Merge pull request #1635 from mthom/rebis-dev

Merge rebis-dev into master

.dockerignore

@@ -0,0 +1,6 @@
+target
+Dockerfile
+README.md
+.git
+.gitignore
+.gitmodules

.gitattributes

@@ -0,0 +1,4 @@
+*.png binary
+*.pl text eol=lf
+*.rs text eol=lf diff=rust
+*.md text eol=lf diff=markdown

.github/workflows/docker-publish.yml

@@ -0,0 +1,52 @@
+name: Docker Publish
+
+on:
+  push:
+    tags: [ 'v*.*.*' ]
+
+env:
+  IMAGE_NAME: mjt128/scryer-prolog
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      # Workaround: https://github.com/docker/build-push-action/issues/461
+      - name: Setup Docker buildx
+        uses: docker/setup-buildx-action@79abd3f86f79a9d68a23c75a09a9a85889262adf
+
+      # Login against Docker registry
+      # https://github.com/docker/login-action
+      - name: Log into registry
+        uses: docker/login-action@28218f9b04b4f3f62068d7b6ce6ca5b26e35336c
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      # Extract Docker image tag from git tag. E.g. if git tag is "v0.19.1" then use 
+      # Docker image tag "0.19.1". Tag "latest" is automatically synced with newest
+      # version.
+      # https://github.com/docker/metadata-action
+      - name: Extract Docker metadata
+        id: meta
+        uses: docker/metadata-action@98669ae865ea3cffbcbaa878cf57c20bbf1c6c38
+        with:
+          images: docker.io/${{ env.IMAGE_NAME }}
+          tags: |
+            type=semver,pattern={{version}}
+
+      # Build and push Docker image with Buildx
+      # https://github.com/docker/build-push-action
+      - name: Build and push Docker image
+        id: build-and-push
+        uses: docker/build-push-action@ad44023a93711e3deb337508980b4b5e9bcdc5dc
+        with:
+          context: .
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}

.github/workflows/test.yml

@@ -0,0 +1,71 @@
+name: Test
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-20.04, macos-10.15]
+        rust-version: [stable, beta]
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: ${{ matrix.rust-version }}
+          override: true
+      - name: Build lib
+        uses: actions-rs/cargo@v1
+        with:
+          command: rustc
+          args: --verbose --lib -- -D warnings
+      - name: Build bin
+        uses: actions-rs/cargo@v1
+        with:
+          command: rustc
+          args: --verbose --bin scryer-prolog -- -D warnings
+      - name: Test
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --verbose --all
+      - name: Num tests
+        uses: actions-rs/cargo@v1
+        continue-on-error: true
+        with:
+          command: test
+          args: --verbose --all --no-default-features --features num
+  msrv:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-20.04, macos-10.15]
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+      - name: Install cargo-msrv
+        uses: baptiste0928/cargo-install@v1.1.0
+        with:
+          crate: cargo-msrv
+      - name: Verify MSRV
+        run: cargo msrv --verify
+  windows:
+    runs-on: windows-latest
+    defaults:
+      run:
+        shell: msys2 {0}
+    steps:
+      - name: Setup MSYS2
+        uses: msys2/setup-msys2@v2
+        with:
+          update: true
+          install: >-
+            base-devel
+            mingw-w64-x86_64-rust
+      - name: Checkout sources
+        uses: actions/checkout@v3
+      - name: Test on Windows
+        run: cargo test --verbose --all

.gitignore

@@ -1,4 +1,5 @@
+src/static_atoms.rs
 target/
-Cargo.lock
+
 
 

.travis.yml

@@ -1,13 +0,0 @@
-language: rust
-rust:
-    - stable
-    - beta
-    - nightly
-matrix:
-    allow_failures:
-        - rust: nightly
-    fast_finish: true
-
-script:
-    - cargo build --verbose --all
-    - cargo test --verbose --all

Cargo.toml

@@ -1,28 +1,76 @@
 [package]
 name = "scryer-prolog"
-version = "0.8.113"
+version = "0.9.1"
 authors = ["Mark Thom <markjordanthom@gmail.com>"]
-build = "build.rs"
-repository = "https://github.com/mthom/scryer-prolog"
+edition = "2021"
 description = "A modern Prolog implementation written mostly in Rust."
+readme = "README.md"
+repository = "https://github.com/mthom/scryer-prolog"
 license = "BSD-3-Clause"
-edition = "2018"
+keywords = ["prolog", "prolog-interpreter", "prolog-system"]
+categories = ["command-line-utilities"]
+build = "build/main.rs"
+rust-version = "1.61"
+
+[features]
+default = ["rug"]
 
 [build-dependencies]
 indexmap = "1.0.2"
+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"
+walkdir = "2"
 
 [dependencies]
-dirs = "2.0.2"
-downcast = "0.10.0"
+cpu-time = "1.0.0"
+crossterm = "0.20.0"
+dirs-next = "2.0.0"
+divrem = "0.1.0"
+fxhash = "0.2.1"
+git-version = "0.3.4"
+hostname = "0.3.1"
 indexmap = "1.0.2"
 lazy_static = "1.4.0"
+lexical = "5.2.2"
 libc = "0.2.62"
-nix = "0.15.0"
-ordered-float = "0.5.0"
-prolog_parser = "0.8.33"
+modular-bitfield = "0.11.2"
+ctrlc = "3.2.2"
+ordered-float = "2.6.0"
+phf = { version = "0.9",  features = ["macros"] }
 ref_thread_local = "0.0.0"
-rug = "1.4.0"
-rustyline = "5.0.3"
+rug = { version = "1.15.0", optional = true }
+rustyline = "9.0.0"
+ring = "0.16.13"
+ripemd160 = "0.8.0"
+sha3 = "0.8.2"
+blake2 = "0.8.1"
+crrl ="0.2.0"
+native-tls = "0.2.4"
+chrono = "0.4.11"
+select = "0.4.3"
+roxmltree = "0.11.0"
+base64 = "0.12.3"
+smallvec = "1.8.0"
+sodiumoxide = "0.2.6"
+static_assertions = "1.1.0"
+ryu = "1.0.9"
+hyper = { version = "0.14", features = ["full"] }
+hyper-tls = "0.5.0"
+tokio = { version = "1", features = ["full"] }
+futures = "0.3"
 
-[dependencies.termion]
-version = "1.4.0"
+[dev-dependencies]
+assert_cmd = "1.0.3"
+predicates-core = "1.0.2"
+serial_test = "0.5.1"
+
+[patch.crates-io]
+modular-bitfield = { git = "https://github.com/mthom/modular-bitfield" }
+
+[profile.release]
+debug = true

Dockerfile

@@ -0,0 +1,26 @@
+# See https://github.com/LukeMathWalker/cargo-chef
+ARG RUST_VERSION=1.60-buster
+FROM rust:${RUST_VERSION} as planner
+WORKDIR /scryer-prolog
+RUN cargo install cargo-chef 
+COPY . .
+RUN cargo chef prepare --recipe-path recipe.json
+
+FROM rust:${RUST_VERSION} as cacher
+WORKDIR /scryer-prolog
+RUN cargo install cargo-chef
+COPY --from=planner /scryer-prolog/recipe.json recipe.json
+RUN cargo chef cook --release --recipe-path recipe.json
+
+FROM rust:${RUST_VERSION} as builder
+WORKDIR /scryer-prolog
+COPY . .
+# Copy over the cached dependencies
+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
+COPY --from=builder /scryer-prolog/target/release/scryer-prolog /usr/local/bin
+ENV RUST_BACKTRACE=1
+ENTRYPOINT ["/usr/local/bin/scryer-prolog"]

README.md

@@ -1,3 +1,4 @@
+
 # Scryer Prolog
 
 Scryer Prolog aims to become to ISO Prolog what GHC is to Haskell: an open
@@ -5,6 +6,8 @@ source industrial strength production environment that is also a
 testbed for bleeding edge research in logic and constraint
 programming, which is itself written in a high-level language.
 
+![Scryer Logo: Cryer](logo/scryer.png)
+
 ## Phase 1
 
 Produce an implementation of the Warren Abstract Machine in Rust, done
@@ -30,10 +33,8 @@ Extend Scryer Prolog to include the following, among other features:
 - [x] Built-in predicates for list processing and top-level declarative
       control (`setup_call_cleanup/3`, `call_with_inference_limit/3`,
       etc.)
-- [x] Default representation of strings as list of chars, using a packed
-      internal representation.
-        - A representation of 'partial strings' as difference lists
-          of characters.
+- [x] ~~Default representation of strings as lists of characters, using a packed
+      internal representation.~~
 - [x] `term_expansion/2` and `goal_expansion/2`.
 - [x] Definite Clause Grammars.
 - [x] Attributed variables using the SICStus Prolog interface and
@@ -42,7 +43,7 @@ Extend Scryer Prolog to include the following, among other features:
   - [x] Support for `verify_attributes/3`
   - [x] Support for `attribute_goals/2` and `project_attributes/2`
   - [x] `call_residue_vars/2`
-- [x] `if_` and related predicates, following the developments of the
+- [x] `if_/3` and related predicates, following the developments of the
       paper "Indexing `dif/2`".
 - [x] All-solutions predicates (`findall/{3,4}`, `bagof/3`, `setof/3`, `forall/2`).
 - [x] Clause creation and destruction (`asserta/1`, `assertz/1`,
@@ -50,11 +51,26 @@ Extend Scryer Prolog to include the following, among other features:
 - [x] Backtrackable and non-backtrackable global variables via `bb_get/2`
       `bb_put/2` (non-backtrackable) and `bb_b_put/2`
       (backtrackable).
-- [ ] Streams and predicates for stream control (_in progress_).
-- [ ] An incremental compacting garbage collector satisfying the five
-      properties of "Precise Garbage Collection in Prolog."
+- [x] Delimited continuations based on reset/3, shift/1 (documented in
+      "Delimited Continuations for Prolog").
+- [x] Tabling library based on delimited continuations
+      (documented in "Tabling as a Library with Delimited Control").
+- [x] A _redone_ representation of strings as difference lists of
+      characters, using a packed internal representation.
+- [x] clp(B) and clp(ℤ) as builtin libraries.
+- [x] Streams and predicates for stream control.
+  - [x] A simple sockets library representing TCP connections as streams.  
+- [x] Incremental compilation and loading process, newly written,
+      primarily in Prolog.
+- [ ] Improvements to the WAM compiler and heap representation:
+  - [ ] Replacing choice points pivoting on inlined semi-deterministic predicates
+        (`atom`, `var`, etc) with if/else ladders. (_in progress_)
+  - [ ] Inlining all built-ins and system call instructions.
+  - [ ] Greatly reducing the number of instructions used to compile disjunctives.
+  - [ ] Storing short atoms to heap cells without writing them to the atom table.
+- [ ] A compacting garbage collector satisfying the five properties of
+      "Precise Garbage Collection in Prolog." (_in progress_)
 - [ ] Mode declarations.
-- [ ] Extensions for clp(FD).
 
 ## Phase 3
 
@@ -79,218 +95,135 @@ Programming?"
 unum implementation or an ad hoc one. Unums are described in
 Gustafson's book "The End of Error."
 
-3. Add support for shift/reset delimited continuations, see "Delimited
-Continuations for Prolog."
-
-4. Add concurrent tables to manage shared references to atoms and
+3. Add concurrent tables to manage shared references to atoms and
 strings.
 
-5. Add optional SLG resolution for fast memoization of predicates.
-
-6. Add some form of JIT predicate indexing.
+4. Add some form of JIT predicate indexing.
 
 ## Installing Scryer Prolog
 
+### Native Install
+
 First, install the latest stable version of
 [Rust](https://www.rust-lang.org/en-US/install.html) using your
-preferred method. Then install the latest Scryer Prolog with cargo,
-like so:
+preferred method. Scryer tends to use features from newer Rust
+releases, whereas Rust packages in Linux distributions, Macports,
+etc. tend to lag behind. [rustup](http://rustup.rs) will keep your
+Rust updated to the latest stable release; any existing Rust
+distribution should be uninstalled from your system before rustup is
+used.
+
+Currently the only way to install the latest version of Scryer is to
+clone directly from this git repository, which can be done as follows:
 
 ```
-$> cargo install scryer-prolog
+$> git clone https://github.com/mthom/scryer-prolog
+$> cd scryer-prolog
+$> cargo run [--release]
 ```
 
-cargo will download and install the libraries Scryer Prolog uses
-automatically. You can find the `scryer-prolog` executable in
-`~/.cargo/bin`.
+The optional `--release` flag will perform various optimizations,
+producing a faster executable.
 
-Note on compatibility: Scryer Prolog should work on Linux, Mac OS X,
-and BSD variants on which Rust runs. Windows support hinges on
-rustyline and Termion being functional in that environment, which to
-my knowledge is not currently the case.
+On Windows, Scryer Prolog is easier to build inside a [MSYS2](https://www.msys2.org/)
+environment as some crates may require native C compilation. However, 
+the resulting binary does not need MSYS2 to run. When executing Scryer in a shell, it is recommended to use a more advanced shell than mintty (the default MSYS2 shell). The [Windows Terminal](https://github.com/microsoft/terminal) works correctly.
 
-## Built-in predicates
+To build a Windows Installer, you'll need first Scryer Prolog compiled in release mode, then, with WiX Toolset installed, execute:
+```
+candle.exe scryer-prolog.wxs
+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.
 
-The following predicates are built-in to Scryer.
+Scryer Prolog must be built with **Rust 1.57 and up**.
 
-* Arithmetic support:
-    * `is/2` works for `(+)/{1,2}`, `(-)/{1,2}`, `(*)/2`, `(//)/2`, `(**)/2`,
-      `(^)/2`, `(div)/2`, `(/)/2`, `(rdiv)/2`, `(xor)/2`, `(rem)/2`,
-      `(mod)/2`, `(/\)/2`, `(\/)/2`, `(>>)/2`,`(<<)/2`, `(\)/1`,
-      `abs/1`, `sin/1`, `cos/1`, `tan/1`, `asin/1`, `acos/1`,
-      `atan/1`, `atan2/2`, `log/1`, `exp/1`, `sqrt/1`, `float/1`,
-      `truncate/1`, `round/1`, `floor/1`, `ceiling/1`, `pi/0`,
-      `min/1`, `max/1`      
-    * Comparison operators: `>`, `<`, `=<`, `>=`, `=:=`, `=\=`.
-* `(:)/2`
-* `(@>)/2`
-* `(@>=)/2`
-* `(@=<)/2`
-* `(@<)/2`
-* `(\+)/1`
-* `(==)/2`
-* `(\==)/2`
-* `(=)/2`
-* `(\=)/2`
-* `(=..)/2`
-* `(->)/2`
-* `(;)/2`
-* `abolish/1`
-* `acyclic_term/2`
-* `append/3`
-* `arg/3`
-* `asserta/1`
-* `assertz/1`
-* `atom/1`
-* `atomic/1`
-* `atom_chars/2`
-* `atom_codes/2`
-* `atom_concat/3`
-* `atom_length/2`
-* `bagof/3`
-* `bb_b_put/2`
-* `bb_get/2`
-* `bb_put/2`
-* `between/3`
-* `call/1..62`
-* `call_cleanup/2`
-* `call_with_inference_limit/3`
-* `call_residue_vars/2`
-* `can_be/2`
-* `catch/3`
-* `clause/2`
-* `compare/3`
-* `compound/1`
-* `copy_term/2`
-* `current_predicate/1`
-* `current_op/3`
-* `cyclic_term/1`
-* `dif/2`
-* `expand_goal/2`
-* `expand_term/2`
-* `fail/0`
-* `false/0`
-* `findall/{3,4}`
-* `float/1`
-* `forall/2`
-* `freeze/2`
-* `functor/3`
-* `gen_int/1`
-* `gen_nat/1`
-* `get_char/1`
-* `goal_expansion/2`
-* `ground/1`
-* `halt/0`
-* `integer/1`
-* `is_list/1`
-* `is_partial_string/1`
-* `keysort/2`
-* `length/2`
-* `maplist/2..9`
-* `member/2`
-* `memberchk/2`
-* `must_be/2`
-* `nl/0`
-* `nonvar/1`
-* `number_chars/2`
-* `number_codes/2`
-* `numbervars/2`
-* `numlist/{2,3}`
-* `once/1`
-* `op/3`
-* `partial_string/2`
-* `phrase/{2,3}`
-* `rational/1`
-* `read/1`
-* `repeat/{0,1}`
-* `retract/1`
-* `reverse/2`
-* `select/3`
-* `setof/3`
-* `setup_call_cleanup/3`
-* `sort/2`
-* `string/1`
-* `sub_atom/5`
-* `subsumes_term/2`
-* `term_expansion/2`
-* `term_variables/2`
-* `throw/1`
-* `true/0`
-* `unify_with_occurs_check/2`
-* `use_module/{1,2}`
-* `user:goal_expansion/2`
-* `user:term_expansion/2`
-* `var/1`
-* `variant/2`
-* `wam_instructions/2`
-* `write/1`
-* `write_canonical/1`
-* `writeq/1`
-* `write_term/2`
+### Docker Install
+
+First, install [Docker](https://docs.docker.com/get-docker/) on Linux,
+Windows, or Mac.
+
+Once Docker is installed, you can download and run Scryer Prolog with a single
+command:
+```
+$> docker run -it mjt128/scryer-prolog
+```
+
+To consult your Prolog files, bind mount your programs folder as a
+[Docker volume](https://docs.docker.com/storage/volumes/):
+
+```
+$> docker run -v /home/user/prolog:/mnt -it mjt128/scryer-prolog
+?- consult('/mnt/program.pl').
+true.
+```
+
+This works on Windows too:
+
+```
+$> docker run -v C:\Users\user\Documents\prolog:/mnt -it mjt128/scryer-prolog
+?- consult('/mnt/program.pl').
+true.
+```
 
