exceeded = true;
+                self.block = block;
+                self.unwind_stack();
 
-                return Err(
-                    functor!(atom!("inference_limit_exceeded"), [fixnum(bp)])
-                );
+                return false;
             } else {
                 self.cwil.count += 1;
             }
         }
 
-        Ok(())
+        true
     }
 
     #[allow(dead_code)]
-    pub(super) fn try_char_list(&mut self, addrs: Vec<HeapCellValue>) -> Result<String, MachineError> {
+    pub(super) fn try_char_list(
+        &mut self,
+        addrs: Vec<HeapCellValue>,
+    ) -> Result<String, MachineError> {
         let mut chars = String::new();
 
         for addr in addrs {
@@ -515,18 +521,25 @@ impl MachineState {
         mut var_list: Vec<(VarKey, HeapCellValue, usize)>,
         singleton_var_list: Vec<HeapCellValue>,
     ) -> CallResult {
-        var_list.sort_by(|(_,_,idx_1),(_,_,idx_2)| idx_1.cmp(idx_2));
+        var_list.sort_by(|(_, _, idx_1), (_, _, idx_2)| idx_1.cmp(idx_2));
 
         let list_of_var_eqs = push_var_eq_functors(
             &mut self.heap,
-            var_list.iter().filter_map(|(var_name, var,_)| if var_name.is_anon() { None } else { Some((var_name,var)) }),
-            &mut self.atom_tbl,
+            var_list.iter().filter_map(|(var_name, var, _)| {
+                if var_name.is_anon() {
+                    None
+                } else {
+                    Some((var_name, var))
+                }
+            }),
+            &self.atom_tbl,
         );
 
         let singleton_addr = self.registers[3];
-        let singletons_offset = heap_loc_as_cell!(
-            iter_to_heap_list(&mut self.heap, singleton_var_list.into_iter())
-        );
+        let singletons_offset = heap_loc_as_cell!(iter_to_heap_list(
+            &mut self.heap,
+            singleton_var_list.into_iter()
+        ));
 
         unify_fn!(*self, singletons_offset, singleton_addr);
 
@@ -535,9 +548,10 @@ impl MachineState {
         }
 
         let vars_addr = self.registers[4];
-        let vars_offset = heap_loc_as_cell!(
-            iter_to_heap_list(&mut self.heap, var_list.into_iter().map(|(_,cell,_)| cell))
-        );
+        let vars_offset = heap_loc_as_cell!(iter_to_heap_list(
+            &mut self.heap,
+            var_list.into_iter().map(|(_, cell, _)| cell)
+        ));
 
         unify_fn!(*self, vars_offset, vars_addr);
 
@@ -546,9 +560,10 @@ impl MachineState {
         }
 
         let var_names_addr = self.registers[5];
-        let var_names_offset = heap_loc_as_cell!(
-            iter_to_heap_list(&mut self.heap, list_of_var_eqs.into_iter())
-        );
+        let var_names_offset = heap_loc_as_cell!(iter_to_heap_list(
+            &mut self.heap,
+            list_of_var_eqs.into_iter()
+        ));
 
         Ok(unify_fn!(*self, var_names_offset, var_names_addr))
     }
@@ -575,7 +590,7 @@ impl MachineState {
 
         let mut singleton_var_set: IndexMap<Ref, bool> = IndexMap::new();
 
-        for cell in stackful_preorder_iter(&mut self.heap, &mut self.stack, heap_loc) {
+        for cell in stackful_preorder_iter::<NonListElider>(&mut self.heap, &mut self.stack, heap_loc) {
             let cell = unmark_cell_bits!(cell);
 
             if let Some(var) = cell.as_var() {
@@ -589,18 +604,21 @@ impl MachineState {
 
         let singleton_var_list = push_var_eq_functors(
             &mut self.heap,
-            term_write_result.var_dict.iter().filter(|(var_name, binding)| {
-                if var_name.is_anon() {
-                    return false;
-                }
+            term_write_result
+                .var_dict
+                .iter()
+                .filter(|(var_name, binding)| {
+                    if var_name.is_anon() {
+                        return false;
+                    }
 
-                if let Some(r) = binding.as_var() {
-                    *singleton_var_set.get(&r).unwrap_or(&false)
-                } else {
-                    false
-                }
-            }),
-            &mut self.atom_tbl,
+                    if let Some(r) = binding.as_var() {
+                        *singleton_var_set.get(&r).unwrap_or(&false)
+                    } else {
+                        false
+                    }
+                }),
+            &self.atom_tbl,
         );
 
         for var in term_write_result.var_dict.values_mut() {
@@ -620,13 +638,11 @@ impl MachineState {
         self.write_read_term_options(var_list, singleton_var_list)
     }
 
-    pub fn read_term_from_user_input_eof_handler(&mut self, stream: Stream) -> Result<OnEOF, MachineStub> {
-        self.eof_action(
-            self.registers[2],
-            stream,
-            atom!("read_term"),
-            3,
-        )?;
+    pub fn read_term_from_user_input_eof_handler(
+        &mut self,
+        stream: Stream,
+    ) -> Result<OnEOF, MachineStub> {
+        self.eof_action(self.registers[2], stream, atom!("read_term"), 3)?;
 
         if stream.options().eof_action() == EOFAction::Reset {
             if self.fail == false {
@@ -639,13 +655,15 @@ impl MachineState {
 
     // Safety: the atom_tbl lives for the lifetime of the machine, as does the helper, so the ptr
     // will always be valid.
-    pub fn read_term_from_user_input(&mut self, stream: Stream, indices: &mut IndexStore) -> CallResult {
-        let atoms_ptr = (&self.atom_tbl.table) as *const indexmap::IndexSet<Atom>;
-
+    pub fn read_term_from_user_input(
+        &mut self,
+        stream: Stream,
+        indices: &mut IndexStore,
+    ) -> CallResult {
         if let Stream::Readline(ptr) = stream {
             unsafe {
                 let readline = ptr.as_ptr().as_mut().unwrap();
-                readline.set_atoms_for_completion(atoms_ptr);
+                readline.set_atoms_for_completion(&self.atom_tbl);
                 return self.read_term(
                     stream,
                     indices,
@@ -654,6 +672,14 @@ impl MachineState {
             }
         }
 
+        if let Stream::Byte(_) = stream {
+            return self.read_term(
+                stream, 
+                indices, 
+                MachineState::read_term_from_user_input_eof_handler
+            )
+        }
+
         unreachable!("Stream must be a Stream::Readline(_)")
     }
 
@@ -663,12 +689,7 @@ impl MachineState {
             stream.set_past_end_of_stream(true);
             return Ok(OnEOF::Return);
         } else if stream.past_end_of_stream() {
-            self.eof_action(
-                self.registers[2],
-                stream,
-                atom!("read_term"),
-                3,
-            )?;
+            self.eof_action(self.registers[2], stream, atom!("read_term"), 3)?;
 
             if stream.options().eof_action() == EOFAction::Reset {
                 if self.fail == false {
@@ -709,7 +730,9 @@ impl MachineState {
                     match &err {
                         CompilationError::ParserError(e) if e.is_unexpected_eof() => {
                             match eof_handler(self, stream)? {
-                                OnEOF::Return => return self.write_read_term_options(vec![], vec![]),
+                                OnEOF::Return => {
+                                    return self.write_read_term_options(vec![], vec![])
+                                }
                                 OnEOF::Continue => continue,
                             }
                         }
@@ -762,14 +785,14 @@ impl MachineState {
                                     }
                                     (HeapCellValueTag::Atom, (name, _arity)) => {
                                         debug_assert_eq!(_arity, 0);
-                                        var_names.insert(var, VarPtr::from(name.as_str()));
+                                        var_names.insert(var, VarPtr::from(&*name.as_str()));
                                     }
                                     (HeapCellValueTag::Str, s) => {
                                         let (name, arity) = cell_as_atom_cell!(self.heap[s])
                                             .get_name_and_arity();
 
                                         debug_assert_eq!(arity, 0);
-                                        var_names.insert(var, VarPtr::from(name.as_str()));
+                                        var_names.insert(var, VarPtr::from(&*name.as_str()));
                                     }
                                     _ => {
                                         unreachable!();
@@ -850,7 +873,7 @@ impl MachineState {
 
                 let mut printer = HCPrinter::new(
                     &mut self.heap,
-                    &mut self.atom_tbl,
+                    Arc::clone(&self.atom_tbl),
                     &mut self.stack,
                     op_dir,
                     PrinterOutputter::new(),
@@ -872,8 +895,10 @@ impl MachineState {
                         }
                     }
                     Ok(Number::Integer(n)) => {
-                        if let Some(n) = n.to_usize() {
-                            printer.max_depth = n;
+                        let result = (&*n).try_into();
+
+                        if let Ok(value) = result {
+                            printer.max_depth = value;
                         } else {
                             self.fail = true;
                             return Ok(None);
@@ -896,7 +921,11 @@ impl MachineState {
         Ok(Some(printer))
     }
 
-    pub(super) fn read_predicate_key(&self, name: HeapCellValue, arity: HeapCellValue) -> (Atom, usize) {
+    pub(super) fn read_predicate_key(
+        &self,
+        name: HeapCellValue,
+        arity: HeapCellValue,
+    ) -> (Atom, usize) {
         let name = cell_as_atom!(self.store(self.deref(name)));
         let arity = cell_as_fixnum!(self.store(self.deref(arity)));
 
@@ -920,13 +949,32 @@ impl MachineState {
             }
         );
     }
+
+    #[inline(always)]
+    pub(super) fn cut_prev_body(&mut self, value: HeapCellValue) {
+        let b = self.b;
+
+        read_heap_cell!(value,
+            (HeapCellValueTag::CutPoint, b0) => {
+                let b0 = b0.get_num() as usize;
+                let b0 = self.stack.index_or_frame(b0).prelude.b;
+
+                if b > b0 {
+                    self.b = b0;
+                }
+            }
+            _ => {
+                self.fail = true;
+            }
+        );
+    }
 }
 
 #[derive(Debug)]
 pub(crate) struct CWIL {
     count: Integer,
     limits: Vec<(Integer, usize)>,
-    inference_limit_exceeded: bool,
+    pub(crate) inference_limit_exceeded: bool,
 }
 
 impl CWIL {
@@ -938,22 +986,22 @@ impl CWIL {
         }
     }
 
-    pub(crate) fn add_limit(&mut self, limit: usize, b: usize) -> &Integer {
+    pub(crate) fn add_limit(&mut self, limit: usize, block: usize) -> &Integer {
         let mut limit = Integer::from(limit);
         limit += &self.count;
 
         match self.limits.last() {
             Some((ref inner_limit, _)) if *inner_limit <= limit => {}
-            _ => self.limits.push((limit, b)),
+            _ => self.limits.push((limit, block)),
         };
 
         &self.count
     }
 
     #[inline(always)]
-    pub(crate) fn remove_limit(&mut self, b: usize) -> &Integer {
-        if let Some((_, bp)) = self.limits.last() {
-            if bp == &b {
+    pub(crate) fn remove_limit(&mut self, block: usize) -> &Integer {
+        if let Some((_, bl)) = self.limits.last() {
+            if bl == &block {
                 self.limits.pop();
             }
         }

src/machine/machine_state_impl.rs

@@ -1,6 +1,5 @@
 use crate::arena::*;
 use crate::atom_table::*;
-use crate::types::*;
 use crate::forms::*;
 use crate::heap_iter::*;
 use crate::machine::attributed_variables::*;
@@ -14,6 +13,7 @@ use crate::machine::stack::*;
 use crate::machine::unify::*;
 use crate::parser::ast::*;
 use crate::parser::dashu::{Integer, Rational};
+use crate::types::*;
 
 use indexmap::IndexSet;
 
@@ -50,7 +50,7 @@ impl MachineState {
             ball: Ball::new(),
             ball_stack: vec![],
             lifted_heap: Heap::new(),
-            interms: vec![Number::default();256],
+            interms: vec![Number::default(); 256],
             cont_pts: Vec::with_capacity(256),
             cwil: CWIL::new(),
             flags: MachineFlags::default(),
@@ -59,8 +59,8 @@ impl MachineState {
             dynamic_mode: FirstOrNext::First,
             unify_fn: MachineState::unify,
             bind_fn: MachineState::bind,
-            run_cleaners_fn: |_| { false },
-            increment_call_count_fn: |_| { Ok(()) },
+            run_cleaners_fn: |_| false,
+            increment_call_count_fn: |_| true,
         }
     }
 
@@ -160,9 +160,8 @@ impl MachineState {
                     key_atom.index as u64,
                 ));
 
-                self.trail.push(TrailEntry::from_bytes(
-                    value_cell.into_bytes(),
-                ));
+                self.trail
+                    .push(TrailEntry::from_bytes(value_cell.into_bytes()));
 
                 self.tr += 2;
             }
@@ -248,9 +247,7 @@ impl MachineState {
         r: Ref,
         value: HeapCellValue,
     ) {
-        let mut unifier = CompositeUnifierForOccursCheckWithError::from(
-            DefaultUnifier::from(self),
-        );
+        let mut unifier = CompositeUnifierForOccursCheckWithError::from(DefaultUnifier::from(self));
 
         unifier.bind(r, value);
     }
@@ -297,12 +294,12 @@ impl MachineState {
 
     pub fn unify_big_int(&mut self, n1: TypedArenaPtr<Integer>, value: HeapCellValue) {
         let mut unifier = DefaultUnifier::from(self);
-        unifier.unify_big_num(n1, value);
+        unifier.unify_big_integer(n1, value);
     }
 
     pub fn unify_rational(&mut self, n1: TypedArenaPtr<Rational>, value: HeapCellValue) {
         let mut unifier = DefaultUnifier::from(self);
-        unifier.unify_big_num(n1, value);
+        unifier.unify_big_rational(n1, value);
     }
 
     pub fn unify_f64(&mut self, f1: F64Ptr, value: HeapCellValue) {
@@ -316,9 +313,7 @@ impl MachineState {
     }
 
     pub(super) fn unify_with_occurs_check_with_error(&mut self) {
-        let mut unifier = CompositeUnifierForOccursCheckWithError::from(
-            DefaultUnifier::from(self),
-        );
+        let mut unifier = CompositeUnifierForOccursCheckWithError::from(DefaultUnifier::from(self));
 
         unifier.unify_internal();
     }
@@ -380,8 +375,7 @@ impl MachineState {
                     }
                 )
             }
-            &mut HeapPtr::PStrChar(h, ref mut n) |
-            &mut HeapPtr::PStrLocation(h, ref mut n) => {
+            &mut HeapPtr::PStrChar(h, ref mut n) | &mut HeapPtr::PStrLocation(h, ref mut n) => {
                 read_heap_cell!(self.heap[h],
                     (HeapCellValueTag::PStr, pstr_atom) => {
                         let pstr = PartialString::from(pstr_atom);
@@ -509,7 +503,7 @@ impl MachineState {
                                     } else {
                                         self.pdl.clear();
                                         return Some(
-                                            n1.chars().next().cmp(&Some(c2))
+                                            n1.as_str().chars().next().cmp(&Some(c2))
                                               .then(Ordering::Greater)
                                         );
                                     }
@@ -539,7 +533,7 @@ impl MachineState {
                                     } else {
                                         self.pdl.clear();
                                         return Some(
-                                            Some(c1).cmp(&n2.chars().next())
+                                            Some(c1).cmp(&n2.as_str().chars().next())
                                                     .then(Ordering::Less)
                                         );
                                     }
@@ -562,7 +556,7 @@ impl MachineState {
                                     } else {
                                         self.pdl.clear();
                                         return Some(
-                                            Some(c1).cmp(&n2.chars().next())
+                                            Some(c1).cmp(&n2.as_str().chars().next())
                                                     .then(Ordering::Less)
                                         );
                                     }
@@ -592,7 +586,7 @@ impl MachineState {
                                     } else {
                                         self.pdl.clear();
                                         return Some(
-                                            n1.chars().next().cmp(&Some(c2))
+                                            n1.as_str().chars().next().cmp(&Some(c2))
                                               .then(Ordering::Greater)
                                         );
                                     }
@@ -639,7 +633,7 @@ impl MachineState {
                                             // iter2 is continuable, so it
                                             // has a tail in the heap at
                                             // focus+1.
-                                            pdl.push(iter2.heap[focus+1]);
+                                            pdl.push(iter2.heap[focus + 1]);
 
                                             return None;
                                         }
@@ -902,8 +896,12 @@ impl MachineState {
 
         let s = string.as_str();
 
-        match heap_pstr_iter.compare_pstr_to_string(s) {
-            Some(PStrPrefixCmpResult { focus, offset, prefix_len }) if prefix_len == s.len() => {
+        match heap_pstr_iter.compare_pstr_to_string(&*s) {
+            Some(PStrPrefixCmpResult {
+                focus,
+                offset,
+                prefix_len,
+            }) if prefix_len == s.len() => {
                 let focus_addr = self.heap[focus];
 
                 read_heap_cell!(focus_addr,
@@ -950,7 +948,10 @@ impl MachineState {
 
                 return;
             }
-            Some(PStrPrefixCmpResult { prefix_len: inner_prefix_len, .. }) => {
+            Some(PStrPrefixCmpResult {
+                prefix_len: inner_prefix_len,
+                ..
+            }) => {
                 prefix_len = inner_prefix_len;
             }
             None => {
@@ -1002,9 +1003,9 @@ impl MachineState {
             self.s_offset = 0;
             self.mode = MachineMode::Read;
 
-            put_partial_string(&mut self.heap, pstr, &mut self.atom_tbl)
+            put_partial_string(&mut self.heap, pstr, &self.atom_tbl)
         } else {
-            put_complete_string(&mut self.heap, pstr, &mut self.atom_tbl)
+            put_complete_string(&mut self.heap, pstr, &self.atom_tbl)
         }
     }
 
@@ -1096,7 +1097,7 @@ impl MachineState {
                 (name, 0, 0)
             }
             (HeapCellValueTag::Char, c) => {
-                (self.atom_tbl.build_with(&c.to_string()), 0, 0)
+                (AtomTable::build_with(&self.atom_tbl, &c.to_string()), 0, 0)
             }
             (HeapCellValueTag::Var | HeapCellValueTag::AttrVar | HeapCellValueTag::StackVar) => {
                 let stub = functor_stub(atom!("call"), arity + 1);
@@ -1130,26 +1131,23 @@ impl MachineState {
 
     #[inline]
     pub fn is_cyclic_term(&mut self, value: HeapCellValue) -> bool {
-        if value.is_constant() {
+        let value = self.store(self.deref(value));
+
+        if value.is_stack_var() || value.is_constant() {
             return false;
         }
 
-        let mut iter = stackful_preorder_iter(&mut self.heap, &mut self.stack, value);
+        let h = self.heap.len();
+        self.heap.push(value);
 
-        while let Some(value) = iter.next() {
-            if value.get_forwarding_bit() {
-                let value = unmark_cell_bits!(heap_bound_store(
-                    iter.heap,
-                    heap_bound_deref(iter.heap, value),
-                ));
+        let cycle_found = {
+            let mut iter = cycle_detecting_stackless_preorder_iter(&mut self.heap, h);
+            while let Some(_) = iter.next() {}
+            iter.cycle_found()
+        };
 
-                if value.is_compound(iter.heap) {
-                    return true;
-                }
-            }
-        }
-
-        false
+        self.heap.pop();
+        cycle_found
     }
 
     // arg(+N, +Term, ?Arg)
@@ -1181,7 +1179,7 @@ impl MachineState {
 
                 let n = match n {
                     Number::Fixnum(n) => n.get_num() as usize,
-                    Number::Integer(n) if *n >= 0 && *n <= std::usize::MAX => n.to_usize().unwrap(),
+                    Number::Integer(n) if usize::try_from(&*n).is_ok() => (&*n).try_into().unwrap(),
                     _ => {
                         self.fail = true;
                         return Ok(());
@@ -1324,7 +1322,7 @@ impl MachineState {
 
         let f_a = if name == atom!(".") && arity == 2 {
             self.heap.push(heap_loc_as_cell!(h));
-            self.heap.push(heap_loc_as_cell!(h+1));
+            self.heap.push(heap_loc_as_cell!(h + 1));
 
             list_loc_as_cell!(h)
         } else {
@@ -1398,9 +1396,15 @@ impl MachineState {
                         let err = self.domain_error(DomainErrorType::NotLessThanZero, n);
                         return Err(self.error_form(err, stub_gen()));
                     }
-                    Ok(Number::Rational(n)) => n.numerator().to_i64().unwrap(),
+                    Ok(Number::Rational(n)) => {
+                        let value: i64 = n.numerator().try_into().unwrap();
+                        value
+                    },
                     Ok(Number::Fixnum(n)) => n.get_num(),
-                    Ok(Number::Integer(n)) => n.to_i64().unwrap(),
+                    Ok(Number::Integer(n)) => {
+                        let value: i64 = (&*n).try_into().unwrap();
+                        value
+                    },
                     Err(_) => {
                         return type_error(arity);
                     }
@@ -1435,7 +1439,7 @@ impl MachineState {
                         }
                     }
                     (HeapCellValueTag::Char, c) => {
-                        let c = self.atom_tbl.build_with(&c.to_string());
+                        let c = AtomTable::build_with(&self.atom_tbl, &c.to_string());
 
                         self.try_functor_fabricate_struct(
                             c,
@@ -1571,8 +1575,7 @@ impl MachineState {
 
         while let Some(iteratee) = heap_pstr_iter.next() {
             match iteratee {
-                PStrIteratee::Char(_, c) =>
-                    chars.push(char_as_cell!(c)),
+                PStrIteratee::Char(_, c) => chars.push(char_as_cell!(c)),
                 PStrIteratee::PStrSegment(_, pstr_atom, n) => {
                     let pstr = PartialString::from(pstr_atom);
                     chars.extend(pstr.as_str_from(n).chars().map(|c| char_as_cell!(c)));
@@ -1614,47 +1617,12 @@ impl MachineState {
 
     // returns true on failure.
     pub fn ground_test(&mut self) -> bool {
-        use fxhash::FxBuildHasher;
+        let iter = eager_stackful_preorder_iter(&mut self.heap, self.registers[1]);
 
-        if self.registers[1].is_constant() {
-            return false;
-        }
-
-        let value = self.store(self.deref(self.registers[1]));
-
-        if value.is_stack_var() {
-            return true;
-        }
-
-        let mut visited = IndexSet::with_hasher(FxBuildHasher::default());
-        let mut iter = stackful_preorder_iter(&mut self.heap, &mut self.stack, value);
-        let mut stack_len = 0;
-
-        while let Some(value) = iter.next() {
-            let mut value = unmark_cell_bits!(value);
-
-            if value.is_var() {
-                value = heap_bound_store(
-                    iter.heap,
-                    heap_bound_deref(iter.heap, value),
-                );
-
-                if value.is_var() {
-                    return true;
-                }
+        for term in iter {
+            if term.is_var() {
+                return true;
             }
-
-            if value.is_compound(iter.heap) {
-                if visited.contains(&value) {
-                    for _ in stack_len .. iter.stack_len() {
-                        iter.pop_stack();
-                    }
-                } else {
-                    visited.insert(value);
-                }
-            }
-
-            stack_len = iter.stack_len();
         }
 
         false
@@ -1681,9 +1649,9 @@ impl MachineState {
                             Err(_) => {}
                         },
                         Ok(Number::Integer(n)) => {
-                            if let Some(b) = n.to_u8() {
-                                bytes.push(b);
-                            }
+                            let b: u8 = (&*n).try_into().unwrap();
+
+                            bytes.push(b);
                         }
                         _ => {}
                     }

src/machine/mock_wam.rs

@@ -2,15 +2,16 @@ pub use crate::arena::*;
 pub use crate::atom_table::*;
 use crate::heap_print::*;
 pub use crate::machine::heap::*;
-pub use crate::machine::*;
 pub use crate::machine::machine_state::*;
 pub use crate::machine::stack::*;
 pub use crate::machine::streams::*;
-pub use crate::macros::*;
+pub use crate::machine::*;
 pub use crate::parser::ast::*;
 use crate::read::*;
 pub use crate::types::*;
 
+use std::sync::Arc;
+
 #[cfg(test)]
 use crate::machine::copier::CopierTarget;
 
@@ -61,7 +62,7 @@ impl MockWAM {
 
         let mut printer = HCPrinter::new(
             &mut self.machine_st.heap,
-            &mut self.machine_st.atom_tbl,
+            Arc::clone(&self.machine_st.atom_tbl),
             &mut self.machine_st.stack,
             &self.op_dir,
             PrinterOutputter::new(),
@@ -71,11 +72,9 @@ impl MockWAM {
         printer.var_names = term_write_result
             .var_dict
             .into_iter()
-            .map(|(var, cell)| {
-                match var {
-                    VarKey::VarPtr(var) => (cell, var.clone()),
-                    VarKey::AnonVar(_) => (cell, VarPtr::from(var.to_string()))
-                }
+            .map(|(var, cell)| match var {
+                VarKey::VarPtr(var) => (cell, var.clone()),
+                VarKey::AnonVar(_) => (cell, VarPtr::from(var.to_string())),
             })
             .collect();
 
@@ -222,111 +221,10 @@ pub(crate) fn parse_and_write_parsed_term_to_heap(
 
 impl Machine {
     pub fn with_test_streams() -> Self {
-        use ref_thread_local::RefThreadLocal;
-
-        let mut machine_st = MachineState::new();
-
-        let user_input = Stream::Null(StreamOptions::default());
-        let user_output = Stream::from_owned_string("".to_owned(), &mut machine_st.arena);
-        let user_error = Stream::stderr(&mut machine_st.arena);
-
-        let runtime = tokio::runtime::Builder::new_current_thread()
-            .enable_all()
-            .build()
-            .unwrap();
-
-        let mut wam = Machine {
-            machine_st,
-            indices: IndexStore::new(),
-            code: Code::new(),
-            user_input,
-            user_output,
-            user_error,
-            load_contexts: vec![],
-            runtime,
-            #[cfg(feature = "ffi")]
-	        foreign_function_table: Default::default(),
-        };
-
-        let mut lib_path = current_dir();
-
-        lib_path.pop();
-        lib_path.push("lib");
-
-        wam.add_impls_to_indices();
-
-        bootstrapping_compile(
-            Stream::from_static_string(
-                LIBRARIES.borrow()["ops_and_meta_predicates"],
-                &mut wam.machine_st.arena,
-            ),
-            &mut wam,
-            ListingSource::from_file_and_path(
-                atom!("ops_and_meta_predicates.pl"),
-                lib_path.clone(),
-            ),
-        )
-            .unwrap();
-
-        bootstrapping_compile(
-            Stream::from_static_string(
-                LIBRARIES.borrow()["builtins"],
-                &mut wam.machine_st.arena,
-            ),
-            &mut wam,
-            ListingSource::from_file_and_path(atom!("builtins.pl"), lib_path.clone()),
-        )
-            .unwrap();
-
-        if let Some(ref mut builtins) = wam.indices.modules.get_mut(&atom!("builtins")) {
-            load_module(
-                &mut wam.machine_st,
-                &mut wam.indices.code_dir,
-                &mut wam.indices.op_dir,
-                &mut wam.indices.meta_predicates,
-                &CompilationTarget::User,
-                builtins,
-            );
-
-            import_builtin_impls(&wam.indices.code_dir, builtins);
-        } else {
-            unreachable!()
-        }
-
-        lib_path.pop(); // remove the "lib" at the end
-
-        bootstrapping_compile(
-            Stream::from_static_string(include_str!("../loader.pl"), &mut wam.machine_st.arena),
-            &mut wam,
-            ListingSource::from_file_and_path(atom!("loader.pl"), lib_path.clone()),
-        )
-            .unwrap();
-
-        wam.configure_modules();
-
-        if let Some(loader) = wam.indices.modules.get(&atom!("loader")) {
-            load_module(
-                &mut wam.machine_st,
-                &mut wam.indices.code_dir,
-                &mut wam.indices.op_dir,
-                &mut wam.indices.meta_predicates,
-                &CompilationTarget::User,
-                loader,
-            );
-        } else {
-            unreachable!()
-        }
-
-        wam.load_special_forms();
-        wam.load_top_level();
-        wam.configure_streams();
-
-        wam
+        Machine::new(MachineConfig::in_memory())
     }
 
     pub fn test_load_file(&mut self, file: &str) -> Vec<u8> {
-        use std::io::Read;
-
         let stream = Stream::from_owned_string(
             std::fs::read_to_string(AsRef::<std::path::Path>::as_ref(file)).unwrap(),
             &mut self.machine_st.arena,
@@ -335,6 +233,17 @@ impl Machine {
         self.load_file(file.into(), stream);
         self.user_output.bytes().map(|b| b.unwrap()).collect()
     }
+
+    pub fn test_load_string(&mut self, code: &str) -> Vec<u8> {
+        let stream = Stream::from_owned_string(
+            code.to_owned(),
+            &mut self.machine_st.arena,
+        );
+
+        self.load_file("<stdin>".into(), stream);
+        self.user_output.bytes().map(|b| b.unwrap()).collect()
+    }
+
 }
 
 #[cfg(test)]
@@ -346,26 +255,11 @@ mod tests {
         let mut wam = MachineState::new();
         let mut op_dir = default_op_dir();
 
-        op_dir.insert(
-            (atom!("+"), Fixity::In),
-            OpDesc::build_with(500, YFX as u8),
-        );
-        op_dir.insert(
-            (atom!("-"), Fixity::In),
-            OpDesc::build_with(500, YFX as u8),
-        );
-        op_dir.insert(
-            (atom!("*"), Fixity::In),
-            OpDesc::build_with(500, YFX as u8),
-        );
-        op_dir.insert(
-            (atom!("/"), Fixity::In),
-            OpDesc::build_with(400, YFX as u8),
-        );
-        op_dir.insert(
-            (atom!("="), Fixity::In),
-            OpDesc::build_with(700, XFX as u8),
-        );
+        op_dir.insert((atom!("+"), Fixity::In), OpDesc::build_with(500, YFX as u8));
+        op_dir.insert((atom!("-"), Fixity::In), OpDesc::build_with(500, YFX as u8));
+        op_dir.insert((atom!("*"), Fixity::In), OpDesc::build_with(500, YFX as u8));
+        op_dir.insert((atom!("/"), Fixity::In), OpDesc::build_with(400, YFX as u8));
+        op_dir.insert((atom!("="), Fixity::In), OpDesc::build_with(700, XFX as u8));
 
         {
             parse_and_write_parsed_term_to_heap(&mut wam, "f(X,X).", &op_dir).unwrap();
@@ -582,22 +476,10 @@ mod tests {
         let mut wam = MachineState::new();
         let mut op_dir = default_op_dir();
 
-        op_dir.insert(
-            (atom!("+"), Fixity::In),
-            OpDesc::build_with(500, YFX as u8),
-        );
-        op_dir.insert(
-            (atom!("-"), Fixity::In),
-            OpDesc::build_with(500, YFX as u8),
-        );
-        op_dir.insert(
-            (atom!("*"), Fixity::In),
-            OpDesc::build_with(400, YFX as u8),
-        );
-        op_dir.insert(
-            (atom!("/"), Fixity::In),
-            OpDesc::build_with(400, YFX as u8),
-        );
+        op_dir.insert((atom!("+"), Fixity::In), OpDesc::build_with(500, YFX as u8));
+        op_dir.insert((atom!("-"), Fixity::In), OpDesc::build_with(500, YFX as u8));
+        op_dir.insert((atom!("*"), Fixity::In), OpDesc::build_with(400, YFX as u8));
+        op_dir.insert((atom!("/"), Fixity::In), OpDesc::build_with(400, YFX as u8));
 
         {
             parse_and_write_parsed_term_to_heap(&mut wam, "f(X,X).", &op_dir).unwrap();
@@ -688,20 +570,12 @@ mod tests {
         wam.heap.push(heap_loc_as_cell!(1));
 
         assert_eq!(
-            compare_term_test!(
-                wam,
-                heap_loc_as_cell!(0),
-                heap_loc_as_cell!(0)
-            ),
+            compare_term_test!(wam, heap_loc_as_cell!(0), heap_loc_as_cell!(0)),
             Some(Ordering::Equal)
         );
 
         assert_eq!(
-            compare_term_test!(
-                wam,
-                heap_loc_as_cell!(0),
-                atom_as_cell!(atom!("a"))
-            ),
+            compare_term_test!(wam, heap_loc_as_cell!(0), atom_as_cell!(atom!("a"))),
             Some(Ordering::Greater)
         );
 
@@ -724,29 +598,17 @@ mod tests {
         wam.heap.push(empty_list_as_cell!());
 
         assert_eq!(
-            compare_term_test!(
-                wam,
-                heap_loc_as_cell!(7),
-                heap_loc_as_cell!(7)
-            ),
+            compare_term_test!(wam, heap_loc_as_cell!(7), heap_loc_as_cell!(7)),
             Some(Ordering::Equal)
         );
 
         assert_eq!(
-            compare_term_test!(
-                wam,
-                heap_loc_as_cell!(0),
-                heap_loc_as_cell!(7)
-            ),
+            compare_term_test!(wam, heap_loc_as_cell!(0), heap_loc_as_cell!(7)),
             Some(Ordering::Greater)
         );
 
         assert_eq!(
-            compare_term_test!(
-                wam,
-                empty_list_as_cell!(),
-                heap_loc_as_cell!(7)
-            ),
+            compare_term_test!(wam, empty_list_as_cell!(), heap_loc_as_cell!(7)),
             Some(Ordering::Less)
         );
 