 ## Tutorial
-To enter a multi-clause predicate, the directive "[user]" is used.
 
-For example,
-```
-?- [user].
-(type Enter + Ctrl-D to terminate the stream when finished)
-p(f(f(X)), h(W), Y) :- g(W), h(W), f(X).
-p(X, Y, Z) :- h(Y), z(Z).
-?- [user].
-(type Enter + Ctrl-D to terminate the stream when finished)
-h(x). h(y).
-h(z).
-```
-In the example, `Enter + Ctrl-D` is used to terminate the standard
-input stream. The instructive message is always printed.
+Prolog files are loaded by specifying them as arguments on the command
+line. For example, to load `program.pl`, use:
 
-Queries are issued as
 ```
-?- p(X, Y, Z).
+$> scryer-prolog program.pl
 ```
 
-Pressing `SPACE` will backtrack through other possible answers, if any exist.
-Pressing `.` will abort the search and return to the prompt.
+Loading a Prolog file is also called “consulting” it. The built-in
+predicate `consult/1` can be used to consult a file from within
+Prolog:
 
-Wildcards work as well:
+```
+?- consult('program.pl').
+```
+
+As an abbreviation for `consult/1`, you can specify a *list* of
+program files, given as *atoms*:
+
+```
+?- ['program.pl'].
+```
+
+The special notation `[user]` is used to read Prolog&nbsp;text from
+standard input. For example,
 
 ```
 ?- [user].
-(type Enter + Ctrl-D to terminate the stream when finished)
-member(X, [X|_]).
-member(X, [_|Xs]) :- member(X, Xs).
-?- member(X, [a, b, c]).
-true .
-X = a ;
-X = b ;
-X = c ;
-false.
-```
-and so do conjunctive queries:
-```
-?- [user].
-(type Enter + Ctrl-D to terminate the stream when finished)
-f(X) :- g(X).
-g(x). g(y). g(z).
-h(call(f, X)).
-?- h(X), X.
-true .
-X = call(f, x) ;
-X = call(f, y) ;
-X = call(f, z).
+hello(declarative_world).
+hello(pure_world).
 ```
 
-Note that the values of variables belonging to successful queries are
-printed out, on one line each. Uninstantiated variables are denoted by
-a number preceded by an underscore (`X = _0` in an example above).
+Pressing `RETURN` followed by `Ctrl-d` stops reading from
+standard&nbsp;input and consults the entered Prolog&nbsp;text.
+
+After a program is consulted, you can ask *queries* about the
+predicates it defines. For example, with the program shown above:
 
-To clear the database, type
 ```
-?- [clear].
+?- hello(What).
+   What = declarative_world
+;  What = pure_world.
 ```
 
-To quit scryer-prolog, type
+Press `SPACE` to show further answers, if any exist. Press `RETURN`
+or&nbsp;`.` to abort the search and return to the
+toplevel&nbsp;prompt. Press&nbsp;`f` to see up to the next multiple of
+5 answers, and `a` to see all answers. Press&nbsp;`h` to show a help
+message.
+
+Use `TAB` to complete atoms and predicate names in queries. For
+instance, after consulting the program above, typing `decl` followed
+by&nbsp;`TAB` yields `declarative_world`. Press&nbsp;`TAB` repeatedly
+to cycle through alternative completions.
+
+To quit Scryer Prolog, use the standard predicate `halt/0`:
+
 ```
 ?- halt.
 ```
@@ -301,42 +234,358 @@ Scryer supports dynamic operators. Using the built-in
 arithmetic operators with the usual precedences,
 
 ```
-?- write_canonical(-5 + 3 - (2 * 4) // 8).
--(+(-(5), 3), //(*(2, 4), 8))
-true.
+?- write_canonical(-5 + 3 - (2 * 4) // 8), nl.
+-(+(-5,3),//(*(2,4),8))
+   true.
 ```
 
 New operators can be defined using the `op` declaration.
 
-### Partial strings
+### First instantiated argument indexing
 
-Scryer has two specialized, non-ISO builtin predicates for handling
-so-called "partial strings". Partial strings imitate difference lists
-of characters, but are much more space efficient. This efficiency
-comes at the cost of full generality -- you cannot unify the tail
-variables of two distinct partial strings, because their buffers will
-always be distinct.
+Scryer Prolog indexes on the leftmost argument that is not a variable
+in all clauses of a predicate's&nbsp;definition. We call this strategy
+first *instantiated* argument indexing.
 
-If `X` is a free variable, the query
+A key motivation for first instantiated argument indexing is to enable
+indexing for meta-predicates such as `maplist/N` and `foldl/N`, whose
+first argument is a partial goal that is a variable in the definition
+of these predicates and therefore cannot be used for indexing.
 
-`?- partial_string("abc", X), X = [a, b, c | Y], is_partial_string(X),
-is_partial_string(Y).`
+For example, a natural definition of `maplist/2` reads:
 
-will succeed. Further, if `Y` a free variable, unifying `Y` against
-another string, "def" in this case, produces the equations
+```
+maplist(_, []).
+maplist(Goal_1, [L|Ls]) :-
+        call(Goal_1, L),
+        maplist(Goal_1, Ls).
+```
 
-`X = [a, b, c, d, e, f], Y = [d, e, f].`
+In this case, first instantiated argument indexing automatically uses
+the *second* argument for indexing, and thus prevents choicepoints for
+calls with lists of fixed lengths (and deterministic goals).
+Conveniently, no auxiliary predicates with reordered arguments are
+needed to benefit from indexing in such cases.
+
+Conventional first argument&nbsp;indexing naturally arises as a
+special case of this strategy, if the first argument is instantiated
+in any clause of a predicate's definition.
+
+### Strings and partial strings
+
+A very compact internal representation of *strings* is one of the key
+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.
+
+Scryer Prolog's compact internal string representation makes it
+ideally suited for the use case Prolog was originally developed for:
+efficient and convenient text processing, especially with definite
+clause grammars (DCGs) as provided by
+[`library(dcgs)`](src/lib/dcgs.pl) and
+[`library(pio)`](src/lib/pio.pl) to transparently apply DCGs to files.
+
+In Scryer Prolog, the default value of the Prolog flag `double_quotes`
+is `chars`, which is also the recommended setting. This means that
+lists of characters can be written as double-quoted strings, in the
+tradition of Marseille&nbsp;Prolog.
+
+For example, the following query succeeds:
+
+```
+?- "abc" = [a,b,c].
+   true.
+```
+
+This shows that the string `"abc"`, which is represented as a sequence
+of 3&nbsp;bytes internally, appears to Prolog programs as a list of
+characters.
+
+Scryer Prolog uses the same efficient encoding for *partial* strings,
+which appear to Prolog code as partial lists of characters. The
+predicate `partial_string/3` from `library(iso_ext)` lets you
+construct partial&nbsp;strings explicitly. For example:
+
+```
+?- partial_string("abc", Ls0, Ls).
+   Ls0 = [a,b,c|Ls].
+```
+
+In this case, and as the answer illustrates, `Ls0` is
+indistinguishable from a partial&nbsp;list with tail&nbsp;`Ls`, while
+the efficient packed representation is used internally.
+
+An important design goal of Scryer Prolog is to *automatically* use
+the efficient string representation whenever possible. Therefore, it
+is only very rarely necessary to use `partial_string/3` explicitly. In
+the above example, posting <tt>Ls0&nbsp;=&nbsp;[a,b,c|Ls]</tt> yields
+the exact same internal representation, and has the advantage that
+only the standard predicate&nbsp;`(=)/2` is used.
+
+The efficient internal representation of strings and partial strings
+was first proposed and explained by Ulrich Neumerkel in
+issues&nbsp;[#24](https://github.com/mthom/scryer-prolog/issues/24)
+and&nbsp;[#95](https://github.com/mthom/scryer-prolog/issues/95), and
+Scryer&nbsp;Prolog is the first Prolog&nbsp;system that implements it.
+
+### Occurs check and cyclic terms
+
+The *occurs&nbsp;check* is an element of algorithms that perform
+syntactic unification, causing the unification to fail if a variable
+is unified with a term that contains that variable as a proper
+subterm. For efficiency, the *occurs&nbsp;check* is omitted by default
+in Scryer&nbsp;Prolog and many other Prolog systems.
+
+In Scryer Prolog, performing unifications which succeed only if the
+*occurs&nbsp;check* is omitted yield *cyclic&nbsp;terms*, also called
+*rational&nbsp;trees*. For example:
+
+```
+?- X = f(X), Y = g(X,Y).
+   X = f(X), Y = g(f(X),Y).
+```
+
+The creation of cyclic terms often indicates a programming mistake in
+the formulation of Prolog predicates, and to obtain logically sound
+results it is desirable to either perform all unifications with
+*occurs&nbsp;check* enabled, or let Prolog throw an error if enabling
+the *occurs&nbsp;check* is necessary to prevent a unification.
+
+Scryer Prolog supports this via the Prolog flag `occurs_check`. It can
+be set to one of the following values to obtain the desired behaviour:
+
+- `false`
+  Do not perform the *occurs&nbsp;check*. This is the default.
+- `true`
+  Perform all unifications with the *occurs&nbsp;check* enabled.
+- `error`
+  Yield an error if a unification is performed that the
+  *occurs&nbsp;check* would have prevented.
+
+Especially when starting with Prolog, we recommend to add the
+following directive to the `~/.scryerrc` configuration file so that
+programming mistakes in predicates that lead to the creation of cyclic
+terms are indicated by errors:
+
+```
+:- set_prolog_flag(occurs_check, error).
+```
+
+Scryer Prolog implements specialized reasoning to make unifications
+fast in many frequently occurring situations also if the
+*occurs&nbsp;check* is enabled.
+
+### Tabling (SLG resolution)
+
+One of the foremost attractions of Prolog is that logical consequences
+of pure&nbsp;programs can be derived by various execution strategies
+that differ regarding essential properties such as termination,
+completeness and efficiency.
+
+The default execution strategy of Prolog is depth-first search with
+chronological backtracking. This strategy is very efficient. Its main
+drawback is that it is *incomplete*: It may fail to find any solution
+even if one exists.
+
+Scryer Prolog supports an alternative execution strategy which is
+called *tabling* and also known as tabled&nbsp;execution and
+SLG&nbsp;resolution. To enable tabled execution for a predicate, use
+[`library(tabling)`](src/lib/tabling.pl) and add a `(table)/1`
+directive for the desired predicate indicator. For example, if we
+write:
+
+```
+:- use_module(library(tabling)).
+:- table a/0.
+
+a :- a.
+```
+
+Then the query `?- a.` *terminates* (and fails), whereas it
+does&nbsp;not terminate with the default execution strategy.
+
+Scryer Prolog implements tabling via *delimited continuations* as
+described in [*Tabling as a Library with Delimited
+Control*](https://biblio.ugent.be/publication/6880648/file/6885145.pdf)
+by Desouter&nbsp;et.&nbsp;al.
+
+### Constraint Logic Programming (CLP)
+
+Scryer Prolog provides excellent support for Constraint Logic
+Programming&nbsp;(CLP), which is the amalgamation of
+Logic&nbsp;Programming&nbsp;(LP) and Constraints.
+
+In addition to built-in support for [`dif/2`](src/lib/dif.pl),
+[`freeze/2`](src/lib/freeze.pl),
+[CLP(B)](src/lib/clpb.pl) and [CLP(ℤ)](src/lib/clpz.pl),
+Scryer provides a convenient way to implement new user-defined
+constraints: *Attributed variables* are available via
+[`library(atts)`](src/lib/atts.pl) as in SICStus&nbsp;Prolog,
+which is one of the most sophisticated and fastest constraint systems
+in existence. In [`library(iso_ext)`](src/lib/iso_ext.pl),
+Scryer provides predicates for backtrackable (`bb_b_put/2`) and
+non-backtrackable (`bb_put/2`) global variables, which are needed to
+implement certain types of constraint&nbsp;solvers.
+
+These features make Scryer Prolog an ideal platform for teaching,
+learning and developing portable CLP&nbsp;applications.
 
 ### Modules
 
 Scryer has a simple predicate-based module system. It provides a
 way to separate units of code into distinct namespaces, for both
-predicates and operators. See the files `src/prolog/lib/*.pl` for
+predicates and operators. See the files
+[`src/lib/*.pl`](src/lib) for
 examples.
 