@@ -769,40 +631,24 @@ mod tests {
         );
 
         assert_eq!(
-            compare_term_test!(
-                wam,
-                empty_list_as_cell!(),
-                atom_as_cell!(atom!("atom"))
-            ),
+            compare_term_test!(wam, empty_list_as_cell!(), atom_as_cell!(atom!("atom"))),
             Some(Ordering::Less)
         );
 
         assert_eq!(
-            compare_term_test!(
-                wam,
-                atom_as_cell!(atom!("atom")),
-                empty_list_as_cell!()
-            ),
+            compare_term_test!(wam, atom_as_cell!(atom!("atom")), empty_list_as_cell!()),
             Some(Ordering::Greater)
         );
 
         let one_p_one = HeapCellValue::from(float_alloc!(1.1, &mut wam.arena));
 
         assert_eq!(
-            compare_term_test!(
-                wam,
-                one_p_one,
-                fixnum_as_cell!(Fixnum::build_with(1))
-            ),
+            compare_term_test!(wam, one_p_one, fixnum_as_cell!(Fixnum::build_with(1))),
             Some(Ordering::Less)
         );
 
         assert_eq!(
-            compare_term_test!(
-                wam,
-                fixnum_as_cell!(Fixnum::build_with(1)),
-                one_p_one
-            ),
+            compare_term_test!(wam, fixnum_as_cell!(Fixnum::build_with(1)), one_p_one),
             Some(Ordering::Greater)
         );
     }
@@ -821,7 +667,8 @@ mod tests {
         all_cells_unmarked(&wam.heap);
         wam.heap.clear();
 
-        wam.heap.extend(functor!(atom!("f"), [atom(atom!("a")), atom(atom!("b"))]));
+        wam.heap
+            .extend(functor!(atom!("f"), [atom(atom!("a")), atom(atom!("b"))]));
 
         assert!(!wam.is_cyclic_term(str_loc_as_cell!(0)));
 

src/machine/mod.rs

@@ -5,18 +5,22 @@ pub mod code_walker;
 #[macro_use]
 pub mod loader;
 pub mod compile;
+pub mod config;
 pub mod copier;
+pub mod cycle_detection;
+pub mod disjuncts;
 pub mod dispatch;
 pub mod gc;
 pub mod heap;
+pub mod lib_machine;
 pub mod load_state;
 pub mod machine_errors;
 pub mod machine_indices;
 pub mod machine_state;
 pub mod machine_state_impl;
 pub mod mock_wam;
+pub mod parsed_results;
 pub mod partial_string;
-pub mod disjuncts;
 pub mod preprocessor;
 pub mod stack;
 pub mod streams;
@@ -27,9 +31,9 @@ pub mod unify;
 use crate::arena::*;
 use crate::arithmetic::*;
 use crate::atom_table::*;
-use crate::forms::*;
 #[cfg(feature = "ffi")]
 use crate::ffi::ForeignFunctionTable;
+use crate::forms::*;
 use crate::instructions::*;
 use crate::machine::args::*;
 use crate::machine::compile::*;
@@ -51,9 +55,14 @@ use ordered_float::OrderedFloat;
 
 use std::cmp::Ordering;
 use std::env;
+use std::io::Read;
 use std::path::PathBuf;
 use std::sync::atomic::AtomicBool;
-use tokio::runtime::Runtime;
+
+use self::config::MachineConfig;
+use self::parsed_results::*;
+use rand::rngs::StdRng;
+use rand::SeedableRng;
 
 lazy_static! {
     pub static ref INTERRUPT: AtomicBool = AtomicBool::new(false);
@@ -68,9 +77,9 @@ pub struct Machine {
     pub(super) user_output: Stream,
     pub(super) user_error: Stream,
     pub(super) load_contexts: Vec<LoadContext>,
-    pub(super) runtime: Runtime,
     #[cfg(feature = "ffi")]
     pub(super) foreign_function_table: ForeignFunctionTable,
+    pub(super) rng: StdRng,
 }
 
 #[derive(Debug)]
@@ -109,6 +118,7 @@ include!(concat!(env!("OUT_DIR"), "/libraries.rs"));
 pub static BREAK_FROM_DISPATCH_LOOP_LOC: usize = 0;
 pub static INSTALL_VERIFY_ATTR_INTERRUPT: usize = 1;
 pub static VERIFY_ATTR_INTERRUPT_LOC: usize = 2;
+pub static LIB_QUERY_SUCCESS: usize = 3;
 
 pub struct MachinePreludeView<'a> {
     pub indices: &'a mut IndexStore,
@@ -163,7 +173,10 @@ pub(crate) fn import_builtin_impls(code_dir: &CodeDir, builtins: &mut Module) {
     for key in keys {
         let idx = code_dir.get(&key).unwrap();
         builtins.code_dir.insert(key, idx.clone());
-        builtins.module_decl.exports.push(ModuleExport::PredicateKey(key));
+        builtins
+            .module_decl
+            .exports
+            .push(ModuleExport::PredicateKey(key));
     }
 }
 
@@ -194,7 +207,7 @@ impl Machine {
                 code: &mut self.code,
                 load_contexts: &mut self.load_contexts,
             },
-            &mut self.machine_st
+            &mut self.machine_st,
         )
     }
 
@@ -206,7 +219,11 @@ impl Machine {
         self.machine_st.throw_exception(err);
     }
 
-    fn run_module_predicate(&mut self, module_name: Atom, key: PredicateKey) -> std::process::ExitCode {
+    fn run_module_predicate(
+        &mut self,
+        module_name: Atom,
+        key: PredicateKey,
+    ) -> std::process::ExitCode {
         if let Some(module) = self.indices.modules.get(&module_name) {
             if let Some(ref code_index) = module.code_dir.get(&key) {
                 let p = code_index.local().unwrap();
@@ -223,23 +240,21 @@ impl Machine {
 
     pub fn load_file(&mut self, path: &str, stream: Stream) {
         self.machine_st.registers[1] = stream_as_cell!(stream);
-        self.machine_st.registers[2] = atom_as_cell!(
-            self.machine_st.atom_tbl.build_with(path)
-        );
+        self.machine_st.registers[2] =
+            atom_as_cell!(AtomTable::build_with(&self.machine_st.atom_tbl, path));
 
         self.run_module_predicate(atom!("loader"), (atom!("file_load"), 2));
     }
 
-    fn load_top_level(&mut self) {
+    fn load_top_level(&mut self, program: &'static str) {
         let mut path_buf = current_dir();
 
         path_buf.push("src/toplevel.pl");
 
         let path = path_buf.to_str().unwrap();
-        let toplevel_stream = Stream::from_static_string(
-            include_str!("../toplevel.pl"),
-            &mut self.machine_st.arena,
-        );
+        let toplevel_stream = 
+            Stream::from_static_string(program, &mut self.machine_st.arena);
+
 
         self.load_file(path, toplevel_stream);
 
@@ -285,26 +300,40 @@ impl Machine {
         }
     }
 
-    pub fn run_top_level(&mut self) -> std::process::ExitCode {
+    pub fn run_top_level(&mut self, module_name: Atom, key: PredicateKey) -> std::process::ExitCode {
         let mut arg_pstrs = vec![];
 
         for arg in env::args() {
             arg_pstrs.push(put_complete_string(
                 &mut self.machine_st.heap,
                 &arg,
-                &mut self.machine_st.atom_tbl,
+                &self.machine_st.atom_tbl,
             ));
         }
 
-        self.machine_st.registers[1] = heap_loc_as_cell!(
-            iter_to_heap_list(&mut self.machine_st.heap, arg_pstrs.into_iter())
-        );
+        self.machine_st.registers[1] = heap_loc_as_cell!(iter_to_heap_list(
+            &mut self.machine_st.heap,
+            arg_pstrs.into_iter()
+        ));
 
-        self.run_module_predicate(atom!("$toplevel"), (atom!("$repl"), 1))
+        self.run_module_predicate(module_name, key)
+    }
+
+    pub fn set_user_input(&mut self, input: String) {
+        self.user_input = Stream::from_owned_string(input, &mut self.machine_st.arena);
+    }
+
+    pub fn get_user_output(&self) -> String {
+        let output_bytes: Vec<_> = self.user_output.bytes().map(|b| b.unwrap()).collect();
+        String::from_utf8(output_bytes).unwrap()
     }
 
     pub(crate) fn configure_modules(&mut self) {
-        fn update_call_n_indices(loader: &Module, target_code_dir: &mut CodeDir, arena: &mut Arena) {
+        fn update_call_n_indices(
+            loader: &Module,
+            target_code_dir: &mut CodeDir,
+            arena: &mut Arena,
+        ) {
             for arity in 1..66 {
                 let key = (atom!("call"), arity);
 
@@ -349,10 +378,18 @@ impl Machine {
             }
 
             for (_, target_module) in self.indices.modules.iter_mut() {
-                update_call_n_indices(&loader, &mut target_module.code_dir, &mut self.machine_st.arena);
+                update_call_n_indices(
+                    &loader,
+                    &mut target_module.code_dir,
+                    &mut self.machine_st.arena,
+                );
             }
 
-            update_call_n_indices(&loader, &mut self.indices.code_dir, &mut self.machine_st.arena);
+            update_call_n_indices(
+                &loader,
+                &mut self.indices.code_dir,
+                &mut self.machine_st.arena,
+            );
 
             self.indices.modules.insert(atom!("loader"), loader);
         } else {
@@ -361,80 +398,90 @@ impl Machine {
     }
 
     pub(crate) fn add_impls_to_indices(&mut self) {
-        let impls_offset = self.code.len() + 3;
+        let impls_offset = self.code.len() + 4;
 
-        self.code.extend(vec![
-            Instruction::BreakFromDispatchLoop,
-            Instruction::InstallVerifyAttr,
-            Instruction::VerifyAttrInterrupt,
-            Instruction::ExecuteTermGreaterThan,
-            Instruction::ExecuteTermLessThan,
-            Instruction::ExecuteTermGreaterThanOrEqual,
-            Instruction::ExecuteTermLessThanOrEqual,
-            Instruction::ExecuteTermEqual,
-            Instruction::ExecuteTermNotEqual,
-            Instruction::ExecuteNumberGreaterThan(ar_reg!(temp_v!(1)), ar_reg!(temp_v!(2))),
-            Instruction::ExecuteNumberLessThan(ar_reg!(temp_v!(1)), ar_reg!(temp_v!(2))),
-            Instruction::ExecuteNumberGreaterThanOrEqual(ar_reg!(temp_v!(1)), ar_reg!(temp_v!(2))),
-            Instruction::ExecuteNumberLessThanOrEqual(ar_reg!(temp_v!(1)), ar_reg!(temp_v!(2))),
-            Instruction::ExecuteNumberEqual(ar_reg!(temp_v!(1)), ar_reg!(temp_v!(2))),
-            Instruction::ExecuteNumberNotEqual(ar_reg!(temp_v!(1)), ar_reg!(temp_v!(2))),
-            Instruction::ExecuteIs(temp_v!(1), ar_reg!(temp_v!(2))),
-            Instruction::ExecuteAcyclicTerm,
-            Instruction::ExecuteArg,
-            Instruction::ExecuteCompare,
-            Instruction::ExecuteCopyTerm,
-            Instruction::ExecuteFunctor,
-            Instruction::ExecuteGround,
-            Instruction::ExecuteKeySort,
-            Instruction::ExecuteSort,
-            Instruction::ExecuteN(1),
-            Instruction::ExecuteN(2),
-            Instruction::ExecuteN(3),
-            Instruction::ExecuteN(4),
-            Instruction::ExecuteN(5),
-            Instruction::ExecuteN(6),
-            Instruction::ExecuteN(7),
-            Instruction::ExecuteN(8),
-            Instruction::ExecuteN(9),
-            Instruction::ExecuteIsAtom(temp_v!(1)),
-            Instruction::ExecuteIsAtomic(temp_v!(1)),
-            Instruction::ExecuteIsCompound(temp_v!(1)),
-            Instruction::ExecuteIsInteger(temp_v!(1)),
-            Instruction::ExecuteIsNumber(temp_v!(1)),
-            Instruction::ExecuteIsRational(temp_v!(1)),
-            Instruction::ExecuteIsFloat(temp_v!(1)),
-            Instruction::ExecuteIsNonVar(temp_v!(1)),
-            Instruction::ExecuteIsVar(temp_v!(1))
-        ].into_iter());
+        self.code.extend(
+            vec![
+                Instruction::BreakFromDispatchLoop,
+                Instruction::InstallVerifyAttr,
+                Instruction::VerifyAttrInterrupt,
+                Instruction::BreakFromDispatchLoop, // the location of LIB_QUERY_SUCCESS
+                Instruction::ExecuteTermGreaterThan,
+                Instruction::ExecuteTermLessThan,
+                Instruction::ExecuteTermGreaterThanOrEqual,
+                Instruction::ExecuteTermLessThanOrEqual,
+                Instruction::ExecuteTermEqual,
+                Instruction::ExecuteTermNotEqual,
+                Instruction::ExecuteNumberGreaterThan(ar_reg!(temp_v!(1)), ar_reg!(temp_v!(2))),
+                Instruction::ExecuteNumberLessThan(ar_reg!(temp_v!(1)), ar_reg!(temp_v!(2))),
+                Instruction::ExecuteNumberGreaterThanOrEqual(
+                    ar_reg!(temp_v!(1)),
+                    ar_reg!(temp_v!(2)),
+                ),
+                Instruction::ExecuteNumberLessThanOrEqual(ar_reg!(temp_v!(1)), ar_reg!(temp_v!(2))),
+                Instruction::ExecuteNumberEqual(ar_reg!(temp_v!(1)), ar_reg!(temp_v!(2))),
+                Instruction::ExecuteNumberNotEqual(ar_reg!(temp_v!(1)), ar_reg!(temp_v!(2))),
+                Instruction::ExecuteIs(temp_v!(1), ar_reg!(temp_v!(2))),
+                Instruction::ExecuteAcyclicTerm,
+                Instruction::ExecuteArg,
+                Instruction::ExecuteCompare,
+                Instruction::ExecuteCopyTerm,
+                Instruction::ExecuteFunctor,
+                Instruction::ExecuteGround,
+                Instruction::ExecuteKeySort,
+                Instruction::ExecuteSort,
+                Instruction::ExecuteN(1),
+                Instruction::ExecuteN(2),
+                Instruction::ExecuteN(3),
+                Instruction::ExecuteN(4),
+                Instruction::ExecuteN(5),
+                Instruction::ExecuteN(6),
+                Instruction::ExecuteN(7),
+                Instruction::ExecuteN(8),
+                Instruction::ExecuteN(9),
+                Instruction::ExecuteIsAtom(temp_v!(1)),
+                Instruction::ExecuteIsAtomic(temp_v!(1)),
+                Instruction::ExecuteIsCompound(temp_v!(1)),
+                Instruction::ExecuteIsInteger(temp_v!(1)),
+                Instruction::ExecuteIsNumber(temp_v!(1)),
+                Instruction::ExecuteIsRational(temp_v!(1)),
+                Instruction::ExecuteIsFloat(temp_v!(1)),
+                Instruction::ExecuteIsNonVar(temp_v!(1)),
+                Instruction::ExecuteIsVar(temp_v!(1)),
+            ]
+            .into_iter(),
+        );
 
-        for (p, instr) in self.code[impls_offset ..].iter().enumerate() {
+        for (p, instr) in self.code[impls_offset..].iter().enumerate() {
             let key = instr.to_name_and_arity();
             self.indices.code_dir.insert(
                 key,
-                CodeIndex::new(IndexPtr::index(p + impls_offset), &mut self.machine_st.arena),
+                CodeIndex::new(
+                    IndexPtr::index(p + impls_offset),
+                    &mut self.machine_st.arena,
+                ),
             );
         }
     }
 
-    pub fn new() -> Self {
+    pub fn new(config: MachineConfig) -> Self {
         use ref_thread_local::RefThreadLocal;
 
         let args = MachineArgs::new();
         let mut machine_st = MachineState::new();
 
-        let user_input = Stream::stdin(&mut machine_st.arena, args.add_history);
-        let user_output = Stream::stdout(&mut machine_st.arena);
-        let user_error = Stream::stderr(&mut machine_st.arena);
-
-        #[cfg(not(target_os = "wasi"))]
-        let runtime = tokio::runtime::Runtime::new()
-            .unwrap();
-        #[cfg(target_os = "wasi")]
-        let runtime = tokio::runtime::Builder::new_current_thread()
-            .enable_all()
-            .build()
-            .unwrap();
+        let (user_input, user_output, user_error) = match config.streams {
+            config::StreamConfig::Stdio => (
+                Stream::stdin(&mut machine_st.arena, args.add_history),
+                Stream::stdout(&mut machine_st.arena),
+                Stream::stderr(&mut machine_st.arena),
+            ),
+            config::StreamConfig::Memory => (
+                Stream::Null(StreamOptions::default()),
+                Stream::from_owned_string("".to_owned(), &mut machine_st.arena),
+                Stream::stderr(&mut machine_st.arena),
+            ),
+        };
 
         let mut wam = Machine {
             machine_st,
@@ -444,9 +491,9 @@ impl Machine {
             user_output,
             user_error,
             load_contexts: vec![],
-            runtime,
             #[cfg(feature = "ffi")]
-	        foreign_function_table: Default::default(),
+            foreign_function_table: Default::default(),
+            rng: StdRng::from_entropy(),
         };
 
         let mut lib_path = current_dir();
@@ -470,10 +517,7 @@ impl Machine {
         .unwrap();
 
         bootstrapping_compile(
-            Stream::from_static_string(
-                LIBRARIES.borrow()["builtins"],
-                &mut wam.machine_st.arena,
-            ),
+            Stream::from_static_string(LIBRARIES.borrow()["builtins"], &mut wam.machine_st.arena),
             &mut wam,
             ListingSource::from_file_and_path(atom!("builtins.pl"), lib_path.clone()),
         )
@@ -519,14 +563,16 @@ impl Machine {
         }
 
         wam.load_special_forms();
-        wam.load_top_level();
+        wam.load_top_level(config.toplevel);
         wam.configure_streams();
 
         wam
     }
 
     pub(crate) fn configure_streams(&mut self) {
-        self.user_input.options_mut().set_alias_to_atom_opt(Some(atom!("user_input")));
+        self.user_input
+            .options_mut()
+            .set_alias_to_atom_opt(Some(atom!("user_input")));
 
         self.indices
             .stream_aliases
@@ -534,7 +580,9 @@ impl Machine {
 
         self.indices.streams.insert(self.user_input);
 
-        self.user_output.options_mut().set_alias_to_atom_opt(Some(atom!("user_output")));
+        self.user_output
+            .options_mut()
+            .set_alias_to_atom_opt(Some(atom!("user_output")));
 
         self.indices
             .stream_aliases
@@ -564,9 +612,16 @@ impl Machine {
 
                     loop {
                         let indexing_code_ptr = match &indexing_lines[oip] {
-                            &IndexingLine::Indexing(IndexingInstruction::SwitchOnTerm(arg, v, c, l, s)) => {
+                            &IndexingLine::Indexing(IndexingInstruction::SwitchOnTerm(
+                                arg,
+                                v,
+                                c,
+                                l,
+                                s,
+                            )) => {
                                 cell = self.deref_register(arg);
-                                self.machine_st.select_switch_on_term_index(cell, v, c, l, s)
+                                self.machine_st
+                                    .select_switch_on_term_index(cell, v, c, l, s)
                             }
                             IndexingLine::Indexing(IndexingInstruction::SwitchOnConstant(hm)) => {
                                 let lit = self.machine_st.constant_to_literal(cell);
@@ -676,7 +731,12 @@ impl Machine {
                         }
                     );
                 }
-                &Instruction::GetPartialString(Level::Shallow, string, RegType::Temp(t), has_tail) => {
+                &Instruction::GetPartialString(
+                    Level::Shallow,
+                    string,
+                    RegType::Temp(t),
+                    has_tail,
+                ) => {
                     let cell = self.deref_register(t);
 
                     read_heap_cell!(cell,
@@ -707,17 +767,17 @@ impl Machine {
                         }
                     );
                 }
-                Instruction::GetConstant(..) |
-                Instruction::GetList(..) |
-                Instruction::GetStructure(..) |
-                Instruction::GetPartialString(..) |
-                &Instruction::UnifyVoid(..) |
-                &Instruction::UnifyConstant(..) |
-                &Instruction::GetVariable(..) |
-                &Instruction::GetValue(..) |
-                &Instruction::UnifyVariable(..) |
-                &Instruction::UnifyValue(..) |
-                &Instruction::UnifyLocalValue(..)  => {
+                Instruction::GetConstant(..)
+                | Instruction::GetList(..)
+                | Instruction::GetStructure(..)
+                | Instruction::GetPartialString(..)
+                | &Instruction::UnifyVoid(..)
+                | &Instruction::UnifyConstant(..)
+                | &Instruction::GetVariable(..)
+                | &Instruction::GetValue(..)
+                | &Instruction::UnifyVariable(..)
+                | &Instruction::UnifyValue(..)
+                | &Instruction::UnifyLocalValue(..) => {
                     offset += 1;
                 }
                 _ => {
@@ -732,9 +792,10 @@ impl Machine {
     fn next_applicable_clause(&mut self, mut offset: usize) -> Option<usize> {
         while !self.next_clause_applicable(self.machine_st.p + offset + 1) {
             match &self.code[self.machine_st.p + offset] {
-                &Instruction::DefaultRetryMeElse(o) | &Instruction::RetryMeElse(o) |
-                &Instruction::DynamicElse(.., NextOrFail::Next(o)) |
-                &Instruction::DynamicInternalElse(.., NextOrFail::Next(o)) => offset += o,
+                &Instruction::DefaultRetryMeElse(o)
+                | &Instruction::RetryMeElse(o)
+                | &Instruction::DynamicElse(.., NextOrFail::Next(o))
+                | &Instruction::DynamicInternalElse(.., NextOrFail::Next(o)) => offset += o,
                 _ => {
                     return None;
                 }
@@ -753,14 +814,16 @@ impl Machine {
                     match &indexing_lines[self.machine_st.oip as usize] {
                         IndexingLine::IndexedChoice(indexed_choice) => {
                             match &indexed_choice[(self.machine_st.iip + inner_offset) as usize] {
-                                &IndexedChoiceInstruction::Retry(o) => {
+                                &IndexedChoiceInstruction::Retry(o)
+                                | &IndexedChoiceInstruction::DefaultRetry(o) => {
                                     if self.next_clause_applicable(self.machine_st.p + o) {
                                         return Some(inner_offset);
                                     }
 
                                     inner_offset += 1;
                                 }
-                                &IndexedChoiceInstruction::Trust(o) => {
+                                &IndexedChoiceInstruction::Trust(o)
+                                | &IndexedChoiceInstruction::DefaultTrust(o) => {
                                     return if self.next_clause_applicable(self.machine_st.p + o) {
                                         Some(inner_offset)
                                     } else {
@@ -813,12 +876,13 @@ impl Machine {
             or_frame.prelude.tr = self.machine_st.tr;
             or_frame.prelude.h = self.machine_st.heap.len();
             or_frame.prelude.b0 = self.machine_st.b0;
-            or_frame.prelude.attr_var_queue_len = self.machine_st.attr_var_init.attr_var_queue.len();
+            or_frame.prelude.attr_var_queue_len =
+                self.machine_st.attr_var_init.attr_var_queue.len();
 
             self.machine_st.b = b;
 
             for i in 0..n {
-                or_frame[i] = self.machine_st.registers[i+1];
+                or_frame[i] = self.machine_st.registers[i + 1];
             }
 
             self.machine_st.hb = self.machine_st.heap.len();
@@ -844,12 +908,13 @@ impl Machine {
             or_frame.prelude.tr = self.machine_st.tr;
             or_frame.prelude.h = self.machine_st.heap.len();
             or_frame.prelude.b0 = self.machine_st.b0;
-            or_frame.prelude.attr_var_queue_len = self.machine_st.attr_var_init.attr_var_queue.len();
+            or_frame.prelude.attr_var_queue_len =
+                self.machine_st.attr_var_init.attr_var_queue.len();
 
             self.machine_st.b = b;
 
             for i in 0..n {
-                or_frame[i] = self.machine_st.registers[i+1];
+                or_frame[i] = self.machine_st.registers[i + 1];
             }
 
             self.machine_st.hb = self.machine_st.heap.len();
@@ -912,7 +977,7 @@ impl Machine {
         let curr_tr = self.machine_st.tr;
 
         for i in 0..n {
-            self.machine_st.registers[i+1] = or_frame[i];
+            self.machine_st.registers[i + 1] = or_frame[i];
         }
 
         self.unwind_trail(old_tr, curr_tr);
@@ -956,7 +1021,7 @@ impl Machine {
         let curr_tr = self.machine_st.tr;
 
         for i in 0..n {
-            self.machine_st.registers[i+1] = or_frame[i];
+            self.machine_st.registers[i + 1] = or_frame[i];
         }
 
         self.unwind_trail(old_tr, curr_tr);
@@ -999,7 +1064,7 @@ impl Machine {
         let n = or_frame.prelude.num_cells;
 
         for i in 0..n {
-            self.machine_st.registers[i+1] = or_frame[i];
+            self.machine_st.registers[i + 1] = or_frame[i];
         }
 
         let old_tr = or_frame.prelude.tr;
@@ -1038,15 +1103,17 @@ impl Machine {
     #[inline(always)]
     fn undefined_procedure(&mut self, name: Atom, arity: usize) -> CallResult {
         match self.machine_st.flags.unknown {
-            Unknown::Error => {
-                Err(self.machine_st.throw_undefined_error(name, arity))
-            }
+            Unknown::Error => Err(self.machine_st.throw_undefined_error(name, arity)),
             Unknown::Fail => {
                 self.machine_st.fail = true;
                 Ok(())
             }
             Unknown::Warn => {
-                println!("warning: predicate {}/{} is undefined", name.as_str(), arity);
+                println!(
+                    "warning: predicate {}/{} is undefined",
+                    name.as_str(),
+                    arity
+                );
                 self.machine_st.fail = true;
                 Ok(())
             }
@@ -1091,9 +1158,7 @@ impl Machine {
                 self.machine_st.dynamic_mode = FirstOrNext::First;
                 self.machine_st.execute_at_index(arity, compiled_tl_index);
             }
-            IndexPtrTag::Index => {
-                self.machine_st.execute_at_index(arity, compiled_tl_index)
-            }
+            IndexPtrTag::Index => self.machine_st.execute_at_index(arity, compiled_tl_index),
         }
 
         Ok(())
@@ -1118,7 +1183,9 @@ impl Machine {
                 }
             } else {
                 let stub = functor_stub(name, arity);
-                let err = self.machine_st.module_resolution_error(module_name, name, arity);
+                let err = self
+                    .machine_st
+                    .existence_error(ExistenceError::QualifiedProcedure { module_name, name, arity });
 
                 Err(self.machine_st.error_form(err, stub))
             }
@@ -1144,7 +1211,9 @@ impl Machine {
                 }
             } else {
                 let stub = functor_stub(name, arity);
-                let err = self.machine_st.module_resolution_error(module_name, name, arity);
+                let err = self
+                    .machine_st
+                    .existence_error(ExistenceError::QualifiedProcedure { module_name, name, arity });
 
                 Err(self.machine_st.error_form(err, stub))
             }
@@ -1178,12 +1247,16 @@ impl Machine {
                 let r_c_wo_h_atom = atom!("run_cleaners_without_handling");
                 let iso_ext = atom!("iso_ext");
 
-                RCWH = self.indices.get_predicate_code_index(r_c_w_h_atom, 0, iso_ext)
-                           .and_then(|item| item.local())
-                           .unwrap();
-                RCWOH = self.indices.get_predicate_code_index(r_c_wo_h_atom, 1, iso_ext)
-                            .and_then(|item| item.local())
-                            .unwrap();
+                RCWH = self
+                    .indices
+                    .get_predicate_code_index(r_c_w_h_atom, 0, iso_ext)
+                    .and_then(|item| item.local())
+                    .unwrap();
+                RCWOH = self
+                    .indices
+                    .get_predicate_code_index(r_c_wo_h_atom, 1, iso_ext)
+                    .and_then(|item| item.local())
+                    .unwrap();
             });
 
             (RCWH, RCWOH)
@@ -1194,9 +1267,8 @@ impl Machine {
                 let (idx, arity) = if self.machine_st.effective_block() > prev_block {
                     (r_c_w_h, 0)
                 } else {
-                    self.machine_st.registers[1] = fixnum_as_cell!(
-                        Fixnum::build_with(b_cutoff as i64)
-                    );
+                    self.machine_st.registers[1] =
+                        fixnum_as_cell!(Fixnum::build_with(b_cutoff as i64));
 
                     (r_c_wo_h, 1)
                 };
@@ -1263,9 +1335,8 @@ impl Machine {
                         None => unreachable!(),
                     }
                 }
-                TrailEntryTag::TrailedAttachedValue => {
-                }
+                TrailEntryTag::TrailedAttachedValue => {}
             }
         }
     }
-}
+}

src/machine/parsed_results.rs

@@ -0,0 +1,285 @@
+use crate::atom_table::*;
+use ordered_float::OrderedFloat;
+use dashu::*;
+use std::collections::BTreeMap;
+use std::collections::HashMap;
+
+pub type QueryResult = Result<QueryResolution, String>;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum QueryResolution {
+    True,
+    False,
+    Matches(Vec<QueryMatch>),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct QueryMatch {
+    pub bindings: BTreeMap<String, Value>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum QueryResolutionLine {
+    True,
+    False,
+    Match(BTreeMap<String, Value>),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Value {
+    Integer(Integer),
+    Rational(Rational),
+    Float(OrderedFloat<f64>),
+    Atom(Atom),
+    String(String),
+    List(Vec<Value>),
+    Structure(Atom, Vec<Value>),
+    Var,
+}
+
+impl From<BTreeMap<&str, Value>> for QueryMatch {
+    fn from(bindings: BTreeMap<&str, Value>) -> Self {
+        QueryMatch {
+            bindings: bindings
+                .into_iter()
+                .map(|(k, v)| (k.to_string(), v))
+                .collect::<BTreeMap<_, _>>(),
+        }
+    }
+}
+
+impl From<BTreeMap<String, Value>> for QueryMatch {
+    fn from(bindings: BTreeMap<String, Value>) -> Self {
+        QueryMatch { bindings }
+    }
+}
+
+impl From<Vec<QueryResolutionLine>> for QueryResolution {
+    fn from(query_result_lines: Vec<QueryResolutionLine>) -> Self {
+        // If there is only one line, and it is true or false, return that.
+        if query_result_lines.len() == 1 {
+            match query_result_lines[0].clone() {
+                QueryResolutionLine::True => return QueryResolution::True,
+                QueryResolutionLine::False => return QueryResolution::False,
+                _ => {}
+            }
+        }
+
+        // If there is only one line, and it is an empty match, return true.
+        if query_result_lines.len() == 1 {
+            match query_result_lines[0].clone() {
+                QueryResolutionLine::Match(m) => {
+                    if m.is_empty() {
+                        return QueryResolution::True;
+                    }
+                }
+                _ => {}
+            }
+        }
+
+        // If there is at least one line with true and no matches, return true.
+        if query_result_lines
+            .iter()
+            .any(|l| l == &QueryResolutionLine::True)
+            && !query_result_lines.iter().any(|l| {
+                if let &QueryResolutionLine::Match(_) = l {
+                    true
+                } else {
+                    false
+                }
+            })
+        {
+            return QueryResolution::True;
+        }
+
+        // If there is at least one match, return all matches.
+        let all_matches = query_result_lines
+            .into_iter()
+            .filter(|l| {
+                if let &QueryResolutionLine::Match(_) = l {
+                    true
+                } else {
+                    false
+                }
+            })
+            .map(|l| match l {
+                QueryResolutionLine::Match(m) => QueryMatch::from(m),
+                _ => unreachable!(),
+            })
+            .collect::<Vec<_>>();
+
+        if !all_matches.is_empty() {
+            return QueryResolution::Matches(all_matches);
+        }
+
+        QueryResolution::False
+    }
+}
+
+fn split_response_string(input: &str) -> Vec<String> {
+    let mut level_bracket = 0;
+    let mut level_parenthesis = 0;
+    let mut in_double_quotes = false;
+    let mut in_single_quotes = false;
+    let mut start = 0;
+    let mut result = Vec::new();
+
+    for (i, c) in input.chars().enumerate() {
+        match c {
+            '[' => level_bracket += 1,
+            ']' => level_bracket -= 1,
+            '(' => level_parenthesis += 1,
+            ')' => level_parenthesis -= 1,
+            '"' => in_double_quotes = !in_double_quotes,
+            '\'' => in_single_quotes = !in_single_quotes,
+            ',' if level_bracket == 0 && level_parenthesis == 0 && !in_double_quotes && !in_single_quotes => {
+                result.push(input[start..i].trim().to_string());
+                start = i + 1;
+            }
+            _ => {}
+        }
+    }
+
+    result.push(input[start..].trim().to_string());
+    result
+}
+
+fn split_key_value_pairs(input: &str) -> Vec<(String, String)> {
+    let items = split_response_string(input);
+    let mut result = Vec::new();
+
+    for item in items {
+        let parts: Vec<&str> = item.splitn(2, '=').collect();
+        if parts.len() == 2 {
+            let key = parts[0].trim().to_string();
+            let value = parts[1].trim().to_string();
+            result.push((key, value));
+        }
+    }
+
+    result
+}
+
+fn parse_prolog_response(input: &str) -> HashMap<String, String> {
+    let mut map: HashMap<String, String> = HashMap::new();
+    // Use regex to match strings including commas inside them
+    for result in split_key_value_pairs(input) {
+        let key = result.0;
+        let value = result.1;
+        // cut off at given characters/strings:
+        let value = value.split("\n").next().unwrap().to_string();
+        let value = value.split("  ").next().unwrap().to_string();
+        let value = value.split("\t").next().unwrap().to_string();
+        let value = value.split("error").next().unwrap().to_string();
+        map.insert(key, value);
+    }
+    
+    map
+}
+
+impl TryFrom<String> for QueryResolutionLine {
+    type Error = ();
+    fn try_from(string: String) -> Result<Self, Self::Error> {
+        match string.as_str() {
+            "true" => Ok(QueryResolutionLine::True),
+            "false" => Ok(QueryResolutionLine::False),
+            _ => Ok(QueryResolutionLine::Match(
+                parse_prolog_response(&string)
+                    .iter()
+                    .map(|(k, v)| -> Result<(String, Value), ()> {
+                        let key = k.to_string();
+                        let value = v.to_string();
+                        Ok((key, Value::try_from(value)?))
+                    })
+                    .filter_map(Result::ok)
+                    .collect::<BTreeMap<_, _>>()
+                )
+            ),
+        }
+    }
+}
+
+fn split_nested_list(input: &str) -> Vec<String> {
+    let mut level = 0;
+    let mut start = 0;
+    let mut result = Vec::new();
+
+    for (i, c) in input.chars().enumerate() {
+        match c {
+            '[' => level += 1,
+            ']' => level -= 1,
+            ',' if level == 0 => {
+                result.push(input[start..i].trim().to_string());
+                start = i + 1;
+            }
+            _ => {}
+        }
+    }
+
+    result.push(input[start..].trim().to_string());
+    result
+}
+
+impl TryFrom<String> for Value {
+    type Error = ();
+    fn try_from(string: String) -> Result<Self, Self::Error> {
+        let trimmed = string.trim();
+
+        if let Ok(float_value) = string.parse::<f64>() {
+            Ok(Value::Float(OrderedFloat(float_value)))
+        } else if let Ok(int_value) = string.parse::<i128>() {
+            Ok(Value::Integer(int_value.into()))
+        } else if trimmed.starts_with("'") && trimmed.ends_with("'") {
+            Ok(Value::String(trimmed[1..trimmed.len() - 1].into()))
+        } else if trimmed.starts_with("\"") && trimmed.ends_with("\"") {
+            Ok(Value::String(trimmed[1..trimmed.len() - 1].into()))
+        } else if trimmed.starts_with("[") && trimmed.ends_with("]") {
+            let split = split_nested_list(&trimmed[1..trimmed.len() - 1]);
+            
+            let values = split
+                .into_iter()
+                .map(Value::try_from)
+                .collect::<Result<Vec<_>, _>>()?;
+
+            Ok(Value::List(values))
+        } else if trimmed.starts_with("{") && trimmed.ends_with("}") {
+            let mut iter = trimmed[1..trimmed.len() - 1].split(",");
+            let mut values = vec![];
+
+            while let Some(value) = iter.next() {
+                let items: Vec<_> = value.split(":").collect();
+                if items.len() == 2 {
+                    let _key = items[0].to_string();
+                    let value = items[1].to_string();
+                    values.push(Value::try_from(value)?);
+                }
+            }
+
+            Ok(Value::Structure(atom!("{}"), values))
+        } else if trimmed.starts_with("<<") && trimmed.ends_with(">>") {
+            let mut iter = trimmed[2..trimmed.len() - 2].split(",");
+            let mut values = vec![];
+
+            while let Some(value) = iter.next() {
+                let items: Vec<_> = value.split(":").collect();
+                if items.len() == 2 {
+                    let _key = items[0].to_string();
+                    let value = items[1].to_string();
+                    values.push(Value::try_from(value)?);
+                }
+            }
+
+            Ok(Value::Structure(atom!("<<>>"), values))
+        } else if !trimmed.contains(",") && !trimmed.contains("'") && !trimmed.contains("\"") {
+            Ok(Value::String(trimmed.into()))
+        } else {
+            Err(())
+        }
+    }
+}
+
+impl From<&str> for Value {
+    fn from(str: &str) -> Self {
+        Value::String(str.to_string())
+    }
+}

src/machine/partial_string.rs

@@ -43,11 +43,10 @@ impl Into<Atom> for PartialString {
 
 impl PartialString {
     #[inline]
-    pub(super) fn new<'a>(src: &'a str, atom_tbl: &mut AtomTable) -> Option<(Self, &'a str)> {
+    pub(super) fn new<'a>(src: &'a str, atom_tbl: &AtomTable) -> Option<(Self, &'a str)> {
         let terminator_idx = scan_for_terminator(src.chars());
-        let pstr = PartialString(atom_tbl.build_with(&src[.. terminator_idx]));
-
-        Some(if terminator_idx <  src.as_bytes().len() {
+        let pstr = PartialString(AtomTable::build_with(&atom_tbl, &src[..terminator_idx]));
+        Some(if terminator_idx < src.as_bytes().len() {
             (pstr, &src[terminator_idx + 1..])
         } else {
             (pstr, "")
@@ -55,8 +54,8 @@ impl PartialString {
     }
 
     #[inline(always)]
-    pub(crate) fn as_str_from(&self, n: usize) -> &str {
-        &self.0.as_str()[n..]
+    pub(crate) fn as_str_from(&self, n: usize) -> AtomString {
+        self.0.as_str().map(|str| &str[n..])
     }
 }
 
@@ -124,11 +123,15 @@ impl<'a> HeapPStrIter<'a> {
 
         let mut final_result = None;
 
-        while let Some(PStrIterStep { iteratee, next_hare }) = self.step(self.brent_st.hare) {
+        while let Some(PStrIterStep {
+            iteratee,
+            next_hare,
+        }) = self.step(self.brent_st.hare)
+        {
             self.brent_st.hare = next_hare;
             self.focus = self.heap[iteratee.focus()];
 
-            result.focus  = iteratee.focus();
+            result.focus = iteratee.focus();
             result.offset = iteratee.offset();
 
             match iteratee {
@@ -151,7 +154,7 @@ impl<'a> HeapPStrIter<'a> {
                     let s = &s[result.prefix_len..];
 
                     if s.len() >= t.len() {
-                        if s.starts_with(t) {
+                        if (&*s).starts_with(&*t) {
                             result.prefix_len += t.len();
                             result.offset += t.len();
                         } else {
@@ -202,7 +205,7 @@ impl<'a> HeapPStrIter<'a> {
         self.brent_st.hare = self.orig_focus;
         self.brent_st.tortoise = self.orig_focus;
 
-        for _ in 0 .. self.brent_st.lam {
+        for _ in 0..self.brent_st.lam {
             self.brent_st.hare = self.step(self.brent_st.hare).unwrap().next_hare;
         }
 
@@ -225,7 +228,7 @@ impl<'a> HeapPStrIter<'a> {
                 }
                 PStrIteratee::PStrSegment(_, pstr_atom, n) => {
                     let pstr = PartialString::from(pstr_atom);
-                    buf += pstr.as_str_from(n);
+                    buf += &*pstr.as_str_from(n);
                 }
             }
         }
@@ -238,43 +241,43 @@ impl<'a> HeapPStrIter<'a> {
         let mut focus = self.focus;
 
         loop {
-           read_heap_cell!(focus,
-               (HeapCellValueTag::CStr | HeapCellValueTag::PStrLoc) => {
-                   return true;
-               }
-               (HeapCellValueTag::Atom, (name, arity)) => { // TODO: use Str here?
-                   return name == atom!(".") && arity == 2;
-               }
-               (HeapCellValueTag::Lis, h) => {
-                   let value = self.heap[h];
-                   let value = heap_bound_store(
-                       self.heap,
-                       heap_bound_deref(self.heap, value),
-                   );
+            read_heap_cell!(focus,
+                (HeapCellValueTag::CStr | HeapCellValueTag::PStrLoc) => {
+                    return true;
+                }
+                (HeapCellValueTag::Atom, (name, arity)) => { // TODO: use Str here?
+                    return name == atom!(".") && arity == 2;
+                }
+                (HeapCellValueTag::Lis, h) => {
+                    let value = self.heap[h];
+                    let value = heap_bound_store(
+                        self.heap,
+                        heap_bound_deref(self.heap, value),
+                    );
 
-                   return read_heap_cell!(value,
-                       (HeapCellValueTag::Atom, (name, arity)) => {
-                           arity == 0 && name.as_char().is_some()
-                       }
-                       (HeapCellValueTag::Char) => {
-                           true
-                       }
-                       _ => {
-                           false
-                       }
-                   );
-               }
-               (HeapCellValueTag::AttrVar | HeapCellValueTag::Var, h) => {
-                   if focus == self.heap[h] {
-                       return false;
-                   }
+                    return read_heap_cell!(value,
+                        (HeapCellValueTag::Atom, (name, arity)) => {
+                            arity == 0 && name.as_char().is_some()
+                        }
+                        (HeapCellValueTag::Char) => {
+                            true
+                        }
+                        _ => {
+                            false
+                        }
+                    );
+                }
+                (HeapCellValueTag::AttrVar | HeapCellValueTag::Var, h) => {
+                    if focus == self.heap[h] {
+                        return false;
+                    }
 
-                   focus = self.heap[h];
-               }
-               _ => {
-                   return false;
-               }
-           );
+                    focus = self.heap[h];
+                }
+                _ => {
+                    return false;
+                }
+            );
         }
     }
 
@@ -381,13 +384,15 @@ impl<'a> HeapPStrIter<'a> {
     }
 
     fn pre_cycle_discovery_stepper(&mut self) -> Option<PStrIteratee> {
-        let PStrIterStep { iteratee, next_hare } =
-            match self.step(self.brent_st.hare) {
-                Some(results) => results,
-                None => {
-                    return None;
-                }
-            };
+        let PStrIterStep {
+            iteratee,
+            next_hare,
+        } = match self.step(self.brent_st.hare) {
+            Some(results) => results,
+            None => {
+                return None;
+            }
+        };
 
         self.focus = self.heap[iteratee.focus()];
 
@@ -421,13 +426,15 @@ impl<'a> HeapPStrIter<'a> {
             return None;
         }
 
-        let PStrIterStep { iteratee, next_hare } =
-            match self.step(self.brent_st.hare) {
-                Some(results) => results,
-                None => {
-                    return None;
-                }
-            };
+        let PStrIterStep {
+            iteratee,
+            next_hare,
+        } = match self.step(self.brent_st.hare) {
+            Some(results) => results,
+            None => {
+                return None;
+            }
+        };
 
         self.focus = self.heap[next_hare];
         self.brent_st.hare = next_hare;
@@ -515,11 +522,8 @@ impl<'a> Iterator for PStrCharsIter<'a> {
 
                     match pstr.as_str_from(n).chars().next() {
                         Some(c) => {
-                            self.item = Some(PStrIteratee::PStrSegment(
-                                f1,
-                                pstr_atom,
-                                n + c.len_utf8(),
-                            ));
+                            self.item =
+                                Some(PStrIteratee::PStrSegment(f1, pstr_atom, n + c.len_utf8()));
 
                             return Some(c);
                         }
@@ -684,8 +688,10 @@ pub fn compare_pstr_prefixes<'a>(
                             }
                         }
                     }
-                    (PStrIteratee::PStrSegment(f1, pstr1_atom, n1),
-                     PStrIteratee::PStrSegment(f2, pstr2_atom, n2)) => {
+                    (
+                        PStrIteratee::PStrSegment(f1, pstr1_atom, n1),
+                        PStrIteratee::PStrSegment(f2, pstr2_atom, n2),
+                    ) => {
                         if pstr1_atom == pstr2_atom && n1 == n2 {
                             cycle_detection_step(i1, i2, &step_1);
                             let both_cyclic = cycle_detection_step(i2, i1, &step_2);
@@ -707,7 +713,7 @@ pub fn compare_pstr_prefixes<'a>(
                         let str2 = pstr2.as_str_from(n2);
 
                         match str1.len().cmp(&str2.len()) {
-                            Ordering::Equal if str1 == str2 => {
+                            Ordering::Equal if &*str1 == &*str2 => {
                                 cycle_detection_step(i1, i2, &step_1);
                                 let both_cyclic = cycle_detection_step(i2, i1, &step_2);
 
@@ -718,8 +724,9 @@ pub fn compare_pstr_prefixes<'a>(
                                     continue;
                                 }
                             }
-                            Ordering::Less if str2.starts_with(str1) => {
-                                step_2.iteratee = PStrIteratee::PStrSegment(f2, pstr2_atom, n2 + str1.len());
+                            Ordering::Less if str2.starts_with(&*str1) => {
+                                step_2.iteratee =
+                                    PStrIteratee::PStrSegment(f2, pstr2_atom, n2 + str1.len());
                                 let c1_result = cycle_detection_step(i1, i2, &step_1);
                                 r1 = step(i1, i1.brent_st.hare);
 
@@ -727,8 +734,9 @@ pub fn compare_pstr_prefixes<'a>(
                                     continue;
                                 }
                             }
-                            Ordering::Greater if str1.starts_with(str2) => {
-                                step_1.iteratee = PStrIteratee::PStrSegment(f1, pstr1_atom, n1 + str2.len());
+                            Ordering::Greater if str1.starts_with(&*str2) => {
+                                step_1.iteratee =
+                                    PStrIteratee::PStrSegment(f1, pstr1_atom, n1 + str2.len());
                                 let c2_result = cycle_detection_step(i2, i1, &step_2);
                                 r2 = step(i2, i2.brent_st.hare);
 
@@ -737,7 +745,7 @@ pub fn compare_pstr_prefixes<'a>(
                                 }
                             }
                             _ => {
-                                return PStrCmpResult::Ordered(str1.cmp(str2));
+                                return PStrCmpResult::Ordered(str1.cmp(&*str2));
                             }
                         }
                     }
@@ -796,11 +804,8 @@ mod test {
     fn pstr_iter_tests() {
         let mut wam = MockWAM::new();
 
-        let pstr_var_cell = put_partial_string(
-            &mut wam.machine_st.heap,
-            "abc ",
-            &mut wam.machine_st.atom_tbl,
-        );
+        let pstr_var_cell =
+            put_partial_string(&mut wam.machine_st.heap, "abc ", &wam.machine_st.atom_tbl);
 
         let pstr_cell = wam.machine_st.heap[pstr_var_cell.get_value() as usize];
 
@@ -819,11 +824,8 @@ mod test {
         wam.machine_st.heap.pop();
         wam.machine_st.heap.push(pstr_loc_as_cell!(2));
 
-        let pstr_second_var_cell = put_partial_string(
-            &mut wam.machine_st.heap,
-            "def",
-            &mut wam.machine_st.atom_tbl,
-        );
+        let pstr_second_var_cell =
+            put_partial_string(&mut wam.machine_st.heap, "def", &wam.machine_st.atom_tbl);
 
         let pstr_second_cell = wam.machine_st.heap[pstr_second_var_cell.get_value() as usize];
 
@@ -836,7 +838,11 @@ mod test {
             );
             assert_eq!(
                 iter.next(),
-                Some(PStrIteratee::PStrSegment(2, cell_as_atom!(pstr_second_cell), 0))
+                Some(PStrIteratee::PStrSegment(
+                    2,
+                    cell_as_atom!(pstr_second_cell),
+                    0
+                ))
             );
 
             assert_eq!(iter.next(), None);
@@ -855,7 +861,11 @@ mod test {
             );
             assert_eq!(
                 iter.next(),
-                Some(PStrIteratee::PStrSegment(2, cell_as_atom!(pstr_second_cell), 0))
+                Some(PStrIteratee::PStrSegment(
+                    2,
+                    cell_as_atom!(pstr_second_cell),
+                    0
+                ))
             );
 
             assert_eq!(iter.next(), None);
@@ -863,10 +873,14 @@ mod test {
         }
 
         wam.machine_st.heap.pop();
-        wam.machine_st.heap.push(pstr_loc_as_cell!(wam.machine_st.heap.len() + 1));
+        wam.machine_st
+            .heap
+            .push(pstr_loc_as_cell!(wam.machine_st.heap.len() + 1));
 
         wam.machine_st.heap.push(pstr_offset_as_cell!(0));
-        wam.machine_st.heap.push(fixnum_as_cell!(Fixnum::build_with(0)));
+        wam.machine_st
+            .heap
+            .push(fixnum_as_cell!(Fixnum::build_with(0)));
 
         {
             let mut iter = HeapPStrIter::new(&wam.machine_st.heap, 0);
@@ -892,31 +906,25 @@ mod test {
             // construct a structurally similar but different cyclic partial string
             // matching the one beginning at wam.machine_st.heap[0].
 
-            put_partial_string(
-                &mut wam.machine_st.heap,
-                "ab",
-                &mut wam.machine_st.atom_tbl,
-            );
+            put_partial_string(&mut wam.machine_st.heap, "ab", &wam.machine_st.atom_tbl);
 
             wam.machine_st.heap.pop();
 
-            wam.machine_st.heap.push(pstr_loc_as_cell!(second_h+2));
+            wam.machine_st.heap.push(pstr_loc_as_cell!(second_h + 2));
 
-            put_partial_string(
-                &mut wam.machine_st.heap,
-                "c ",
-                &mut wam.machine_st.atom_tbl,
-            );
+            put_partial_string(&mut wam.machine_st.heap, "c ", &wam.machine_st.atom_tbl);
 
             wam.machine_st.heap.pop();
 
-            wam.machine_st.heap.push(pstr_loc_as_cell!(second_h+4));
+            wam.machine_st.heap.push(pstr_loc_as_cell!(second_h + 4));
 
             wam.machine_st.heap.push(pstr_second_cell);
-            wam.machine_st.heap.push(pstr_loc_as_cell!(second_h+6));
+            wam.machine_st.heap.push(pstr_loc_as_cell!(second_h + 6));
 
             wam.machine_st.heap.push(pstr_offset_as_cell!(second_h));
-            wam.machine_st.heap.push(fixnum_as_cell!(Fixnum::build_with(0)));
+            wam.machine_st
+                .heap
+                .push(fixnum_as_cell!(Fixnum::build_with(0)));
 
             let mut iter1 = HeapPStrIter::new(&wam.machine_st.heap, 0);
             let mut iter2 = HeapPStrIter::new(&wam.machine_st.heap, second_h);
@@ -929,11 +937,7 @@ mod test {
 
         wam.machine_st.heap.clear();
 
-        put_partial_string(
-            &mut wam.machine_st.heap,
-            "abc ",
-            &mut wam.machine_st.atom_tbl,
-        );
+        put_partial_string(&mut wam.machine_st.heap, "abc ", &wam.machine_st.atom_tbl);
 
         let pstr_cell = wam.machine_st.heap[0];
 
@@ -963,11 +967,8 @@ mod test {
 
         wam.machine_st.heap.clear();
 
-        let cstr_var_cell = put_complete_string(
-            &mut wam.machine_st.heap,
-            "abc",
-            &mut wam.machine_st.atom_tbl,
-        );
+        let cstr_var_cell =
+            put_complete_string(&mut wam.machine_st.heap, "abc", &wam.machine_st.atom_tbl);
 
         wam.machine_st.heap.push(list_loc_as_cell!(2));
         wam.machine_st.heap.push(heap_loc_as_cell!(2));
@@ -982,30 +983,18 @@ mod test {
 
         unify!(wam.machine_st, cstr_var_cell, heap_loc_as_cell!(1));
 
-        assert_eq!(
-            wam.machine_st.heap[2],
-            char_as_cell!('a'),
-        );
+        assert_eq!(wam.machine_st.heap[2], char_as_cell!('a'),);
 
-        assert_eq!(
-            wam.machine_st.heap[4],
-            char_as_cell!('b'),
-        );
+        assert_eq!(wam.machine_st.heap[4], char_as_cell!('b'),);
 
-        assert_eq!(
-            wam.machine_st.heap[6],
-            char_as_cell!('c'),
-        );
+        assert_eq!(wam.machine_st.heap[6], char_as_cell!('c'),);
 
         // test "abc" = [X,Y,Z|D].
 
         wam.machine_st.heap.clear();
 
-        let cstr_var_cell = put_complete_string(
-            &mut wam.machine_st.heap,
-            "abc",
-            &mut wam.machine_st.atom_tbl,
-        );
+        let cstr_var_cell =
+            put_complete_string(&mut wam.machine_st.heap, "abc", &wam.machine_st.atom_tbl);
 
         wam.machine_st.heap.push(list_loc_as_cell!(2));
         wam.machine_st.heap.push(heap_loc_as_cell!(2)); // X
@@ -1022,35 +1011,20 @@ mod test {
 
         assert_eq!(wam.machine_st.fail, false);
 
-        assert_eq!(
-            wam.machine_st.heap[2],
-            char_as_cell!('a'),
-        );
+        assert_eq!(wam.machine_st.heap[2], char_as_cell!('a'),);
 
-        assert_eq!(
-            wam.machine_st.heap[4],
-            char_as_cell!('b'),
-        );
+        assert_eq!(wam.machine_st.heap[4], char_as_cell!('b'),);
 
-        assert_eq!(
-            wam.machine_st.heap[6],
-            char_as_cell!('c'),
-        );
+        assert_eq!(wam.machine_st.heap[6], char_as_cell!('c'),);
 
-        assert_eq!(
-            wam.machine_st.heap[7],
-            empty_list_as_cell!(),
-        );
+        assert_eq!(wam.machine_st.heap[7], empty_list_as_cell!(),);
 
         // test "d" = [d].
 
         wam.machine_st.heap.clear();
 
-        let cstr_var_cell = put_complete_string(
-            &mut wam.machine_st.heap,
-            "d",
-            &mut wam.machine_st.atom_tbl,
-        );
+        let cstr_var_cell =
+            put_complete_string(&mut wam.machine_st.heap, "d", &wam.machine_st.atom_tbl);
 
         wam.machine_st.heap.push(list_loc_as_cell!(2));
         wam.machine_st.heap.push(char_as_cell!('d'));
@@ -1064,11 +1038,8 @@ mod test {
 
         wam.machine_st.heap.clear();
 
-        let cstr_var_cell = put_complete_string(
-            &mut wam.machine_st.heap,
-            "abc",
-            &mut wam.machine_st.atom_tbl,
-        );
+        let cstr_var_cell =
+            put_complete_string(&mut wam.machine_st.heap, "abc", &wam.machine_st.atom_tbl);
 
         wam.machine_st.heap.push(list_loc_as_cell!(2));
         wam.machine_st.heap.push(heap_loc_as_cell!(2));
@@ -1085,30 +1056,17 @@ mod test {
 
         assert_eq!(wam.machine_st.fail, false);
 
-        assert_eq!(
-            wam.machine_st.heap[2],
-            char_as_cell!('a'),
-        );
+        assert_eq!(wam.machine_st.heap[2], char_as_cell!('a'),);
 
-        assert_eq!(
-            wam.machine_st.heap[4],
-            char_as_cell!('b'),
-        );
+        assert_eq!(wam.machine_st.heap[4], char_as_cell!('b'),);
 
-        assert_eq!(
-            wam.machine_st.heap[6],
-            char_as_cell!('c'),
-        );
+        assert_eq!(wam.machine_st.heap[6], char_as_cell!('c'),);
 
         // test "abcdef" = [a,b,c|X].
 
         wam.machine_st.heap.clear();
 
-        put_complete_string(
-            &mut wam.machine_st.heap,
-            "abcdef",
-            &mut wam.machine_st.atom_tbl,
-        );
+        put_complete_string(&mut wam.machine_st.heap, "abcdef", &wam.machine_st.atom_tbl);
 
         wam.machine_st.heap.push(pstr_as_cell!(atom!("abc")));
         wam.machine_st.heap.push(heap_loc_as_cell!(2));
@@ -1123,7 +1081,10 @@ mod test {
         assert_eq!(wam.machine_st.heap[3], pstr_loc_as_cell!(1));
         assert_eq!(wam.machine_st.heap[4], atom_as_cstr_cell!(atom!("abcdef")));
         assert_eq!(wam.machine_st.heap[5], pstr_offset_as_cell!(4));
-        assert_eq!(wam.machine_st.heap[6], fixnum_as_cell!(Fixnum::build_with("abc".len() as i64)));
+        assert_eq!(
+            wam.machine_st.heap[6],
+            fixnum_as_cell!(Fixnum::build_with("abc".len() as i64))
+        );
 
         // test iteration on X = [b,c,b,c,b,c,b,c|...] as an offset.
 
@@ -1132,7 +1093,9 @@ mod test {
         wam.machine_st.heap.push(pstr_as_cell!(atom!("abc")));
         wam.machine_st.heap.push(pstr_loc_as_cell!(2));
         wam.machine_st.heap.push(pstr_offset_as_cell!(0));
-        wam.machine_st.heap.push(fixnum_as_cell!(Fixnum::build_with(1)));
+        wam.machine_st
+            .heap
+            .push(fixnum_as_cell!(Fixnum::build_with(1)));
 
         {
             let mut iter = HeapPStrIter::new(&wam.machine_st.heap, 2);

src/machine/preprocessor.rs

@@ -12,11 +12,7 @@ use indexmap::IndexSet;
 use std::cell::Cell;
 use std::convert::TryFrom;
 
-pub(crate) fn to_op_decl(
-    prec: u16,
-    spec: Atom,
-    name: Atom,
-) -> Result<OpDecl, CompilationError> {
+pub(crate) fn to_op_decl(prec: u16, spec: Atom, name: Atom) -> Result<OpDecl, CompilationError> {
     match spec {
         atom!("xfx") => Ok(OpDecl::new(OpDesc::build_with(prec, XFX as u8), name)),
         atom!("xfy") => Ok(OpDecl::new(OpDesc::build_with(prec, XFY as u8), name)),
@@ -29,19 +25,16 @@ pub(crate) fn to_op_decl(
     }
 }
 
-fn setup_op_decl(
-    mut terms: Vec<Term>,
-    atom_tbl: &mut AtomTable,
-) -> Result<OpDecl, CompilationError> {
+fn setup_op_decl(mut terms: Vec<Term>, atom_tbl: &AtomTable) -> Result<OpDecl, CompilationError> {
     let name = match terms.pop().unwrap() {
         Term::Literal(_, Literal::Atom(name)) => name,
-        Term::Literal(_, Literal::Char(c)) => atom_tbl.build_with(&c.to_string()),
+        Term::Literal(_, Literal::Char(c)) => AtomTable::build_with(atom_tbl, &c.to_string()),
         _ => return Err(CompilationError::InconsistentEntry),
     };
 
     let spec = match terms.pop().unwrap() {
         Term::Literal(_, Literal::Atom(name)) => name,
-        Term::Literal(_, Literal::Char(c)) => atom_tbl.build_with(&c.to_string()),
+        Term::Literal(_, Literal::Char(c)) => AtomTable::build_with(atom_tbl, &c.to_string()),
         _ => return Err(CompilationError::InconsistentEntry),
     };
 
@@ -65,15 +58,17 @@ fn setup_predicate_indicator(term: &mut Term) -> Result<PredicateKey, Compilatio
             let name = terms.pop().unwrap();
 
             let arity = match arity {
-                Term::Literal(_, Literal::Integer(n)) => n.to_usize(),
+                Term::Literal(_, Literal::Integer(n)) => (&*n).try_into().ok(),
                 Term::Literal(_, Literal::Fixnum(n)) => usize::try_from(n.get_num()).ok(),
                 _ => None,
-            }.ok_or(CompilationError::InvalidModuleExport)?;
+            }
+            .ok_or(CompilationError::InvalidModuleExport)?;
 
             let name = match name {
                 Term::Literal(_, Literal::Atom(name)) => Some(name),
                 _ => None,
-            }.ok_or(CompilationError::InvalidModuleExport)?;
+            }
+            .ok_or(CompilationError::InvalidModuleExport)?;
 
             if *slash == atom!("/") {
                 Ok((name, arity))
@@ -87,7 +82,7 @@ fn setup_predicate_indicator(term: &mut Term) -> Result<PredicateKey, Compilatio
 
 fn setup_module_export(
     mut term: Term,
-    atom_tbl: &mut AtomTable,
+    atom_tbl: &AtomTable,
 ) -> Result<ModuleExport, CompilationError> {
     setup_predicate_indicator(&mut term)
         .map(ModuleExport::PredicateKey)
@@ -113,7 +108,7 @@ pub(crate) fn build_rule_body(vars: &[Term], body_term: Term) -> Term {
 
 pub(super) fn setup_module_export_list(
     mut export_list: Term,
-    atom_tbl: &mut AtomTable,
+    atom_tbl: &AtomTable,
 ) -> Result<Vec<ModuleExport>, CompilationError> {
     let mut exports = vec![];
 
@@ -133,7 +128,7 @@ pub(super) fn setup_module_export_list(
 
 fn setup_module_decl(
     mut terms: Vec<Term>,
-    atom_tbl: &mut AtomTable,
+    atom_tbl: &AtomTable,
 ) -> Result<ModuleDecl, CompilationError> {
     let export_list = terms.pop().unwrap();
     let name = terms.pop().unwrap();
@@ -141,7 +136,8 @@ fn setup_module_decl(
     let name = match name {
         Term::Literal(_, Literal::Atom(name)) => Some(name),
         _ => None,
-    }.ok_or(CompilationError::InvalidModuleDecl)?;
+    }
+    .ok_or(CompilationError::InvalidModuleDecl)?;
 
     let exports = setup_module_export_list(export_list, atom_tbl)?;
 
@@ -150,9 +146,7 @@ fn setup_module_decl(
 
 fn setup_use_module_decl(mut terms: Vec<Term>) -> Result<ModuleSource, CompilationError> {
     match terms.pop().unwrap() {
-        Term::Clause(_, name, mut terms)
-            if name == atom!("library") && terms.len() == 1 =>
-        {
+        Term::Clause(_, name, mut terms) if name == atom!("library") && terms.len() == 1 => {
             match terms.pop().unwrap() {
                 Term::Literal(_, Literal::Atom(name)) => Ok(ModuleSource::Library(name)),
                 _ => Err(CompilationError::InvalidModuleDecl),
@@ -167,13 +161,11 @@ type UseModuleExport = (ModuleSource, IndexSet<ModuleExport>);
 
 fn setup_qualified_import(
     mut terms: Vec<Term>,
-    atom_tbl: &mut AtomTable,
+    atom_tbl: &AtomTable,
 ) -> Result<UseModuleExport, CompilationError> {
     let mut export_list = terms.pop().unwrap();
     let module_src = match terms.pop().unwrap() {
-        Term::Clause(_, name, mut terms)
-            if name == atom!("library") && terms.len() == 1 =>
-        {
+        Term::Clause(_, name, mut terms) if name == atom!("library") && terms.len() == 1 => {
             match terms.pop().unwrap() {
                 Term::Literal(_, Literal::Atom(name)) => Ok(ModuleSource::Library(name)),
                 _ => Err(CompilationError::InvalidModuleDecl),
@@ -318,11 +310,11 @@ pub(super) fn setup_declaration<'a, LS: LoadState<'a>>(
             }
             (atom!("module"), 2) => {
                 let atom_tbl = &mut LS::machine_st(&mut loader.payload).atom_tbl;
-                Ok(Declaration::Module(setup_module_decl(terms, atom_tbl)?))
+                Ok(Declaration::Module(setup_module_decl(terms, &atom_tbl)?))
             }
             (atom!("op"), 3) => {
                 let atom_tbl = &mut LS::machine_st(&mut loader.payload).atom_tbl;
-                Ok(Declaration::Op(setup_op_decl(terms, atom_tbl)?))
+                Ok(Declaration::Op(setup_op_decl(terms, &atom_tbl)?))
             }
             (atom!("non_counted_backtracking"), 1) => {
                 let (name, arity) = setup_predicate_indicator(&mut terms.pop().unwrap())?;
@@ -331,7 +323,7 @@ pub(super) fn setup_declaration<'a, LS: LoadState<'a>>(
             (atom!("use_module"), 1) => Ok(Declaration::UseModule(setup_use_module_decl(terms)?)),
             (atom!("use_module"), 2) => {
                 let atom_tbl = &mut LS::machine_st(&mut loader.payload).atom_tbl;
-                let (name, exports) = setup_qualified_import(terms, atom_tbl)?;
+                let (name, exports) = setup_qualified_import(terms, &atom_tbl)?;
 