-At the time of this writing, several control and list processing
-operators and predicates are hidden in their own modules that have not
-been exported to the toplevel. To export them, write
+At the time of this writing, many predicates reside in their own
+modules that need to be imported before they can be used.
+The modules that ship with Scryer&nbsp;Prolog are also called
+*library*&nbsp;modules or *libraries*, and include:
+
+* [`lists`](src/lib/lists.pl)
+  providing `length/2`, `member/2`, `select/3`, `append/[2,3]`,
+  `foldl/[4,5]`, `maplist/[2-9]`, `same_length/2`, `transpose/2` etc.
+* [`dcgs`](src/lib/dcgs.pl)
+  Definite Clause Grammars (DCGs), a built-in grammar mechanism
+  that uses the operator `(-->)/2` to define grammar rules,
+  and the predicates `phrase/[2,3]` to invoke them.
+* [`dif`](src/lib/dif.pl)
+  The predicate `dif/2` provides declarative disequality:
+  It is true if and only if its arguments are different, and
+  delays the test until a sound decision can be made.
+* [`reif`](src/lib/reif.pl)
+  providing `if_/3`, `tfilter/3` and related predicates
+  as described in *Indexing&nbsp;dif/2*.
+* [`clpz`](src/lib/clpz.pl)
+  CLP(ℤ): Constraint Logic Programming over Integers,
+  providing declarative integer arithmetic via `(#=)/2`, `(#\=)/2`,
+  `(#>=)/2` etc., and various global constraints and
+  enumeration predicates for solving combinatorial tasks.
+* [`pairs`](src/lib/pairs.pl)
+  By convention, *pairs* are Prolog terms with
+  principal&nbsp;functor `(-)/2`, written as `Key-Value`.
+  This library provides `pairs_keys_values/3`,
+  `pairs_keys/2`, and other predicates to reason about pairs.
+* [`si`](src/lib/si.pl)
+  The predicates `atom_si/1`, `integer_si/1`, `atomic_si/1`
+  and `list_si/1` implement sound type checks. They raise
+  instantiation errors if no decision can be made.
+  They are declarative replacements for logically flawed
+  lower-level type tests. For instance, instead of `integer(X)`,
+  write `integer_si(X)` to ensure soundness of your programs.
+  "si" stands for *sufficiently instantiated*, and also for
+  *sound&nbsp;inference*.
+* [`debug`](src/lib/debug.pl)
+  Various predicates that allow for declarative debugging.
+* [`pio`](src/lib/pio.pl)
+  `phrase_from_file/2` applies a DCG nonterminal to the contents of a
+  file, reading lazily only as much as is needed. Due to the compact
+  internal string representation, also extremely large files can be
+  efficiently processed with Scryer&nbsp;Prolog in this way.
+  `phrase_to_file/2` and `phrase_to_stream/2` write lists of
+  characters described by DCGs to files and streams, respectively.
+* [`lambda`](src/lib/lambda.pl)
+  Lambda expressions to simplify higher order programming.
+* [`charsio`](src/lib/charsio.pl) Various predicates that are useful
+  for parsing and reasoning about characters, notably `char_type/2` to
+  classify characters according to their type, and conversion
+  predicates for different encodings of strings.
+* [`error`](src/lib/error.pl)
+  `must_be/2` and `can_be/2` complement the type checks provided by
+  [`library(si)`](src/lib/si.pl), and are especially useful for
+  Prolog library authors.
+* [`tabling`](src/lib/tabling.pl)
+  The operator `(table)/1` is used in directives that prepare
+  predicates for tabled execution (SLG&nbsp;resolution).
+* [`format`](src/lib/format.pl)
+  The nonterminal `format_//2` is used to describe formatted output,
+  arranging arguments according to a given format&nbsp;string.
+  The predicates `format/[2,3]`, `portray_clause/[1,2]` and `listing/1`
+  provide formatted *impure* output.
+* [`assoc`](src/lib/assoc.pl)
+  providing `empty_assoc/1`, `get_assoc/3`, `put_assoc/4` etc.
+  to manage elements in AVL&nbsp;trees which ensure
+  *O*(log(*N*))&nbsp;access.
+* [`ordsets`](src/lib/ordsets.pl)
+  represents ordered sets as lists.
+* [`clpb`](src/lib/clpb.pl)
+  CLP(B): Constraint Logic Programming over Boolean variables,
+  a BDD-based SAT&nbsp;solver provided via the predicates
+  `sat/1`, `taut/2`, `labeling/1` etc.
+* [`arithmetic`](src/lib/arithmetic.pl)
+  Arithmetic predicates such as `lsb/2`, `msb/2` and
+  `number_to_rational/2`.
+* [`time`](src/lib/time.pl) Predicates for reasoning about
+  time, including `time/1` to measure the CPU&nbsp;time of a goal,
+  `current_time/1` to obtain the current system time, the nonterminal
+  `format_time//2` to describe strings with dates and times, and
+  `sleep/1` to slow down a computation.
+* [`files`](src/lib/files.pl)
+  Predicates for reasoning about files and directories, such as
+  `directory_files/2`, `file_exists/1` and `file_size/2`.
+* [`cont`](src/lib/cont.pl)
+  Provides *delimited continuations* via `reset/3` and `shift/1`.
+* [`random`](src/lib/random.pl)
+  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.
+* [`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
+  [`library(xpath)`](src/lib/iso_ext.pl) to extract information from
+  parsed documents.
+* [`csv`](src/lib/csv.pl)
+  `parse_csv//1` and `parse_csv//2` can be used with [`phrase_from_file/2`](src/lib/pio.pl)
+  or [`phrase/2`](src/lib/dcgs.pl) to parse csv
+* [`serialization/abnf`](src/lib/serialization/abnf.pl)
+  DCGs describing the
+  [ABNF grammar core (RFC 5234)](https://tools.ietf.org/html/rfc5234#appendix-B.1),
+  which is used to describe many [IETF](https://www.ietf.org/standards/rfcs/)
+  syntaxes, such as [HTTP v1.1](https://www.rfc-editor.org/rfc/rfc7230.html#page-82),
+  [SMTP](https://www.rfc-editor.org/rfc/rfc5321.html),
+  [iCalendar](https://www.rfc-editor.org/rfc/rfc5545.html), and more.
+* [`serialization/json`](src/lib/serialization/json.pl)
+  `json_chars//1` can be used with [`phrase_from_file/2`](src/lib/pio.pl)
+  or [`phrase/2`](src/lib/dcgs.pl) to parse and generate
+  [JSON](https://www.json.org/json-en.html).
+* [`xpath`](src/lib/xpath.pl)
+  The predicate `xpath/3` is used for convenient reasoning about HTML
+  and XML&nbsp;documents, inspired by the XPath language. This library
+  is often used together with [`library(sgml)`](src/lib/sgml.pl).
+* [`sockets`](src/lib/sockets.pl)
+  Predicates for opening and accepting TCP connections as streams.
+* [`os`](src/lib/os.pl)
+  Predicates for reasoning about environment&nbsp;variables.
+* [`iso_ext`](src/lib/iso_ext.pl)
+  Conforming extensions to and candidates for inclusion in the Prolog
+  ISO&nbsp;standard, such as `setup_call_cleanup/3`, `call_nth/2` and
+  `call_with_inference_limit/3`.
+* [`crypto`](src/lib/crypto.pl)
+  Cryptographically secure random numbers and hashes, HMAC-based key
+  derivation&nbsp;(HKDF), password-based key derivation&nbsp;(PBKDF2),
+  public key signatures and signature verification with&nbsp;Ed25519,
+  ECDH key&nbsp;exchange over Curve25519 (X25519), authenticated symmetric
+  encryption with ChaCha20-Poly1305, and reasoning about elliptic curves.
+* [`uuid`](src/lib/uuid.pl) UUIDv4 generation and hex representation
+* [`tls`](src/lib/tls.pl)
+  Predicates for negotiating TLS connections explicitly.
+* [`ugraphs`](src/lib/ugraphs.pl) Graph manipulation library
+* [`simplex`](src/lib/simplex.pl) Providing `assignment/2`,
+  `transportation/4` and other predicates for solving linear
+  programming problems.
+
+To use predicates provided by the `lists` library, write:
 
 ```
 ?- use_module(library(lists)).
@@ -371,7 +620,6 @@ REPL:
 
 ```
 ?- [user].
-(type Enter + Ctrl-D to terminate the stream when finished)
 :- module(test, [local_member/2]).
 :- use_module(library(lists)).
 