                 Ok(Declaration::UseQualifiedModule(name, exports))
             }
@@ -381,19 +373,28 @@ fn build_meta_predicate_clause<'a, LS: LoadState<'a>>(
                 }
 
                 fn tag_with_module_name(module_name: Atom, term: Term) -> Term {
-                    Term::Clause(Cell::default(), atom!(":"), vec![
-                        Term::Literal(Cell::default(), Literal::Atom(module_name)),
-                        term
-                    ])
+                    Term::Clause(
+                        Cell::default(),
+                        atom!(":"),
+                        vec![
+                            Term::Literal(Cell::default(), Literal::Atom(module_name)),
+                            term,
+                        ],
+                    )
                 }
 
                 let process_term: fn(Atom, Term) -> Term;
 
                 let (module_name, key, term) = match term {
                     Term::Clause(cell, atom!(":"), mut terms) if terms.len() == 2 => {
-                        if let Some((module_name, name)) = get_qualified_name(&terms[0], &terms[1]) {
+                        if let Some((module_name, name)) = get_qualified_name(&terms[0], &terms[1])
+                        {
                             process_term = tag_with_module_name;
-                            (module_name, (name, terms[1].arity() + supp_args), terms.pop().unwrap())
+                            (
+                                module_name,
+                                (name, terms[1].arity() + supp_args),
+                                terms.pop().unwrap(),
+                            )
                         } else {
                             arg_terms.push(Term::Clause(cell, atom!(":"), terms));
                             continue;
@@ -408,10 +409,8 @@ fn build_meta_predicate_clause<'a, LS: LoadState<'a>>(
                 let term = match term {
                     Term::Clause(cell, name, mut terms) => {
                         if let Some(Term::Literal(_, Literal::CodeIndex(_))) = terms.last() {
-                            arg_terms.push(process_term(
-                                module_name,
-                                Term::Clause(cell, name, terms),
-                            ));
+                            arg_terms
+                                .push(process_term(module_name, Term::Clause(cell, name, terms)));
 
                             continue;
                         }
@@ -424,11 +423,14 @@ fn build_meta_predicate_clause<'a, LS: LoadState<'a>>(
                     Term::Literal(cell, Literal::Atom(name)) => {
                         let idx = loader.get_or_insert_qualified_code_index(module_name, key);
 
-                        process_term(module_name, Term::Clause(
-                            cell,
-                            name,
-                            vec![Term::Literal(Cell::default(), Literal::CodeIndex(idx))],
-                        ))
+                        process_term(
+                            module_name,
+                            Term::Clause(
+                                cell,
+                                name,
+                                vec![Term::Literal(Cell::default(), Literal::CodeIndex(idx))],
+                            ),
+                        )
                     }
                     term => term,
                 };
@@ -462,12 +464,7 @@ pub(super) fn clause_to_query_term<'a, LS: LoadState<'a>>(
     if let ClauseType::Named(arity, name, idx) = ct {
         if let Some(meta_specs) = loader.get_meta_specs(name, arity).cloned() {
             let module_name = loader.payload.compilation_target.module_name();
-            let terms = build_meta_predicate_clause(
-                loader,
-                module_name,
-                terms,
-                meta_specs,
-            );
+            let terms = build_meta_predicate_clause(loader, module_name, terms, meta_specs);
 
             return QueryTerm::Clause(
                 Cell::default(),
@@ -501,12 +498,7 @@ pub(super) fn qualified_clause_to_query_term<'a, LS: LoadState<'a>>(
 
     if let ClauseType::Named(arity, name, idx) = ct {
         if let Some(meta_specs) = loader.get_meta_specs(name, arity).cloned() {
-            let terms = build_meta_predicate_clause(
-                loader,
-                module_name,
-                terms,
-                meta_specs,
-            );
+            let terms = build_meta_predicate_clause(loader, module_name, terms, meta_specs);
 
             return QueryTerm::Clause(
                 Cell::default(),
@@ -529,17 +521,13 @@ pub(crate) struct Preprocessor {
 
 impl Preprocessor {
     pub(super) fn new(settings: CodeGenSettings) -> Self {
-        Preprocessor {
-            settings,
-        }
+        Preprocessor { settings }
     }
 
     fn setup_fact(&mut self, term: Term) -> Result<(Fact, VarData), CompilationError> {
         match term {
             Term::Clause(..) | Term::Literal(_, Literal::Atom(..)) => {
-                let classifier = VariableClassifier::new(
-                    self.settings.default_call_policy(),
-                );
+                let classifier = VariableClassifier::new(self.settings.default_call_policy());
 
                 let (head, var_data) = classifier.classify_fact(term)?;
                 Ok((Fact { head }, var_data))
@@ -554,21 +542,25 @@ impl Preprocessor {
         head: Term,
         body: Term,
     ) -> Result<(Rule, VarData), CompilationError> {
-        let classifier = VariableClassifier::new(
-            self.settings.default_call_policy(),
-        );
+        let classifier = VariableClassifier::new(self.settings.default_call_policy());
 
         let (head, clauses, var_data) = classifier.classify_rule(loader, head, body)?;
 
         match head {
-            Term::Clause(_, name, terms) => Ok((Rule {
-                head: (name, terms),
-                clauses,
-            }, var_data)),
-            Term::Literal(_, Literal::Atom(name)) => Ok((Rule {
-                head: (name, vec![]),
-                clauses,
-            }, var_data)),
+            Term::Clause(_, name, terms) => Ok((
+                Rule {
+                    head: (name, terms),
+                    clauses,
+                },
+                var_data,
+            )),
+            Term::Literal(_, Literal::Atom(name)) => Ok((
+                Rule {
+                    head: (name, vec![]),
+                    clauses,
+                },
+                var_data,
+            )),
             _ => Err(CompilationError::InvalidRuleHead),
         }
     }

src/machine/stack.rs

@@ -30,12 +30,6 @@ pub struct Stack {
     _marker: PhantomData<HeapCellValue>,
 }
 
-impl Drop for Stack {
-    fn drop(&mut self) {
-        self.buf.deallocate();
-    }
-}
-
 #[derive(Debug)]
 pub(crate) struct AndFramePrelude {
     pub(crate) num_cells: usize,
@@ -189,7 +183,7 @@ impl Stack {
         let frame_size = AndFrame::size_of(num_cells);
 
         unsafe {
-            let e = self.buf.ptr as usize - self.buf.base as usize;
+            let e = (*self.buf.ptr.get_mut()) as usize - self.buf.base as usize;
             let new_ptr = self.alloc(frame_size);
             let mut offset = prelude_size::<AndFramePrelude>();
 
@@ -213,7 +207,7 @@ impl Stack {
         let frame_size = OrFrame::size_of(num_cells);
 
         unsafe {
-            let b = self.buf.ptr as usize - self.buf.base as usize;
+            let b = (*self.buf.ptr.get_mut()) as usize - self.buf.base as usize;
             let new_ptr = self.alloc(frame_size);
             let mut offset = prelude_size::<OrFramePrelude>();
 
@@ -269,8 +263,8 @@ impl Stack {
     pub(crate) fn truncate(&mut self, b: usize) {
         let base = self.buf.base as usize + b;
 
-        if base < self.buf.ptr as usize {
-            self.buf.ptr = base as *mut _;
+        if base < (*self.buf.ptr.get_mut()) as usize {
+            *self.buf.ptr.get_mut() = base as *mut _;
         }
     }
 }
@@ -290,7 +284,7 @@ mod tests {
 
         assert_eq!(
             e,
-            0// 10 * mem::size_of::<HeapCellValue>() + prelude_size::<AndFrame>()
+            0 // 10 * mem::size_of::<HeapCellValue>() + prelude_size::<AndFrame>()
         );
 
         assert_eq!(and_frame.prelude.num_cells, 10);
@@ -315,7 +309,10 @@ mod tests {
         let and_frame = wam.machine_st.stack.index_and_frame_mut(next_e);
 
         for idx in 0..9 {
-            assert_eq!(and_frame[idx + 1], stack_loc_as_cell!(AndFrame, next_e, idx + 1));
+            assert_eq!(
+                and_frame[idx + 1],
+                stack_loc_as_cell!(AndFrame, next_e, idx + 1)
+            );
         }
 
         let and_frame = wam.machine_st.stack.index_and_frame(e);

src/machine/streams.rs

@@ -4,13 +4,13 @@ use crate::parser::ast::*;
 use crate::parser::char_reader::*;
 use crate::read::*;
 
+#[cfg(feature = "http")]
+use crate::http::HttpResponse;
 use crate::machine::heap::*;
 use crate::machine::machine_errors::*;
 use crate::machine::machine_indices::*;
 use crate::machine::machine_state::*;
 use crate::types::*;
-#[cfg(feature = "http")]
-use crate::http::HttpResponse;
 
 pub use modular_bitfield::prelude::*;
 
@@ -19,17 +19,22 @@ use std::error::Error;
 use std::fmt;
 use std::fmt::Debug;
 use std::fs::{File, OpenOptions};
-use std::hash::{Hash};
+use std::hash::Hash;
 use std::io;
-use std::io::{BufRead, Cursor, ErrorKind, Read, Seek, SeekFrom, Write};
+use std::io::{Cursor, ErrorKind, Read, Seek, SeekFrom, Write};
+#[cfg(feature = "http")]
+use std::io::BufRead;
 use std::mem;
-use std::net::{TcpStream, Shutdown};
+use std::net::{Shutdown, TcpStream};
 use std::ops::{Deref, DerefMut};
 use std::ptr;
 
 #[cfg(feature = "tls")]
 use native_tls::TlsStream;
 
+#[cfg(feature = "http")]
+use warp::hyper;
+
 #[derive(Debug, BitfieldSpecifier, Clone, Copy, PartialEq, Eq, Hash)]
 #[bits = 1]
 pub enum StreamType {
@@ -154,8 +159,10 @@ impl StreamLayout<CharReader<InputFileStream>> {
     fn position(&mut self) -> Option<u64> {
         // stream is the internal CharReader. subtract
         // its pending buffer length from position.
-        self.get_mut().file.seek(SeekFrom::Current(0))
-            .map(|pos| pos  - self.stream.rem_buf_len() as u64)
+        self.get_mut()
+            .file
+            .seek(SeekFrom::Current(0))
+            .map(|pos| pos - self.stream.rem_buf_len() as u64)
             .ok()
     }
 }
@@ -195,7 +202,7 @@ impl CharRead for StaticStringStream {
     #[inline(always)]
     fn peek_char(&mut self) -> Option<std::io::Result<char>> {
         let pos = self.stream.position() as usize;
-        self.stream.get_ref()[pos ..].chars().next().map(Ok)
+        self.stream.get_ref()[pos..].chars().next().map(Ok)
     }
 
     #[inline(always)]
@@ -205,7 +212,9 @@ impl CharRead for StaticStringStream {
 
     #[inline(always)]
     fn put_back_char(&mut self, c: char) {
-        self.stream.seek(SeekFrom::Current(- (c.len_utf8() as i64))).unwrap();
+        self.stream
+            .seek(SeekFrom::Current(-(c.len_utf8() as i64)))
+            .unwrap();
     }
 }
 
@@ -286,15 +295,15 @@ impl Read for HttpReadStream {
 #[cfg(feature = "http")]
 pub struct HttpWriteStream {
     status_code: u16,
-    headers: hyper::HeaderMap,
+    headers: mem::ManuallyDrop<hyper::HeaderMap>,
     response: TypedArenaPtr<HttpResponse>,
-    buffer: Vec<u8>,
+    buffer: mem::ManuallyDrop<Vec<u8>>,
 }
 
 #[cfg(feature = "http")]
 impl Debug for HttpWriteStream {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-	    write!(f, "Http Write Stream")
+        write!(f, "Http Write Stream")
     }
 }
 
@@ -302,31 +311,39 @@ impl Debug for HttpWriteStream {
 impl Write for HttpWriteStream {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
-	self.buffer.extend_from_slice(buf);
-	Ok(buf.len())
+        self.buffer.extend_from_slice(buf);
+        Ok(buf.len())
     }
 
     #[inline]
     fn flush(&mut self) -> std::io::Result<()> {
+	Ok(())
+    }
+}
+
+#[cfg(feature = "http")]
+impl HttpWriteStream {
+    fn drop(&mut self) {
+	let headers = unsafe { mem::ManuallyDrop::take(&mut self.headers) };
+	let buffer = unsafe { mem::ManuallyDrop::take(&mut self.buffer) };
+	
 	let (ready, response, cvar) = &**self.response;
 
 	let mut ready = ready.lock().unwrap();
 	{
 	    let mut response = response.lock().unwrap();
 	
-	    let bytes = bytes::Bytes::copy_from_slice(&self.buffer);
-	    let mut response_ = hyper::Response::builder()
+	    let mut response_ = warp::http::Response::builder()
 	        .status(self.status_code);
-	    *response_.headers_mut().unwrap() = self.headers.clone();
-	    *response = Some(response_.body(http_body_util::Full::new(bytes)).unwrap());
+	    *response_.headers_mut().unwrap() = headers;
+	    *response = Some(response_.body(warp::hyper::Body::from(buffer)).unwrap());
 	}
 	*ready = true;
 	cvar.notify_one();
-
-	Ok(())
     }
 }
 
+
 #[derive(Debug)]
 pub struct StandardOutputStream {}
 
@@ -510,7 +527,9 @@ impl Stream {
     #[inline]
     pub fn from_owned_string(string: String, arena: &mut Arena) -> Stream {
         Stream::Byte(arena_alloc!(
-            StreamLayout::new(CharReader::new(ByteStream(Cursor::new(string.into_bytes())))),
+            StreamLayout::new(CharReader::new(ByteStream(Cursor::new(
+                string.into_bytes()
+            )))),
             arena
         ))
     }
@@ -546,7 +565,7 @@ impl Stream {
             #[cfg(feature = "http")]
             ArenaHeaderTag::HttpReadStream => Stream::HttpRead(TypedArenaPtr::new(ptr as *mut _)),
             #[cfg(feature = "http")]
-	        ArenaHeaderTag::HttpWriteStream => Stream::HttpWrite(TypedArenaPtr::new(ptr as *mut _)),
+            ArenaHeaderTag::HttpWriteStream => Stream::HttpWrite(TypedArenaPtr::new(ptr as *mut _)),
             ArenaHeaderTag::ReadlineStream => Stream::Readline(TypedArenaPtr::new(ptr as *mut _)),
             ArenaHeaderTag::StaticStringStream => {
                 Stream::StaticString(TypedArenaPtr::new(ptr as *mut _))
@@ -603,7 +622,7 @@ impl Stream {
             #[cfg(feature = "http")]
             Stream::HttpRead(ptr) => ptr.header_ptr(),
             #[cfg(feature = "http")]
-	        Stream::HttpWrite(ptr) => ptr.header_ptr(),
+            Stream::HttpWrite(ptr) => ptr.header_ptr(),
             Stream::Null(_) => ptr::null(),
             Stream::Readline(ptr) => ptr.header_ptr(),
             Stream::StandardOutput(ptr) => ptr.header_ptr(),
@@ -728,14 +747,14 @@ impl CharRead for Stream {
             Stream::StaticString(src) => (*src).peek_char(),
             Stream::Byte(cursor) => (*cursor).peek_char(),
             #[cfg(feature = "http")]
-	        Stream::HttpWrite(_) => Some(Err(std::io::Error::new(
+            Stream::HttpWrite(_) => Some(Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::ReadFromOutputStream,
             ))),
-            Stream::OutputFile(_) |
-            Stream::StandardError(_) |
-            Stream::StandardOutput(_) |
-            Stream::Null(_) => Some(Err(std::io::Error::new(
+            Stream::OutputFile(_)
+            | Stream::StandardError(_)
+            | Stream::StandardOutput(_)
+            | Stream::Null(_) => Some(Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::ReadFromOutputStream,
             ))),
@@ -754,14 +773,14 @@ impl CharRead for Stream {
             Stream::StaticString(src) => (*src).read_char(),
             Stream::Byte(cursor) => (*cursor).read_char(),
             #[cfg(feature = "http")]
-	        Stream::HttpWrite(_) => Some(Err(std::io::Error::new(
+            Stream::HttpWrite(_) => Some(Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::ReadFromOutputStream,
             ))),
-            Stream::OutputFile(_) |
-            Stream::StandardError(_) |
-            Stream::StandardOutput(_) |
-            Stream::Null(_) => Some(Err(std::io::Error::new(
+            Stream::OutputFile(_)
+            | Stream::StandardError(_)
+            | Stream::StandardOutput(_)
+            | Stream::Null(_) => Some(Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::ReadFromOutputStream,
             ))),
@@ -780,11 +799,11 @@ impl CharRead for Stream {
             Stream::StaticString(src) => src.put_back_char(c),
             Stream::Byte(cursor) => cursor.put_back_char(c),
             #[cfg(feature = "http")]
-	        Stream::HttpWrite(_) => {}
-            Stream::OutputFile(_) |
-            Stream::StandardError(_) |
-            Stream::StandardOutput(_) |
-            Stream::Null(_) => {}
+            Stream::HttpWrite(_) => {}
+            Stream::OutputFile(_)
+            | Stream::StandardError(_)
+            | Stream::StandardOutput(_)
+            | Stream::Null(_) => {}
         }
     }
 
@@ -800,11 +819,11 @@ impl CharRead for Stream {
             Stream::StaticString(ref mut src) => src.consume(nread),
             Stream::Byte(ref mut cursor) => cursor.consume(nread),
             #[cfg(feature = "http")]
-	        Stream::HttpWrite(_) => {}
-            Stream::OutputFile(_) |
-            Stream::StandardError(_) |
-            Stream::StandardOutput(_) |
-            Stream::Null(_) => {}
+            Stream::HttpWrite(_) => {}
+            Stream::OutputFile(_)
+            | Stream::StandardError(_)
+            | Stream::StandardOutput(_)
+            | Stream::Null(_) => {}
         }
     }
 }
@@ -823,17 +842,17 @@ impl Read for Stream {
             Stream::StaticString(src) => (*src).read(buf),
             Stream::Byte(cursor) => (*cursor).read(buf),
             #[cfg(feature = "http")]
-	        Stream::HttpWrite(_) => Err(std::io::Error::new(
+            Stream::HttpWrite(_) => Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::ReadFromOutputStream,
             )),
             Stream::OutputFile(_)
-                | Stream::StandardError(_)
-	            | Stream::StandardOutput(_)
-                | Stream::Null(_) => Err(std::io::Error::new(
-                    ErrorKind::PermissionDenied,
-                    StreamError::ReadFromOutputStream,
-                )),
+            | Stream::StandardError(_)
+            | Stream::StandardOutput(_)
+            | Stream::Null(_) => Err(std::io::Error::new(
+                ErrorKind::PermissionDenied,
+                StreamError::ReadFromOutputStream,
+            )),
         };
 
         bytes_read
@@ -851,16 +870,16 @@ impl Write for Stream {
             Stream::StandardOutput(stream) => stream.write(buf),
             Stream::StandardError(stream) => stream.write(buf),
             #[cfg(feature = "http")]
-	        Stream::HttpWrite(ref mut stream) => stream.get_mut().write(buf),
+            Stream::HttpWrite(ref mut stream) => stream.get_mut().write(buf),
             #[cfg(feature = "http")]
             Stream::HttpRead(_) => Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::WriteToInputStream,
             )),
-            Stream::StaticString(_) |
-            Stream::Readline(_) |
-            Stream::InputFile(..) |
-            Stream::Null(_) => Err(std::io::Error::new(
+            Stream::StaticString(_)
+            | Stream::Readline(_)
+            | Stream::InputFile(..)
+            | Stream::Null(_) => Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::WriteToInputStream,
             )),
@@ -877,16 +896,16 @@ impl Write for Stream {
             Stream::StandardError(stream) => stream.stream.flush(),
             Stream::StandardOutput(stream) => stream.stream.flush(),
             #[cfg(feature = "http")]
-	        Stream::HttpWrite(ref mut stream) => stream.stream.get_mut().flush(),
-            #[cfg(feature = "http")] 
+            Stream::HttpWrite(ref mut stream) => stream.stream.get_mut().flush(),
+            #[cfg(feature = "http")]
             Stream::HttpRead(_) => Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::FlushToInputStream,
             )),
-            Stream::StaticString(_) |
-            Stream::Readline(_) |
-            Stream::InputFile(_) |
-            Stream::Null(_) => Err(std::io::Error::new(
+            Stream::StaticString(_)
+            | Stream::Readline(_)
+            | Stream::InputFile(_)
+            | Stream::Null(_) => Err(std::io::Error::new(
                 ErrorKind::PermissionDenied,
                 StreamError::FlushToInputStream,
             )),
@@ -898,8 +917,10 @@ impl Write for Stream {
 enum StreamError {
     PeekByteFailed,
     PeekByteFromNonPeekableStream,
-    #[allow(unused)] PeekCharFailed,
-    #[allow(unused)] PeekCharFromNonPeekableStream,
+    #[allow(unused)]
+    PeekCharFailed,
+    #[allow(unused)]
+    PeekCharFromNonPeekableStream,
     ReadFromOutputStream,
     WriteToInputStream,
     FlushToInputStream,
@@ -958,7 +979,11 @@ impl PartialEq for Stream {
 
 impl Eq for Stream {}
 
-fn cursor_position<T>(past_end_of_stream: &mut bool, cursor: &Cursor<T>, cursor_len: u64) -> AtEndOfStream {
+fn cursor_position<T>(
+    past_end_of_stream: &mut bool,
+    cursor: &Cursor<T>,
+    cursor_len: u64,
+) -> AtEndOfStream {
     let position = cursor.position();
 
     let at_end_of_stream = match position.cmp(&cursor_len) {
@@ -984,17 +1009,10 @@ impl Stream {
             Stream::StaticString(string_stream_layout) => {
                 Some(string_stream_layout.stream.stream.position())
             }
-            Stream::InputFile(file_stream) => {
-                file_stream.position()
-            }
+            Stream::InputFile(file_stream) => file_stream.position(),
             #[cfg(feature = "tls")]
-            Stream::NamedTls(..) => {
-                Some(0)
-            }
-            Stream::NamedTcp(..) 
-            | Stream::Readline(..) => {
-                Some(0)
-            }
+            Stream::NamedTls(..) => Some(0),
+            Stream::NamedTcp(..) | Stream::Readline(..) => Some(0),
             _ => None,
         };
 
@@ -1011,7 +1029,11 @@ impl Stream {
                     ..
                 } = &mut **stream_layout;
 
-                stream.get_mut().file.seek(SeekFrom::Start(position)).unwrap();
+                stream
+                    .get_mut()
+                    .file
+                    .seek(SeekFrom::Start(position))
+                    .unwrap();
                 stream.reset_buffer(); // flush the internal buffer.
 
                 if let Ok(metadata) = stream.get_ref().file.metadata() {
@@ -1127,9 +1149,7 @@ impl Stream {
                     }
                 }
             }
-            _ => {
-                AtEndOfStream::Not
-            }
+            _ => AtEndOfStream::Not,
         }
     }
 
@@ -1153,14 +1173,16 @@ impl Stream {
             #[cfg(feature = "tls")]
             Stream::NamedTls(..) => atom!("read_append"),
             Stream::Byte(_)
-                | Stream::Readline(_)
-                | Stream::StaticString(_)
-                | Stream::InputFile(..) => atom!("read"),
+            | Stream::Readline(_)
+            | Stream::StaticString(_)
+            | Stream::InputFile(..) => atom!("read"),
             Stream::NamedTcp(..) => atom!("read_append"),
             Stream::OutputFile(file) if file.is_append => atom!("append"),
             #[cfg(feature = "http")]
             Stream::HttpWrite(_) => atom!("write"),
-            Stream::OutputFile(_) | Stream::StandardError(_) | Stream::StandardOutput(_) => atom!("write"),
+            Stream::OutputFile(_) | Stream::StandardError(_) | Stream::StandardOutput(_) => {
+                atom!("write")
+            }
             Stream::Null(_) => atom!(""),
         }
     }
@@ -1182,11 +1204,7 @@ impl Stream {
     }
 
     #[inline]
-    pub(crate) fn from_tcp_stream(
-        address: Atom,
-        tcp_stream: TcpStream,
-        arena: &mut Arena,
-    ) -> Self {
+    pub(crate) fn from_tcp_stream(address: Atom, tcp_stream: TcpStream, arena: &mut Arena) -> Self {
         tcp_stream.set_read_timeout(None).unwrap();
         tcp_stream.set_write_timeout(None).unwrap();
 
@@ -1234,17 +1252,17 @@ impl Stream {
     #[cfg(feature = "http")]
     #[inline]
     pub(crate) fn from_http_sender(
-	response: TypedArenaPtr<HttpResponse>,
-	status_code: u16,
-	headers: hyper::HeaderMap,
-	arena: &mut Arena,
+        response: TypedArenaPtr<HttpResponse>,
+        status_code: u16,
+        headers: hyper::HeaderMap,
+        arena: &mut Arena,
     ) -> Self {
 	Stream::HttpWrite(arena_alloc!(
 	    StreamLayout::new(CharReader::new(HttpWriteStream {
 		response,
 		status_code,
-		headers,
-		buffer: Vec::new(),
+		headers: mem::ManuallyDrop::new(headers),
+		buffer: mem::ManuallyDrop::new(Vec::new()),
 	    })),
 	    arena
 	))
@@ -1282,11 +1300,9 @@ impl Stream {
         match stream {
             Stream::NamedTcp(ref mut tcp_stream) => {
                 tcp_stream.inner_mut().tcp_stream.shutdown(Shutdown::Both)
-            },
-            #[cfg(feature = "tls")]
-            Stream::NamedTls(ref mut tls_stream) => {
-                tls_stream.inner_mut().tls_stream.shutdown()
             }
+            #[cfg(feature = "tls")]
+            Stream::NamedTls(ref mut tls_stream) => tls_stream.inner_mut().tls_stream.shutdown(),
             #[cfg(feature = "http")]
             Stream::HttpRead(ref mut http_stream) => {
                 unsafe {
@@ -1297,14 +1313,15 @@ impl Stream {
                 Ok(())
             }
             #[cfg(feature = "http")]
-	        Stream::HttpWrite(ref mut http_stream) => {
+	    Stream::HttpWrite(ref mut http_stream) => {
+		http_stream.inner_mut().drop();
                 unsafe {
                     http_stream.set_tag(ArenaHeaderTag::Dropped);
                     std::ptr::drop_in_place(&mut http_stream.inner_mut().buffer as *mut _);
                 }
 
                 Ok(())
-	        }
+            }
             Stream::InputFile(mut file_stream) => {
                 // close the stream by dropping the inner File.
                 unsafe {
@@ -1323,7 +1340,7 @@ impl Stream {
 
                 Ok(())
             }
-            _ => Ok(())
+            _ => Ok(()),
         }
     }
 
@@ -1344,10 +1361,10 @@ impl Stream {
             #[cfg(feature = "http")]
             Stream::HttpRead(..) => true,
             Stream::NamedTcp(..)
-                | Stream::Byte(_)
-                | Stream::Readline(_)
-                | Stream::StaticString(_)
-                | Stream::InputFile(..) => true,
+            | Stream::Byte(_)
+            | Stream::Readline(_)
+            | Stream::StaticString(_)
+            | Stream::InputFile(..) => true,
             _ => false,
         }
     }
@@ -1360,10 +1377,10 @@ impl Stream {
             #[cfg(feature = "http")]
             Stream::HttpWrite(..) => true,
             Stream::StandardError(_)
-                | Stream::StandardOutput(_)
-                | Stream::NamedTcp(..)
-                | Stream::Byte(_)
-                | Stream::OutputFile(..) => true,
+            | Stream::StandardOutput(_)
+            | Stream::NamedTcp(..)
+            | Stream::Byte(_)
+            | Stream::OutputFile(..) => true,
             _ => false,
         }
     }
@@ -1381,7 +1398,12 @@ impl Stream {
                     return true;
                 }
                 Stream::InputFile(ref mut file_stream) => {
-                    file_stream.stream.get_mut().file.seek(SeekFrom::Start(0)).unwrap();
+                    file_stream
+                        .stream
+                        .get_mut()
+                        .file
+                        .seek(SeekFrom::Start(0))
+                        .unwrap();
                     return true;
                 }
                 Stream::Readline(ref mut readline_stream) => {
@@ -1410,17 +1432,13 @@ impl Stream {
                     _ => Err(std::io::Error::new(ErrorKind::UnexpectedEof, "end of file")),
                 }
             }
-            Stream::InputFile(ref mut file) => {
-                match file.peek_byte() {
-                    Some(result) => {
-                        Ok(result?)
-                    }
-                    _ => Err(std::io::Error::new(
-                        ErrorKind::UnexpectedEof,
-                        StreamError::PeekByteFailed,
-                    )),
-                }
-            }
+            Stream::InputFile(ref mut file) => match file.peek_byte() {
+                Some(result) => Ok(result?),
+                _ => Err(std::io::Error::new(
+                    ErrorKind::UnexpectedEof,
+                    StreamError::PeekByteFailed,
+                )),
+            },
             Stream::Readline(ref mut stream) => stream.stream.peek_byte(),
             Stream::NamedTcp(ref mut stream) => {
                 let mut b = [0u8; 1];
@@ -1663,7 +1681,10 @@ impl MachineState {
         }
     }
 
-    pub(crate) fn open_parsing_stream(&mut self, mut stream: Stream) -> Result<Stream, ParserError> {
+    pub(crate) fn open_parsing_stream(
+        &mut self,
+        mut stream: Stream,
+    ) -> Result<Stream, ParserError> {
         match stream.peek_char() {
             None => Ok(stream), // empty stream is handled gracefully by Lexer::eof
             Some(Err(e)) => Err(ParserError::IO(e)),
@@ -1687,7 +1708,7 @@ impl MachineState {
         arity: usize,
     ) -> MachineStub {
         let stub = functor_stub(caller, arity);
-        let err  = self.permission_error(
+        let err = self.permission_error(
             perm,
             err_atom,
             if let Some(alias) = stream.options().get_alias() {
@@ -1723,7 +1744,7 @@ impl MachineState {
         stub_arity: usize,
     ) -> MachineStub {
         let stub = functor_stub(stub_name, stub_arity);
-        let err  = self.permission_error(Permission::Open, atom!("source_sink"), culprit);
+        let err = self.permission_error(Permission::Open, atom!("source_sink"), culprit);
 
         self.error_form(err, stub)
     }
@@ -1798,7 +1819,7 @@ impl MachineState {
     ) -> Result<Stream, MachineStub> {
         if file_spec == atom!("") {
             let stub = functor_stub(atom!("open"), 4);
-            let err = self.domain_error(DomainErrorType::SourceSink, self[temp_v!(1)]);
+            let err = self.domain_error(DomainErrorType::SourceSink, self.registers[1]);
 
             return Err(self.error_form(err, stub));
         }
@@ -1810,9 +1831,7 @@ impl MachineState {
             }
         }
 
-        let mode = MachineState::deref(self, self[temp_v!(2)]);
-        let mode = cell_as_atom!(self.store(mode));
-
+        let mode = cell_as_atom!(self.store(MachineState::deref(self, self.registers[2])));
         let mut open_options = OpenOptions::new();
 
         let (is_input_file, in_append_mode) = match mode {
@@ -1847,7 +1866,7 @@ impl MachineState {
             }
         };
 
-        let file = match open_options.open(file_spec.as_str()) {
+        let file = match open_options.open(&*file_spec.as_str()) {
             Ok(file) => file,
             Err(err) => {
                 match err.kind() {
@@ -1855,19 +1874,23 @@ impl MachineState {
                         // 8.11.5.3j)
                         let stub = functor_stub(atom!("open"), 4);
 
-                        let err = self.existence_error(
-                            ExistenceError::SourceSink(self[temp_v!(1)]),
-                        );
+                        let err =
+                            self.existence_error(ExistenceError::SourceSink(self[temp_v!(1)]));
 
                         return Err(self.error_form(err, stub));
                     }
                     ErrorKind::PermissionDenied => {
                         // 8.11.5.3k)
-                        return Err(self.open_permission_error(self.registers[1], atom!("open"), 4));
+                        return Err(self.open_permission_error(
+                            self.registers[1],
+                            atom!("open"),
+                            4,
+                        ));
                     }
                     _ => {
+                        // assume the OS is out of file descriptors.
                         let stub = functor_stub(atom!("open"), 4);
-                        let err = self.syntax_error(ParserError::IO(err));
+                        let err = self.resource_error(ResourceError::OutOfFiles);
 
                         return Err(self.error_form(err, stub));
                     }

src/machine/term_stream.rs

@@ -1,8 +1,8 @@
 use crate::forms::*;
-use crate::machine::*;
 use crate::machine::load_state::*;
 use crate::machine::loader::*;
 use crate::machine::machine_errors::*;
+use crate::machine::*;
 use crate::parser::ast::*;
 use crate::parser::parser::*;
 use crate::read::devour_whitespace;
@@ -45,7 +45,10 @@ impl<'a> BootstrappingTermStream<'a> {
         listing_src: ListingSource,
     ) -> Self {
         let parser = Parser::new(stream, machine_st);
-        Self { parser, listing_src }
+        Self {
+            parser,
+            listing_src,
+        }
     }
 }
 
@@ -101,7 +104,7 @@ impl<TS> LoadStatePayload<TS> {
             non_counted_bt_preds: IndexSet::with_hasher(FxBuildHasher::default()),
             predicates: predicate_queue![],
             clause_clauses: vec![],
-         }
+        }
     }
 }
 
@@ -122,20 +125,18 @@ impl TermStream for LiveTermStream {
     }
 }
 
-pub struct InlineTermStream {
-}
+pub struct InlineTermStream {}
 
 impl TermStream for InlineTermStream {
     fn next(&mut self, _: &CompositeOpDir) -> Result<Term, CompilationError> {
-	    Err(CompilationError::from(ParserError::unexpected_eof()))
+        Err(CompilationError::from(ParserError::unexpected_eof()))
     }
 
     fn eof(&mut self) -> Result<bool, CompilationError> {
-	    Ok(true)
+        Ok(true)
     }
 
     fn listing_src(&self) -> &ListingSource {
-	    &ListingSource::User
+        &ListingSource::User
     }
 }
-

src/machine/unify.rs

@@ -1,9 +1,9 @@
 use crate::arena::*;
 use crate::forms::*;
-use crate::heap_iter::stackful_preorder_iter;
-use crate::machine::*;
+use crate::heap_iter::{NonListElider, stackful_preorder_iter};
 use crate::machine::machine_state::*;
 use crate::machine::partial_string::*;
+use crate::machine::*;
 use crate::types::*;
 
 use std::cmp::Ordering;
@@ -12,6 +12,7 @@ use std::ops::{Deref, DerefMut};
 use derive_deref::*;
 use fxhash::FxBuildHasher;
 use indexmap::IndexSet;
+use num_order::NumOrd;
 
 pub(crate) trait Unifier: DerefMut<Target = MachineState> {
     fn unify_structure(&mut self, s1: usize, value: HeapCellValue) {
@@ -190,8 +191,8 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
                     machine_st.pdl.push(pstr_iter1.focus);
                 }
             }
-            continuable @ PStrCmpResult::FirstIterContinuable(iteratee) |
-            continuable @ PStrCmpResult::SecondIterContinuable(iteratee) => {
+            continuable @ PStrCmpResult::FirstIterContinuable(iteratee)
+            | continuable @ PStrCmpResult::SecondIterContinuable(iteratee) => {
                 if continuable.is_second_iter() {
                     std::mem::swap(&mut pstr_iter1, &mut pstr_iter2);
                 }
@@ -426,8 +427,8 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
         match Number::try_from(value) {
             Ok(n2) => match n2 {
                 Number::Fixnum(n2) if n1.get_num() == n2.get_num() => {}
-                Number::Integer(n2) if n1.get_num() == *n2 => {}
-                Number::Rational(n2) if n1.get_num() == *n2 => {}
+                Number::Integer(n2) if (*n2).num_eq(&n1.get_num()) => {}
+                Number::Rational(n2) if (*n2).num_eq(&Integer::from(n1.get_num())) => {}
                 _ => {
                     self.fail = true;
                 }
@@ -439,10 +440,8 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
     }
 
     fn unify_big_num<N>(&mut self, n1: TypedArenaPtr<N>, value: HeapCellValue)
-        where N: PartialEq<Rational>
-               + PartialEq<Integer>
-               + PartialEq<i64>
-               + ArenaAllocated
+    where
+        N: PartialEq<Rational> + PartialEq<Integer> + PartialEq<i64> + ArenaAllocated,
     {
         if let Some(r) = value.as_var() {
             Self::bind(self, r, typed_arena_ptr_as_cell!(n1));
@@ -464,6 +463,48 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
         }
     }
 
+    fn unify_big_integer(&mut self, n1: TypedArenaPtr<Integer>, value: HeapCellValue) {
+        if let Some(r) = value.as_var() {
+            Self::bind(self, r, typed_arena_ptr_as_cell!(n1));
+            return;
+        }
+
+        match Number::try_from(value) {
+            Ok(n2) => match n2 {
+                Number::Fixnum(n2) if (*n1).num_eq(&n2.get_num()) => {}
+                Number::Integer(n2) if (*n1).num_eq(&*n2) => {}
+                Number::Rational(n2) if (*n2).num_eq(&*n1) => {}
+                _ => {
+                    self.fail = true;
+                }
+            },
+            Err(_) => {
+                self.fail = true;
+            }
+        }
+    }
+
+    fn unify_big_rational(&mut self, n1: TypedArenaPtr<Rational>, value: HeapCellValue) {
+        if let Some(r) = value.as_var() {
+            Self::bind(self, r, typed_arena_ptr_as_cell!(n1));
+            return;
+        }
+
+        match Number::try_from(value) {
+            Ok(n2) => match n2 {
+                Number::Fixnum(n2) if (*n1).num_eq(&Integer::from(n2.get_num())) => {}
+                Number::Integer(n2) if (*n1).num_eq(&*n2) => {}
+                Number::Rational(n2) if n1 == n2 => {}
+                _ => {
+                    self.fail = true;
+                }
+            },
+            Err(_) => {
+                self.fail = true;
+            }
+        }
+    }
+
     fn unify_f64(&mut self, f1: F64Ptr, value: HeapCellValue) {
         if let Some(r) = value.as_var() {
             Self::bind(self, r, HeapCellValue::from(f1));
@@ -489,10 +530,10 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
 
         match_untyped_arena_ptr!(ptr,
              (ArenaHeaderTag::Integer, int_ptr) => {
-                 Self::unify_big_num(self, int_ptr, value);
+                 Self::unify_big_integer(self, int_ptr, value);
              }
              (ArenaHeaderTag::Rational, rat_ptr) => {
-                 Self::unify_big_num(self, rat_ptr, value);
+                 Self::unify_big_rational(self, rat_ptr, value);
              }
              (ArenaHeaderTag::Stream, stream) => {
                  read_heap_cell!(value,
@@ -650,6 +691,9 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
                     (HeapCellValueTag::Cons, ptr_1) => {
                         Self::unify_constant(self, ptr_1, d2);
                     }
+                    (HeapCellValueTag::CutPoint, n1) => {
+                        Self::unify_fixnum(self, n1, d2);
+                    }
                     _ => {
                         unreachable!();
                     }
@@ -676,7 +720,7 @@ fn bind_with_occurs_check<U: Unifier>(unifier: &mut U, r: Ref, value: HeapCellVa
     if !value.is_constant() {
         let machine_st: &mut MachineState = unifier.deref_mut();
 
-        for cell in stackful_preorder_iter(&mut machine_st.heap, &mut machine_st.stack, value) {
+        for cell in stackful_preorder_iter::<NonListElider>(&mut machine_st.heap, &mut machine_st.stack, value) {
             let cell = unmark_cell_bits!(cell);
 
             if let Some(inner_r) = cell.as_var() {

src/macros.rs

@@ -57,13 +57,6 @@ macro_rules! atom_as_cell {
     };
 }
 
-macro_rules! cell_as_ossified_op_dir {
-    ($cell:expr) => {{
-        let ptr_u64 = cell_as_untyped_arena_ptr!($cell);
-        TypedArenaPtr::new(ptr_u64.payload_offset() as *mut OssifiedOpDir)
-    }};
-}
-
 macro_rules! cell_as_string {
     ($cell:expr) => {
         PartialString::from(cell_as_atom!($cell))
@@ -88,7 +81,7 @@ macro_rules! cell_as_atom_cell {
 macro_rules! cell_as_f64_ptr {
     ($cell:expr) => {{
         let offset = $cell.get_value() as usize;
-        F64Ptr::from_offset(offset)
+        F64Ptr::from_offset(F64Offset::new(offset))
     }};
 }
 
@@ -236,12 +229,14 @@ macro_rules! cell_as_stream {
 }
 
 macro_rules! cell_as_load_state_payload {
-    ($cell:expr) => { unsafe {
-        let ptr = cell_as_untyped_arena_ptr!($cell);
-        let ptr = std::mem::transmute::<_, *mut LiveLoadState>(ptr.payload_offset());
+    ($cell:expr) => {
+        unsafe {
+            let ptr = cell_as_untyped_arena_ptr!($cell);
+            let ptr = std::mem::transmute::<_, *mut LiveLoadState>(ptr.payload_offset());
 
-        TypedArenaPtr::new(ptr)
-    }};
+            TypedArenaPtr::new(ptr)
+        }
+    };
 }
 
 macro_rules! match_untyped_arena_ptr_pat_body {
@@ -258,13 +253,15 @@ macro_rules! match_untyped_arena_ptr_pat_body {
         $code
     }};
     ($ptr:ident, OssifiedOpDir, $n:ident, $code:expr) => {{
-        let payload_ptr = unsafe { std::mem::transmute::<_, *mut OssifiedOpDir>($ptr.payload_offset()) };
+        let payload_ptr =
+            unsafe { std::mem::transmute::<_, *mut OssifiedOpDir>($ptr.payload_offset()) };
         let $n = TypedArenaPtr::new(payload_ptr);
         #[allow(unused_braces)]
         $code
     }};
     ($ptr:ident, LiveLoadState, $n:ident, $code:expr) => {{
-        let payload_ptr = unsafe { std::mem::transmute::<_, *mut LiveLoadState>($ptr.payload_offset()) };
+        let payload_ptr =
+            unsafe { std::mem::transmute::<_, *mut LiveLoadState>($ptr.payload_offset()) };
         let $n = TypedArenaPtr::new(payload_ptr);
         #[allow(unused_braces)]
         $code
@@ -275,21 +272,24 @@ macro_rules! match_untyped_arena_ptr_pat_body {
         $code
     }};
     ($ptr:ident, TcpListener, $listener:ident, $code:expr) => {{
-        let payload_ptr = unsafe { std::mem::transmute::<_, *mut TcpListener>($ptr.payload_offset()) };
+        let payload_ptr =
+            unsafe { std::mem::transmute::<_, *mut TcpListener>($ptr.payload_offset()) };
         #[allow(unused_mut)]
         let mut $listener = TypedArenaPtr::new(payload_ptr);
         #[allow(unused_braces)]
         $code
     }};
     ($ptr:ident, HttpListener, $listener:ident, $code:expr) => {{
-        let payload_ptr = unsafe { std::mem::transmute::<_, *mut HttpListener>($ptr.payload_offset()) };
+        let payload_ptr =
+            unsafe { std::mem::transmute::<_, *mut HttpListener>($ptr.payload_offset()) };
         #[allow(unused_mut)]
         let mut $listener = TypedArenaPtr::new(payload_ptr);
         #[allow(unused_braces)]
         $code
     }};
     ($ptr:ident, HttpResponse, $listener:ident, $code:expr) => {{
-        let payload_ptr = unsafe { std::mem::transmute::<_, *mut HttpResponse>($ptr.payload_offset()) };
+        let payload_ptr =
+            unsafe { std::mem::transmute::<_, *mut HttpResponse>($ptr.payload_offset()) };
         #[allow(unused_mut)]
         let mut $listener = TypedArenaPtr::new(payload_ptr);
         #[allow(unused_braces)]
@@ -297,7 +297,8 @@ macro_rules! match_untyped_arena_ptr_pat_body {
     }};
     ($ptr:ident, IndexPtr, $ip:ident, $code:expr) => {{
         #[allow(unused_mut)]
-        let mut $ip = TypedArenaPtr::new(unsafe { std::mem::transmute::<_, *mut IndexPtr>($ptr.get_ptr()) });
+        let mut $ip =
+            TypedArenaPtr::new(unsafe { std::mem::transmute::<_, *mut IndexPtr>($ptr.get_ptr()) });
         #[allow(unused_braces)]
         $code
     }};
@@ -315,7 +316,7 @@ macro_rules! match_untyped_arena_ptr_pat {
             | ArenaHeaderTag::NamedTcpStream
             | ArenaHeaderTag::NamedTlsStream
             | ArenaHeaderTag::HttpReadStream
-	    | ArenaHeaderTag::HttpWriteStream
+            | ArenaHeaderTag::HttpWriteStream
             | ArenaHeaderTag::ReadlineStream
             | ArenaHeaderTag::StaticStringStream
             | ArenaHeaderTag::ByteStream
@@ -323,10 +324,10 @@ macro_rules! match_untyped_arena_ptr_pat {
             | ArenaHeaderTag::StandardErrorStream
     };
     (IndexPtr) => {
-        ArenaHeaderTag::IndexPtrUndefined |
-        ArenaHeaderTag::IndexPtrDynamicUndefined |
-        ArenaHeaderTag::IndexPtrDynamicIndex |
-        ArenaHeaderTag::IndexPtrIndex
+        ArenaHeaderTag::IndexPtrUndefined
+            | ArenaHeaderTag::IndexPtrDynamicUndefined
+            | ArenaHeaderTag::IndexPtrDynamicIndex
+            | ArenaHeaderTag::IndexPtrIndex
     };
     ($tag:ident) => {
         ArenaHeaderTag::$tag
@@ -347,71 +348,71 @@ macro_rules! match_untyped_arena_ptr {
 }
 
 macro_rules! read_heap_cell_pat_body {
-    ($cell:ident, Cons, $n:ident, $code:expr) => ({
+    ($cell:ident, Cons, $n:ident, $code:expr) => {{
         let $n = cell_as_untyped_arena_ptr!($cell);
         #[allow(unused_braces)]
         $code
-    });
-    ($cell:ident, F64, $n:ident, $code:expr) => ({
+    }};
+    ($cell:ident, F64, $n:ident, $code:expr) => {{
         let $n = cell_as_f64_ptr!($cell);
         #[allow(unused_braces)]
         $code
-    });
-    ($cell:ident, Atom, ($name:ident, $arity:ident), $code:expr) => ({
+    }};
+    ($cell:ident, Atom, ($name:ident, $arity:ident), $code:expr) => {{
         let ($name, $arity) = cell_as_atom_cell!($cell).get_name_and_arity();
         #[allow(unused_braces)]
         $code
-    });
-    ($cell:ident, PStr, $atom:ident, $code:expr) => ({
+    }};
+    ($cell:ident, PStr, $atom:ident, $code:expr) => {{
         let $atom = cell_as_atom!($cell);
         #[allow(unused_braces)]
         $code
-    });
-    ($cell:ident, CStr, $atom:ident, $code:expr) => ({
+    }};
+    ($cell:ident, CStr, $atom:ident, $code:expr) => {{
         let $atom = cell_as_atom!($cell);
         #[allow(unused_braces)]
         $code
-    });
-    ($cell:ident, CStr | PStr, $atom:ident, $code:expr) => ({
+    }};
+    ($cell:ident, CStr | PStr, $atom:ident, $code:expr) => {{
         let $atom = cell_as_atom!($cell);
         #[allow(unused_braces)]
         $code
-    });
-    ($cell:ident, PStr | CStr, $atom:ident, $code:expr) => ({
+    }};
+    ($cell:ident, PStr | CStr, $atom:ident, $code:expr) => {{
         let $atom = cell_as_atom!($cell);
         #[allow(unused_braces)]
         $code
-    });
-    ($cell:ident, Fixnum, $value:ident, $code:expr) => ({
+    }};
+    ($cell:ident, Fixnum, $value:ident, $code:expr) => {{
         let $value = Fixnum::from_bytes($cell.into_bytes());
         #[allow(unused_braces)]
         $code
-    });
-    ($cell:ident, CutPoint, $value:ident, $code:expr) => ({
+    }};
+    ($cell:ident, CutPoint, $value:ident, $code:expr) => {{
         let $value = Fixnum::from_bytes($cell.into_bytes());
         #[allow(unused_braces)]
         $code
-    });
-    ($cell:ident, Fixnum | CutPoint, $value:ident, $code:expr) => ({
+    }};
+    ($cell:ident, Fixnum | CutPoint, $value:ident, $code:expr) => {{
         let $value = Fixnum::from_bytes($cell.into_bytes());
         #[allow(unused_braces)]
         $code
-    });
-    ($cell:ident, CutPoint | Fixnum, $value:ident, $code:expr) => ({
+    }};
+    ($cell:ident, CutPoint | Fixnum, $value:ident, $code:expr) => {{
         let $value = Fixnum::from_bytes($cell.into_bytes());
         #[allow(unused_braces)]
         $code
-    });
-    ($cell:ident, Char, $value:ident, $code:expr) => ({
+    }};
+    ($cell:ident, Char, $value:ident, $code:expr) => {{
         let $value = unsafe { char::from_u32_unchecked($cell.get_value() as u32) };
         #[allow(unused_braces)]
         $code
-    });
-    ($cell:ident, $($tags:tt)|+, $value:ident, $code:expr) => ({
+    }};
+    ($cell:ident, $($tags:tt)|+, $value:ident, $code:expr) => {{
         let $value = $cell.get_value() as usize;
         #[allow(unused_braces)]
         $code
-    });
+    }};
 }
 
 macro_rules! read_heap_cell_pat {
@@ -596,7 +597,9 @@ macro_rules! index_store {
         IndexStore {
             code_dir: $code_dir,
             extensible_predicates: ExtensiblePredicates::with_hasher(FxBuildHasher::default()),
-            local_extensible_predicates: LocalExtensiblePredicates::with_hasher(FxBuildHasher::default()),
+            local_extensible_predicates: LocalExtensiblePredicates::with_hasher(
+                FxBuildHasher::default(),
+            ),
             global_variables: GlobalVarDir::with_hasher(FxBuildHasher::default()),
             goal_expansion_indices: GoalExpansionIndices::with_hasher(FxBuildHasher::default()),
             meta_predicates: MetaPredicateDir::with_hasher(FxBuildHasher::default()),

src/parser/ast.rs

@@ -10,6 +10,7 @@ use std::hash::{Hash, Hasher};
 use std::io::{Error as IOError, ErrorKind};
 use std::ops::{Deref, Neg};
 use std::rc::Rc;
+use std::sync::Arc;
 use std::vec::Vec;
 
 use crate::parser::dashu::{Integer, Rational};
@@ -33,6 +34,7 @@ pub const FY: u32 = 0x0080;
 pub const DELIMITER: u32 = 0x0100;
 pub const TERM: u32 = 0x1000;
 pub const LTERM: u32 = 0x3000;
+pub const BTERM: u32 = 0x11000;
 
 pub const NEGATIVE_SIGN: u32 = 0x0200;
 
@@ -258,7 +260,8 @@ impl GenContext {
 pub struct OpDesc {
     prec: B11,
     spec: B8,
-    #[allow(unused)] padding: B13,
+    #[allow(unused)]
+    padding: B13,
 }
 
 impl OpDesc {
@@ -417,13 +420,13 @@ pub enum ParserError {
 impl ParserError {
     pub fn line_and_col_num(&self) -> Option<(usize, usize)> {
         match self {
-            &ParserError::BackQuotedString(line_num, col_num) |
-            &ParserError::IncompleteReduction(line_num, col_num) |
-            &ParserError::MissingQuote(line_num, col_num) |
-            &ParserError::NonPrologChar(line_num, col_num) |
-            &ParserError::ParseBigInt(line_num, col_num) |
-            &ParserError::UnexpectedChar(_, line_num, col_num) |
-            &ParserError::Utf8Error(line_num, col_num) => Some((line_num, col_num)),
+            &ParserError::BackQuotedString(line_num, col_num)
+            | &ParserError::IncompleteReduction(line_num, col_num)
+            | &ParserError::MissingQuote(line_num, col_num)
+            | &ParserError::NonPrologChar(line_num, col_num)
+            | &ParserError::ParseBigInt(line_num, col_num)
+            | &ParserError::UnexpectedChar(_, line_num, col_num)
+            | &ParserError::Utf8Error(line_num, col_num) => Some((line_num, col_num)),
             _ => None,
         }
     }
@@ -432,8 +435,12 @@ impl ParserError {
         match self {
             ParserError::BackQuotedString(..) => atom!("back_quoted_string"),
             ParserError::IncompleteReduction(..) => atom!("incomplete_reduction"),
-            ParserError::InvalidSingleQuotedCharacter(..) => atom!("invalid_single_quoted_character"),
-            ParserError::IO(e) if e.kind() == ErrorKind::UnexpectedEof => atom!("unexpected_end_of_file"),
+            ParserError::InvalidSingleQuotedCharacter(..) => {
+                atom!("invalid_single_quoted_character")
+            }
+            ParserError::IO(e) if e.kind() == ErrorKind::UnexpectedEof => {
+                atom!("unexpected_end_of_file")
+            }
             ParserError::IO(_) => atom!("input_output_error"),
             ParserError::LexicalError(_) => atom!("lexical_error"),
             ParserError::MissingQuote(..) => atom!("missing_quote"),
@@ -522,9 +529,12 @@ pub enum Fixity {
 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
 pub struct Fixnum {
     num: B56,
-    #[allow(unused)] f: bool,
-    #[allow(unused)] m: bool,
-    #[allow(unused)] tag: B6,
+    #[allow(unused)]
+    f: bool,
+    #[allow(unused)]
+    m: bool,
+    #[allow(unused)]
+    tag: B6,
 }
 
 impl Fixnum {
@@ -623,7 +633,7 @@ impl fmt::Display for Literal {
 }
 
 impl Literal {
-    pub fn to_atom(&self, atom_tbl: &mut AtomTable) -> Option<Atom> {
+    pub fn to_atom(&self, atom_tbl: &Arc<AtomTable>) -> Option<Atom> {
         match self {
             Literal::Atom(atom) => Some(atom.defrock_brackets(atom_tbl)),
             _ => None,
@@ -631,7 +641,6 @@ impl Literal {
     }
 }
 
-
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct VarPtr(Rc<RefCell<Var>>);
 
@@ -800,7 +809,7 @@ pub fn source_arity(terms: &[Term]) -> usize {
     terms.len()
 }
 
-fn unfold_by_str_once(term: &mut Term, s: Atom) -> Option<(Term, Term)> {
+pub(crate) fn unfold_by_str_once(term: &mut Term, s: Atom) -> Option<(Term, Term)> {
     if let Term::Clause(_, ref name, ref mut subterms) = term {
         if let Some(last_arg) = subterms.last() {
             if let Term::Literal(_, Literal::CodeIndex(_)) = last_arg {

src/parser/char_reader.rs

@@ -20,7 +20,7 @@ use std::str;
 
 pub struct CharReader<R> {
     inner: R,
-    buf: SmallVec<[u8;32]>,
+    buf: SmallVec<[u8; 32]>,
     pos: usize,
 }
 
@@ -78,7 +78,7 @@ pub trait CharRead {
                 self.consume(c.len_utf8());
                 Some(Ok(c))
             }
-            result => result
+            result => result,
         }
     }
 
@@ -161,9 +161,7 @@ impl<R: Read> CharRead for CharReader<R> {
 
                         return Some(Ok(c));
                     }
-                    Err(e) => {
-                        e
-                    }
+                    Err(e) => e,
                 };
 
                 if buf.len() - e.valid_up_to() >= 4 {
@@ -192,13 +190,15 @@ impl<R: Read> CharRead for CharReader<R> {
                     // the buffer, it will be returned on the next
                     // loop.
 
-                    return Some(Err(io::Error::new(io::ErrorKind::InvalidData,
-                                                   BadUtf8Error { bytes: badbytes })));
+                    return Some(Err(io::Error::new(
+                        io::ErrorKind::InvalidData,
+                        BadUtf8Error { bytes: badbytes },
+                    )));
                 } else {
                     if self.pos >= self.buf.len() {
                         return None;
                     } else if self.buf.len() - self.pos >= 4 {
-                        return match str::from_utf8(&self.buf[self.pos .. e.valid_up_to()]) {
+                        return match str::from_utf8(&self.buf[self.pos..e.valid_up_to()]) {
                             Ok(s) => {
                                 let mut chars = s.chars();
                                 let c = chars.next().unwrap();
@@ -206,10 +206,12 @@ impl<R: Read> CharRead for CharReader<R> {
                                 Some(Ok(c))
                             }
                             Err(e) => {
-                                let badbytes = self.buf[self.pos .. e.valid_up_to()].to_vec();
+                                let badbytes = self.buf[self.pos..e.valid_up_to()].to_vec();
 
-                                Some(Err(io::Error::new(io::ErrorKind::InvalidData,
-                                                        BadUtf8Error { bytes: badbytes })))
+                                Some(Err(io::Error::new(
+                                    io::ErrorKind::InvalidData,
+                                    BadUtf8Error { bytes: badbytes },
+                                )))
                             }
                         };
                     } else {
@@ -223,7 +225,7 @@ impl<R: Read> CharRead for CharReader<R> {
 
                         let buf_len = self.buf.len();
 
-                        let mut word = [0u8;4];
+                        let mut word = [0u8; 4];
                         let word_slice = &mut word[buf_len..4];
 
                         match self.inner.read(word_slice) {
@@ -250,7 +252,7 @@ impl<R: Read> CharRead for CharReader<R> {
         let c_len = c.len_utf8();
         let mut shifted_slice = [0u8; 32];
 
-        shifted_slice[0..src_len].copy_from_slice(&self.buf[self.pos .. self.buf.len()]);
+        shifted_slice[0..src_len].copy_from_slice(&self.buf[self.pos..self.buf.len()]);
 
         self.buf.resize(c_len, 0);
         self.buf.extend_from_slice(&shifted_slice[0..src_len]);
@@ -311,7 +313,10 @@ impl<R: Read> Read for CharReader<R> {
         }
 
         if !buf.is_empty() {
-            Err(io::Error::new(ErrorKind::UnexpectedEof, "failed to fill whole buffer"))
+            Err(io::Error::new(
+                ErrorKind::UnexpectedEof,
+                "failed to fill whole buffer",
+            ))
         } else {
             Ok(())
         }
@@ -364,12 +369,14 @@ where
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt.debug_struct("CharReader")
             .field("reader", &self.inner)
-            .field("buf", &format_args!("{}/{}", self.buf.capacity() - self.pos, self.buf.len()))
+            .field(
+                "buf",
+                &format_args!("{}/{}", self.buf.capacity() - self.pos, self.buf.len()),
+            )
             .finish()
     }
 }
 
-
 #[cfg(test)]
 mod tests {
     use crate::parser::char_reader::*;

src/parser/lexer.rs

@@ -86,14 +86,14 @@ impl<'a, R: CharRead> Lexer<'a, R> {
     pub fn lookahead_char(&mut self) -> Result<char, ParserError> {
         match self.reader.peek_char() {
             Some(Ok(c)) => Ok(c),
-            _ => Err(ParserError::unexpected_eof())
+            _ => Err(ParserError::unexpected_eof()),
         }
     }
 
     pub fn read_char(&mut self) -> Result<char, ParserError> {
         match self.reader.read_char() {
             Some(Ok(c)) => Ok(c),
-            _ => Err(ParserError::unexpected_eof())
+            _ => Err(ParserError::unexpected_eof()),
         }
     }
 
@@ -168,13 +168,15 @@ impl<'a, R: CharRead> Lexer<'a, R> {
 
             match comment_loop() {
                 Err(e) if e.is_unexpected_eof() => {
-                    return Err(ParserError::IncompleteReduction(self.line_num, self.col_num));
+                    return Err(ParserError::IncompleteReduction(
+                        self.line_num,
+                        self.col_num,
+                    ));
                 }
                 Err(e) => {
                     return Err(e);
                 }
-                Ok(_) => {
-                }
+                Ok(_) => {}
             }
 
             if prolog_char!(c) {
@@ -362,7 +364,10 @@ impl<'a, R: CharRead> Lexer<'a, R> {
         if hexadecimal_digit_char!(c) {
             self.escape_sequence_to_char(|c| hexadecimal_digit_char!(c), 16)
         } else {
-            Err(ParserError::IncompleteReduction(self.line_num, self.col_num))
+            Err(ParserError::IncompleteReduction(
+                self.line_num,
+                self.col_num,
+            ))
         }
     }
 
@@ -395,7 +400,10 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                 },
             )
         } else {
-            Err(ParserError::IncompleteReduction(self.line_num, self.col_num))
+            Err(ParserError::IncompleteReduction(
+                self.line_num,
+                self.col_num,
+            ))
         }
     }
 
@@ -463,9 +471,12 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                 .map(|n| Token::Literal(fixnum!(Literal, n, &mut self.machine_st.arena)))
                 .or_else(|_| {
                     Integer::from_str_radix(&token, 16)
-                        .map(|n| Token::Literal(Literal::Integer(
-                            arena_alloc!(n, &mut self.machine_st.arena)
-                        )))
+                        .map(|n| {
+                            Token::Literal(Literal::Integer(arena_alloc!(
+                                n,
+                                &mut self.machine_st.arena
+                            )))
+                        })
                         .map_err(|_| ParserError::ParseBigInt(self.line_num, self.col_num))
                 })
         } else {
@@ -495,9 +506,12 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                 .map(|n| Token::Literal(fixnum!(Literal, n, &mut self.machine_st.arena)))
                 .or_else(|_| {
                     Integer::from_str_radix(&token, 8)
-                        .map(|n| Token::Literal(Literal::Integer(
-                            arena_alloc!(n, &mut self.machine_st.arena)
-                        )))
+                        .map(|n| {
+                            Token::Literal(Literal::Integer(arena_alloc!(
+                                n,
+                                &mut self.machine_st.arena
+                            )))
+                        })
                         .map_err(|_| ParserError::ParseBigInt(self.line_num, self.col_num))
                 })
         } else {
@@ -527,9 +541,12 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                 .map(|n| Token::Literal(fixnum!(Literal, n, &mut self.machine_st.arena)))
                 .or_else(|_| {
                     Integer::from_str_radix(&token, 2)
-                        .map(|n| Token::Literal(Literal::Integer(
-                            arena_alloc!(n, &mut self.machine_st.arena)
-                        )))
+                        .map(|n| {
+                            Token::Literal(Literal::Integer(arena_alloc!(
+                                n,
+                                &mut self.machine_st.arena
+                            )))
+                        })
                         .map_err(|_| ParserError::ParseBigInt(self.line_num, self.col_num))
                 })
         } else {
@@ -620,16 +637,20 @@ impl<'a, R: CharRead> Lexer<'a, R> {
         if token.as_str() == "[]" {
             Ok(Token::Literal(Literal::Atom(atom!("[]"))))
         } else {
-            Ok(Token::Literal(Literal::Atom(
-                self.machine_st.atom_tbl.build_with(&token),
-            )))
+            Ok(Token::Literal(Literal::Atom(AtomTable::build_with(
+                &self.machine_st.atom_tbl,
+                &token,
+            ))))
         }
     }
 
     fn vacate_with_float(&mut self, mut token: String) -> Result<Token, ParserError> {
         self.return_char(token.pop().unwrap());
         let n = parse_lossy::<f64, _>(token.as_bytes())?;
-        Ok(Token::Literal(Literal::from(float_alloc!(n, self.machine_st.arena))))
+        Ok(Token::Literal(Literal::from(float_alloc!(
+            n,
+            self.machine_st.arena
+        ))))
     }
 
     fn skip_underscore_in_number(&mut self) -> Result<char, ParserError> {
@@ -675,7 +696,10 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                         token
                             .parse::<Integer>()
                             .map(|n| {
-                                Token::Literal(Literal::Integer(arena_alloc!(n, &mut self.machine_st.arena)))
+                                Token::Literal(Literal::Integer(arena_alloc!(
+                                    n,
+                                    &mut self.machine_st.arena
+                                )))
                             })
                             .map_err(|_| ParserError::ParseBigInt(self.line_num, self.col_num))
                     })
@@ -740,17 +764,19 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                         }
 
                         let n = parse_lossy::<f64, _>(token.as_bytes())?;
-                        Ok(Token::Literal(Literal::from(
-                            float_alloc!(n, self.machine_st.arena)
-                        )))
+                        Ok(Token::Literal(Literal::from(float_alloc!(
+                            n,
+                            self.machine_st.arena
+                        ))))
                     } else {
                         return Ok(self.vacate_with_float(token)?);
                     }
                 } else {
                     let n = parse_lossy::<f64, _>(token.as_bytes())?;
-                    Ok(Token::Literal(Literal::from(
-                        float_alloc!(n, self.machine_st.arena)
-                    )))
+                    Ok(Token::Literal(Literal::from(float_alloc!(
+                        n,
+                        self.machine_st.arena
+                    ))))
                 }
             } else {
                 self.return_char('.');
@@ -761,7 +787,10 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                         token
                             .parse::<Integer>()
                             .map(|n| {
-                                Token::Literal(Literal::Integer(arena_alloc!(n, &mut self.machine_st.arena)))
+                                Token::Literal(Literal::Integer(arena_alloc!(
+                                    n,
+                                    &mut self.machine_st.arena
+                                )))
                             })
                             .map_err(|_| ParserError::ParseBigInt(self.line_num, self.col_num))
                     })
@@ -772,7 +801,9 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                     self.hexadecimal_constant(c).or_else(|e| {
                         if let ParserError::ParseBigInt(..) = e {
                             i64::from_str_radix(&token, 10)
-                                .map(|n| Token::Literal(fixnum!(Literal, n, &mut self.machine_st.arena)))
+                                .map(|n| {
+                                    Token::Literal(fixnum!(Literal, n, &mut self.machine_st.arena))
+                                })
                                 .or_else(|_| {
                                     token
                                         .parse::<Integer>()
@@ -794,7 +825,9 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                     self.octal_constant(c).or_else(|e| {
                         if let ParserError::ParseBigInt(..) = e {
                             i64::from_str_radix(&token, 10)
-                                .map(|n| Token::Literal(fixnum!(Literal, n, &mut self.machine_st.arena)))
+                                .map(|n| {
+                                    Token::Literal(fixnum!(Literal, n, &mut self.machine_st.arena))
+                                })
                                 .or_else(|_| {
                                     token
                                         .parse::<Integer>()
@@ -816,7 +849,9 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                     self.binary_constant(c).or_else(|e| {
                         if let ParserError::ParseBigInt(..) = e {
                             i64::from_str_radix(&token, 10)
-                                .map(|n| Token::Literal(fixnum!(Literal, n, &mut self.machine_st.arena)))
+                                .map(|n| {
+                                    Token::Literal(fixnum!(Literal, n, &mut self.machine_st.arena))
+                                })
                                 .or_else(|_| {
                                     token
                                         .parse::<Integer>()
@@ -856,15 +891,16 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                         .map(|c| Token::Literal(Literal::Fixnum(Fixnum::build_with(c as i64))))
                         .or_else(|err| {
                             match err {
-                                ParserError::UnexpectedChar('\'', ..) => {
-                                }
+                                ParserError::UnexpectedChar('\'', ..) => {}
                                 err => return Err(err),
                             }
 