@@ -379,4 +627,56 @@ local_member(X, Xs) :- member(X, Xs).
 ```
 
 The user listing can also be terminated by placing `end_of_file.` at
-the end of the stream.
+the end of the stream.
+
+### Configuration file
+
+At startup, Scryer Prolog consults the file `~/.scryerrc`, if the file
+exists. This file is useful to automatically load libraries and define
+predicates that you need often.
+
+For example, a sensible starting point for `~/.scryerrc` is:
+
+```
+:- use_module(library(lists)).
+:- use_module(library(dcgs)).
+:- use_module(library(reif)).
+```
+
+### Development environment
+
+To write and edit Prolog programs, we recommend
+[GNU&nbsp;Emacs](https://www.gnu.org/software/emacs/) with the
+[Prolog&nbsp;mode](https://bruda.ca/emacs/prolog_mode_for_emacs)
+maintained by Stefan Bruda.
+
+Use [ediprolog](https://www.metalevel.at/ediprolog/) to consult
+Prolog&nbsp;code and evaluate Prolog queries in arbitrary
+Emacs&nbsp;buffers.
+
+Emacs definitions that show Prolog terms as trees are available
+in&nbsp;[tools](tools).
+
+To *debug* Prolog code, we recommend the predicates from
+[**`library(debug)`**](src/lib/debug.pl), most notably:
+
+- `(*)/1` to *"generalize&nbsp;away"* a Prolog goal. Use it to debug
+  unexpected failures by generalizing your definitions until they
+  succeed. Simply place&nbsp;`*` in front of a goal to generalize it away.
+- `($)/1` to emit a *trace* of the execution, showing when a goal
+  is invoked, and when it has succeeded. Place&nbsp;`$` in front of a goal
+  to emit this information for that goal.
+
+This way of debugging Prolog code has several major benefits, such as:
+It stays close to the actual Prolog code under consideration, it does
+not need additional tools and formalisms for its application, and
+further, it encourages declarative reasoning that can in principle
+also be performed automatically.
+
+## Support and discussions
+
+If Scryer Prolog crashes or yields unexpected errors, consider filing
+an&nbsp;[issue](https://github.com/mthom/scryer-prolog/issues).
+
+To get in touch with the Scryer Prolog community, participate in
+[discussions](https://github.com/mthom/scryer-prolog/discussions)!

build.rs

@@ -1,56 +0,0 @@
-extern crate indexmap;
-
-use indexmap::IndexSet;
-
-use std::env;
-use std::fs::{File, copy, read_dir};
-use std::io::Write;
-use std::path::Path;
-
-fn main()
-{
-    let out_dir = env::var("OUT_DIR").unwrap();
-    let dest_path = Path::new(&out_dir).join("libraries.rs");
-
-    let mut libraries = File::create(&dest_path).unwrap();
-    let mut library_index = IndexSet::new();
-
-    let paths = read_dir("./src/prolog/lib").unwrap();
-
-    for item in paths {
-        let item = item.unwrap().path();
-
-        if let Some(file_name) = item.file_name() {
-            if let Some(ext) = item.extension() {
-                if ext == "pl" {
-                    let file_stem = item.file_stem().unwrap();
-                    let file_str  = file_stem.to_string_lossy().to_uppercase();
-                    let dest = Path::new(&out_dir).join(file_name);
-
-                    match copy(&item, dest) {
-                        Ok(_) => {},
-                        Err(e) => panic!("die: {:?}", e)
-                    };
-
-                    let include_line = format!("static {}: &str = include_str!(\"{}.pl\");\n",
-                                               file_str, file_stem.to_string_lossy());
-
-                    libraries.write_all(include_line.as_bytes()).unwrap();
-                    library_index.insert(file_stem.to_string_lossy().to_string());
-                }
-            }
-        }
-    }
-
-    libraries.write_all(b"\nref_thread_local! {
-    pub static managed LIBRARIES: IndexMap<&'static str, &'static str> = {
-        let mut m = IndexMap::new();\n").unwrap();
-
-    for item in library_index {
-        let line = format!("\n        m.insert(\"{}\", {});", item, item.to_uppercase());
-        libraries.write_all(line.as_bytes()).unwrap();
-    }
-
-    libraries.write_all(b"\n\n        m\n    };
-}").unwrap();
-}

build/main.rs

@@ -0,0 +1,114 @@
+mod instructions_template;
+mod static_string_indexing;
+
+use instructions_template::generate_instructions_rs;
+use static_string_indexing::index_static_strings;
+
+use std::env;
+use std::fs;
+use std::fs::File;
+use std::io::Write;
+use std::path::Path;
+use std::process::{Command, Stdio};
+
+fn find_prolog_files(libraries: &mut File, prefix: &str, current_dir: &Path) {
+    let entries = match current_dir.read_dir() {
+        Ok(entries) => entries,
+        Err(_) => return,
+    };
+
+    for entry in entries.filter_map(Result::ok).map(|e| e.path()) {
+        if entry.is_dir() {
+            if let Some(file_name) = entry.file_name() {
+                let new_prefix = prefix.to_owned() + file_name.to_str().unwrap() + "/";
+                find_prolog_files(libraries, &new_prefix, &entry);
+            }
+        } else if entry.is_file() {
+            let ext = std::ffi::OsStr::new("pl");
+            if entry.extension() == Some(ext) {
+                let contain = String::from_utf8(fs::read(&entry).unwrap()).unwrap();
+                let name = entry.file_stem().unwrap().to_str().unwrap();
+
+                let line = format!(
+                    "        m.insert(\"{}\",\n{:?});\n",
+                    prefix.to_owned() + name,
+                    contain
+                );
+
+                libraries.write_all(line.as_bytes()).unwrap();
+            }
+        }
+    }
+}
+
+fn main() {
+    let has_rustfmt = Command::new("rustfmt")
+        .arg("--version")
+        .stdin(Stdio::inherit())
+        .status()
+        .is_ok();
+
+    if !has_rustfmt {
+        println!("Failed to run rustfmt, will skip formatting generated files.")
+    }
+
+    let out_dir = env::var("OUT_DIR").unwrap();
+    let dest_path = Path::new(&out_dir).join("libraries.rs");
+
+    let mut libraries = File::create(&dest_path).unwrap();
+    let lib_path = Path::new("src/lib");
+
+    libraries
+        .write_all(
+            b"ref_thread_local::ref_thread_local! {
+    pub(crate) static managed LIBRARIES: IndexMap<&'static str, &'static str> = {
+        let mut m = IndexMap::new();\n",
+        )
+        .unwrap();
+
+    find_prolog_files(&mut libraries, "", &lib_path);
+    libraries.write_all(b"\n        m\n    };\n}\n").unwrap();
+
+    let instructions_path = Path::new(&out_dir).join("instructions.rs");
+    let mut instructions_file = File::create(&instructions_path).unwrap();
+
+    let quoted_output = generate_instructions_rs();
+
+    instructions_file
+        .write_all(quoted_output.to_string().as_bytes())
+        .unwrap();
+
+    if has_rustfmt {
+        format_generated_file(instructions_path.as_path());
+    }
+
+    let static_atoms_path = Path::new(&out_dir).join("static_atoms.rs");
+    let mut static_atoms_file = File::create(&static_atoms_path).unwrap();
+
+    let quoted_output = index_static_strings(&instructions_path);
+
+    static_atoms_file
+        .write_all(quoted_output.to_string().as_bytes())
+        .unwrap();
+
+    if has_rustfmt {
+        format_generated_file(static_atoms_path.as_path());
+    }
+
+    println!("cargo:rerun-if-changed=src/");
+}
+
+fn format_generated_file(path: &Path) {
+    Command::new("rustfmt")
+        .arg(path.as_os_str())
+        .spawn()
+        .unwrap_or_else(|err| {
+            panic!(
+                "{}: rustfmt was detected as available, but failed to format generated file '{}'",
+                err,
+                path.display()
+            );
+        })
+        .wait()
+        .unwrap();
+}

build/static_string_indexing.rs

@@ -0,0 +1,177 @@
+use proc_macro2::TokenStream;
+use syn::*;
+use syn::parse::*;
+use syn::visit::*;
+
+use indexmap::IndexSet;
+
+struct StaticStrVisitor {
+    static_strs: IndexSet<String>,
+}
+
+impl StaticStrVisitor {
+    fn new() -> Self {
+        Self { static_strs: IndexSet::new() }
+    }
+}
+
+struct MacroFnArgs {
+    args: Vec<Expr>,
+}
+
+struct ReadHeapCellExprAndArms {
+    expr: Expr,
+    arms: Vec<Arm>,
+}
+
+impl Parse for ReadHeapCellExprAndArms {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let mut arms = vec![];
+        let expr = input.parse()?;
+
+        input.parse::<Token![,]>()?;
+        arms.push(input.parse()?);
+
+        while !input.is_empty() {
+            if let Ok(_) = input.parse::<Token![,]>() {}
+            arms.push(input.parse()?);
+        }
+
+        Ok(ReadHeapCellExprAndArms { expr, arms })
+    }
+}
+
+impl Parse for MacroFnArgs {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let mut args = vec![];
+
+        if !input.is_empty() {
+            args.push(input.parse()?);
+        }
+
+        while !input.is_empty() {
+            if let Ok(_) = input.parse::<Token![,]>() {}
+            args.push(input.parse()?);
+        }
+
+        Ok(MacroFnArgs { args })
+    }
+}
+
+impl<'ast> Visit<'ast> for StaticStrVisitor {
+    fn visit_macro(&mut self, m: &'ast Macro) {
+        let Macro { path, .. } = m;
+
+        if path.is_ident("atom") {
+            if let Some(Lit::Str(string)) = m.parse_body::<Lit>().ok() {
+                self.static_strs.insert(string.value());
+            }
+        } else if path.is_ident("read_heap_cell") || path.is_ident("match_untyped_arena_ptr") {
+            if let Some(m) = m.parse_body::<ReadHeapCellExprAndArms>().ok() {
+                self.visit_expr(&m.expr);
+
+                for e in m.arms {
+                    self.visit_arm(&e);
+                }
+            }
+        } else {
+            if let Some(m) = m.parse_body::<MacroFnArgs>().ok() {
+                for e in m.args {
+                    self.visit_expr(&e);
+                }
+            }
+        }
+    }
+}
+
+pub fn index_static_strings(instruction_rs_path: &std::path::Path) -> TokenStream {
+    use quote::*;
+
+    use std::ffi::OsStr;
+    use std::fs::File;
+    use std::io::Read;
+
+    use walkdir::WalkDir;
+
+    fn filter_rust_files(e: &walkdir::DirEntry) -> bool {
+        if e.path().is_dir() {
+            return true;
+        }
+
+        e.path().extension().and_then(OsStr::to_str) == Some("rs")
+    }
+
+    let mut visitor = StaticStrVisitor::new();
+
+    fn process_filepath(path: &std::path::Path) -> std::result::Result<syn::File, ()> {
+        let mut src = String::new();
+
+        let mut file = match File::open(path) {
+            Ok(file) => file,
+            Err(_) => return Err(()),
+        };
+
+        match file.read_to_string(&mut src) {
+            Ok(_) => {}
+            Err(e) => {
+                panic!("error reading file: {:?}", e);
+            }
+        }
+
+        let syntax = match syn::parse_file(&src) {
+            Ok(s) => s,
+            Err(e) => {
+                panic!("parse error: {} in file {:?}", e, path);
+            }
+        };
+        Ok(syntax)
+    }
+
+    for entry in WalkDir::new("src/")
+        .into_iter()
+        .filter_entry(filter_rust_files)
+    {
+        let entry = entry.unwrap();
+
+        if entry.path().is_dir() {
+            continue;
+        }
+
+        let syntax = match process_filepath(entry.path()) {
+            Ok(syntax) => syntax,
+            Err(_) => continue,
+        };
+
+        visitor.visit_file(&syntax);
+    }
+
+    match process_filepath(instruction_rs_path) {
+        Ok(syntax) => visitor.visit_file(&syntax),
+        Err(_) => {}
+    }
+
+    let indices = (0..visitor.static_strs.len()).map(|i| i << 3);
+    let indices_iter = indices.clone();
+
+    let static_strs_len = visitor.static_strs.len();
+    let static_strs: &Vec<_> = &visitor.static_strs.into_iter().collect();
+
+    quote! {
+        use phf;
+
+        static STRINGS: [&'static str; #static_strs_len] = [
+            #(
+                #static_strs,
+            )*
+        ];
+
+        #[macro_export]
+        macro_rules! atom {
+            #((#static_strs) => { Atom { index: #indices_iter } };)*
+        }
+
+        pub static STATIC_ATOMS_MAP: phf::Map<&'static str, Atom> = phf::phf_map! {
+            #(#static_strs => { Atom { index: #indices } },)*
+        };
+    }
+}

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+</svg>

scryer-prolog.wxs

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
+  <Product Name="Scryer Prolog" Manufacturer="Scryer Prolog contributors" Id="*" UpgradeCode="cfb2dee4-5dd5-4d7d-b426-cd7340810559" Language="1033" Codepage="1252" Version="0.9.0">
+    <Package Description="An open source industrial strength production environment for ISO Prolog that is also a testbed for bleeding edge research in logic and constraint programming, which is itself written in a high-level language." Platform="x64" Keywords="prolog" Id="*" Compressed="yes" InstallScope="perMachine" InstallerVersion="300" Languages="1033" SummaryCodepage="1252" Manufacturer="Scryer Prolog contributors"/>
+    <Property Id="APPHELPLINK" Value="https://github.com/mthom/scryer-prolog"/>
+    <Media Id="1" Cabinet="scryer.cab" EmbedCab="yes" />
+    
+    <Directory Id="TARGETDIR" Name="SourceDir">
+      <Directory Id="ProgramFilesFolder" Name="PFiles">
+        <Directory Id="INSTALLDIR" Name="Scryer Prolog">
+          <Component Id="MainExecutable" Guid="1b41ceda-ba18-47f9-911b-ee41b4f20921">
+            <File Id="ScryerPrologEXE" Name="scryer-prolog.exe" DiskId="1" Source="target/release/scryer-prolog.exe" KeyPath="yes" Checksum="yes"/>
+          </Component>
+        </Directory>
+      </Directory>
+      <Directory Id="ProgramMenuFolder">
+	<Component Id="ApplicationShortcut" Guid="8c9b14a3-e7b1-4d30-a892-61d7371dcae2">
+          <Shortcut Id="ApplicationStarMenuShortcut" Name="Scryer Prolog" Description="Launch Scryer Prolog" Target="[#ScryerPrologEXE]" WorkingDirectory="INSTALLDIR"/>
+	  <RemoveFolder Id="ApplicationShortcut" On="uninstall"/>
+	  <RegistryValue Root="HKCU" Key="Software\Microsoft\ScryerProlog" Name="installed" Type="integer" Value="1" KeyPath="yes"/>
+	</Component>
+      </Directory>
+    </Directory>
+
+    <Feature Id="Complete" Level="1" Display="expand" ConfigurableDirectory="INSTALLDIR">
+      <ComponentRef Id="MainExecutable"/>
+      <ComponentRef Id="ApplicationShortcut"/>
+    </Feature>
+  </Product>
+</Wix>
+  

src/allocator.rs

@@ -1,41 +1,57 @@
-use prolog_parser::ast::*;
+use crate::parser::ast::*;
+use crate::temp_v;
 
-use crate::prolog::fixtures::*;
-use crate::prolog::forms::*;
-use crate::prolog::machine::machine_indices::*;
-use crate::prolog::targets::*;
+use crate::fixtures::*;
+use crate::forms::*;
+use crate::instructions::*;
+use crate::machine::machine_indices::*;
+use crate::targets::*;
 
 use std::cell::Cell;
 use std::rc::Rc;
 
-pub trait Allocator<'a> {
+pub(crate) trait Allocator {
     fn new() -> Self;
 
-    fn mark_anon_var<Target>(&mut self, _: Level, _: GenContext, _: &mut Vec<Target>)
-    where
-        Target: CompilationTarget<'a>;
-    fn mark_non_var<Target>(&mut self, _: Level, _: GenContext, _: &'a Cell<RegType>, _: &mut Vec<Target>)
-    where
-        Target: CompilationTarget<'a>;
-    fn mark_reserved_var<Target>(
+    fn mark_anon_var<'a, Target: CompilationTarget<'a>>(
         &mut self,
-        _: Rc<Var>,
-        _: Level,
-        _: &'a Cell<VarReg>,
-        _: GenContext,
-        _: &mut Vec<Target>,
-        _: RegType,
-        _: bool,
-    ) where
-        Target: CompilationTarget<'a>;
-    fn mark_var<Target>(&mut self, _: Rc<Var>, _: Level, _: &'a Cell<VarReg>, _: GenContext, _: &mut Vec<Target>)
-    where
-        Target: CompilationTarget<'a>;
+        lvl: Level,
+        context: GenContext,
+        code: &mut Code,
+    );
+
+    fn mark_non_var<'a, Target: CompilationTarget<'a>>(
+        &mut self,
+        lvl: Level,
+        context: GenContext,
+        cell: &'a Cell<RegType>,
+        code: &mut Code,
+    );
+
+    fn mark_reserved_var<'a, Target: CompilationTarget<'a>>(
+        &mut self,
+        var_name: Rc<String>,
+        lvl: Level,
+        cell: &'a Cell<VarReg>,
+        term_loc: GenContext,
+        code: &mut Code,
+        r: RegType,
+        is_new_var: bool,
+    );
+
+    fn mark_var<'a, Target: CompilationTarget<'a>>(
+        &mut self,
+        var_name: Rc<String>,
+        lvl: Level,