                             self.return_char(c);
 
                             i64::from_str_radix(&token, 10)
-                                .map(|n| Token::Literal(fixnum!(Literal, n, &mut self.machine_st.arena)))
+                                .map(|n| {
+                                    Token::Literal(fixnum!(Literal, n, &mut self.machine_st.arena))
+                                })
                                 .or_else(|_| {
                                     token
                                         .parse::<Integer>()
@@ -901,7 +937,10 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                         token
                             .parse::<Integer>()
                             .map(|n| {
-                                Token::Literal(Literal::Integer(arena_alloc!(n, &mut self.machine_st.arena)))
+                                Token::Literal(Literal::Integer(arena_alloc!(
+                                    n,
+                                    &mut self.machine_st.arena
+                                )))
                             })
                             .map_err(|_| ParserError::ParseBigInt(self.line_num, self.col_num))
                     })
@@ -940,11 +979,12 @@ impl<'a, R: CharRead> Lexer<'a, R> {
 
     pub fn scan_for_layout(&mut self) -> Result<bool, ParserError> {
         match self.lookahead_char() {
-            Err(e) => {
-                Err(e)
-            }
+            Err(e) => Err(e),
             Ok(c) => {
-                let mut layout_info = LayoutInfo { inserted: false, more: true };
+                let mut layout_info = LayoutInfo {
+                    inserted: false,
+                    more: true,
+                };
                 let mut cr = Some(c);
 
                 loop {
@@ -1044,7 +1084,7 @@ impl<'a, R: CharRead> Lexer<'a, R> {
 
                 if c == '"' {
                     let s = self.char_code_list_token(c)?;
-                    let atom = self.machine_st.atom_tbl.build_with(&s);
+                    let atom = AtomTable::build_with(&self.machine_st.atom_tbl, &s);
 
                     return if let DoubleQuotes::Atom = self.machine_st.flags.double_quotes {
                         Ok(Token::Literal(Literal::Atom(atom)))
@@ -1054,7 +1094,7 @@ impl<'a, R: CharRead> Lexer<'a, R> {
                 }
 
                 if c == '\u{0}' {
-                    return Err(ParserError::unexpected_eof())
+                    return Err(ParserError::unexpected_eof());
                 }
 
                 self.name_token(c)

src/parser/macros.rs

@@ -7,13 +7,14 @@ macro_rules! char_class {
 #[macro_export]
 macro_rules! alpha_char {
     ($c: expr) => {
-        (!$c.is_numeric() &&
-         !$c.is_whitespace() &&
-         !$c.is_control() &&
-         !$crate::graphic_token_char!($c) &&
-         !$crate::layout_char!($c) &&
-         !$crate::meta_char!($c) &&
-         !$crate::solo_char!($c)) || $c == '_'
+        (!$c.is_numeric()
+            && !$c.is_whitespace()
+            && !$c.is_control()
+            && !$crate::graphic_token_char!($c)
+            && !$crate::layout_char!($c)
+            && !$crate::meta_char!($c)
+            && !$crate::solo_char!($c))
+            || $c == '_'
     };
 }
 
@@ -131,7 +132,7 @@ macro_rules! hexadecimal_digit_char {
 #[macro_export]
 macro_rules! layout_char {
     ($c: expr) => {
-        $crate::char_class!($c, [' ', '\n', '\t', '\u{0B}', '\u{0C}'])
+        $crate::char_class!($c, [' ', '\r', '\n', '\t', '\u{0B}', '\u{0C}'])
     };
 }
 

src/parser/parser.rs

@@ -7,7 +7,6 @@ use crate::parser::ast::*;
 use crate::parser::char_reader::*;
 use crate::parser::lexer::*;
 
-
 use std::cell::Cell;
 use std::mem;
 use std::ops::Neg;
@@ -59,6 +58,7 @@ struct TokenDesc {
     tt: TokenType,
     priority: usize,
     spec: u32,
+    unfold_bounds: usize,
 }
 
 pub(crate) fn as_partial_string(
@@ -108,7 +108,7 @@ pub(crate) fn as_partial_string(
                 tail_ref = tail;
             }
             Term::CompleteString(_, cstr) => {
-                string += cstr.as_str();
+                string += &*cstr.as_str();
                 tail = Term::Literal(Cell::default(), Literal::Atom(atom!("[]")));
                 break;
             }
@@ -120,26 +120,17 @@ pub(crate) fn as_partial_string(
     }
 
     match &tail {
-        Term::AnonVar | Term::Var(..) => {
-            Ok((string, Some(Box::new(tail))))
-        }
-        Term::Literal(_, Literal::Atom(atom!("[]"))) => {
-            Ok((string, None))
-        }
+        Term::AnonVar | Term::Var(..) => Ok((string, Some(Box::new(tail)))),
+        Term::Literal(_, Literal::Atom(atom!("[]"))) => Ok((string, None)),
         Term::Literal(_, Literal::String(tail)) => {
-            string += tail.as_str();
+            string += &*tail.as_str();
             Ok((string, None))
         }
-        _ => {
-            Ok((string, Some(Box::new(tail))))
-        }
+        _ => Ok((string, Some(Box::new(tail)))),
     }
 }
 
-pub fn get_op_desc(
-    name: Atom,
-    op_dir: &CompositeOpDir,
-) -> Option<CompositeOpDesc> {
+pub fn get_op_desc(name: Atom, op_dir: &CompositeOpDir) -> Option<CompositeOpDesc> {
     let mut op_desc = CompositeOpDesc {
         pre: 0,
         inf: 0,
@@ -295,17 +286,17 @@ fn read_tokens<R: CharRead>(lexer: &mut Lexer<R>) -> Result<Vec<Token>, ParserEr
     Ok(tokens)
 }
 
-fn atomize_term(atom_tbl: &mut AtomTable, term: &Term) -> Option<Atom> {
+fn atomize_term(atom_tbl: &AtomTable, term: &Term) -> Option<Atom> {
     match term {
         Term::Literal(_, ref c) => atomize_constant(atom_tbl, *c),
         _ => None,
     }
 }
 
-fn atomize_constant(atom_tbl: &mut AtomTable, c: Literal) -> Option<Atom> {
+fn atomize_constant(atom_tbl: &AtomTable, c: Literal) -> Option<Atom> {
     match c {
         Literal::Atom(ref name) => Some(*name),
-        Literal::Char(c) => Some(atom_tbl.build_with(&c.to_string())),
+        Literal::Char(c) => Some(AtomTable::build_with(atom_tbl, &c.to_string())),
         _ => None,
     }
 }
@@ -381,6 +372,7 @@ impl<'a, R: CharRead> Parser<'a, R> {
                         tt: TokenType::Term,
                         priority: td.priority,
                         spec,
+                        unfold_bounds: 0,
                     });
                 }
             }
@@ -402,6 +394,7 @@ impl<'a, R: CharRead> Parser<'a, R> {
                         tt: TokenType::Term,
                         priority: td.priority,
                         spec,
+                        unfold_bounds: 0,
                     });
                 }
             }
@@ -409,17 +402,21 @@ impl<'a, R: CharRead> Parser<'a, R> {
     }
 
     fn promote_atom_op(&mut self, atom: Atom, priority: usize, assoc: u32) {
-        self.terms.push(Term::Literal(Cell::default(), Literal::Atom(atom)));
+        self.terms
+            .push(Term::Literal(Cell::default(), Literal::Atom(atom)));
         self.stack.push(TokenDesc {
             tt: TokenType::Term,
             priority,
             spec: assoc,
+            unfold_bounds: 0,
         });
     }
 
     fn shift(&mut self, token: Token, priority: usize, spec: Specifier) {
         let tt = match token {
-            Token::Literal(Literal::String(s)) if self.lexer.machine_st.flags.double_quotes.is_codes() => {
+            Token::Literal(Literal::String(s))
+                if self.lexer.machine_st.flags.double_quotes.is_codes() =>
+            {
                 let mut list = Term::Literal(Cell::default(), Literal::Atom(atom!("[]")));
 
                 for c in s.as_str().chars().rev() {
@@ -436,7 +433,9 @@ impl<'a, R: CharRead> Parser<'a, R> {
                 self.terms.push(list);
                 TokenType::Term
             }
-            Token::Literal(Literal::String(s)) if self.lexer.machine_st.flags.double_quotes.is_chars() => {
+            Token::Literal(Literal::String(s))
+                if self.lexer.machine_st.flags.double_quotes.is_chars() =>
+            {
                 self.terms.push(Term::CompleteString(Cell::default(), s));
                 TokenType::Term
             }
@@ -465,7 +464,7 @@ impl<'a, R: CharRead> Parser<'a, R> {
             Token::End => TokenType::End,
         };
 
-        self.stack.push(TokenDesc { tt, priority, spec });
+        self.stack.push(TokenDesc { tt, priority, spec, unfold_bounds: 0, });
     }
 
     fn reduce_op(&mut self, priority: usize) {
@@ -573,7 +572,7 @@ impl<'a, R: CharRead> Parser<'a, R> {
         let idx = self.terms.len() - arity;
 
         if TokenType::Term == self.stack[stack_len].tt {
-            if atomize_term(&mut self.lexer.machine_st.atom_tbl, &self.terms[idx - 1]).is_some() {
+            if atomize_term(&self.lexer.machine_st.atom_tbl, &self.terms[idx - 1]).is_some() {
                 self.stack.truncate(stack_len + 1);
 
                 let mut subterms: Vec<_> = self.terms.drain(idx..).collect();
@@ -581,38 +580,46 @@ impl<'a, R: CharRead> Parser<'a, R> {
                 if let Some(name) = self
                     .terms
                     .pop()
-                    .and_then(|t| atomize_term(&mut self.lexer.machine_st.atom_tbl, &t))
+                    .and_then(|t| atomize_term(&self.lexer.machine_st.atom_tbl, &t))
                 {
                     // reduce the '.' functor to a cons cell if it applies.
                     if name == atom!(".") && subterms.len() == 2 {
                         let tail = subterms.pop().unwrap();
                         let head = subterms.pop().unwrap();
 
-                        self.terms.push(
-                            match as_partial_string(head, tail) {
-                                Ok((string_buf, Some(tail))) => {
-                                    Term::PartialString(Cell::default(), string_buf, tail)
-                                }
-                                Ok((string_buf, None)) => {
-                                    let atom = self.lexer.machine_st.atom_tbl.build_with(&string_buf);
-                                    Term::CompleteString(Cell::default(), atom)
-                                }
-                                Err(term) => term,
-                            },
-                        );
+                        self.terms.push(match as_partial_string(head, tail) {
+                            Ok((string_buf, Some(tail))) => {
+                                Term::PartialString(Cell::default(), string_buf, tail)
+                            }
+                            Ok((string_buf, None)) => {
+                                let atom = AtomTable::build_with(
+                                    &self.lexer.machine_st.atom_tbl,
+                                    &string_buf,
+                                );
+                                Term::CompleteString(Cell::default(), atom)
+                            }
+                            Err(term) => term,
+                        });
                     } else {
-                        self.terms.push(Term::Clause(Cell::default(), name, subterms));
+                        self.terms
+                            .push(Term::Clause(Cell::default(), name, subterms));
                     }
 
                     if let Some(&mut TokenDesc {
+                        ref mut tt,
                         ref mut priority,
                         ref mut spec,
-                        ref mut tt,
+                        ref mut unfold_bounds,
                     }) = self.stack.last_mut()
                     {
+                        if *spec == BTERM {
+                            return false;
+                        }
+
                         *tt = TokenType::Term;
                         *priority = 0;
                         *spec = TERM;
+                        *unfold_bounds = 0;
                     }
 
                     return true;
@@ -628,8 +635,8 @@ impl<'a, R: CharRead> Parser<'a, R> {
     }
 
     fn expand_comma_compacted_terms(&mut self, index: usize) -> usize {
-        if let Some(term) = self.terms.pop() {
-            let op_desc = self.stack[index - 1];
+        if let Some(mut term) = self.terms.pop() {
+            let mut op_desc = self.stack[index - 1];
 
             if 0 < op_desc.priority && op_desc.priority < self.stack[index].priority {
                 /* '|' is a head-tail separator here, not
@@ -637,7 +644,26 @@ impl<'a, R: CharRead> Parser<'a, R> {
                  * terms it compacted out again. */
                 match (term.name(), term.arity()) {
                     (Some(name), 2) if name == atom!(",") => {
-                        let terms = unfold_by_str(term, name); // notice: name == "," here.
+                        let terms = if op_desc.unfold_bounds == 0 {
+                            unfold_by_str(term, atom!(","))
+                        } else {
+                            let mut terms = vec![];
+
+                            while let Some((fst, snd)) = unfold_by_str_once(&mut term, atom!(",")) {
+                                terms.push(fst);
+                                term = snd;
+
+                                op_desc.unfold_bounds -= 2;
+
+                                if op_desc.unfold_bounds == 0 {
+                                    break;
+                                }
+                            }
+
+                            terms.push(term);
+                            terms
+                        };
+
                         let arity = terms.len() - 1;
 
                         self.terms.extend(terms.into_iter());
@@ -695,7 +721,8 @@ impl<'a, R: CharRead> Parser<'a, R> {
                 td.tt = TokenType::Term;
                 td.priority = 0;
 
-                self.terms.push(Term::Literal(Cell::default(), Literal::Atom(atom!("[]"))));
+                self.terms
+                    .push(Term::Literal(Cell::default(), Literal::Atom(atom!("[]"))));
                 return Ok(true);
             }
         }
@@ -736,8 +763,8 @@ impl<'a, R: CharRead> Parser<'a, R> {
         if arity > self.terms.len() {
             return Err(ParserError::IncompleteReduction(
                 self.lexer.line_num,
-                self.lexer.col_num
-            ))
+                self.lexer.col_num,
+            ));
         }
 
         let idx = self.terms.len() - arity;
@@ -752,21 +779,20 @@ impl<'a, R: CharRead> Parser<'a, R> {
             tt: TokenType::Term,
             priority: 0,
             spec: TERM,
+            unfold_bounds: 0,
         });
 
         self.terms.push(match list {
-            Term::Cons(_, head, tail) => {
-                match as_partial_string(*head, *tail) {
-                    Ok((string_buf, Some(tail))) => {
-                        Term::PartialString(Cell::default(), string_buf, tail)
-                    }
-                    Ok((string_buf, None)) => {
-                        let atom = self.lexer.machine_st.atom_tbl.build_with(&string_buf);
-                        Term::CompleteString(Cell::default(), atom)
-                    }
-                    Err(term) => term,
+            Term::Cons(_, head, tail) => match as_partial_string(*head, *tail) {
+                Ok((string_buf, Some(tail))) => {
+                    Term::PartialString(Cell::default(), string_buf, tail)
                 }
-            }
+                Ok((string_buf, None)) => {
+                    let atom = AtomTable::build_with(&self.lexer.machine_st.atom_tbl, &string_buf);
+                    Term::CompleteString(Cell::default(), atom)
+                }
+                Err(term) => term,
+            },
             term => term,
         });
 
@@ -784,10 +810,7 @@ impl<'a, R: CharRead> Parser<'a, R> {
                 td.priority = 0;
                 td.spec = TERM;
 
-                let term = Term::Literal(
-                    Cell::default(),
-                    Literal::Atom(atom!("{}")),
-                );
+                let term = Term::Literal(Cell::default(), Literal::Atom(atom!("{}")));
 
                 self.terms.push(term);
                 return Ok(true);
@@ -818,11 +841,8 @@ impl<'a, R: CharRead> Parser<'a, R> {
                             }
                         };
 
-                        self.terms.push(Term::Clause(
-                            Cell::default(),
-                            atom!("{}"),
-                            vec![term],
-                        ));
+                        self.terms
+                            .push(Term::Clause(Cell::default(), atom!("{}"), vec![term]));
 
                         return Ok(true);
                     }
@@ -862,7 +882,7 @@ impl<'a, R: CharRead> Parser<'a, R> {
                         .push(Term::Literal(Cell::default(), Literal::Atom(atom)));
                 }
 
-                self.stack[idx].spec = TERM;
+                self.stack[idx].spec = if self.stack[idx].priority > 0 { TERM } else { BTERM };
                 self.stack[idx].tt = TokenType::Term;
                 self.stack[idx].priority = 0;
 
@@ -933,7 +953,8 @@ impl<'a, R: CharRead> Parser<'a, R> {
             if let Some(term) = self.terms.last().cloned() {
                 match term {
                     Term::Literal(_, Literal::Atom(name))
-                        if name == atom!("-") && (is_prefix!(desc.spec) || is_negate!(desc.spec)) =>
+                        if name == atom!("-")
+                            && (is_prefix!(desc.spec) || is_negate!(desc.spec)) =>
                     {
                         self.stack.pop();
                         self.terms.pop();
@@ -983,7 +1004,9 @@ impl<'a, R: CharRead> Parser<'a, R> {
                 |n, arena| Literal::from(float_alloc!(n, arena)),
             ),
             Token::Literal(c) => {
-                if let Some(name) = atomize_constant(&mut self.lexer.machine_st.atom_tbl, c) {
+                let atomized = atomize_constant(&self.lexer.machine_st.atom_tbl, c);
+
+                if let Some(name) = atomized {
                     if !self.shift_op(name, op_dir)? {
                         self.shift(Token::Literal(c), 0, TERM);
                     }
@@ -1026,13 +1049,20 @@ impl<'a, R: CharRead> Parser<'a, R> {
                 /* '|' as an operator must have priority > 1000 and can only be infix.
                  * See: http://www.complang.tuwien.ac.at/ulrich/iso-prolog/dtc2#Res_A78
                  */
-                let bar_atom = atom!("|");
-
-                let (priority, spec) = get_op_desc(bar_atom, op_dir)
+                let (priority, spec) = get_op_desc(atom!("|"), op_dir)
                     .map(|CompositeOpDesc { inf, spec, .. }| (inf, spec))
                     .unwrap_or((1000, DELIMITER));
 
+                let old_stack_len = self.stack.len();
+
                 self.reduce_op(priority);
+
+                let new_stack_len = self.stack.len();
+
+                if let Some(term_desc) = self.stack.last_mut() {
+                    term_desc.unfold_bounds = old_stack_len - new_stack_len;
+                }
+
                 self.shift(Token::HeadTailSeparator, priority, spec);
             }
             Token::Comma => {
@@ -1069,7 +1099,11 @@ impl<'a, R: CharRead> Parser<'a, R> {
     }
 
     // on success, returns the parsed term and the number of lines read.
-    pub fn read_term(&mut self, op_dir: &CompositeOpDir, tokens: Tokens) -> Result<Term, ParserError> {
+    pub fn read_term(
+        &mut self,
+        op_dir: &CompositeOpDir,
+        tokens: Tokens,
+    ) -> Result<Term, ParserError> {
         self.tokens = match tokens {
             Tokens::Default => read_tokens(&mut self.lexer)?,
             Tokens::Provided(tokens) => tokens,

src/raw_block.rs

@@ -1,6 +1,7 @@
 use core::marker::PhantomData;
 
 use std::alloc;
+use std::cell::UnsafeCell;
 use std::ptr;
 
 pub trait RawBlockTraits {
@@ -12,7 +13,7 @@ pub trait RawBlockTraits {
 pub struct RawBlock<T: RawBlockTraits> {
     pub base: *const u8,
     pub top: *const u8,
-    pub ptr: *mut u8,
+    pub ptr: UnsafeCell<*mut u8>,
     _marker: PhantomData<T>,
 }
 
@@ -22,7 +23,7 @@ impl<T: RawBlockTraits> RawBlock<T> {
         RawBlock {
             base: ptr::null(),
             top: ptr::null(),
-            ptr: ptr::null_mut(),
+            ptr: UnsafeCell::new(ptr::null_mut()),
             _marker: PhantomData,
         }
     }
@@ -42,7 +43,7 @@ impl<T: RawBlockTraits> RawBlock<T> {
 
         self.base = alloc::alloc(layout) as *const _;
         self.top = (self.base as usize + cap) as *const _;
-        self.ptr = self.base as *mut _;
+        *self.ptr.get_mut() = self.base as *mut _;
     }
 
     pub unsafe fn grow(&mut self) {
@@ -54,7 +55,25 @@ impl<T: RawBlockTraits> RawBlock<T> {
 
             self.base = alloc::realloc(self.base as *mut _, layout, size * 2) as *const _;
             self.top = (self.base as usize + size * 2) as *const _;
-            self.ptr = (self.base as usize + size) as *mut _;
+            *self.ptr.get_mut() = (self.base as usize + size) as *mut _;
+        }
+    }
+
+    pub unsafe fn grow_new(&self) -> Option<Self> {
+        if self.base.is_null() {
+            Some(Self::new())
+        } else {
+            let mut new_block = Self::empty_block();
+            new_block.init_at_size(self.size() * 2);
+            if new_block.base.is_null() {
+                // allocation failed
+                None
+            } else {
+                let allocated = (*self.ptr.get()) as usize - self.base as usize;
+                self.base.copy_to(new_block.base.cast_mut(), allocated);
+                *new_block.ptr.get_mut() = new_block.base.offset(allocated as isize).cast_mut();
+                Some(new_block)
+            }
         }
     }
 
@@ -64,35 +83,39 @@ impl<T: RawBlockTraits> RawBlock<T> {
     }
 
     #[inline(always)]
-    fn free_space(&self) -> usize {
+    unsafe fn free_space(&self) -> usize {
         debug_assert!(
-            self.ptr as *const _ >= self.base,
+            *self.ptr.get() as *const _ >= self.base,
             "self.ptr = {:?} < {:?} = self.base",
-            self.ptr,
+            *self.ptr.get(),
             self.base
         );
 
-        self.top as usize - self.ptr as usize
+        self.top as usize - (*self.ptr.get()) as usize
     }
 
-    pub unsafe fn alloc(&mut self, size: usize) -> *mut u8 {
+    pub unsafe fn alloc(&self, size: usize) -> *mut u8 {
         if self.free_space() >= size {
-            let ptr = self.ptr;
-            self.ptr = (self.ptr as usize + size) as *mut _;
+            let ptr = *self.ptr.get();
+            *self.ptr.get() = (ptr as usize + size) as *mut _;
             ptr
         } else {
             ptr::null_mut()
         }
     }
+}
 
-    pub fn deallocate(&mut self) {
-        unsafe {
-            let layout = alloc::Layout::from_size_align_unchecked(self.size(), T::align());
-            alloc::dealloc(self.base as *mut _, layout);
+impl<T: RawBlockTraits> Drop for RawBlock<T> {
+    fn drop(&mut self) {
+        if !self.base.is_null() {
+            unsafe {
+                let layout = alloc::Layout::from_size_align_unchecked(self.size(), T::align());
+                alloc::dealloc(self.base as *mut _, layout);
+            }
 
             self.top = ptr::null();
             self.base = ptr::null();
-            self.ptr = ptr::null_mut();
+            *self.ptr.get_mut() = ptr::null_mut();
         }
     }
 }

src/rcu.rs

@@ -0,0 +1,220 @@
+use std::{
+    cell::OnceCell,
+    fmt::Debug,
+    mem::ManuallyDrop,
+    ops::Deref,
+    ptr::NonNull,
+    sync::{
+        atomic::{AtomicPtr, AtomicU8},
+        Arc, Weak, RwLock
+    },
+};
+
+// the epoch counters of all threads that have ever accessed an Rcu
+// threads that have finished will have a dangling Weak reference and can be cleand up
+// having this be shared between all Rcu's is a tradeof,
+// writes will be slower as more epoch counters need to be waited for
+// reads should be faster as a thread only needs to register itself once on the first read
+//
+static EPOCH_COUNTERS: RwLock<Vec<Weak<AtomicU8>>> = RwLock::new(Vec::new());
+
+thread_local! {
+    // odd value means the current thread is about to access the active_epoch of an Rcu
+    // a thread has a single epoch counter for all Rcu it accesses,
+    // as a thread can only access one Rcu at a time
+    static THREAD_EPOCH_COUNTER: OnceCell<Arc<AtomicU8>> = OnceCell::new();
+}
+
+pub struct Rcu<T> {
+    active_value: AtomicPtr<T>,
+}
+
+impl<T: std::fmt::Debug> std::fmt::Debug for Rcu<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let active_epoch = self.active_epoch();
+        f.debug_struct("Rcu")
+            .field("active_value", &active_epoch)
+            .finish()
+    }
+}
+
+impl<T> Rcu<T> {
+    pub fn new(initial_value: T) -> Self {
+        Rcu {
+            active_value: AtomicPtr::new(Arc::into_raw(Arc::new(initial_value)).cast_mut()),
+        }
+    }
+
+    pub fn active_epoch(&self) -> RcuRef<T, T> {
+        THREAD_EPOCH_COUNTER.with(|epoch_counter| {
+            let epoch_counter = epoch_counter.get_or_init(|| {
+                let epoch_counter = Arc::new(AtomicU8::new(0));
+                // register the current threads epoch counter on init
+                EPOCH_COUNTERS
+                    .write()
+		    .unwrap()
+                    .push(Arc::downgrade(&epoch_counter));
+                epoch_counter
+            });
+
+            let old = epoch_counter.fetch_add(1, std::sync::atomic::Ordering::AcqRel);
+            assert!(old % 2 == 0, "Old Epoch counter value should be even!");
+        });
+
+        let arc_ptr = self.active_value.load(std::sync::atomic::Ordering::Acquire);
+
+        let arc = unsafe {
+            // Safety:
+            // - the ptr was created in Rcu::new or Rcu::replace with Arc::into_raw
+            // - the Rcu is responsible for of the arc's strong refrences
+            // - the Rcu is alive as this function takes a reference to the Rcu
+            // - replace will wait with decrementing the old values strong count until our epoich counter is even again
+            Arc::increment_strong_count(arc_ptr);
+            // Safety:
+            // - the ptr was created in Rcu::new or Rcu::replace with Arc::into_raw
+            // - we have just ensured an additional strong count by incrementing the count
+            Arc::from_raw(arc_ptr)
+        };
+
+        THREAD_EPOCH_COUNTER.with(|epoch_counter| {
+            let old = epoch_counter
+                .get().expect("we initialized the OnceCell when we incremented the epoch counter the fist time")
+                .fetch_add(1, std::sync::atomic::Ordering::AcqRel);
+            assert!(old % 2 != 0, "Old Epoch counter value should be odd!");
+        });
+
+        RcuRef {
+            data: arc.deref().into(),
+            arc,
+        }
+    }
+
+    /*
+     *  replace the Rcu'S content with a new value
+     *
+     *  This does not syncronize write and last to update the active_value pointer wins,
+     *  all writes that do not win will be lost, though not leaked.
+     *  This will block untill the old value can be reclaimed,
+     *  i.e. all threads whitnest to be in the read critical sections
+     *       have been witnest to have left the critical section at least once
+     */
+    pub fn replace(&self, new_value: T) {
+        let arc_ptr = self.active_value.swap(
+            Arc::into_raw(Arc::new(new_value)).cast_mut(),
+            std::sync::atomic::Ordering::AcqRel,
+        );
+
+        // maually drop as we need to ensure not to drop the arc while
+        // we have not witnest all threads to be or have been outside the read critical section
+        // i.e. even epoch counter or different odd epoch counter
+        // Safety:
+        // - the ptr was created in Rcu::new or Rcu::replace with Arc::into_raw
+        // - the Rcu itself holds one strong count
+        let arc = unsafe { ManuallyDrop::new(Arc::from_raw(arc_ptr)) };
+
+        let epochs = EPOCH_COUNTERS.read().unwrap().clone();
+        let mut epochs = epochs
+            .into_iter()
+            .flat_map(|elem| {
+                let arc = elem.upgrade()?;
+                let init_val = arc.load(std::sync::atomic::Ordering::Acquire);
+                if init_val % 2 == 0 {
+                    // already even can be ignored
+                    return None;
+                }
+                // odd initial value thread is in read critical section
+                // need to wait for the value to change before we can drop the arc
+                Some((init_val, elem))
+            })
+            .collect::<Vec<_>>();
+
+        while !epochs.is_empty() {
+            epochs.retain(|elem| {
+                let Some(arc) = elem.1.upgrade() else {
+                    // as the thread is dead it can't have a ref to old arc
+                    return false;
+                };
+                // the epoch counter has not changed so the thread is still in the same instance of the critical section
+                // any different value is ok as
+                // - even values indicate the thread is outside the critical section
+                // - a diffrent odd value indicates the thread has left the critical section and can subsequently only read the new active_value
+                arc.load(std::sync::atomic::Ordering::Acquire) == elem.0
+            })
+        }
+
+        // Safety:
+        // - we have not dropped the arc another way
+        // - we witnessed all threads either with an even epoch count or with a new odd count
+        //   as such they must have left the critical section at some point
+        ManuallyDrop::into_inner(arc);
+    }
+}
+
+pub struct RcuRef<T, M>
+where
+    T: ?Sized,
+    M: ?Sized,
+{
+    arc: Arc<T>,
+    data: NonNull<M>,
+}
+
+impl<T: ?Sized, M: ?Sized + Debug> Debug for RcuRef<T, M> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("RcuRef")
+            .field("data", &self.deref())
+            .finish()
+    }
+}
+
+// use assoiated functions rather than methods so that we don't overlap
+// with functions of the Deref Target type
+impl<T: ?Sized, M: ?Sized> RcuRef<T, M> {
+    pub fn map<N: ?Sized, F: for<'a> FnOnce(&'a M) -> &'a N>(referece: Self, f: F) -> RcuRef<T, N> {
+        RcuRef {
+            arc: referece.arc,
+            data: f(unsafe { referece.data.as_ref() }).into(),
+        }
+    }
+
+    pub fn try_map<N: ?Sized, F: for<'a> FnOnce(&'a M) -> Option<&'a N>>(
+        referece: Self,
+        f: F,
+    ) -> Option<RcuRef<T, N>> {
+        let val = f(unsafe { referece.data.as_ref() })?;
+        Some(RcuRef {
+            arc: Arc::clone(&referece.arc),
+            data: val.into(),
+        })
+    }
+
+    pub fn same_epoch<M2>(this: &Self, other: &RcuRef<T, M2>) -> bool {
+        Arc::ptr_eq(&this.arc, &other.arc)
+    }
+
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        this.data == other.data
+    }
+
+    pub fn clone(this: &Self) -> Self {
+        Self {
+            arc: Arc::clone(&this.arc),
+            data: this.data,
+        }
+    }
+
+    pub fn get_root(this: &Self) -> &T {
+        &this.arc
+    }
+}
+
+impl<T: ?Sized, M: ?Sized> Deref for RcuRef<T, M> {
+    type Target = M;
+
+    fn deref(&self) -> &Self::Target {
+        // Safety: The pointer points into the arc we are holding
+        // while we are alive so is the target
+        // as the content is in an Rcu no mutable acess is given out
+        unsafe { self.data.as_ref() }
+    }
+}

src/read.rs

@@ -16,8 +16,6 @@ use crate::types::*;
 
 use fxhash::FxBuildHasher;
 
-use indexmap::IndexSet;
-
 #[cfg(feature = "repl")]
 use rustyline::error::ReadlineError;
 #[cfg(feature = "repl")]
@@ -26,19 +24,20 @@ use rustyline::history::DefaultHistory;
 use rustyline::{Config, Editor};
 
 use std::collections::VecDeque;
-use std::io::{Cursor, Error, ErrorKind, Read};
+use std::io::{Cursor, Read};
+#[cfg(feature = "repl")]
+use std::io::{Error, ErrorKind};
+use std::sync::Arc;
 
 type SubtermDeque = VecDeque<(usize, usize)>;
 
-pub(crate) fn devour_whitespace<'a, R: CharRead>(parser: &mut Parser<'a, R>) -> Result<bool, ParserError> {
+pub(crate) fn devour_whitespace<'a, R: CharRead>(
+    parser: &mut Parser<'a, R>,
+) -> Result<bool, ParserError> {
     match parser.lexer.scan_for_layout() {
-        Err(e) if e.is_unexpected_eof() => {
-            Ok(true)
-        }
+        Err(e) if e.is_unexpected_eof() => Ok(true),
         Err(e) => Err(e),
-        Ok(_) => {
-            Ok(false)
-        }
+        Ok(_) => Ok(false),
     }
 }
 