+        cell: &'a Cell<VarReg>,
+        context: GenContext,
+        code: &mut Code,
+    );
 
     fn reset(&mut self);
     fn reset_contents(&mut self) {}
-    fn reset_arg(&mut self, _: usize);
-    fn reset_at_head(&mut self, _: &Vec<Box<Term>>);
+    fn reset_arg(&mut self, arg_num: usize);
+    fn reset_at_head(&mut self, args: &Vec<Term>);
 
     fn advance_arg(&mut self);
 
@@ -43,11 +59,12 @@ pub trait Allocator<'a> {
     fn bindings_mut(&mut self) -> &mut AllocVarDict;
 
     fn take_bindings(self) -> AllocVarDict;
+    fn max_reg_allocated(&self) -> usize;
 
-    fn drain_var_data(
+    fn drain_var_data<'a>(
         &mut self,
         vs: VariableFixtures<'a>,
-        num_of_chunks: usize
+        num_of_chunks: usize,
     ) -> VariableFixtures<'a> {
         let mut perm_vs = VariableFixtures::new();
 
@@ -71,17 +88,17 @@ pub trait Allocator<'a> {
         perm_vs
     }
 
-    fn get(&self, var: Rc<Var>) -> RegType {
+    fn get(&self, var: Rc<String>) -> RegType {
         self.bindings()
             .get(&var)
             .map_or(temp_v!(0), |v| v.as_reg_type())
     }
 
-    fn is_unbound(&self, var: Rc<Var>) -> bool {
+    fn is_unbound(&self, var: Rc<String>) -> bool {
         self.get(var).reg_num() == 0
     }
 
-    fn record_register(&mut self, var: Rc<Var>, r: RegType) {
+    fn record_register(&mut self, var: Rc<String>, r: RegType) {
         match self.bindings_mut().get_mut(&var).unwrap() {
             &mut VarData::Temp(_, ref mut s, _) => *s = r.reg_num(),
             &mut VarData::Perm(ref mut s) => *s = r.reg_num(),

src/arithmetic.rs

@@ -0,0 +1,724 @@
+use crate::allocator::*;
+use crate::arena::*;
+use crate::atom_table::*;
+use crate::debray_allocator::*;
+use crate::forms::*;
+use crate::instructions::*;
+use crate::iterators::*;
+use crate::targets::QueryInstruction;
+use crate::types::*;
+
+use crate::parser::ast::*;
+use crate::parser::rug::ops::PowAssign;
+use crate::parser::rug::{Assign, Integer, Rational};
+
+use crate::machine::machine_errors::*;
+
+use ordered_float::*;
+
+use std::cell::Cell;
+use std::cmp::{max, min, Ordering};
+use std::convert::TryFrom;
+use std::f64;
+use std::num::FpCategory;
+use std::ops::Div;
+use std::rc::Rc;
+use std::vec::Vec;
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum ArithmeticTerm {
+    Reg(RegType),
+    Interm(usize),
+    Number(Number),
+}
+
+impl ArithmeticTerm {
+    pub(crate) fn interm_or(&self, interm: usize) -> usize {
+        if let &ArithmeticTerm::Interm(interm) = self {
+            interm
+        } else {
+            interm
+        }
+    }
+}
+
+impl Default for ArithmeticTerm {
+    fn default() -> Self {
+        ArithmeticTerm::Number(Number::default())
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct ArithInstructionIterator<'a> {
+    state_stack: Vec<TermIterState<'a>>,
+}
+
+pub(crate) type ArithCont = (Code, Option<ArithmeticTerm>);
+
+impl<'a> ArithInstructionIterator<'a> {
+    fn push_subterm(&mut self, lvl: Level, term: &'a Term) {
+        self.state_stack
+            .push(TermIterState::subterm_to_state(lvl, term));
+    }
+
+    fn from(term: &'a Term) -> Result<Self, ArithmeticError> {
+        let state = match term {
+            Term::AnonVar => return Err(ArithmeticError::UninstantiatedVar),
+            Term::Clause(cell, name, terms) => {
+                TermIterState::Clause(Level::Shallow, 0, cell, *name, terms)
+            }
+            /* match ClauseType::from(*name, terms.len()) {
+                ct @ ClauseType::Named(..) => {
+                    Ok(TermIterState::Clause(Level::Shallow, 0, cell, ct, terms))
+                }
+                ct @ ClauseType::Inlined(InlinedClauseType::IsFloat(_)) => {
+                    // let ct = ClauseType::Named(1, atom!("float"), CodeIndex::default());
+                    Ok(TermIterState::Clause(Level::Shallow, 0, cell, ct, terms))
+                }
+                _ => Err(ArithmeticError::NonEvaluableFunctor(
+                    Literal::Atom(*name),
+                    terms.len(),
+                )),
+            }?,*/
+            Term::Literal(cell, cons) => TermIterState::Literal(Level::Shallow, cell, cons),
+            Term::Cons(..) | Term::PartialString(..) | Term::CompleteString(..) => {
+                return Err(ArithmeticError::NonEvaluableFunctor(
+                    Literal::Atom(atom!(".")),
+                    2,
+                ))
+            }
+            Term::Var(cell, var) => TermIterState::Var(Level::Shallow, cell, var.clone()),
+        };
+
+        Ok(ArithInstructionIterator {
+            state_stack: vec![state],
+        })
+    }
+}
+
+#[derive(Debug)]
+pub(crate) enum ArithTermRef<'a> {
+    Literal(&'a Literal),
+    Op(Atom, usize), // name, arity.
+    Var(Level, &'a Cell<VarReg>, Rc<String>),
+}
+
+impl<'a> Iterator for ArithInstructionIterator<'a> {
+    type Item = Result<ArithTermRef<'a>, ArithmeticError>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while let Some(iter_state) = self.state_stack.pop() {
+            match iter_state {
+                TermIterState::AnonVar(_) => return Some(Err(ArithmeticError::UninstantiatedVar)),
+                TermIterState::Clause(lvl, child_num, cell, name, subterms) => {
+                    let arity = subterms.len();
+
+                    if child_num == arity {
+                        return Some(Ok(ArithTermRef::Op(name, arity)));
+                    } else {
+                        self.state_stack.push(TermIterState::Clause(
+                            lvl,
+                            child_num + 1,
+                            cell,
+                            name,
+                            subterms,
+                        ));
+
+                        self.push_subterm(lvl.child_level(), &subterms[child_num]);
+                    }
+                }
+                TermIterState::Literal(_, _, c) => return Some(Ok(ArithTermRef::Literal(c))),
+                TermIterState::Var(lvl, cell, var) => {
+                    return Some(Ok(ArithTermRef::Var(lvl, cell, var.clone())));
+                }
+                _ => {
+                    return Some(Err(ArithmeticError::NonEvaluableFunctor(
+                        Literal::Atom(atom!(".")),
+                        2,
+                    )));
+                }
+            };
+        }
+
+        None
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct ArithmeticEvaluator<'a> {
+    marker: &'a mut DebrayAllocator,
+    interm: Vec<ArithmeticTerm>,
+    interm_c: usize,
+}
+
+pub(crate) trait ArithmeticTermIter<'a> {
+    type Iter: Iterator<Item = Result<ArithTermRef<'a>, ArithmeticError>>;
+
+    fn iter(self) -> Result<Self::Iter, ArithmeticError>;
+}
+
+impl<'a> ArithmeticTermIter<'a> for &'a Term {
+    type Iter = ArithInstructionIterator<'a>;
+
+    fn iter(self) -> Result<Self::Iter, ArithmeticError> {
+        ArithInstructionIterator::from(self)
+    }
+}
+
+fn push_literal(interm: &mut Vec<ArithmeticTerm>, c: &Literal) -> Result<(), ArithmeticError> {
+    match c {
+        Literal::Fixnum(n) => interm.push(ArithmeticTerm::Number(Number::Fixnum(*n))),
+        Literal::Integer(n) => interm.push(ArithmeticTerm::Number(Number::Integer(*n))),
+        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))
+        )),
+        Literal::Atom(name) if name == &atom!("pi") => interm.push(ArithmeticTerm::Number(
+            Number::Float(OrderedFloat(std::f64::consts::PI))
+        )),
+        Literal::Atom(name) if name == &atom!("epsilon") => interm.push(ArithmeticTerm::Number(
+            Number::Float(OrderedFloat(std::f64::EPSILON))
+        )),
+        _ => return Err(ArithmeticError::NonEvaluableFunctor(*c, 0)),
+    }
+
+    Ok(())
+}
+
+impl<'a> ArithmeticEvaluator<'a> {
+    pub(crate) fn new(marker: &'a mut DebrayAllocator, target_int: usize) -> Self {
+        ArithmeticEvaluator {
+            marker,
+            interm: Vec::new(),
+            interm_c: target_int,
+        }
+    }
+
+    fn get_unary_instr(
+        &self,
+        name: Atom,
+        a1: ArithmeticTerm,
+        t: usize,
+    ) -> Result<Instruction, ArithmeticError> {
+        match name {
+            atom!("abs") => Ok(Instruction::Abs(a1, t)),
+            atom!("-") => Ok(Instruction::Neg(a1, t)),
+            atom!("+") => Ok(Instruction::Plus(a1, t)),
+            atom!("cos") => Ok(Instruction::Cos(a1, t)),
+            atom!("sin") => Ok(Instruction::Sin(a1, t)),
+            atom!("tan") => Ok(Instruction::Tan(a1, t)),
+            atom!("log") => Ok(Instruction::Log(a1, t)),
+            atom!("exp") => Ok(Instruction::Exp(a1, t)),
+            atom!("sqrt") => Ok(Instruction::Sqrt(a1, t)),
+            atom!("acos") => Ok(Instruction::ACos(a1, t)),
+            atom!("asin") => Ok(Instruction::ASin(a1, t)),
+            atom!("atan") => Ok(Instruction::ATan(a1, t)),
+            atom!("float") => Ok(Instruction::Float(a1, t)),
+            atom!("truncate") => Ok(Instruction::Truncate(a1, t)),
+            atom!("round") => Ok(Instruction::Round(a1, t)),
+            atom!("ceiling") => Ok(Instruction::Ceiling(a1, t)),
+            atom!("floor") => Ok(Instruction::Floor(a1, t)),
+            atom!("sign") => Ok(Instruction::Sign(a1, t)),
+            atom!("\\") => Ok(Instruction::BitwiseComplement(a1, t)),
+            _ => Err(ArithmeticError::NonEvaluableFunctor(Literal::Atom(name), 1)),
+        }
+    }
+
+    fn get_binary_instr(
+        &self,
+        name: Atom,
+        a1: ArithmeticTerm,
+        a2: ArithmeticTerm,
+        t: usize,
+    ) -> Result<Instruction, ArithmeticError> {
+        match name {
+            atom!("+") => Ok(Instruction::Add(a1, a2, t)),
+            atom!("-") => Ok(Instruction::Sub(a1, a2, t)),
+            atom!("/") => Ok(Instruction::Div(a1, a2, t)),
+            atom!("//") => Ok(Instruction::IDiv(a1, a2, t)),
+            atom!("max") => Ok(Instruction::Max(a1, a2, t)),
+            atom!("min") => Ok(Instruction::Min(a1, a2, t)),
+            atom!("div") => Ok(Instruction::IntFloorDiv(a1, a2, t)),
+            atom!("rdiv") => Ok(Instruction::RDiv(a1, a2, t)),
+            atom!("*") => Ok(Instruction::Mul(a1, a2, t)),
+            atom!("**") => Ok(Instruction::Pow(a1, a2, t)),
+            atom!("^") => Ok(Instruction::IntPow(a1, a2, t)),
+            atom!(">>") => Ok(Instruction::Shr(a1, a2, t)),
+            atom!("<<") => Ok(Instruction::Shl(a1, a2, t)),
+            atom!("/\\") => Ok(Instruction::And(a1, a2, t)),
+            atom!("\\/") => Ok(Instruction::Or(a1, a2, t)),
+            atom!("xor") => Ok(Instruction::Xor(a1, a2, t)),
+            atom!("mod") => Ok(Instruction::Mod(a1, a2, t)),
+            atom!("rem") => Ok(Instruction::Rem(a1, a2, t)),
+            atom!("gcd") => Ok(Instruction::Gcd(a1, a2, t)),
+            atom!("atan2") => Ok(Instruction::ATan2(a1, a2, t)),
+            _ => Err(ArithmeticError::NonEvaluableFunctor(Literal::Atom(name), 2)),
+        }
+    }
+
+    fn incr_interm(&mut self) -> usize {
+        let temp = self.interm_c;
+
+        self.interm.push(ArithmeticTerm::Interm(temp));
+        self.interm_c += 1;
+
+        temp
+    }
+
+    fn instr_from_clause(
+        &mut self,
+        name: Atom,
+        arity: usize,
+    ) -> Result<Instruction, ArithmeticError> {
+        match arity {
+            1 => {
+                let a1 = self.interm.pop().unwrap();
+
+                let ninterm = if a1.interm_or(0) == 0 {
+                    self.incr_interm()
+                } else {
+                    self.interm.push(a1.clone());
+                    a1.interm_or(0)
+                };
+
+                self.get_unary_instr(name, a1, ninterm)
+            }
+            2 => {
+                let a2 = self.interm.pop().unwrap();
+                let a1 = self.interm.pop().unwrap();
+
+                let min_interm = min(a1.interm_or(0), a2.interm_or(0));
+
+                let ninterm = if min_interm == 0 {
+                    let max_interm = max(a1.interm_or(0), a2.interm_or(0));
+
+                    if max_interm == 0 {
+                        self.incr_interm()
+                    } else {
+                        self.interm.push(ArithmeticTerm::Interm(max_interm));
+                        self.interm_c = max_interm + 1;
+                        max_interm
+                    }
+                } else {
+                    self.interm.push(ArithmeticTerm::Interm(min_interm));
+                    self.interm_c = min_interm + 1;
+                    min_interm
+                };
+
+                self.get_binary_instr(name, a1, a2, ninterm)
+            }
+            _ => Err(ArithmeticError::NonEvaluableFunctor(
+                Literal::Atom(name),
+                arity,
+            )),
+        }
+    }
+
+    pub(crate) fn compile_is(
+        &mut self,
+        src: &'a Term,
+        term_loc: GenContext,
+        arg: usize,
+    ) -> Result<ArithCont, ArithmeticError>
+    {
+        let mut code = vec![];
+        let mut iter = src.iter()?;
+
+        while let Some(term_ref) = iter.next() {
+            match term_ref? {
+                ArithTermRef::Literal(c) => push_literal(&mut self.interm, c)?,
+                ArithTermRef::Var(lvl, cell, name) => {
+                    let r = if lvl == Level::Shallow {
+                        self.marker.mark_non_callable(
+                            name.clone(),
+                            arg,
+                            term_loc,
+                            cell,
+                            &mut code,
+                        )
+                    } else if term_loc.is_last() || cell.get().norm().reg_num() == 0 {
+                        self.marker.mark_var::<QueryInstruction>(
+                            name.clone(),
+                            lvl,
+                            cell,
+                            term_loc,
+                            &mut code,
+                        );
+
+                        self.marker.get_binding(&name).unwrap()
+                    } else {
+                        cell.get().norm()
+                    };
+
+                    self.interm.push(ArithmeticTerm::Reg(r));
+                }
+                ArithTermRef::Op(name, arity) => {
+                    code.push(self.instr_from_clause(name, arity)?);
+                }
+            }
+        }
+
+        Ok((code, self.interm.pop()))
+    }
+}
+
+// integer division rounding function -- 9.1.3.1.
+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)
+            } else {
+                *n
+            }
+        }
+        &Number::Fixnum(_) => *n,
+        &Number::Float(f) => {
+            let f = f.floor();
+
+            const I64_MIN_TO_F: OrderedFloat<f64> = OrderedFloat(i64::MIN as f64);
+            const I64_MAX_TO_F: OrderedFloat<f64> = OrderedFloat(i64::MAX as f64);
+
+            if I64_MIN_TO_F <= f && f <= I64_MAX_TO_F {
+                fixnum!(Number, f.into_inner() as i64, arena)
+            } else {
+                Number::Integer(arena_alloc!(Integer::from_f64(f.into_inner()).unwrap(), arena))
+            }
+        }
+        &Number::Rational(ref r) => {
+            let r_ref = r.fract_floor_ref();
+            let (mut fract, mut floor) = (Rational::new(), Integer::new());
+            (&mut fract, &mut floor).assign(r_ref);
+
+            if let Some(floor) = floor.to_i64() {
+                fixnum!(Number, floor, arena)
+            } else {
+                Number::Integer(arena_alloc!(floor, arena))
+            }
+        }
+    }
+}
+
+impl From<Fixnum> for Integer {
+    #[inline]
+    fn from(n: Fixnum) -> Integer {
+        Integer::from(n.get_num())
+    }
+}
+
+// floating point rounding function -- 9.1.4.1.
+pub(crate) fn rnd_f(n: &Number) -> f64 {
+    match n {
+        &Number::Fixnum(n) => n.get_num() as f64,
+        &Number::Integer(ref n) => n.to_f64(),
+        &Number::Float(OrderedFloat(f)) => f,
+        &Number::Rational(ref r) => r.to_f64(),
+    }
+}
+
+// floating point result function -- 9.1.4.2.
+pub(crate) fn result_f(n: &Number) -> Result<f64, EvalError> {
+    classify_float(rnd_f(n))
+}
+
+fn classify_float(f: f64) -> Result<f64, EvalError> {
+    match f.classify() {