@@ -60,7 +59,6 @@ pub(crate) fn error_after_read_term<R>(
     CompilationError::from(err)
 }
 
-
 impl MachineState {
     pub(crate) fn read(
         &mut self,
@@ -74,18 +72,20 @@ impl MachineState {
 
             parser.add_lines_read(prior_num_lines_read);
 
-            let term = parser.read_term(&op_dir, Tokens::Default)
+            let term = parser
+                .read_term(&op_dir, Tokens::Default)
                 .map_err(|err| error_after_read_term(err, prior_num_lines_read, &parser))?; // CompilationError::from
 
             (term, parser.lines_read() - prior_num_lines_read)
         };
 
         inner.add_lines_read(num_lines_read);
-        write_term_to_heap(&term, &mut self.heap, &mut self.atom_tbl)
+        write_term_to_heap(&term, &mut self.heap, &self.atom_tbl)
     }
 }
 
 static mut PROMPT: bool = false;
+#[cfg(feature = "repl")]
 const HISTORY_FILE: &'static str = ".scryer_history";
 
 pub(crate) fn set_prompt(value: bool) {
@@ -94,6 +94,7 @@ pub(crate) fn set_prompt(value: bool) {
     }
 }
 
+#[cfg(feature = "repl")]
 #[inline]
 fn get_prompt() -> &'static str {
     unsafe {
@@ -110,55 +111,54 @@ pub struct ReadlineStream {
     #[cfg(feature = "repl")]
     rl: Editor<Helper, DefaultHistory>,
     pending_input: CharReader<Cursor<String>>,
+    #[allow(dead_code)]
     add_history: bool,
 }
 
 impl ReadlineStream {
-    #[cfg(feature = "repl")]
     #[inline]
     pub fn new(pending_input: &str, add_history: bool) -> Self {
-        let config = Config::builder()
-            .check_cursor_position(true)
-            .build();
+        #[cfg(feature = "repl")]
+        {
+            let config = Config::builder().check_cursor_position(true).build();
 
-        let helper = Helper::new();
+            let helper = Helper::new();
 
-        let mut rl = Editor::with_config(config).unwrap();
-        rl.set_helper(Some(helper));
+            let mut rl = Editor::with_config(config).unwrap();
+            rl.set_helper(Some(helper));
 
-        if let Some(mut path) = dirs_next::home_dir() {
-            path.push(HISTORY_FILE);
-            if path.exists() && rl.load_history(&path).is_err() {
-                println!("Warning: loading history failed");
+            if let Some(mut path) = dirs_next::home_dir() {
+                path.push(HISTORY_FILE);
+                if path.exists() && rl.load_history(&path).is_err() {
+                    println!("Warning: loading history failed");
+                }
+            }
+
+            ReadlineStream {
+                rl,
+                pending_input: CharReader::new(Cursor::new(pending_input.to_owned())),
+                add_history: add_history,
             }
         }
 
-        ReadlineStream {
-            rl,
-            pending_input: CharReader::new(Cursor::new(pending_input.to_owned())),
-            add_history: add_history,
+        #[cfg(not(feature = "repl"))]
+        {
+            ReadlineStream {
+                pending_input: CharReader::new(Cursor::new(pending_input.to_owned())),
+                add_history: add_history,
+            }
         }
     }
 
-    #[cfg(not(feature = "repl"))]
-    #[inline]
-    pub fn new(pending_input: &str, add_history: bool) -> Self {
-        ReadlineStream {
-            pending_input: CharReader::new(Cursor::new(pending_input.to_owned())),
-            add_history: add_history,
+    #[allow(unused_variables)]
+    pub fn set_atoms_for_completion(&mut self, atoms: &Arc<AtomTable>) {
+        #[cfg(feature = "repl")]
+        {
+            let helper = self.rl.helper_mut().unwrap();
+            helper.atoms = Arc::downgrade(atoms);
         }
     }
 
-    #[cfg(feature = "repl")]
-    pub fn set_atoms_for_completion(&mut self, atoms: *const IndexSet<Atom>) {
-        let helper = self.rl.helper_mut().unwrap();
-        helper.atoms = atoms;
-    }
-
-    #[cfg(not(feature = "repl"))]
-    pub fn set_atoms_for_completion(&mut self, atoms: *const IndexSet<Atom>) {
-    }
-
     #[inline]
     pub fn reset(&mut self) {
         self.pending_input.reset_buffer();
@@ -180,7 +180,9 @@ impl ReadlineStream {
 
                 unsafe {
                     if PROMPT {
-                        self.rl.add_history_entry(self.pending_input.get_ref().get_ref()).unwrap();
+                        self.rl
+                            .add_history_entry(self.pending_input.get_ref().get_ref())
+                            .unwrap();
                         self.save_history();
                         PROMPT = false;
                     }
@@ -219,9 +221,9 @@ impl ReadlineStream {
         }
     }
 
+    #[allow(dead_code)]
     #[cfg(not(feature = "repl"))]
-    fn save_history(&mut self) {
-    }
+    fn save_history(&mut self) {}
 
     #[inline]
     pub(crate) fn peek_byte(&mut self) -> std::io::Result<u8> {
@@ -253,7 +255,7 @@ impl Read for ReadlineStream {
                 self.call_readline()?;
                 self.pending_input.read(buf)
             }
-            result => result
+            result => result,
         }
     }
 }
@@ -266,16 +268,14 @@ impl CharRead for ReadlineStream {
                 Some(Ok(c)) => {
                     return Some(Ok(c));
                 }
-                _ => {
-                    match self.call_readline() {
-                        Err(e) => {
-                            return Some(Err(e));
-                        }
-                        _ => {
-                            set_prompt(false);
-                        }
+                _ => match self.call_readline() {
+                    Err(e) => {
+                        return Some(Err(e));
                     }
-                }
+                    _ => {
+                        set_prompt(false);
+                    }
+                },
             }
         }
     }
@@ -295,7 +295,7 @@ impl CharRead for ReadlineStream {
 pub(crate) fn write_term_to_heap<'a, 'b>(
     term: &'a Term,
     heap: &'b mut Heap,
-    atom_tbl: &mut AtomTable,
+    atom_tbl: &AtomTable,
 ) -> Result<TermWriteResult, CompilationError> {
     let term_writer = TermWriter::new(heap, atom_tbl);
     term_writer.write_term_to_heap(term)
@@ -304,7 +304,7 @@ pub(crate) fn write_term_to_heap<'a, 'b>(
 #[derive(Debug)]
 struct TermWriter<'a, 'b> {
     heap: &'a mut Heap,
-    atom_tbl: &'b mut AtomTable,
+    atom_tbl: &'b AtomTable,
     queue: SubtermDeque,
     var_dict: HeapVarDict,
 }
@@ -317,7 +317,7 @@ pub struct TermWriteResult {
 
 impl<'a, 'b> TermWriter<'a, 'b> {
     #[inline]
-    fn new(heap: &'a mut Heap, atom_tbl: &'b mut AtomTable) -> Self {
+    fn new(heap: &'a mut Heap, atom_tbl: &'b AtomTable) -> Self {
         TermWriter {
             heap,
             atom_tbl,
@@ -347,17 +347,18 @@ impl<'a, 'b> TermWriter<'a, 'b> {
         match term {
             &TermRef::Cons(..) => list_loc_as_cell!(h),
             &TermRef::AnonVar(_) | &TermRef::Var(..) => heap_loc_as_cell!(h),
-            &TermRef::CompleteString(_, _, ref src) =>
+            &TermRef::CompleteString(_, _, ref src) => {
                 if src.as_str().is_empty() {
                     empty_list_as_cell!()
                 } else if self.heap[h].get_tag() == HeapCellValueTag::CStr {
                     heap_loc_as_cell!(h)
                 } else {
                     pstr_loc_as_cell!(h)
-                },
+                }
+            }
             &TermRef::PartialString(..) => pstr_loc_as_cell!(h),
             &TermRef::Literal(_, _, literal) => HeapCellValue::from(*literal),
-            &TermRef::Clause(_,_,_,subterms) if subterms.len() == 0 => heap_loc_as_cell!(h),
+            &TermRef::Clause(_, _, _, subterms) if subterms.len() == 0 => heap_loc_as_cell!(h),
             &TermRef::Clause(..) => str_loc_as_cell!(h),
         }
     }
@@ -427,7 +428,8 @@ impl<'a, 'b> TermWriter<'a, 'b> {
                 }
                 &TermRef::AnonVar(_) => {
                     if let Some((arity, site_h)) = self.queue.pop_front() {
-                        self.var_dict.insert(VarKey::AnonVar(h), heap_loc_as_cell!(site_h));
+                        self.var_dict
+                            .insert(VarKey::AnonVar(h), heap_loc_as_cell!(site_h));
 
                         if arity > 1 {
                             self.queue.push_front((arity - 1, site_h + 1));
@@ -437,7 +439,8 @@ impl<'a, 'b> TermWriter<'a, 'b> {
                     continue;
                 }
                 &TermRef::CompleteString(_, _, ref src) => {
-                    put_complete_string(self.heap, src.as_str(), self.atom_tbl);
+                    let src = src.as_str().to_owned();
+                    put_complete_string(self.heap, &src, self.atom_tbl);
                 }
                 &TermRef::PartialString(lvl, _, ref src, _) => {
                     if let Level::Root = lvl {

src/repl_helper.rs

@@ -1,23 +1,24 @@
-use indexmap::IndexSet;
-use rustyline::completion::{Completer, Candidate};
+use rustyline::completion::Completer;
+use rustyline::highlight::{Highlighter, MatchingBracketHighlighter};
 use rustyline::hint::Hinter;
 use rustyline::validate::Validator;
-use rustyline::highlight::{MatchingBracketHighlighter, Highlighter};
-use rustyline::{Helper as RlHelper, Result, Context};
+use rustyline::{Context, Helper as RlHelper, Result};
 
-use crate::atom_table::{Atom, STATIC_ATOMS_MAP};
+use std::sync::Weak;
+
+use crate::atom_table::{AtomString, AtomTable, STATIC_ATOMS_MAP};
 
 // TODO: Maybe add validation to the helper
 pub struct Helper {
     highligher: MatchingBracketHighlighter,
-    pub atoms: *const IndexSet<Atom>,
+    pub atoms: Weak<AtomTable>,
 }
 
 impl Helper {
     pub fn new() -> Self {
         Self {
             highligher: MatchingBracketHighlighter::new(),
-            atoms: std::ptr::null(),
+            atoms: Weak::new(),
         }
     }
 }
@@ -43,7 +44,7 @@ fn get_prefix(line: &str, pos: usize) -> Option<usize> {
         }
 
         if i == pos {
-            break
+            break;
         }
     }
 
@@ -54,39 +55,33 @@ fn get_prefix(line: &str, pos: usize) -> Option<usize> {
     start_of_atom
 }
 
-pub struct StrPtr(*const str);
-
-impl Candidate for StrPtr {
-    fn display(&self) -> &str {
-        unsafe {
-            self.0.as_ref().unwrap()
-        }
-    }
-
-    fn replacement(&self) -> &str {
-        unsafe {
-            self.0.as_ref().unwrap()
-        }
-    }
-}
-
 impl Completer for Helper {
-    type Candidate = StrPtr;
+    type Candidate = AtomString<'static>;
 
-    fn complete(&self, line: &str, pos: usize, _ctx: &Context<'_>) -> Result<(usize, Vec<Self::Candidate>)> {
+    fn complete(
+        &self,
+        line: &str,
+        pos: usize,
+        _ctx: &Context<'_>,
+    ) -> Result<(usize, Vec<Self::Candidate>)> {
         let start_of_prefix = get_prefix(line, pos);
         if let Some(idx) = start_of_prefix {
             let sub_str = line.get(idx..pos).unwrap();
-            Ok((idx, unsafe {
-                let mut matching = (*self.atoms).iter()
-                    .chain(STATIC_ATOMS_MAP.values())
-                    .filter(|a| a.as_str().starts_with(sub_str))
-                    .map(|s| StrPtr(s.as_str()))
-                    .collect::<Vec<_>>();
 
-                matching.sort_unstable_by(|a, b| Ord::cmp(&(*a.0).len(), &(*b.0).len()));
-                matching
-            }))
+            let atom_table = self.atoms.upgrade().unwrap();
+
+            let index_set = atom_table.active_table();
+
+            let mut matching = index_set
+                .iter()
+                .chain(STATIC_ATOMS_MAP.values())
+                .map(|a| a.as_str())
+                .filter(|a| a.starts_with(sub_str))
+                .collect::<Vec<_>>();
+
+            matching.sort_unstable_by(|a, b| Ord::cmp(&a.len(), &b.len()));
+
+            Ok((idx, matching))
         } else {
             Ok((0, vec![]))
         }

src/tests/acyclic_term.pl

@@ -0,0 +1,306 @@
+:- use_module(library(dcgs)).
+:- use_module(library(format)).
+
+term1(A) :-
+   B=[C|D],
+   A=[D|C],
+   B=[C|B].
+
+term2(A) :-
+   A=[B|C],
+   D=[C|C],
+   D=[B|D].
+
+term3(A) :-
+   A=[_B|C],
+   D=[C|_E],
+   A=[C|D].
+
+term4(A) :-
+   A=[B|C],
+   C=[C|B].
+
+term5(A) :-
+   A=[_B|C],
+   D=[_E|C],
+   A=[C|D].
+
+term6(A) :-
+   A=[B|B],
+   B=[C|C].
+
+term7(A) :-
+   B=[C|D],
+   A=[D|C],
+   B=[B|D].
+
+term8(A) :-
+   B=C,
+   B=[C|_D],
+   A=[C|_E].
+
+test("acyclic_term_1", (
+    L = [_Y,[M,B],B|M], acyclic_term(L)
+)).
+
+test("acyclic_term_2", (
+    L = [_Y,[M,_B,L]|M], \+ acyclic_term(L)
+)).
+
+test("acyclic_term_3", (
+    L = [_Y,[M,B,L,B]|M], \+ acyclic_term(L)
+)).
+
+test("acyclic_term_4", (
+    L = [_Y,[L,_A,_B]|_M], \+ acyclic_term(L)
+)).
+
+test("acyclic_term_5", (
+    L = [_Y,[M,_A,_B]|M], acyclic_term(L)
+)).
+
+test("acyclic_term_6", (
+    L = [_Y,[L,_A,_B]|_M], \+ acyclic_term(L)
+)).
+
+test("acyclic_term_7", (
+    L = [A], A = [T], T = [_|X], X = Y, Y = L, \+ acyclic_term(T)
+)).
+
+test("acyclic_term_8", (
+    L = [A], A = [T], T = [_|X], X = Y, Y = L, \+ acyclic_term(L)
+)).
+
+test("acyclic_term_9", (
+    L = [A], A = [T], T = [_|X], X = Y, Y = L, \+ acyclic_term(A)
+)).
+
+test("acyclic_term_10", (
+    L = [A], A = [T], T = [_|X], X = Y, Y = L, \+ acyclic_term(Y)
+)).
+
+test("acyclic_term_11", (
+    L = [A], A = [T], T = [_|X], X = Y, Y = L, \+ acyclic_term(X)
+)).
+
+test("acyclic_term_12", (
+    A = [1|2], X = A, T=a(X, A), acyclic_term(T)
+)).
+
+test("acyclic_term_13", (
+    A = [A|2], X = A, T=a(X, A), \+ acyclic_term(T)
+)).
+
+test("acyclic_term_14", (
+    A = [T|2], X = A, T=a(X, A), \+ acyclic_term(T)
+)).
+
+test("acyclic_term_15", (
+    T = [_A|T], \+ acyclic_term(T)
+)).
+
+test("acyclic_term_16", (
+    T = [T|_L], \+ acyclic_term(T)
+)).
+
+test("acyclic_term_17", (
+    A = [1|A], X = A, T=a(X, A), \+ acyclic_term(T)
+)).
+
+test("acyclic_term_18", (
+    T = [_A| [[[[L|T]|[]]]]], acyclic_term(L)
+)).
+
+test("acyclic_term_19", (
+    T = [A| [[[[_L|T]|[]]]]], acyclic_term(A)
+)).
+
+test("acyclic_term_20", (
+    T = [_A| [[[[_L|T]|[]]]]], \+ acyclic_term(T)
+)).
+
+test("acyclic_term_21", (
+    A = [_C|_B], X = A, T=a(t(X,A), A), acyclic_term(T)
+)).
+
+test("acyclic_term_22", (
+    X = [a | Rest], Rest = [_Y | Rest], \+ acyclic_term(X)
+)).
+
+test("acyclic_term_23", (
+    _X = [a | Rest], Rest = [_Y | Rest], \+ acyclic_term(Rest)
+)).
+
+test("acyclic_term_24", (
+    T = [[_A, T]], G = [1|T], \+ acyclic_term(G)
+)).
+
+test("acyclic_term_25", (
+    T = [[_A, T]], \+ acyclic_term(T)
+)).
+
+test("acyclic_term_26", (
+    T = [[_, _], T], \+ acyclic_term(T)
+)).
+
+test("acyclic_term_27", (
+    T = [[T, _], 1], \+ acyclic_term(T)
+)).
+
+test("acyclic_term_28", (
+    T = str(A,A), acyclic_term(T)
+)).
+
+test("acyclic_term_29", (
+    T = str(A,A,A), acyclic_term(T)
+)).
+
+test("acyclic_term_30", (
+    A = s(B, d(Y)), Y = B, acyclic_term(A),
+    acyclic_term(B), acyclic_term(Y)
+)).
+
+test("acyclic_term_31", (
+    A=str(B,B,B), C=str(A,_D,B), acyclic_term(C),
+    acyclic_term(A), acyclic_term(B)
+)).
+
+test("acyclic_term_32", (
+    A=B*C,A=[]*B*D*B, \+ acyclic_term(A),
+    \+ acyclic_term(B), \+ acyclic_term(C),
+    acyclic_term(D)
+)).
+
+test("acyclic_term_33", (
+    A=B*C,A=B*[]*B, \+ acyclic_term(A),
+    \+ acyclic_term(B), \+ acyclic_term(C)
+)).
+
+test("acyclic_term#2111_1", (
+    term1(A), \+ acyclic_term(A)
+)).
+
+test("acyclic_term#2111_2", (
+    term2(A), \+ acyclic_term(A)
+)).
+
+test("acyclic_term#2111_3", (
+    term3(A), \+ acyclic_term(A)
+)).
+
+test("acyclic_term#2111_4", (
+    term4(A), \+ acyclic_term(A)
+)).
+
+test("acyclic_term#2111_5", (
+    term5(A), \+ acyclic_term(A)
+)).
+
+test("acyclic_term#2111_6", (
+    term6(A), acyclic_term(A)
+)).
+
+test("acyclic_term#2113", (
+    A=[]*B,B=[]*B, \+ acyclic_term(A)
+)).
+
+test("acyclic_term#2114", (
+    A=B*B, acyclic_term(A)
+)).
+
+test("acyclic_term#2116", (
+    A=B*B,B=[]*[], acyclic_term(A)
+)).
+
+test("acyclic_term#2117", (
+    A=[]*A,B=[]*A, \+ acyclic_term(B)
+)).
+
+test("acyclic_term#2121", (
+    A=B*B, C=A*B, acyclic_term(C),
+    acyclic_term(A), acyclic_term(B)
+)).
+
+test("acyclic_term#2122", (
+    A=B*C,A=[]*B*B, \+ acyclic_term(A),
+    \+ acyclic_term(B), \+ acyclic_term(C)
+)).
+
+test("acyclic_term#2123", (
+    A=B*B,C=A*B,B=[]*[], acyclic_term(A),
+    acyclic_term(B), acyclic_term(C)
+)).
+
+test("acyclic_term#2124", (
+    A=B*C,B=[]*C,C=[]*B, \+ acyclic_term(A),
+    \+ acyclic_term(B), \+ acyclic_term(C)
+)).
+
+test("acyclic_term#2125", (
+    A=B*[],
+    D=B*[],
+    A=B,
+    \+ acyclic_term(D),
+    \+ acyclic_term(A),
+    \+ acyclic_term(B)
+)).
+
+test("acyclic_term#2130_1", (
+    term7(T),
+    \+ acyclic_term(T)
+)).
+
+test("acyclic_term#2130_2", (
+    term8(T),
+    \+ acyclic_term(T)
+)).
+
+test("acyclic_term#2131", (
+    A=[B],C=[B],C=[A],
+    \+ acyclic_term(C)
+)).
+
+main :-
+    findall(test(Name, Goal), test(Name, Goal), Tests),
+    run_tests(Tests, Failed),
+    show_failed(Failed),
+    halt.
+
+main_quiet :-
+    findall(test(Name, Goal), test(Name, Goal), Tests),
+    run_tests_quiet(Tests, Failed),
+    (   Failed = [] ->
+        format("All tests passed", [])
+    ;   format("Some tests failed", [])
+    ),
+    halt.
+
+run_tests([], []).
+run_tests([test(Name, Goal)|Tests], Failed) :-
+    format("Running test \"~s\"~n", [Name]),
+    (   call(Goal) ->
+        Failed = Failed1
+    ;   format("Failed test \"~s\"~n", [Name]),
+        Failed = [Name|Failed1]
+    ),
+    run_tests(Tests, Failed1).
+
+run_tests_quiet([], []).
+run_tests_quiet([test(Name, Goal)|Tests], Failed) :-
+    (   call(Goal) ->
+        Failed = Failed1
+    ;   Failed = [Name|Failed1]
+    ),
+    run_tests_quiet(Tests, Failed1).
+
+show_failed(Failed) :-
+    phrase(portray_failed(Failed), F),
+    format("~s", [F]).
+
+portray_failed_([]) --> [].
+portray_failed_([F|Fs]) -->
+    "\"", F, "\"",  "\n", portray_failed_(Fs).
+
+portray_failed([]) --> [].
+portray_failed([F|Fs]) -->
+    "\n", "Failed tests:", "\n", portray_failed_([F|Fs]).

src/tests/dif.pl

@@ -0,0 +1,270 @@
+/**/
+
+:- use_module(library(format)).
+:- use_module(library(dcgs)).
+:- use_module(library(lists)).
+:- use_module(library(debug)).
+:- use_module(library(atts)).
+:- use_module(library(dif)).
+
+% Tests from https://www.complang.tuwien.ac.at/ulrich/iso-prolog/dif
+
+test("dif#1",(
+    call_residual_goals(dif(1,2), Res),
+    Res = []
+)).
+
+test("dif#2",(
+    \+ (dif(1,Y), Y = 1)
+)).
+
+test("dif#3",(
+    call_residual_goals((dif(1,Y), Y=2), Res),
+    Y == 2,
+    Res = []
+)).
+
+test("dif#4",(
+    \+ (dif(X,-Y), X= -Y)
+)).
+
+test("dif#5",(
+    \+ (dif(X,Y), X=Y)
+)).
+
+test("dif#6",(
+    \+ (dif(X,Y), X=Y, X=1)
+)).
+
+test("dif#7",(
+    \+ (dif(-X,-Y), X=Y)
+)).
+
+test("dif#8",(
+    \+ (dif(-X,-Y), X=Y, X=1)
+)).
+
+% I don't understand exactly what is expected for dif#9 and dif#10
+
+test("dif#11",(
+    call_residual_goals((X=Y, dif(X-Y,1-2)), Res),
+    X == Y,
+    Res = []
+)).
+
+test("dif#12",(
+    call_residual_goals((dif(X-Y,1-2), X=Y), Res),
+    X == Y,
+    Res = []
+)).
+
+test("dif#13",(
+    call_residual_goals((X=Y, Y=1, dif(X-Y,1-2)), Res),
+    X == 1,
+    Y == 1,
+    Res = []
+)).
+
+test("dif#14",(
+    call_residual_goals((dif(X-Y,1-2), X=Y, Y=1), Res),
+    X == 1,
+    Y == 1,
+    Res = []
+)).
+
+test("dif#15",(
+    call_residual_goals((dif(X-Y,1-2), X=Y, X=2), Res),
+    X == 2,
+    Y == 2,
+    Res = []
+)).
+
+test("dif#16",(
+    call_residual_goals((dif(A-C,B-D), C-D=z-z, A-B=1-2), Res),
+    A == 1,
+    B == 2,
+    C == z,
+    D == z,
+    Res = []
+)).
+
+test("dif#17",(
+    call_residual_goals((A-B=1-2, C-D=z-z, dif(A-C,B-D)), Res),
+    A == 1,
+    B == 2,
+    C == z,
+    D == z,
+    Res = []
+)).
+
+test("dif#18",(
+    call_residual_goals((dif(A,[C|B]), A=[[]|_], A=[B]), Res),
+    A == [[]],
+    B == [],
+    Res = [dif:dif([[]], [C])]
+)).
+
+test("dif#19",(
+    call_residual_goals((dif([E],[/]), E=1), Res),
+    E == 1,
+    Res = []
+)).
+
+test("dif#20",(
+    call_residual_goals((dif([a],B), B=[_|_], B=[b]), Res),
+    B == [b],
+    Res = []
+)).
+
+test("dif#21",(
+    call_residual_goals((dif([],A), A = [_]), Res),
+    A = [_],
+    Res = []
+)).
+
+test("dif#22",(
+    call_residual_goals((A = [_], dif([],A)), Res),
+    A = [_],
+    Res = []
+)).
+
+test("dif#t1",(
+    set_prolog_flag(occurs_check, false),
+    \+ \+ -X=X
+)).
+
+test("dif#t2",(
+    set_prolog_flag(occurs_check, false),
+    \+ (-X=X, -Y=Y, X\=Y)
+)).
+
+test("dif#t3",(
+    set_prolog_flag(occurs_check, false),
+    call_residual_goals((-X=X, dif(X,1)), Res),
+    X == -X,
+    Res = []
+)).
+
+test("dif#t4",(
+    set_prolog_flag(occurs_check, false),
+    \+ (-X=X, -Y=Y, dif(X,Y))
+)).
+
+test("dif#t5",(
+    set_prolog_flag(occurs_check, false),
+    \+ (dif(X,Y), -X=X, -Y=Y)
+)).
+
+test("dif#t6",(
+    set_prolog_flag(occurs_check, false),
+    \+ (A=[[]|A],dif(A,B),B=[[]|A])
+)).
+
+test("dif#t7",(
+    set_prolog_flag(occurs_check, false),
+    \+ (dif(-X,X),-Y=Y,X=Y)
+)).
+
+test("dif#o1",(
+    set_prolog_flag(occurs_check, true),
+    \+ (-X = X)
+)).
+
+test("dif#o2",(
+    set_prolog_flag(occurs_check, true),
+    call_residual_goals((dif(-X,X)), Res),
+    Res = []
+)).
+
+test("dif#o3",(
+    set_prolog_flag(occurs_check, true),
+    call_residual_goals((dif(-X,Y), X=Y), Res),
+    X == Y,
+    Res = []
+)).
+
+test("dif#12 but with multiple variables in the residuals",(
+    call_residual_goals((dif(X-Y-_, 1-2-3), X = Y), Res),
+    X == Y,
+    Res = []
+)).
+
+% https://github.com/mthom/scryer-prolog/issues/1956
+test("scryer-prolog#1956",(
+    call_residue_vars((dif(a-a,X-_),X=b), Res),
+    X == b,
+    Res = []
+)).
+
+% https://github.com/mthom/scryer-prolog/issues/2056
+test("scryer-prolog#2056",(
+    set_prolog_flag(occurs_check, false),
+    C=[D|E],
+    D=[C],
+    A=[A],
+    dif(A,[D]),
+
+    \+ E=[]
+)).
+
+main :-
+    findall(test(Name, Goal), test(Name, Goal), Tests),
+    run_tests(Tests, Failed),
+    show_failed(Failed),
+    halt.
+
+main_quiet :-
+    findall(test(Name, Goal), test(Name, Goal), Tests),
+    run_tests_quiet(Tests, Failed),
+    (   Failed = [] ->
+        format("All tests passed", [])
+    ;   format("Some tests failed", [])
+    ),
+    halt.
+
+portray_failed_([]) --> [].
+portray_failed_([F|Fs]) -->
+    "\"", F, "\"",  "\n", portray_failed_(Fs).
+
+portray_failed([]) --> [].
+portray_failed([F|Fs]) -->
+    "\n", "Failed tests:", "\n", portray_failed_([F|Fs]).
+
+show_failed(Failed) :-
+    phrase(portray_failed(Failed), F),
+    format("~s", [F]).
+
+run_tests([], []).
+run_tests([test(Name, Goal)|Tests], Failed) :-
+    format("Running test \"~s\"~n", [Name]),
+    (   call(Goal) ->
+        Failed = Failed1
+    ;   format("Failed test \"~s\"~n", [Name]),
+        Failed = [Name|Failed1]
+    ),
+    run_tests(Tests, Failed1).
+
+run_tests_quiet([], []).
+run_tests_quiet([test(Name, Goal)|Tests], Failed) :-
+    (   call(Goal) ->
+        Failed = Failed1
+    ;   Failed = [Name|Failed1]
+    ),
+    run_tests_quiet(Tests, Failed1).
+
+assert_p(A, B) :-
+    phrase(portray_clause_(A), Portrayed),
+    phrase((B, ".\n"), Portrayed).
+
+call_residual_goals(Goal, ResidualGoals) :-
+    call_residue_vars(Goal, Vars),
+    variables_residual_goals(Vars, ResidualGoals).
+
+variables_residual_goals(Vars, Goals) :-
+    phrase(variables_residual_goals(Vars), Goals).
+
+variables_residual_goals([]) --> [].
+variables_residual_goals([Var|Vars]) -->
+    dif:attribute_goals(Var),
+    variables_residual_goals(Vars).
+

src/tests/ground.pl

@@ -0,0 +1,83 @@
+/**/
+
+:- use_module(library(format)).
+:- use_module(library(dcgs)).
+:- use_module(library(lists)).
+:- use_module(library(debug)).
+:- use_module(library(atts)).
+
+:- attribute a/1.
+
+a(Var) :- put_atts(Var, +a(hello)).
+
+test("ground#239", (
+    % double negate to avoid residual goal being printed
+    \+ \+ (a(X), var(X), \+ ground(X))
+)).
+
+test("ground#1411",(
+    G_0 = ( A=s(A) ), G_0,
+    ground(A), ground(G_0)
+)).
+
+test("ground#2065",(
+    A = [B|_C], B = [A], \+ ground(B), \+ground([B])
+)).
+
+test("ground#2073",(
+    \+ ground(_-1+_-1),
+    \+ ground(1-1-_)
+)).
+
+test("ground#2075",(
+    G_0 = (_,_,ground(_)),
+    G_0 = (D=[D|_],_=D*[],ground(D)),
+    \+ G_0,
+    _=_B*_,_D=_B*_A,_B=_B*_D,\+ ground(_B),
+    A=[A|B],B=A*B,ground(A)
+)).
+
+main :-
+    findall(test(Name, Goal), test(Name, Goal), Tests),
+    run_tests(Tests, Failed),
+    show_failed(Failed),
+    halt.
+
+main_quiet :-
+    findall(test(Name, Goal), test(Name, Goal), Tests),
+    run_tests_quiet(Tests, Failed),
+    (   Failed = [] ->
+        format("All tests passed", [])
+    ;   format("Some tests failed", [])
+    ),
+    halt.
+
+run_tests([], []).
+run_tests([test(Name, Goal)|Tests], Failed) :-
+    format("Running test \"~s\"~n", [Name]),
+    (   call(Goal) ->
+        Failed = Failed1
+    ;   format("Failed test \"~s\"~n", [Name]),
+        Failed = [Name|Failed1]
+    ),
+    run_tests(Tests, Failed1).
+
+run_tests_quiet([], []).
+run_tests_quiet([test(Name, Goal)|Tests], Failed) :-
+    (   call(Goal) ->
+        Failed = Failed1
+    ;   Failed = [Name|Failed1]
+    ),
+    run_tests_quiet(Tests, Failed1).
+
+portray_failed_([]) --> [].
+portray_failed_([F|Fs]) -->
+    "\"", F, "\"",  "\n", portray_failed_(Fs).
+
+portray_failed([]) --> [].
+portray_failed([F|Fs]) -->
+    "\n", "Failed tests:", "\n", portray_failed_([F|Fs]).
+
+show_failed(Failed) :-
+    phrase(portray_failed(Failed), F),
+    format("~s", [F]).

src/tests/term_variables.pl

@@ -0,0 +1,117 @@
+/**/
+
+:- use_module(library(format)).
+:- use_module(library(dcgs)).
+:- use_module(library(lists)).
+:- use_module(library(debug)).
+
+test("term_variables#1400", (
+    term_variables(A+B*C/B-D, Vars),
+    term_variables(t(A,B,C,D), Vars),
+    Vars = [A,B,C,D]
+)).
+
+test("term_variables#1405", (
+    \+ (B=[C|D],C=[_|D],C=[B|B], term_variables(B,_), false)
+)).
+
+test("term_variables#1409", (
+    G_0 = (A=[B|B],A=[C|C]), G_0, term_variables(G_0, Vars), Vars = [B]
+)).
+
+test("term_variables#1410", (
+    \+ \+ (G_0 = ( A=s(A) ), G_0, term_variables(G_0, Vars), Vars = []),
+    E_0 = (_=[B|B]), G_0 = (E_0,\_=B), G_0, term_variables(G_0, Vars)
+)).
+
+test("term_variables#1412", (
+    G_0 = =([A|B],[A|B]), G_0, term_variables(G_0, Vars),
+    Vars = [A,B]
+)).
+
+test("term_variables#1414", (
+    \+ (\B=A,C=[A|D],B=[a,b|E],C=[D|E], term_variables(\E,_), false)
+)).
+
+test("term_variables#2063", (
+    A=[B|C], B=[A], term_variables([B], Vars),
+    Vars = [C]
+)).
+
+test("term_variables#2097", (
+    termt(T), term_variables(T,Vs),
+    T = [[[A|B]|A]|A], Vs == [A,B]
+)).
+
+test("term_variables#2100", (
+    termt2(T), term_variables(T,Vs),
+    T = [[T|A]|B], Vs == [A,B]
+)).
+
+test("term_variables#2101", (
+    termt3(T), term_variables(T,Vs),
+    T = [[[[A|B]|A]|A]|A], Vs == [A, B]
+)).
+
+termt(T) :-
+   T = [T1|T2],
+   T1 = [T3|A],
+   T3 = [A|_],
+   T2 = A.
+
+termt2(T) :-
+   T = [T1|_B],
+   T1 = [T|_A].
+
+termt3(T) :-
+   T = [T1|T0],
+   T1 = [T2|T3],
+   T2 = [T4|A],
+   T4 = [A|_],
+   T3 = A,
+   T0 = A.
+
+main :-
+    findall(test(Name, Goal), test(Name, Goal), Tests),
+    run_tests(Tests, Failed),
+    show_failed(Failed),
+    halt.
+
+main_quiet :-
+    findall(test(Name, Goal), test(Name, Goal), Tests),
+    run_tests_quiet(Tests, Failed),
+    (   Failed = [] ->
+        format("All tests passed", [])
+    ;   format("Some tests failed", [])
+    ),
+    halt.
+
+run_tests([], []).
+run_tests([test(Name, Goal)|Tests], Failed) :-
+    format("Running test \"~s\"~n", [Name]),
+    (   call(Goal) ->
+        Failed = Failed1
+    ;   format("Failed test \"~s\"~n", [Name]),
+        Failed = [Name|Failed1]
+    ),
+    run_tests(Tests, Failed1).
+
+run_tests_quiet([], []).
+run_tests_quiet([test(Name, Goal)|Tests], Failed) :-
+    (   call(Goal) ->
+        Failed = Failed1
+    ;   Failed = [Name|Failed1]
+    ),
+    run_tests_quiet(Tests, Failed1).
+
+portray_failed_([]) --> [].
+portray_failed_([F|Fs]) -->
+    "\"", F, "\"",  "\n", portray_failed_(Fs).
+
+portray_failed([]) --> [].
+portray_failed([F|Fs]) -->
+    "\n", "Failed tests:", "\n", portray_failed_([F|Fs]).
+
+show_failed(Failed) :-
+    phrase(portray_failed(Failed), F),
+    format("~s", [F]).

src/toplevel.pl

@@ -235,8 +235,12 @@ double_quotes_option(DQ) :-
     ;   DQ = false
     ).
 