+        FpCategory::Normal | FpCategory::Zero => Ok(f),
+        FpCategory::Infinite => {
+            if OrderedFloat(f) == OrderedFloat(f64::MAX) {
+                Ok(f)
+            } else {
+                Err(EvalError::FloatOverflow)
+            }
+        }
+        FpCategory::Nan => Err(EvalError::Undefined),
+        _ => Ok(f)
+    }
+}
+
+#[inline]
+pub(crate) fn float_fn_to_f(n: i64) -> Result<f64, EvalError> {
+    classify_float(n as f64)
+}
+
+#[inline]
+pub(crate) fn float_i_to_f(n: &Integer) -> Result<f64, EvalError> {
+    classify_float(n.to_f64())
+}
+
+#[inline]
+pub(crate) fn float_r_to_f(r: &Rational) -> Result<f64, EvalError> {
+    classify_float(r.to_f64())
+}
+
+#[inline]
+pub(crate) fn add_f(f1: f64, f2: f64) -> Result<OrderedFloat<f64>, EvalError> {
+    Ok(OrderedFloat(classify_float(f1 + f2)?))
+}
+
+#[inline]
+pub(crate) fn mul_f(f1: f64, f2: f64) -> Result<OrderedFloat<f64>, EvalError> {
+    Ok(OrderedFloat(classify_float(f1 * f2)?))
+}
+
+#[inline]
+fn div_f(f1: f64, f2: f64) -> Result<OrderedFloat<f64>, EvalError> {
+    if FpCategory::Zero == f2.classify() {
+        Err(EvalError::ZeroDivisor)
+    } else {
+        Ok(OrderedFloat(classify_float(f1 / f2)?))
+    }
+}
+
+impl Div<Number> for Number {
+    type Output = Result<Number, EvalError>;
+
+    fn div(self, rhs: Number) -> Self::Output {
+        match (self, rhs) {
+            (Number::Fixnum(n1), Number::Fixnum(n2)) => Ok(Number::Float(div_f(
+                float_fn_to_f(n1.get_num())?,
+                float_fn_to_f(n2.get_num())?,
+            )?)),
+            (Number::Fixnum(n1), Number::Integer(n2)) => Ok(Number::Float(div_f(
+                float_fn_to_f(n1.get_num())?,
+                float_i_to_f(&n2)?,
+            )?)),
+            (Number::Integer(n1), Number::Fixnum(n2)) => Ok(Number::Float(div_f(
+                float_i_to_f(&n1)?,
+                float_fn_to_f(n2.get_num())?,
+            )?)),
+            (Number::Fixnum(n1), Number::Rational(n2)) => Ok(Number::Float(div_f(
+                float_fn_to_f(n1.get_num())?,
+                float_r_to_f(&n2)?,
+            )?)),
+            (Number::Rational(n1), Number::Fixnum(n2)) => Ok(Number::Float(div_f(
+                float_r_to_f(&n1)?,
+                float_fn_to_f(n2.get_num())?,
+            )?)),
+            (Number::Fixnum(n1), Number::Float(OrderedFloat(n2))) => {
+                Ok(Number::Float(div_f(float_fn_to_f(n1.get_num())?, n2)?))
+            }
+            (Number::Float(OrderedFloat(n1)), Number::Fixnum(n2)) => {
+                Ok(Number::Float(div_f(n1, float_fn_to_f(n2.get_num())?)?))
+            }
+            (Number::Integer(n1), Number::Integer(n2)) => Ok(Number::Float(div_f(
+                float_i_to_f(&n1)?,
+                float_i_to_f(&n2)?,
+            )?)),
+            (Number::Integer(n1), Number::Float(OrderedFloat(n2))) => {
+                Ok(Number::Float(div_f(float_i_to_f(&n1)?, n2)?))
+            }
+            (Number::Float(OrderedFloat(n2)), Number::Integer(n1)) => {
+                Ok(Number::Float(div_f(n2, float_i_to_f(&n1)?)?))
+            }
+            (Number::Integer(n1), Number::Rational(n2)) => Ok(Number::Float(div_f(
+                float_i_to_f(&n1)?,
+                float_r_to_f(&n2)?,
+            )?)),
+            (Number::Rational(n2), Number::Integer(n1)) => Ok(Number::Float(div_f(
+                float_r_to_f(&n2)?,
+                float_i_to_f(&n1)?,
+            )?)),
+            (Number::Rational(n1), Number::Float(OrderedFloat(n2))) => {
+                Ok(Number::Float(div_f(float_r_to_f(&n1)?, n2)?))
+            }
+            (Number::Float(OrderedFloat(n2)), Number::Rational(n1)) => {
+                Ok(Number::Float(div_f(n2, float_r_to_f(&n1)?)?))
+            }
+            (Number::Float(OrderedFloat(f1)), Number::Float(OrderedFloat(f2))) => {
+                Ok(Number::Float(div_f(f1, f2)?))
+            }
+            (Number::Rational(r1), Number::Rational(r2)) => Ok(Number::Float(div_f(
+                float_r_to_f(&r1)?,
+                float_r_to_f(&r2)?,
+            )?)),
+        }
+    }
+}
+
+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::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()).eq(n2),
+            (&Number::Float(n1), &Number::Integer(ref n2)) => n1.eq(&OrderedFloat(n2.to_f64())),
+            (&Number::Integer(ref n1), &Number::Rational(ref n2)) => {
+                #[cfg(feature = "num")]
+                {
+                    &Rational::from(&**n1) == &**n2
+                }
+                #[cfg(not(feature = "num"))]
+                {
+                    &**n1 == &**n2
+                }
+            }
+            (&Number::Rational(ref n1), &Number::Integer(ref n2)) => {
+                #[cfg(feature = "num")]
+                {
+                    &**n1 == &Rational::from(&**n2)
+                }
+                #[cfg(not(feature = "num"))]
+                {
+                    &**n1 == &**n2
+                }
+            }
+            (&Number::Rational(ref n1), &Number::Float(n2)) => OrderedFloat(n1.to_f64()).eq(&n2),
+            (&Number::Float(n1), &Number::Rational(ref n2)) => n1.eq(&OrderedFloat(n2.to_f64())),
+            (&Number::Float(f1), &Number::Float(f2)) => f1.eq(&f2),
+            (&Number::Rational(ref r1), &Number::Rational(ref r2)) => r1.eq(&r2),
+        }
+    }
+}
+
+impl Eq for Number {}
+
+impl PartialOrd<usize> for Number {
+    #[inline]
+    fn partial_cmp(&self, rhs: &usize) -> Option<Ordering> {
+        match self {
+            Number::Fixnum(n) => {
+                let n = n.get_num();
+
+                if n < 0i64 {
+                    Some(Ordering::Less)
+                } else {
+                    (n as usize).partial_cmp(rhs)
+                }
+            }
+            Number::Integer(n) => (&**n).partial_cmp(rhs),
+            Number::Rational(r) => (&**r).partial_cmp(rhs),
+            Number::Float(f) => f.partial_cmp(&OrderedFloat(*rhs as f64)),
+        }
+    }
+}
+
+impl PartialEq<usize> for Number {
+    #[inline]
+    fn eq(&self, rhs: &usize) -> bool {
+        match self {
+            Number::Fixnum(n) => {
+                let n = n.get_num();
+
+                if n < 0i64 {
+                    false
+                } else {
+                    (n as usize).eq(rhs)
+                }
+            }
+            Number::Integer(n) => (&**n).eq(rhs),
+            Number::Rational(r) => (&**r).eq(rhs),
+            Number::Float(f) => f.eq(&OrderedFloat(*rhs as f64)),
+        }
+    }
+}
+
+impl PartialOrd for Number {
+    fn partial_cmp(&self, rhs: &Number) -> Option<Ordering> {
+        Some(self.cmp(rhs))
+    }
+}
+
+impl Ord for Number {
+    fn cmp(&self, rhs: &Number) -> Ordering {
+        match (self, rhs) {
+            (&Number::Fixnum(n1), &Number::Fixnum(n2)) => n1.get_num().cmp(&n2.get_num()),
+            (&Number::Fixnum(n1), Number::Integer(n2)) => Integer::from(n1.get_num()).cmp(&*n2),
+            (Number::Integer(n1), &Number::Fixnum(n2)) => (&**n1).cmp(&Integer::from(n2.get_num())),
+            (&Number::Fixnum(n1), Number::Rational(n2)) => Rational::from(n1.get_num()).cmp(&*n2),
+            (Number::Rational(n1), &Number::Fixnum(n2)) => {
+                (&**n1).cmp(&Rational::from(n2.get_num()))
+            }
+            (&Number::Fixnum(n1), &Number::Float(n2)) => OrderedFloat(n1.get_num() as f64).cmp(&n2),
+            (&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()).cmp(n2),
+            (&Number::Float(n1), &Number::Integer(ref n2)) => n1.cmp(&OrderedFloat(n2.to_f64())),
+            (&Number::Integer(n1), &Number::Rational(n2)) => {
+                #[cfg(feature = "num")]
+                {
+                    Rational::from(&**n1).cmp(n2)
+                }
+                #[cfg(not(feature = "num"))]
+                {
+                    (&*n1).partial_cmp(&*n2).unwrap_or(Ordering::Less)
+                }
+            }
+            (&Number::Rational(n1), &Number::Integer(n2)) => {
+                #[cfg(feature = "num")]
+                {
+                    (&**n1).cmp(&Rational::from(&**n2))
+                }
+                #[cfg(not(feature = "num"))]
+                {
+                    (&*n1).partial_cmp(&*n2).unwrap_or(Ordering::Less)
+                }
+            }
+            (&Number::Rational(n1), &Number::Float(n2)) => OrderedFloat(n1.to_f64()).cmp(&n2),
+            (&Number::Float(n1), &Number::Rational(n2)) => n1.cmp(&OrderedFloat(n2.to_f64())),
+            (&Number::Float(f1), &Number::Float(f2)) => f1.cmp(&f2),
+            (&Number::Rational(r1), &Number::Rational(r2)) => (*r1).cmp(&*r2),
+        }
+    }
+}
+
+impl TryFrom<HeapCellValue> for Number {
+    type Error = ();
+
+    #[inline]
+    fn try_from(value: HeapCellValue) -> Result<Number, Self::Error> {
+        read_heap_cell!(value,
+           (HeapCellValueTag::Cons, c) => {
+               match_untyped_arena_ptr!(c,
+                  (ArenaHeaderTag::Integer, n) => {
+                      Ok(Number::Integer(n))
+                  }
+                  (ArenaHeaderTag::Rational, n) => {
+                      Ok(Number::Rational(n))
+                  }
+                  _ => {
+                      Err(())
+                  }
+               )
+           }
+           (HeapCellValueTag::F64, n) => {
+               Ok(Number::Float(*n))
+           }
+           (HeapCellValueTag::Fixnum, n) => {
+               Ok(Number::Fixnum(n))
+           }
+           _ => {
+               Err(())
+           }
+        )
+    }
+}
+
+// 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_ref());
+
+    if power == 0 {
+        return Integer::from(1);
+    }
+
+    let mut oddand = Integer::from(1);
+
+    while power > 1 {
+        if power.is_odd() {
+            oddand *= &n;
+        }
+
+        n.pow_assign(2);
+        power >>= 1;
+    }
+
+    n * oddand
+}

src/atom_table.rs

@@ -0,0 +1,366 @@
+use crate::parser::ast::MAX_ARITY;
+use crate::raw_block::*;
+use crate::types::*;
+
+use std::borrow::Borrow;
+use std::cmp::Ordering;
+use std::hash::{Hash, Hasher};
+use std::mem;
+use std::ptr;
+use std::slice;
+use std::str;
+
+use indexmap::IndexSet;
+
+use modular_bitfield::prelude::*;
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct Atom {
+    pub index: usize,
+}
+
+const_assert!(mem::size_of::<Atom>() == 8);
+
+include!(concat!(env!("OUT_DIR"), "/static_atoms.rs"));
+
+impl<'a> From<&'a Atom> for Atom {
+    #[inline]
+    fn from(atom: &'a Atom) -> Self {
+        *atom
+    }
+}
+
+impl From<bool> for Atom {
+    #[inline]
+    fn from(value: bool) -> Self {
+        if value { atom!("true") } else { atom!("false") }
+    }
+}
+
+#[cfg(test)]
+use std::cell::RefCell;
+
+const ATOM_TABLE_INIT_SIZE: usize = 1 << 16;
+const ATOM_TABLE_ALIGN: usize = 8;
+
+#[cfg(test)]
+thread_local! {
+    static ATOM_TABLE_BUF_BASE: RefCell<*const u8> = RefCell::new(ptr::null_mut());
+}
+
+#[cfg(not(test))]
+static mut ATOM_TABLE_BUF_BASE: *const u8 = ptr::null_mut();
+
+#[cfg(test)]
+fn set_atom_tbl_buf_base(ptr: *const u8) {
+    ATOM_TABLE_BUF_BASE.with(|atom_table_buf_base| {
+        *atom_table_buf_base.borrow_mut() = ptr;
+    });
+}
+
+#[cfg(test)]
+pub(crate) fn get_atom_tbl_buf_base() -> *const u8 {
+    ATOM_TABLE_BUF_BASE.with(|atom_table_buf_base| *atom_table_buf_base.borrow())
+}
+
+#[cfg(not(test))]
+fn set_atom_tbl_buf_base(ptr: *const u8) {
+    unsafe {
+        ATOM_TABLE_BUF_BASE = ptr;
+    }
+}
+
+#[cfg(not(test))]
+pub(crate) fn get_atom_tbl_buf_base() -> *const u8 {
+    unsafe { ATOM_TABLE_BUF_BASE }
+}
+
+impl RawBlockTraits for AtomTable {
+    #[inline]
+    fn init_size() -> usize {
+        ATOM_TABLE_INIT_SIZE
+    }
+
+    #[inline]
+    fn align() -> usize {
+        ATOM_TABLE_ALIGN
+    }
+}
+
+#[bitfield]
+#[derive(Copy, Clone, Debug)]
+struct AtomHeader {
+    #[allow(unused)] m: bool,
+    len: B50,
+    #[allow(unused)] padding: B13,
+}
+
+impl AtomHeader {
+    fn build_with(len: u64) -> Self {
+        AtomHeader::new().with_len(len).with_m(false)
+    }
+}
+
+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) {
+        self.as_str().hash(hasher)
+        // hasher.write_usize(self.index)
+    }
+}
+
+#[macro_export]
+macro_rules! is_char {
+    ($s:expr) => {
+        !$s.is_empty() && $s.chars().nth(1).is_none()
+    };
+}
+
+impl Atom {
+    #[inline]
+    pub fn buf(self) -> *const u8 {
+        let ptr = self.as_ptr();
+
+        if ptr.is_null() {
+            return ptr::null();
+        }
+
+        (ptr as usize + mem::size_of::<AtomHeader>()) as *const u8
+    }
+
+    #[inline(always)]
+    pub fn is_static(self) -> bool {
+        self.index < STRINGS.len() << 3
+    }
+
+    #[inline(always)]
+    pub fn as_ptr(self) -> *const u8 {
+        if self.is_static() {
+            ptr::null()
+        } else {
+            (get_atom_tbl_buf_base() as usize + self.index - (STRINGS.len() << 3)) as *const u8
+        }
+    }
+
+    #[inline(always)]
+    pub fn from(index: usize) -> Self {
+        Self { index }
+    }
+
+    #[inline(always)]
+    pub fn len(self) -> usize {
+        if self.is_static() {
+            STRINGS[self.index >> 3].len()
+        } else {
+            unsafe { ptr::read(self.as_ptr() as *const AtomHeader).len() as _ }
+        }
+    }
+
+    #[inline(always)]
+    pub fn flat_index(self) -> u64 {
+        (self.index >> 3) as u64
+    }
+
+    pub fn as_char(self) -> Option<char> {
+        let s = self.as_str();
+        let mut it = s.chars();
+
+        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];
+            }
+
+            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))
+        }
+    }
+
+    pub fn defrock_brackets(&self, atom_tbl: &mut AtomTable) -> Self {
+        let s = self.as_str();
+
+        let s = if s.starts_with('(') && s.ends_with(')') {
+            &s['('.len_utf8()..s.len() - ')'.len_utf8()]
+        } else {
+            return *self;
+        };
+
+        atom_tbl.build_with(s)
+    }
+}
+
+unsafe fn write_to_ptr(string: &str, ptr: *mut u8) {
+    ptr::write(ptr as *mut _, AtomHeader::build_with(string.len() as u64));
+    let str_ptr = (ptr as usize + mem::size_of::<AtomHeader>()) as *mut u8;
+    ptr::copy_nonoverlapping(string.as_ptr(), str_ptr as *mut u8, string.len());
+}
+
+impl PartialOrd for Atom {
+    #[inline]
+    fn partial_cmp(&self, other: &Atom) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for Atom {
+    #[inline]
+    fn cmp(&self, other: &Atom) -> Ordering {
+        self.as_str().cmp(other.as_str())
+    }
+}
+
+#[derive(Debug)]
+pub struct AtomTable {
+    block: RawBlock<AtomTable>,
+    pub table: IndexSet<Atom>,
+}
+
+impl Drop for AtomTable {
+    fn drop(&mut self) {
+        self.block.deallocate();
+    }
+}
+
+impl AtomTable {
+    #[inline]
+    pub fn new() -> Self {
+        let table = Self {
+            block: RawBlock::new(),
+            table: IndexSet::new(),
+        };
+
+        set_atom_tbl_buf_base(table.block.base);
+        table
+    }
+
+    #[inline]
+    pub fn buf(&self) -> *const u8 {
+        self.block.base as *const u8
+    }
+
+    #[inline]
+    pub fn top(&self) -> *const u8 {
+        self.block.top
+    }
+
+    #[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(&mut self, string: &str) -> Atom {
+        if let Some(atom) = self.lookup_str(string) {
+            return atom;
+        }
+
+        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);
+
+                    if ptr.is_null() {
+                        self.block.grow();
+                        set_atom_tbl_buf_base(self.block.base);
+                    } else {
+                        break;
+                    }
+                }
+
+                ptr
+            };
+
+            let ptr_base = self.block.base as usize;
+
+            write_to_ptr(string, len_ptr);
+
+            let atom = Atom {
+                index: (STRINGS.len() << 3) + len_ptr as usize - ptr_base,
+            };
+
+            self.table.insert(atom);
+
+            atom
+        }
+    }
+}
+
+#[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,
+}
+
+impl AtomCell {
+    #[inline]
+    pub fn build_with(name: u64, arity: u16, tag: HeapCellValueTag) -> Self {