+answer_write_options(Os) :-
+    current_prolog_flag(answer_write_options, Os).
+
 write_goal(G, VarList, MaxDepth) :-
     double_quotes_option(DQ),
+    answer_write_options(Os),
     (  G = (Var = Value) ->
        (  var(Value) ->
           select((Var = _), VarList, NewVarList)
@@ -246,17 +250,18 @@ write_goal(G, VarList, MaxDepth) :-
        write(' = '),
        (  needs_bracketing(Value, =) ->
           write('('),
-          write_term(Value, [quoted(true), variable_names(NewVarList), max_depth(MaxDepth), double_quotes(DQ)]),
+          write_term(Value, [quoted(true), variable_names(NewVarList), max_depth(MaxDepth), double_quotes(DQ)|Os]),
           write(')')
-       ;  write_term(Value, [quoted(true), variable_names(NewVarList), max_depth(MaxDepth), double_quotes(DQ)])
+       ;  write_term(Value, [quoted(true), variable_names(NewVarList), max_depth(MaxDepth), double_quotes(DQ)|Os])
        )
     ;  G == [] ->
        write('true')
-    ;  write_term(G, [quoted(true), variable_names(VarList), max_depth(MaxDepth), double_quotes(DQ)])
+    ;  write_term(G, [quoted(true), variable_names(VarList), max_depth(MaxDepth), double_quotes(DQ)|Os])
     ).
 
 write_last_goal(G, VarList, MaxDepth) :-
     double_quotes_option(DQ),
+    answer_write_options(Os),
     (  G = (Var = Value) ->
        (  var(Value) ->
           select((Var = _), VarList, NewVarList)
@@ -266,9 +271,9 @@ write_last_goal(G, VarList, MaxDepth) :-
        write(' = '),
        (  needs_bracketing(Value, =) ->
           write('('),
-          write_term(Value, [quoted(true), variable_names(NewVarList), max_depth(MaxDepth), double_quotes(DQ)]),
+          write_term(Value, [quoted(true), variable_names(NewVarList), max_depth(MaxDepth), double_quotes(DQ)|Os]),
           write(')')
-       ;  write_term(Value, [quoted(true), variable_names(NewVarList), max_depth(MaxDepth), double_quotes(DQ)]),
+       ;  write_term(Value, [quoted(true), variable_names(NewVarList), max_depth(MaxDepth), double_quotes(DQ)|Os]),
           (  trailing_period_is_ambiguous(Value) ->
              write(' ')
           ;  true
@@ -276,7 +281,7 @@ write_last_goal(G, VarList, MaxDepth) :-
        )
     ;  G == [] ->
        write('true')
-    ;  write_term(G, [quoted(true), variable_names(VarList), max_depth(MaxDepth), double_quotes(DQ)])
+    ;  write_term(G, [quoted(true), variable_names(VarList), max_depth(MaxDepth), double_quotes(DQ)|Os])
     ).
 
 write_eq((G1, G2), VarList, MaxDepth) :-
@@ -447,3 +452,4 @@ print_exception_with_check(E) :-
     % is expected to be printed instead.
     ;  print_exception(E)
     ).
+    

src/types.rs

@@ -24,7 +24,7 @@ pub enum HeapCellValueTag {
     PStrOffset = 0b001111,
     // constants.
     Cons = 0b0,
-    F64  = 0b010001,
+    F64 = 0b010001,
     Fixnum = 0b010011,
     Char = 0b010101,
     Atom = 0b010111,
@@ -45,7 +45,7 @@ pub enum HeapCellValueView {
     PStrOffset = 0b001111,
     // constants.
     Cons = 0b0,
-    F64  = 0b010001,
+    F64 = 0b010001,
     Fixnum = 0b010011,
     Char = 0b010101,
     Atom = 0b010111,
@@ -56,9 +56,9 @@ pub enum HeapCellValueView {
     TrailedHeapVar = 0b101111,
     TrailedStackVar = 0b101011,
     TrailedAttrVar = 0b100001,
-    TrailedAttrVarListLink =  0b100011,
-    TrailedAttachedValue =    0b100101,
-    TrailedBlackboardEntry =  0b100111,
+    TrailedAttrVarListLink = 0b100011,
+    TrailedAttachedValue = 0b100101,
+    TrailedBlackboardEntry = 0b100111,
     TrailedBlackboardOffset = 0b110011,
 }
 
@@ -88,7 +88,7 @@ impl ConsPtr {
             .with_tag(tag)
     }
 
-    #[cfg(target_pointer_width="32")]
+    #[cfg(target_pointer_width = "32")]
     #[inline(always)]
     pub fn as_ptr(self) -> *mut u8 {
         let bytes = self.into_bytes();
@@ -96,7 +96,7 @@ impl ConsPtr {
         unsafe { mem::transmute(raw_ptr_bytes) }
     }
 
-    #[cfg(target_pointer_width="64")]
+    #[cfg(target_pointer_width = "64")]
     #[inline(always)]
     pub fn as_ptr(self) -> *mut u8 {
         self.ptr() as *mut _
@@ -121,28 +121,24 @@ pub(crate) enum RefTag {
 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
 pub struct Ref {
     val: B56,
-    #[allow(unused)] m: bool,
-    #[allow(unused)] f: bool,
+    #[allow(unused)]
+    m: bool,
+    #[allow(unused)]
+    f: bool,
     tag: RefTag,
 }
 
 impl Ord for Ref {
     fn cmp(&self, rhs: &Ref) -> Ordering {
         match self.get_tag() {
-            RefTag::HeapCell | RefTag::AttrVar => {
-                match rhs.get_tag() {
-                    RefTag::StackCell => Ordering::Less,
-                    _ => self.get_value().cmp(&rhs.get_value()),
-                }
-            }
-            RefTag::StackCell => {
-                match rhs.get_tag() {
-                    RefTag::StackCell =>
-                        self.get_value().cmp(&rhs.get_value()),
-                    _ =>
-                        Ordering::Greater,
-                }
-            }
+            RefTag::HeapCell | RefTag::AttrVar => match rhs.get_tag() {
+                RefTag::StackCell => Ordering::Less,
+                _ => self.get_value().cmp(&rhs.get_value()),
+            },
+            RefTag::StackCell => match rhs.get_tag() {
+                RefTag::StackCell => self.get_value().cmp(&rhs.get_value()),
+                _ => Ordering::Greater,
+            },
         }
     }
 }
@@ -204,9 +200,9 @@ pub(crate) enum TrailEntryTag {
     TrailedHeapVar = 0b101111,
     TrailedStackVar = 0b101011,
     TrailedAttrVar = 0b100001,
-    TrailedAttrVarListLink =  0b100011,
-    TrailedAttachedValue =    0b100101,
-    TrailedBlackboardEntry =  0b100111,
+    TrailedAttrVarListLink = 0b100011,
+    TrailedAttachedValue = 0b100101,
+    TrailedBlackboardEntry = 0b100111,
     TrailedBlackboardOffset = 0b110011,
 }
 
@@ -215,9 +211,12 @@ pub(crate) enum TrailEntryTag {
 #[repr(u64)]
 pub(crate) struct TrailEntry {
     val: B56,
-    #[allow(unused)] f: bool,
-    #[allow(unused)] m: bool,
-    #[allow(unused)] tag: TrailEntryTag,
+    #[allow(unused)]
+    f: bool,
+    #[allow(unused)]
+    m: bool,
+    #[allow(unused)]
+    tag: TrailEntryTag,
 }
 
 impl TrailEntry {
@@ -233,9 +232,9 @@ impl TrailEntry {
     #[inline(always)]
     pub(crate) fn get_tag(self) -> TrailEntryTag {
         match self.tag_or_err() {
-	        Ok(tag) => tag,
-	        Err(_) => TrailEntryTag::TrailedAttachedValue,
-	    }
+            Ok(tag) => tag,
+            Err(_) => TrailEntryTag::TrailedAttachedValue,
+        }
     }
 
     #[inline]
@@ -257,14 +256,13 @@ pub struct HeapCellValue {
 impl fmt::Debug for HeapCellValue {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> fmt::Result {
         match self.get_tag() {
-            HeapCellValueTag::F64 => {
-                f.debug_struct("HeapCellValue")
-                    .field("tag", &HeapCellValueTag::F64)
-                    .field("offset", &self.get_value())
-                    .field("m", &self.m())
-                    .field("f", &self.f())
-                    .finish()
-            }
+            HeapCellValueTag::F64 => f
+                .debug_struct("HeapCellValue")
+                .field("tag", &HeapCellValueTag::F64)
+                .field("offset", &self.get_value())
+                .field("m", &self.m())
+                .field("f", &self.f())
+                .finish(),
             HeapCellValueTag::Cons => {
                 let cons_ptr = ConsPtr::from_bytes(self.into_bytes());
 
@@ -276,8 +274,7 @@ impl fmt::Debug for HeapCellValue {
                     .finish()
             }
             HeapCellValueTag::Atom => {
-                let (name, arity) = cell_as_atom_cell!(self)
-                     .get_name_and_arity();
+                let (name, arity) = cell_as_atom_cell!(self).get_name_and_arity();
 
                 f.debug_struct("HeapCellValue")
                     .field("tag", &HeapCellValueTag::Atom)
@@ -288,8 +285,7 @@ impl fmt::Debug for HeapCellValue {
                     .finish()
             }
             HeapCellValueTag::PStr => {
-                let (name, _) = cell_as_atom_cell!(self)
-                     .get_name_and_arity();
+                let (name, _) = cell_as_atom_cell!(self).get_name_and_arity();
 
                 f.debug_struct("HeapCellValue")
                     .field("tag", &HeapCellValueTag::PStr)
@@ -298,14 +294,13 @@ impl fmt::Debug for HeapCellValue {
                     .field("f", &self.f())
                     .finish()
             }
-            tag => {
-                f.debug_struct("HeapCellValue")
-                    .field("tag", &tag)
-                    .field("value", &self.get_value())
-                    .field("m", &self.get_mark_bit())
-                    .field("f", &self.get_forwarding_bit())
-                    .finish()
-            }
+            tag => f
+                .debug_struct("HeapCellValue")
+                .field("tag", &tag)
+                .field("value", &self.get_value())
+                .field("m", &self.get_mark_bit())
+                .field("f", &self.get_forwarding_bit())
+                .finish(),
         }
     }
 }
@@ -320,10 +315,7 @@ impl<T: ArenaAllocated> From<TypedArenaPtr<T>> for HeapCellValue {
 impl From<F64Ptr> for HeapCellValue {
     #[inline]
     fn from(f64_ptr: F64Ptr) -> HeapCellValue {
-        HeapCellValue::build_with(
-            HeapCellValueTag::F64,
-            f64_ptr.as_offset().to_u64(),
-        )
+        HeapCellValue::build_with(HeapCellValueTag::F64, f64_ptr.as_offset().to_u64())
     }
 }
 
@@ -402,9 +394,13 @@ impl HeapCellValue {
     #[inline]
     pub fn is_ref(self) -> bool {
         match self.get_tag() {
-            HeapCellValueTag::Str | HeapCellValueTag::Lis | HeapCellValueTag::Var |
-            HeapCellValueTag::StackVar | HeapCellValueTag::AttrVar | HeapCellValueTag::PStrLoc |
-            HeapCellValueTag::PStrOffset => true,
+            HeapCellValueTag::Str
+            | HeapCellValueTag::Lis
+            | HeapCellValueTag::Var
+            | HeapCellValueTag::StackVar
+            | HeapCellValueTag::AttrVar
+            | HeapCellValueTag::PStrLoc
+            | HeapCellValueTag::PStrOffset => true,
             _ => false,
         }
     }
@@ -431,16 +427,14 @@ impl HeapCellValue {
     #[inline]
     pub fn is_constant(self) -> bool {
         match self.get_tag() {
-            HeapCellValueTag::Cons | HeapCellValueTag::F64 | HeapCellValueTag::Fixnum |
-            HeapCellValueTag::Char | HeapCellValueTag::CStr => {
-                true
-            }
-            HeapCellValueTag::Atom => {
-                cell_as_atom_cell!(self).get_arity() == 0
-            }
-            _ => {
-                false
-            }
+            HeapCellValueTag::Cons
+            | HeapCellValueTag::F64
+            | HeapCellValueTag::Fixnum
+            | HeapCellValueTag::CutPoint
+            | HeapCellValueTag::Char
+            | HeapCellValueTag::CStr => true,
+            HeapCellValueTag::Atom => cell_as_atom_cell!(self).get_arity() == 0,
+            _ => false,
         }
     }
 
@@ -455,17 +449,13 @@ impl HeapCellValue {
             HeapCellValueTag::Str => {
                 cell_as_atom_cell!(heap[self.get_value() as usize]).get_arity() > 0
             }
-            HeapCellValueTag::Lis |
-            HeapCellValueTag::CStr |
-            HeapCellValueTag::PStr |
-            HeapCellValueTag::PStrLoc |
-            HeapCellValueTag::PStrOffset => {
-               true
-            }
-            HeapCellValueTag::Atom => {
-                cell_as_atom_cell!(self).get_arity() > 0
-            }
-            _ => { false }
+            HeapCellValueTag::Lis
+            | HeapCellValueTag::CStr
+            | HeapCellValueTag::PStr
+            | HeapCellValueTag::PStrLoc
+            | HeapCellValueTag::PStrOffset => true,
+            HeapCellValueTag::Atom => cell_as_atom_cell!(self).get_arity() > 0,
+            _ => false,
         }
     }
 
@@ -530,9 +520,7 @@ impl HeapCellValue {
     #[inline]
     pub fn to_pstr(self) -> Option<PartialString> {
         match self.tag() {
-            HeapCellValueTag::PStr => {
-                Some(PartialString::from(Atom::from(self.val() << 3)))
-            }
+            HeapCellValueTag::PStr => Some(PartialString::from(Atom::from(self.val() << 3))),
             _ => None,
         }
     }
@@ -545,26 +533,35 @@ impl HeapCellValue {
         }
     }
 
-    #[cfg(target_pointer_width="32")]
+    #[cfg(target_pointer_width = "32")]
     #[inline]
     pub fn from_raw_ptr_bytes(ptr_bytes: [u8; 4]) -> Self {
-        HeapCellValue::from_bytes([ptr_bytes[0], ptr_bytes[1], ptr_bytes[2], ptr_bytes[3], 0, 0, 0, 0])
+        HeapCellValue::from_bytes([
+            ptr_bytes[0],
+            ptr_bytes[1],
+            ptr_bytes[2],
+            ptr_bytes[3],
+            0,
+            0,
+            0,
+            0,
+        ])
     }
-    #[cfg(target_pointer_width="64")]
+    #[cfg(target_pointer_width = "64")]
     #[inline]
     pub fn from_raw_ptr_bytes(ptr_bytes: [u8; 8]) -> Self {
         HeapCellValue::from_bytes(ptr_bytes)
     }
 
     #[inline]
-    #[cfg(target_pointer_width="32")]
+    #[cfg(target_pointer_width = "32")]
     pub fn to_raw_ptr_bytes(self) -> [u8; 4] {
         let bytes = self.into_bytes();
         [bytes[0], bytes[1], bytes[2], bytes[3]]
     }
 
     #[inline]
-    #[cfg(target_pointer_width="64")]
+    #[cfg(target_pointer_width = "64")]
     pub fn to_raw_ptr_bytes(self) -> [u8; 8] {
         self.into_bytes()
     }
@@ -577,7 +574,9 @@ impl HeapCellValue {
     #[inline]
     pub fn to_untyped_arena_ptr(self) -> Option<UntypedArenaPtr> {
         match self.get_tag() {
-            HeapCellValueTag::Cons => Some(UntypedArenaPtr::from_bytes(self.to_untyped_arena_ptr_bytes())),
+            HeapCellValueTag::Cons => Some(UntypedArenaPtr::from_bytes(
+                self.to_untyped_arena_ptr_bytes(),
+            )),
             _ => None,
         }
     }
@@ -586,7 +585,7 @@ impl HeapCellValue {
     pub fn get_forwarding_bit(self) -> bool {
         match self.get_tag() {
             HeapCellValueTag::Cons => ConsPtr::from_bytes(self.into_bytes()).f(),
-            _ => self.f()
+            _ => self.f(),
         }
     }
 
@@ -604,9 +603,7 @@ impl HeapCellValue {
     #[inline(always)]
     pub fn get_mark_bit(self) -> bool {
         match self.get_tag() {
-            HeapCellValueTag::Cons => {
-                ConsPtr::from_bytes(self.into_bytes()).m()
-            }
+            HeapCellValueTag::Cons => ConsPtr::from_bytes(self.into_bytes()).m(),
             _ => self.m(),
         }
     }
@@ -633,15 +630,12 @@ impl HeapCellValue {
                     Some(TermOrderCategory::Variable)
                 }
                 HeapCellValueTag::Char => Some(TermOrderCategory::Atom),
-                HeapCellValueTag::Atom => {
-                    Some(if cell_as_atom_cell!(self).get_arity() > 0 {
-                        TermOrderCategory::Compound
-                    } else {
-                        TermOrderCategory::Atom
-                    })
-                }
-                HeapCellValueTag::Lis | HeapCellValueTag::PStrLoc |
-                HeapCellValueTag::CStr => {
+                HeapCellValueTag::Atom => Some(if cell_as_atom_cell!(self).get_arity() > 0 {
+                    TermOrderCategory::Compound
+                } else {
+                    TermOrderCategory::Atom
+                }),
+                HeapCellValueTag::Lis | HeapCellValueTag::PStrLoc | HeapCellValueTag::CStr => {
                     Some(TermOrderCategory::Compound)
                 }
                 HeapCellValueTag::Str => {
@@ -654,9 +648,7 @@ impl HeapCellValue {
                         Some(TermOrderCategory::Compound)
                     }
                 }
-                _ => {
-                    None
-                }
+                _ => None,
             },
         }
     }
@@ -680,16 +672,17 @@ const_assert!(mem::size_of::<HeapCellValue>() == 8);
 #[repr(u64)]
 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
 pub struct UntypedArenaPtr {
-    #[allow(unused)] ptr: B61,
+    #[allow(unused)]
+    ptr: B61,
     m: bool,
-    #[allow(unused)] padding: B2,
+    #[allow(unused)]
+    padding: B2,
 }
 
 impl UntypedArenaPtr {
     #[inline(always)]
     pub fn build_with(ptr: usize) -> Self {
-        UntypedArenaPtr::new()
-            .with_ptr(ptr as u64)
+        UntypedArenaPtr::new().with_ptr(ptr as u64)
     }
 }
 
@@ -722,7 +715,7 @@ impl UntypedArenaPtr {
         self.set_m(m);
     }
 
-    #[cfg(target_pointer_width="32")]
+    #[cfg(target_pointer_width = "32")]
     #[inline]
     pub fn get_ptr(self) -> *const u8 {
         let bytes = self.into_bytes();
@@ -730,10 +723,10 @@ impl UntypedArenaPtr {
         unsafe { mem::transmute(raw_ptr_bytes) }
     }
 
-    #[cfg(target_pointer_width="64")]
+    #[cfg(target_pointer_width = "64")]
     #[inline]
     pub fn get_ptr(self) -> *const u8 {
-        self.ptr() as *const u8    
+        self.ptr() as *const u8
     }
 
     #[inline]
@@ -763,17 +756,15 @@ impl Add<usize> for HeapCellValue {
 
     fn add(self, rhs: usize) -> Self::Output {
         match self.get_tag() {
-            tag @ HeapCellValueTag::Str |
-            tag @ HeapCellValueTag::Lis |
-            tag @ HeapCellValueTag::PStrOffset |
-            tag @ HeapCellValueTag::PStrLoc |
-            tag @ HeapCellValueTag::Var |
-            tag @ HeapCellValueTag::AttrVar => {
+            tag @ HeapCellValueTag::Str
+            | tag @ HeapCellValueTag::Lis
+            | tag @ HeapCellValueTag::PStrOffset
+            | tag @ HeapCellValueTag::PStrLoc
+            | tag @ HeapCellValueTag::Var
+            | tag @ HeapCellValueTag::AttrVar => {
                 HeapCellValue::build_with(tag, (self.get_value() as usize + rhs) as u64)
             }
-            _ => {
-                self
-            }
+            _ => self,
         }
     }
 }
@@ -783,17 +774,15 @@ impl Sub<usize> for HeapCellValue {
 
     fn sub(self, rhs: usize) -> Self::Output {
         match self.get_tag() {
-            tag @ HeapCellValueTag::Str |
-            tag @ HeapCellValueTag::Lis |
-            tag @ HeapCellValueTag::PStrOffset |
-            tag @ HeapCellValueTag::PStrLoc |
-            tag @ HeapCellValueTag::Var |
-            tag @ HeapCellValueTag::AttrVar => {
+            tag @ HeapCellValueTag::Str
+            | tag @ HeapCellValueTag::Lis
+            | tag @ HeapCellValueTag::PStrOffset
+            | tag @ HeapCellValueTag::PStrLoc
+            | tag @ HeapCellValueTag::Var
+            | tag @ HeapCellValueTag::AttrVar => {
                 HeapCellValue::build_with(tag, (self.get_value() as usize - rhs) as u64)
             }
-            _ => {
-                self
-            }
+            _ => self,
         }
     }
 }
@@ -811,21 +800,18 @@ impl Sub<i64> for HeapCellValue {
     fn sub(self, rhs: i64) -> Self::Output {
         if rhs < 0 {
             match self.get_tag() {
-                tag @ HeapCellValueTag::Str |
-                tag @ HeapCellValueTag::Lis |
-                tag @ HeapCellValueTag::PStrOffset |
-                tag @ HeapCellValueTag::PStrLoc |
-                tag @ HeapCellValueTag::Var |
-                tag @ HeapCellValueTag::AttrVar => {
+                tag @ HeapCellValueTag::Str
+                | tag @ HeapCellValueTag::Lis
+                | tag @ HeapCellValueTag::PStrOffset
+                | tag @ HeapCellValueTag::PStrLoc
+                | tag @ HeapCellValueTag::Var
+                | tag @ HeapCellValueTag::AttrVar => {
                     HeapCellValue::build_with(tag, self.get_value() + rhs.abs() as u64)
                 }
-                _ => {
-                    self
-                }
+                _ => self,
             }
         } else {
             self.sub(rhs as usize)
         }
     }
 }
-

src/variable_records.rs

@@ -56,8 +56,10 @@ impl VarSafetyStatus {
 
 #[derive(Debug, Clone, Copy)]
 pub enum PermVarAllocation {
-    Done { shallow_safety: VarSafetyStatus,
-           deep_safety: VarSafetyStatus },
+    Done {
+        shallow_safety: VarSafetyStatus,
+        deep_safety: VarSafetyStatus,
+    },
     Pending,
 }
 
@@ -81,11 +83,13 @@ impl PermVarAllocation {
 
 #[derive(Debug, Clone)]
 pub enum VarAlloc {
-    Temp { term_loc: GenContext,
-           temp_reg: usize,
-           temp_var_data: TempVarData,
-           safety: VarSafetyStatus,
-           to_perm_var_num: Option<usize> },
+    Temp {
+        term_loc: GenContext,
+        temp_reg: usize,
+        temp_var_data: TempVarData,
+        safety: VarSafetyStatus,
+        to_perm_var_num: Option<usize>,
+    },
     Perm(usize, PermVarAllocation), // stack offset, allocation info
 }
 
@@ -102,7 +106,9 @@ impl VarAlloc {
     pub(crate) fn set_register(&mut self, reg_num: usize) {
         match self {
             VarAlloc::Perm(ref mut p, _) => *p = reg_num,
-            VarAlloc::Temp { ref mut temp_reg, .. } => *temp_reg = reg_num,
+            VarAlloc::Temp {
+                ref mut temp_reg, ..
+            } => *temp_reg = reg_num,
         };
     }
 }
@@ -191,7 +197,8 @@ impl VariableRecords {
         // Compute the conflict set of u.
 
         // 1.
-        let mut use_sets: IndexMap<usize, IndexSet<(GenContext, usize), FxBuildHasher>> = IndexMap::new();
+        let mut use_sets: IndexMap<usize, IndexSet<(GenContext, usize), FxBuildHasher>> =
+            IndexMap::new();
 
         for (var_gen_index, record) in self.0.iter_mut().enumerate() {
             match &mut record.allocation {
@@ -203,8 +210,7 @@ impl VariableRecords {
 
                     use_sets.insert(var_gen_index, use_set);
                 }
-                _ => {
-                }
+                _ => {}
             }
         }
 
@@ -214,7 +220,11 @@ impl VariableRecords {
                 if let GenContext::Last(cn_u) = term_loc {
                     for (var_gen_index, record) in self.0.iter_mut().enumerate() {
                         match &mut record.allocation {
-                            VarAlloc::Temp { term_loc, temp_var_data, .. } => {
+                            VarAlloc::Temp {
+                                term_loc,
+                                temp_var_data,
+                                ..
+                            } => {
                                 if cn_u == term_loc.chunk_num() && u != var_gen_index {
                                     if !temp_var_data.uses_reg(reg) {
                                         temp_var_data.no_use_set.insert(reg);
@@ -228,7 +238,7 @@ impl VariableRecords {
             }
 
             // 3.
-            if let VarAlloc::Temp{ temp_var_data, .. } = &mut self[u].allocation {
+            if let VarAlloc::Temp { temp_var_data, .. } = &mut self[u].allocation {
                 temp_var_data.use_set = use_set;
                 temp_var_data.populate_conflict_set();
             }

tests-pl/iso-conformity-tests.pl

@@ -467,13 +467,14 @@ test_195_205_196_197 :-
     setup_call_cleanup(op(100,xf,''),
                        (  read_from_chars("(0 '') = ''(X).", T0),
                           call(T0),
-                          T0 = (_ = ('')(0)),
+                          writeq_term_to_chars(T0, C0),
+                          C0 == "0 ''=0 ''",
                           read_from_chars("0 ''.", T1),
-                          writeq_term_to_chars(T1, C0),
-                          C0 == "0 ''",
+                          writeq_term_to_chars(T1, C1),
+                          C1 == "0 ''",
                           read_from_chars("0''.", T2),
-                          writeq_term_to_chars(T2, C1),
-                          C1 == "0 ''" ),
+                          writeq_term_to_chars(T2, C2),
+                          C2 == "0 ''" ),
                        op(0,xf,'')).
 
 test_118_119_120 :-
@@ -774,7 +775,7 @@ test_175 :- T = t(0b1,0o1,0x1),
 test_176 :- X is 0b1mod 2,
             X == 1.
 
-test_217_181_290 :-
+test_217_181_290_317 :-
      setup_call_cleanup((  current_op(P, xfy, '|') ->
                            true
                         ;  P = 0
@@ -785,7 +786,10 @@ test_217_181_290 :-
                            C0 == "a-->b,c | d",
                            read_from_chars("[(a|b)].", T1),
                            writeq_term_to_chars(T1, C1),
-                           C1 == "[(a | b)]"
+                           C1 == "[(a | b)]",
+                           read_from_chars("[a,(b,c)|[]].", T2),
+                           writeq_term_to_chars(T2, C2),
+                           C2 == "[a,(b,c)]"
                         ),
                         op(P, xfy, '|')).
 

tests/scryer/issues.rs

@@ -1,5 +1,4 @@
 use crate::helper::{load_module_test, run_top_level_test_no_args, run_top_level_test_with_args};
-use scryer_prolog::machine::Machine;
 use serial_test::serial;
 
 // issue #857
@@ -30,7 +29,7 @@ fn do_not_duplicate_path_components() {
         ['tests-pl/issue852-throw_e.pl'].\n\
         halt.\n\
         ",
-        "   throw(e).\n   false.\n   throw(e).\n   false.\n",
+        "   throw(e).\n   throw(e).\n",
     );
 }
 
@@ -171,16 +170,3 @@ fn call_0() {
         "   error(existence_error(procedure,call/0),call/0).\n",
     );
 }
-
-// issue #1206
-#[serial]
-#[test]
-#[should_panic(expected = "Overwriting atom table base pointer")]
-fn atomtable_is_not_concurrency_safe() {
-    // this is basically the same test as scryer_prolog::atom_table::atomtable_is_not_concurrency_safe
-    // but for this integration test scryer_prolog is compiled with cfg!(not(test))  while for the unit test it is compiled with cfg!(test)
-    // as the atom table implementation differ between cfg!(test) and cfg!(not(test)) both test serve a pourpose
-    // Note: this integration test itself is compiled with cfg!(test) independent of scryer_prolog itself
-    let _machine_a = Machine::with_test_streams();
-    let _machine_b = Machine::with_test_streams();
-}

tests/scryer/src_tests.rs

@@ -73,8 +73,41 @@ fn clpz_load() {
 #[serial]
 #[test]
 fn iso_conformity_tests() {
-    load_module_test(
-        "tests-pl/iso-conformity-tests.pl",
+    load_module_test("tests-pl/iso-conformity-tests.pl", "All tests passed");
+}
+
+#[test]
+fn dif_tests() {
+    run_top_level_test_with_args(
+        &["src/tests/dif.pl", "-f", "-g", "main_quiet"],
+        "",
+        "All tests passed",
+    );
+}
+
+#[test]
+fn ground_tests() {
+    run_top_level_test_with_args(
+        &["src/tests/ground.pl", "-f", "-g", "main_quiet"],
+        "",
+        "All tests passed",
+    );
+}
+
+#[test]
+fn term_variables_tests() {
+    run_top_level_test_with_args(
+        &["src/tests/term_variables.pl", "-f", "-g", "main_quiet"],
+        "",
+        "All tests passed",
+    );
+}
+
+#[test]
+fn acyclic_term_tests() {
+    run_top_level_test_with_args(
+        &["src/tests/acyclic_term.pl", "-f", "-g", "main_quiet"],
+        "",
         "All tests passed",
     );
 }