+        if arity > 0 {
+            debug_assert!(arity as usize <= MAX_ARITY);
+
+            AtomCell::new()
+                .with_name(name)
+                .with_arity(arity)
+                .with_f(false)
+                .with_tag(tag as u8)
+        } else {
+            AtomCell::new()
+                .with_name(name)
+                .with_f(false)
+                .with_tag(tag as u8)
+        }
+    }
+
+    #[inline]
+    pub fn get_index(self) -> usize {
+        self.name() as usize
+    }
+
+    #[inline]
+    pub fn get_name(self) -> Atom {
+        Atom::from(self.get_index() << 3)
+    }
+
+    #[inline]
+    pub fn get_arity(self) -> usize {
+        self.arity() as usize
+    }
+
+    #[inline]
+    pub fn get_name_and_arity(self) -> (Atom, usize) {
+        (Atom::from(self.get_index() << 3), self.get_arity())
+    }
+}

src/bin/scryer-prolog.rs

@@ -0,0 +1,11 @@
+fn main() {
+    use std::sync::atomic::Ordering;
+    use scryer_prolog::*;
+
+    ctrlc::set_handler(move || {
+        scryer_prolog::machine::INTERRUPT.store(true, Ordering::Relaxed);
+    }).unwrap();
+
+    let mut wam = machine::Machine::new();
+    wam.run_top_level();
+}

src/debray_allocator.rs

@@ -1,35 +1,40 @@
 use indexmap::IndexMap;
 
-use prolog_parser::ast::*;
+use crate::allocator::*;
+use crate::fixtures::*;
+use crate::forms::Level;
+use crate::instructions::*;
+use crate::machine::machine_indices::*;
+use crate::parser::ast::*;
+use crate::targets::CompilationTarget;
 
-use crate::prolog::allocator::*;
-use crate::prolog::fixtures::*;
-use crate::prolog::forms::*;
-use crate::prolog::machine::machine_indices::*;
-use crate::prolog::targets::*;
+use crate::temp_v;
+
+use fxhash::FxBuildHasher;
 
 use std::cell::Cell;
 use std::collections::BTreeSet;
 use std::rc::Rc;
 
-pub struct DebrayAllocator {
-    bindings: IndexMap<Rc<Var>, VarData>,
+#[derive(Debug)]
+pub(crate) struct DebrayAllocator {
+    bindings: IndexMap<Rc<String>, VarData, FxBuildHasher>,
     arg_c: usize,
     temp_lb: usize,
     arity: usize, // 0 if not at head.
-    contents: IndexMap<usize, Rc<Var>>,
+    contents: IndexMap<usize, Rc<String>, FxBuildHasher>,
     in_use: BTreeSet<usize>,
 }
 
 impl DebrayAllocator {
-    fn is_curr_arg_distinct_from(&self, var: &Var) -> bool {
+    fn is_curr_arg_distinct_from(&self, var: &String) -> bool {
         match self.contents.get(&self.arg_c) {
             Some(t_var) if **t_var != *var => true,
             _ => false,
         }
     }
 
-    fn occurs_shallowly_in_head(&self, var: &Var, r: usize) -> bool {
+    fn occurs_shallowly_in_head(&self, var: &String, r: usize) -> bool {
         match self.bindings.get(var).unwrap() {
             &VarData::Temp(_, _, ref tvd) => tvd.use_set.contains(&(GenContext::Head, r)),
             _ => false,
@@ -42,7 +47,7 @@ impl DebrayAllocator {
         in_use_range || self.in_use.contains(&r)
     }
 
-    fn alloc_with_cr(&self, var: &Var) -> usize {
+    fn alloc_with_cr(&self, var: &String) -> usize {
         match self.bindings.get(var) {
             Some(&VarData::Temp(_, _, ref tvd)) => {
                 for &(_, reg) in tvd.use_set.iter() {
@@ -68,7 +73,7 @@ impl DebrayAllocator {
         }
     }
 
-    fn alloc_with_ca(&self, var: &Var) -> usize {
+    fn alloc_with_ca(&self, var: &String) -> usize {
         match self.bindings.get(var) {
             Some(&VarData::Temp(_, _, ref tvd)) => {
                 for &(_, reg) in tvd.use_set.iter() {
@@ -96,7 +101,7 @@ impl DebrayAllocator {
         }
     }
 
-    fn alloc_in_last_goal_hint(&self, chunk_num: usize) -> Option<(Rc<Var>, usize)> {
+    fn alloc_in_last_goal_hint(&self, chunk_num: usize) -> Option<(Rc<String>, usize)> {
         // we want to allocate a register to the k^{th} parameter, par_k.
         // par_k may not be a temporary variable.
         let k = self.arg_c;
@@ -121,10 +126,11 @@ impl DebrayAllocator {
         }
     }
 
-    fn evacuate_arg<'a, Target>(&mut self, chunk_num: usize, target: &mut Vec<Target>)
-    where
-        Target: CompilationTarget<'a>,
-    {
+    fn evacuate_arg<'a, Target: CompilationTarget<'a>>(
+        &mut self,
+        chunk_num: usize,
+        code: &mut Code,
+    ) {
         match self.alloc_in_last_goal_hint(chunk_num) {
             Some((var, r)) => {
                 let k = self.arg_c;
@@ -132,7 +138,7 @@ impl DebrayAllocator {
                 if r != k {
                     let r = RegType::Temp(r);
 
-                    target.push(Target::move_to_register(r, k));
+                    code.push(Target::move_to_register(r, k));
 
                     self.contents.swap_remove(&k);
                     self.contents.insert(r.reg_num(), var.clone());
@@ -145,20 +151,17 @@ impl DebrayAllocator {
         };
     }
 
-    fn alloc_reg_to_var<'a, Target>(
+    fn alloc_reg_to_var<'a, Target: CompilationTarget<'a>>(
         &mut self,
-        var: &Var,
+        var: &String,
         lvl: Level,
         term_loc: GenContext,
-        target: &mut Vec<Target>,
-    ) -> usize
-    where
-        Target: CompilationTarget<'a>,
-    {
+        target: &mut Vec<Instruction>,
+    ) -> usize {
         match term_loc {
             GenContext::Head => {
                 if let Level::Shallow = lvl {
-                    self.evacuate_arg(0, target);
+                    self.evacuate_arg::<Target>(0, target);
                     self.alloc_with_cr(var)
                 } else {
                     self.alloc_with_ca(var)
@@ -167,7 +170,7 @@ impl DebrayAllocator {
             GenContext::Mid(_) => self.alloc_with_ca(var),
             GenContext::Last(chunk_num) => {
                 if let Level::Shallow = lvl {
-                    self.evacuate_arg(chunk_num, target);
+                    self.evacuate_arg::<Target>(chunk_num, target);
                     self.alloc_with_cr(var)
                 } else {
                     self.alloc_with_ca(var)
@@ -191,7 +194,7 @@ impl DebrayAllocator {
         final_index
     }
 
-    fn in_place(&self, var: &Var, term_loc: GenContext, r: RegType, k: usize) -> bool {
+    fn in_place(&self, var: &String, term_loc: GenContext, r: RegType, k: usize) -> bool {
         match term_loc {
             GenContext::Head if !r.is_perm() => r.reg_num() == k,
             _ => match self.bindings().get(var).unwrap() {
@@ -202,49 +205,49 @@ impl DebrayAllocator {
     }
 }
 
-impl<'a> Allocator<'a> for DebrayAllocator {
+impl Allocator for DebrayAllocator {
     fn new() -> DebrayAllocator {
         DebrayAllocator {
             arity: 0,
             arg_c: 1,
             temp_lb: 1,
-            bindings: IndexMap::new(),
-            contents: IndexMap::new(),
+            bindings: IndexMap::with_hasher(FxBuildHasher::default()),
+            contents: IndexMap::with_hasher(FxBuildHasher::default()),
             in_use: BTreeSet::new(),
         }
     }
 
-    fn mark_anon_var<Target>(&mut self, lvl: Level, term_loc: GenContext, target: &mut Vec<Target>)
-    where
-        Target: CompilationTarget<'a>,
-    {
+    fn mark_anon_var<'a, Target: CompilationTarget<'a>>(
+        &mut self,
+        lvl: Level,
+        term_loc: GenContext,
+        code: &mut Code,
+    ) {
         let r = RegType::Temp(self.alloc_reg_to_non_var());
 
         match lvl {
-            Level::Deep => target.push(Target::subterm_to_variable(r)),
+            Level::Deep => code.push(Target::subterm_to_variable(r)),
             Level::Root | Level::Shallow => {
                 let k = self.arg_c;
 
                 if let GenContext::Last(chunk_num) = term_loc {
-                    self.evacuate_arg(chunk_num, target);
+                    self.evacuate_arg::<Target>(chunk_num, code);
                 }
 
                 self.arg_c += 1;
 
-                target.push(Target::argument_to_variable(r, k));
+                code.push(Target::argument_to_variable(r, k));
             }
         };
     }
 
-    fn mark_non_var<Target>(
+    fn mark_non_var<'a, Target: CompilationTarget<'a>>(
         &mut self,
         lvl: Level,
         term_loc: GenContext,
-        cell: &Cell<RegType>,
-        target: &mut Vec<Target>,
-    ) where
-        Target: CompilationTarget<'a>,
-    {
+        cell: &'a Cell<RegType>,
+        code: &mut Code,
+    ) {
         let r = cell.get();
 
         let r = match lvl {
@@ -252,7 +255,7 @@ impl<'a> Allocator<'a> for DebrayAllocator {
                 let k = self.arg_c;
 
                 if let GenContext::Last(chunk_num) = term_loc {
-                    self.evacuate_arg(chunk_num, target);
+                    self.evacuate_arg::<Target>(chunk_num, code);
                 }
 
                 self.arg_c += 1;
@@ -268,20 +271,18 @@ impl<'a> Allocator<'a> for DebrayAllocator {
         cell.set(r);
     }
 
-    fn mark_var<Target>(
+    fn mark_var<'a, Target: CompilationTarget<'a>>(
         &mut self,
-        var: Rc<Var>,
+        var: Rc<String>,
         lvl: Level,
         cell: &'a Cell<VarReg>,
         term_loc: GenContext,
-        target: &mut Vec<Target>,
-    ) where
-        Target: CompilationTarget<'a>,
-    {
+        code: &mut Code,
+    ) {
         let (r, is_new_var) = match self.get(var.clone()) {
             RegType::Temp(0) => {
                 // here, r is temporary *and* unassigned.
-                let o = self.alloc_reg_to_var(&var, lvl, term_loc, target);
+                let o = self.alloc_reg_to_var::<Target>(&var, lvl, term_loc, code);
                 cell.set(VarReg::Norm(RegType::Temp(o)));
 
                 (RegType::Temp(o), true)
@@ -295,27 +296,25 @@ impl<'a> Allocator<'a> for DebrayAllocator {
             r => (r, false),
         };
 
-        self.mark_reserved_var(var, lvl, cell, term_loc, target, r, is_new_var);
+        self.mark_reserved_var::<Target>(var, lvl, cell, term_loc, code, r, is_new_var);
     }
 
-    fn mark_reserved_var<Target>(
+    fn mark_reserved_var<'a, Target: CompilationTarget<'a>>(
         &mut self,
-        var: Rc<Var>,
+        var: Rc<String>,
         lvl: Level,
         cell: &'a Cell<VarReg>,
         term_loc: GenContext,
-        target: &mut Vec<Target>,
+        code: &mut Code,
         r: RegType,
         is_new_var: bool,
-    ) where
-        Target: CompilationTarget<'a>,
-    {
+    ) {
         match lvl {
             Level::Root | Level::Shallow => {
                 let k = self.arg_c;
 
                 if self.is_curr_arg_distinct_from(&var) {
-                    self.evacuate_arg(term_loc.chunk_num(), target);
+                    self.evacuate_arg::<Target>(term_loc.chunk_num(), code);
                 }
 
                 self.arg_c += 1;
@@ -324,24 +323,24 @@ impl<'a> Allocator<'a> for DebrayAllocator {
 
                 if !self.in_place(&var, term_loc, r, k) {
                     if is_new_var {
-                        target.push(Target::argument_to_variable(r, k));
+                        code.push(Target::argument_to_variable(r, k));
                     } else {
-                        target.push(Target::argument_to_value(r, k));
+                        code.push(Target::argument_to_value(r, k));
                     }
                 }
             }
             Level::Deep if is_new_var => {
                 if let GenContext::Head = term_loc {
                     if self.occurs_shallowly_in_head(&var, r.reg_num()) {
-                        target.push(Target::subterm_to_value(r));
+                        code.push(Target::subterm_to_value(r));
                     } else {
-                        target.push(Target::subterm_to_variable(r));
+                        code.push(Target::subterm_to_variable(r));
                     }
                 } else {
-                    target.push(Target::subterm_to_variable(r));
+                    code.push(Target::subterm_to_variable(r));
                 }
             }
-            Level::Deep => target.push(Target::subterm_to_value(r)),
+            Level::Deep => code.push(Target::subterm_to_value(r)),
         };
 
         if !r.is_perm() {
@@ -380,12 +379,12 @@ impl<'a> Allocator<'a> for DebrayAllocator {
         self.bindings
     }
 
-    fn reset_at_head(&mut self, args: &Vec<Box<Term>>) {
+    fn reset_at_head(&mut self, args: &Vec<Term>) {
         self.reset_arg(args.len());
         self.arity = args.len();
 
         for (idx, arg) in args.iter().enumerate() {
-            if let &Term::Var(_, ref var) = arg.as_ref() {
+            if let &Term::Var(_, ref var) = arg {
                 let r = self.get(var.clone());
 
                 if !r.is_perm() && r.reg_num() == 0 {
@@ -402,4 +401,9 @@ impl<'a> Allocator<'a> for DebrayAllocator {
         self.arg_c = 1;
         self.temp_lb = arity + 1;
     }
+
+    #[inline(always)]
+    fn max_reg_allocated(&self) -> usize {
+        std::cmp::max(self.temp_lb, self.arg_c)
+    }
 }

src/examples/bimetatrans/README.md

@@ -0,0 +1,219 @@
+### BiMetaTrans 1.0
+
+BiMetaTrans(Prolog, RuleML) is a bidirectional translator capable of
+parsing and generating a well-formed sublanguage of RuleML/XML to/from
+a metalogical encoding of our own design called Prolog/'$V'. For later
+ease of reference:
+
+* Prolog/'$V' stands for "Metalogic Prolog with variable-as-'$V'-term encoding"
+* RuleML/XML stands for "RuleML in XML with any kind of rendering"
+* RuleML/xmL stands for "RuleML in minified XML"
+* RuleML/Xml stands for "RuleML in indented XML"
+
+"Minified XML" refers to XML with only necessary whitespace, between
+element names and attributes, and pairs of attributes, with all
+indentation stripped out. "Indented XML" contains indentation and
+newlines, and is usually formatted for human readers.
+
+The specification of Prolog/'$V', and of the NafHornlogEq sublanguage
+of RuleML/XML targeted by BiMetaTrans, is contained in the preprint
+[Invertible Bidirectional Metalogical Translation Between Prolog and
+RuleML/XML for Knowledge Representation and
+Querying](http://ruleml.org/papers/RuleMLXMLBiDirTransScryer.pdf) and
+its accompanying talk
+[slides](http://ruleml.org/talks/RuleMLXMLBiDirTransScryer-talk.pdf). The
+preprint and talk also describe the implementation of BiMetaTrans
+found here, and outlines a strategy for proving the invertibility of
+BiMetaTrans.
+
+BiMetaTrans exports a single public predicate subsuming its user
+API, `parse_ruleml/3`. It has two modes, each corresponding to a single
+direction of translation:
+
+```
+parse_ruleml(+AssertItems, +QueryItems, ?XML)    (Prolog->RuleML)
+parse_ruleml(?AssertItems, ?QueryItems, +XML)    (RuleML->Prolog)
+```
+
+The modes constrain the inputs to fit one of two patterns, the
+first where AssertItems and QueryItems are instantiated and XML is
+possibly a variable, and conversely for the second. Instantiated
+inputs are expected to be ground, meaning they should not contain
+free variables.
+
+We explore several examples of its use in Scryer Prolog.
+
+Loading BiMetaTrans from the Scryer REPL:
+
+```
+?- use_module('src/examples/bimetatrans/bimetatrans').
+```
+
+Using `write/1` to print the string to standard output, capturing the
+`Prolog->RuleML` direction (`write/1` is used because it does not
+print strings with escape characters, ie., `\"` for double quote):
+
+```
+?- parse_ruleml([people('Alex',male),people('Alex',female),people('Siri',female)], [], XML),
+   write(XML).
+"<Assert mapClosure="universal"><Atom><Rel>people</Rel><Ind>Alex</Ind><Data iso:type="symbol">male</Data></Atom><Atom><Rel>people</Rel><Ind>Alex</Ind><Data iso:type="symbol">female</Data></Atom><Atom><Rel>people</Rel><Ind>Siri</Ind><Data iso:type="symbol">female</Data></Atom></Assert>"   XML = "<Assert mapClosure= ...".
+```
+
+Note that the XML input can contain extraneous whitespace and
+indentation while generated XML never does (ie., the XML generated by
+BiMetaTrans is always Ruleml/xmL). `\` is used to continue ISO Prolog
+strings to the next line but is never stored to the string by the
+Prolog reader.
+
+Performing the inverse translation of the previous example
+(`RuleML->Prolog`), in RuleML/Xml:
+
+```
+?- parse_ruleml(AssertItems, QueryItems,
+                "<Assert mapClosure=\"universal\">\
+                   <Atom>\
+                           <Rel>people</Rel>\
+                           <Ind>Alex</Ind>\
+                           <Data iso:type=\"symbol\">male</Data>\
+                   </Atom>\
+                   <Atom>\
+                           <Rel>people</Rel>\
+                           <Ind>Alex</Ind>\
+                           <Data iso:type=\"symbol\">female</Data>\
+                   </Atom>\
+                   <Atom>\
+                           <Rel>people</Rel>\
+                           <Ind>Siri</Ind>\
+                           <Data iso:type=\"symbol\">female</Data>\
+                   </Atom>\
+                </Assert>").
+   AssertItems = [people('Alex',male),people('Alex',female),people('Siri',female)], QueryItems = [].
+```
+
+Double quote characters within strings must be escaped as in
+`\"`. Non-empty AssertItems and QueryItems lists generated to
+RuleML/xmL simultaneously:
+
+```
+?- parse_ruleml([a(item), b(item), c(item)], [(?- p, q, r(1), s(-2.222342432), t("attached")), (?- u, v('$V'(q)))], XML),
+   write(XML).
+"<Assert mapClosure="universal"><Atom><Rel>a</Rel><Data iso:type="symbol">item</Data></Atom><Atom><Rel>b</Rel><Data iso:type="symbol">item</Data></Atom><Atom><Rel>c</Rel><Data iso:type="symbol">item</Data></Atom></Assert><Query closure="existential"><And><Atom><Rel>p</Rel></Atom><Atom><Rel>q</Rel></Atom><Atom><Rel>r</Rel><Data iso:type="number">1</Data></Atom><Atom><Rel>s</Rel><Data iso:type="number">-2.222342432</Data></Atom><Atom><Rel>t</Rel><Data iso:type="string">"attached"</Data></Atom></And></Query><Query closure="existential"><And><Atom><Rel>u</Rel></Atom><Atom><Rel>v</Rel><Var>q</Var></Atom></And></Query>"   XML = "<Assert mapClosure= ...".
+```
+
+To insert escape characters into the printed RuleML/xmL, we use
+`writeq/1` in place of `write/1`:
+
+```
+?- parse_ruleml([a(item), b(item), c(item)], [(?- p, q, r(1), s(-2.222342432), t("attached")), (?- u, v('$V'(q)))], XML),
+   writeq(XML).
+"<Assert mapClosure=\"universal\"><Atom><Rel>a</Rel><Data iso:type=\"symbol\">item</Data></Atom><Atom><Rel>b</Rel><Data iso:type=\"symbol\">item</Data></Atom><Atom><Rel>c</Rel><Data iso:type=\"symbol\">item</Data></Atom></Assert><Query closure=\"existential\"><And><Atom><Rel>p</Rel></Atom><Atom><Rel>q</Rel></Atom><Atom><Rel>r</Rel><Data iso:type=\"number\">1</Data></Atom><Atom><Rel>s</Rel><Data iso:type=\"number\">-2.222342432</Data></Atom><Atom><Rel>t</Rel><Data iso:type=\"string\">\"attached\"</Data></Atom></And></Query><Query closure=\"existential\"><And><Atom><Rel>u</Rel></Atom><Atom><Rel>v</Rel><Var>q</Var></Atom></And></Query>"   XML = "<Assert mapClosure= ...".
+```
+
+XML can be pretty printed using a [free online XML pretty
+printer](https://codebeautify.org/xmlviewer), as here:
+
+```
+<Assert mapClosure=\"universal\">
+	<Atom>
+		<Rel>a</Rel>
+		<Data iso:type=\"symbol\">item</Data>
+	</Atom>
+	<Atom>
+		<Rel>b</Rel>
+		<Data iso:type=\"symbol\">item</Data>
+	</Atom>
+	<Atom>
+		<Rel>c</Rel>
+		<Data iso:type=\"symbol\">item</Data>
+	</Atom>
+</Assert>
+<Query closure=\"existential\">
+	<And>
+		<Atom>
+			<Rel>p</Rel>
+		</Atom>
+		<Atom>
+			<Rel>q</Rel>
+		</Atom>
+		<Atom>
+			<Rel>r</Rel>
+			<Data iso:type=\"number\">1</Data>
+		</Atom>
+		<Atom>
+			<Rel>s</Rel>
+			<Data iso:type=\"number\">-2.222342432</Data>
+		</Atom>
+		<Atom>
+			<Rel>t</Rel>
+			<Data iso:type=\"string\">\"attached\"</Data>
+		</Atom>
+	</And>
+</Query>
+<Query closure=\"existential\">
+	<And>
+		<Atom>
+			<Rel>u</Rel>
+		</Atom>
+		<Atom>
+			<Rel>v</Rel>
+			<Var>q</Var>
+		</Atom>
+	</And>
+</Query>
+```
+
+The AssertItems and QueryItems lists can then be recovered using this
+RuleML/Xml string, with the `\` character added to the end of each
+line:
+
+```
+?- parse_ruleml(AssertItems, QueryItems,
+                "<Assert mapClosure=\"universal\">\
+                    <Atom>\
+                        <Rel>a</Rel>\
+                        <Data iso:type=\"symbol\">item</Data>\
+                    </Atom>\
+                    <Atom>\
+                        <Rel>b</Rel>\
+                        <Data iso:type=\"symbol\">item</Data>\
+                    </Atom>\
+                    <Atom>\
+                        <Rel>c</Rel>\
+                        <Data iso:type=\"symbol\">item</Data>\
+                    </Atom>\
+                </Assert>\
+                <Query closure=\"existential\">\
+                    <And>\
+                        <Atom>\
+                            <Rel>p</Rel>\
+                        </Atom>\
+                        <Atom>\
+                            <Rel>q</Rel>\
+                        </Atom>\
+                        <Atom>\
+                            <Rel>r</Rel>\
+                            <Data iso:type=\"number\">1</Data>\
+                        </Atom>\
+                        <Atom>\
+                            <Rel>s</Rel>\
+                            <Data iso:type=\"number\">-2.222342432</Data>\
+                        </Atom>\
+                        <Atom>\
+                            <Rel>t</Rel>\
+                            <Data iso:type=\"string\">\"attached\"</Data>\
+                        </Atom>\
+                    </And>\
+                </Query>\
+                <Query closure=\"existential\">\
+                    <And>\
+                        <Atom>\
+                            <Rel>u</Rel>\
+                        </Atom>\
+                        <Atom>\
+                            <Rel>v</Rel>\
+                            <Var>q</Var>\
+                        </Atom>\
+                    </And>\
+                </Query>").
+   AssertItems = [a(item),b(item),c(item)], QueryItems = [(?-p,q,r(1),s(-2.222342432),t("attached")),(?-u,v('$V'(q)))].
+```

src/examples/domain.pl

@@ -22,7 +22,6 @@ verify_attributes(Var, Other, Goals) :-
                 (   Els = [] ->             % exactly one element
                     Goals = [Other=El]      % implied binding
                 ;   Goals = [],
-		    put_atts(Other, -dom(_)),
                     put_atts(Other, dom(Dc))% rescue intersection
                 )
             ;   Goals = [],

src/examples/echo_server.pl

@@ -0,0 +1,31 @@
+:- module(echo_server, [echo_server/0,
+                        echo_server/1]).
+
+:- use_module(library(format)).
+:- use_module(library(sockets)).
+
+
+echo_server :-
+    echo_server('127.0.0.1').
+
+
+echo_server(Addr) :-
+    socket_server_open(Addr:Port, ServerSocket),
+    format("echo_server: connection opened at ~w:~d~n", [Addr, Port]),
+    socket_server_accept(ServerSocket, Client, Stream, [eof_action(eof_code)]),
+    format("echo_server: connection accepted from ~a~n", [Client]),
+    !,
+    echo_loop(Stream),
+    socket_server_close(ServerSocket).
+
+
+echo_loop(Stream) :-
+    read_term(Stream, Term, []),
+    (  Term == end_of_file ->
+       true
+    ;
+       format("received: ~w~n", [Term]),
+       !,
+       echo_loop(Stream)
+    ).
+

src/examples/least_time.pl

@@ -0,0 +1,51 @@
+/*  least_time.pl
+ *
+ *  By Mark Thom, 2020
+ *
+ *  find_min_time/2 solves a problem sometimes posed in the first round
+ *  of Google interviews: given a time of day in 24 H format, what is the
+ *  lexicographically least permutation of the time that is itself a
+ *  valid time in 24 H format?
+ *
+ *  Full generality is achieved using the reif library.
+ */
+
+:- module(least_time, [find_min_time/2,
+                       write_time_nl/1]).
+
+
+:- use_module(library(dcgs)).
+:- use_module(library(format)).
+:- use_module(library(lists)).
+:- use_module(library(reif)).
+
+
+valid_time([H1,H2,M1,M2], T) :-
+    memberd_t(H1, [0,1,2], TH1),
+    memberd_t(H2, [0,1,2,3,4,5,6,7,8,9], TH2),
+    memberd_t(M1, [0,1,2,3,4,5], TM1),
+    memberd_t(M2, [0,1,2,3,4,5,6,7,8,9], TM2),
+    (  maplist(=(true), [TH1, TH2, TM1, TM2]) ->
+       (  H1 =:= 2 ->
+          (  H2 =< 3 ->
+             T = true
+          ;  T = false
+          )
+       ;  T = true
+       )
+    ;  T = false
+    ).
+
+
+permuted_times(Time, PermutedTimes) :-
+    setof(P, permutation(Time, P), PermutedTimes0),
+    tfilter(valid_time, PermutedTimes0, PermutedTimes).
+
+
+find_min_time(Time, Min) :-
+    valid_time(Time, true),
+    permuted_times(Time, [Min|_]).
+
+
+write_time_nl(Time) :-
+    format("\"~w~w:~w~w\"~n", Time).

src/examples/plres.pl

@@ -31,6 +31,7 @@
 
 :- use_module(library(dcgs)).
 :- use_module(library(dif)).
+:- use_module(library(format)).
 :- use_module(library(lists)).
 
 pl_resolution(Clauses0, Chain) :-

src/examples/utf8.pl

@@ -0,0 +1,31 @@
+:- use_module(library(charsio)).
+:- use_module(library(lists)).
+
+:- initialization(unit_test).
+
+unit_test :-
+  chars_utf8bytes("a£\x2124\", Bs),
+  Bs = [97, 194, 163, 226, 132, 164],
+  chars_utf8bytes(Cs, Bs),
+  Cs = "a£\x2124\".
+
+write_f :-
+  open('x.txt', write, Stream, [type(binary)]),
+  F = put_byte(Stream),
+  chars_utf8bytes("£\x2124\\x2764\\x1F496\\n", Bs),
+  maplist(F, Bs),
+  close(Stream).
+
+get_bytes(Stream, Res) :- get_bytes(Stream, [], Res).
+get_bytes(Stream, Acc, Res) :-
+  get_byte(Stream, B),
+  (B =:= -1 ->
+    reverse(Acc, Res)
+  ; get_bytes(Stream, [B|Acc], Res)).
+
+read_f :-
+  open('x.txt', read, Stream, [type(binary)]),
+  get_bytes(Stream, Bs),
+  chars_utf8bytes(Cs, Bs),
+  write(Cs),
+  close(Stream).

src/fixtures.rs

@@ -1,9 +1,8 @@
-use prolog_parser::ast::*;
+use crate::parser::ast::*;
 
-use crate::prolog::allocator::*;
-use crate::prolog::forms::*;
-use crate::prolog::instructions::*;
-use crate::prolog::iterators::*;
+use crate::forms::*;
+use crate::instructions::*;
+use crate::iterators::*;
 
 use indexmap::{IndexMap, IndexSet};
 
@@ -14,22 +13,24 @@ use std::rc::Rc;
 use std::vec::Vec;
 
 // labeled with chunk numbers.
-pub enum VarStatus {
+#[derive(Debug)]
+pub(crate) enum VarStatus {
     Perm(usize),
     Temp(usize, TempVarData), // Perm(chunk_num) | Temp(chunk_num, _)
 }
 
-pub type OccurrenceSet = BTreeSet<(GenContext, usize)>;
+pub(crate) type OccurrenceSet = BTreeSet<(GenContext, usize)>;
 
 // Perm: 0 initially, a stack register once processed.
 // Temp: labeled with chunk_num and temp offset (unassigned if 0).
-pub enum VarData {
+#[derive(Debug)]
+pub(crate) enum VarData {
     Perm(usize),
     Temp(usize, usize, TempVarData),
 }
 
 impl VarData {
-    pub fn as_reg_type(&self) -> RegType {
+    pub(crate) fn as_reg_type(&self) -> RegType {
         match self {
             &VarData::Temp(_, r, _) => RegType::Temp(r),
             &VarData::Perm(r) => RegType::Perm(r),
@@ -37,15 +38,16 @@ impl VarData {
     }
 }
 
-pub struct TempVarData {
-    pub last_term_arity: usize,
-    pub use_set: OccurrenceSet,
-    pub no_use_set: BTreeSet<usize>,
-    pub conflict_set: BTreeSet<usize>,
+#[derive(Debug)]
+pub(crate) struct TempVarData {
+    pub(crate) last_term_arity: usize,
+    pub(crate) use_set: OccurrenceSet,
+    pub(crate) no_use_set: BTreeSet<usize>,
+    pub(crate) conflict_set: BTreeSet<usize>,
 }
 
 impl TempVarData {
-    pub fn new(last_term_arity: usize) -> Self {
+    pub(crate) fn new(last_term_arity: usize) -> Self {
         TempVarData {
             last_term_arity: last_term_arity,
             use_set: BTreeSet::new(),
@@ -54,7 +56,7 @@ impl TempVarData {
         }
     }
 
-    pub fn uses_reg(&self, reg: usize) -> bool {
+    pub(crate) fn uses_reg(&self, reg: usize) -> bool {
         for &(_, nreg) in self.use_set.iter() {
             if reg == nreg {
                 return true;
@@ -64,7 +66,7 @@ impl TempVarData {
         return false;
     }
 
-    pub fn populate_conflict_set(&mut self) {
+    pub(crate) fn populate_conflict_set(&mut self) {
         if self.last_term_arity > 0 {
             let arity = self.last_term_arity;
             let mut conflict_set: BTreeSet<usize> = (1..arity).collect();
@@ -80,30 +82,30 @@ impl TempVarData {
 
 type VariableFixture<'a> = (VarStatus, Vec<&'a Cell<VarReg>>);
 
-pub struct VariableFixtures<'a>{
-    perm_vars: IndexMap<Rc<Var>, VariableFixture<'a>>,
-    last_chunk_temp_vars: IndexSet<Rc<Var>>
+#[derive(Debug)]
+pub(crate) struct VariableFixtures<'a> {
+    perm_vars: IndexMap<Rc<String>, VariableFixture<'a>>,
+    last_chunk_temp_vars: IndexSet<Rc<String>>,
 }
 
 impl<'a> VariableFixtures<'a> {
-    pub fn new() -> Self {
+    pub(crate) fn new() -> Self {
         VariableFixtures {
             perm_vars: IndexMap::new(),
-            last_chunk_temp_vars: IndexSet::new()
+            last_chunk_temp_vars: IndexSet::new(),
         }
-                          
     }
 
-    pub fn insert(&mut self, var: Rc<Var>, vs: VariableFixture<'a>) {
+    pub(crate) fn insert(&mut self, var: Rc<String>, vs: VariableFixture<'a>) {
         self.perm_vars.insert(var, vs);
     }
 
-    pub fn insert_last_chunk_temp_var(&mut self, var: Rc<Var>) {
+    pub(crate) fn insert_last_chunk_temp_var(&mut self, var: Rc<String>) {
         self.last_chunk_temp_vars.insert(var);
     }
 
     // computes no_use and conflict sets for all temp vars.
-    pub fn populate_restricting_sets(&mut self) {
+    pub(crate) fn populate_restricting_sets(&mut self) {
         // three stages:
         // 1. move the use sets of each variable to a local IndexMap, use_set
         // (iterate mutably, swap mutable refs).
@@ -113,7 +115,7 @@ impl<'a> VariableFixtures<'a> {
         // Compute the conflict set of u.
 
         // 1.
-        let mut use_sets: IndexMap<Rc<Var>, OccurrenceSet> = IndexMap::new();
+        let mut use_sets: IndexMap<Rc<String>, OccurrenceSet> = IndexMap::new();
 
         for (var, &mut (ref mut var_status, _)) in self.iter_mut() {
             if let &mut VarStatus::Temp(_, ref mut var_data) = var_status {
@@ -151,11 +153,11 @@ impl<'a> VariableFixtures<'a> {
         }
     }
 
-    fn get_mut(&mut self, u: Rc<Var>) -> Option<&mut VariableFixture<'a>> {
+    fn get_mut(&mut self, u: Rc<String>) -> Option<&mut VariableFixture<'a>> {
         self.perm_vars.get_mut(&u)
     }
 
-    fn iter_mut(&mut self) -> indexmap::map::IterMut<Rc<Var>, VariableFixture<'a>> {
+    fn iter_mut(&mut self) -> indexmap::map::IterMut<Rc<String>, VariableFixture<'a>> {
         self.perm_vars.iter_mut()
     }
 
@@ -168,7 +170,7 @@ impl<'a> VariableFixtures<'a> {
         };
     }
 
-    pub fn vars_above_threshold(&self, index: usize) -> usize {
+    pub(crate) fn vars_above_threshold(&self, index: usize) -> usize {
         let mut var_count = 0;
 
         for &(ref var_status, _) in self.values() {
@@ -182,7 +184,7 @@ impl<'a> VariableFixtures<'a> {
         var_count
     }
 
-    pub fn mark_vars_in_chunk<I>(&mut self, iter: I, lt_arity: usize, term_loc: GenContext)
+    pub(crate) fn mark_vars_in_chunk<I>(&mut self, iter: I, lt_arity: usize, term_loc: GenContext)
     where
         I: Iterator<Item = TermRef<'a>>,
     {
@@ -216,19 +218,19 @@ impl<'a> VariableFixtures<'a> {
         }
     }
 
-    pub fn into_iter(self) -> indexmap::map::IntoIter<Rc<Var>, VariableFixture<'a>> {
+    pub(crate) fn into_iter(self) -> indexmap::map::IntoIter<Rc<String>, VariableFixture<'a>> {
         self.perm_vars.into_iter()
     }
 
-    fn values(&self) -> indexmap::map::Values<Rc<Var>, VariableFixture<'a>> {
+    fn values(&self) -> indexmap::map::Values<Rc<String>, VariableFixture<'a>> {
         self.perm_vars.values()
     }
 
-    pub fn size(&self) -> usize {
+    pub(crate) fn size(&self) -> usize {
         self.perm_vars.len()
     }
 
-    pub fn set_perm_vals(&self, has_deep_cuts: bool) {
+    pub(crate) fn set_perm_vals(&self, has_deep_cuts: bool) {
         let mut values_vec: Vec<_> = self
             .values()
             .filter_map(|ref v| match &v.0 {
@@ -249,68 +251,67 @@ impl<'a> VariableFixtures<'a> {
     }
 }
 
-pub struct UnsafeVarMarker {
-    pub unsafe_vars: IndexMap<RegType, bool>,
+#[derive(Debug)]
+pub(crate) struct UnsafeVarMarker {
+    pub(crate) unsafe_vars: IndexMap<RegType, usize>,
+    pub(crate) safe_vars: IndexSet<RegType>,
 }
 
 impl UnsafeVarMarker {
-    pub fn new() -> Self {
+    pub(crate) fn new() -> Self {
         UnsafeVarMarker {
             unsafe_vars: IndexMap::new(),
+            safe_vars: IndexSet::new(),
         }
     }
 
-    pub fn record_unsafe_vars<'a, Alloc: Allocator<'a>>(
-        &mut self,
-        fixtures: &VariableFixtures,
-        marker: &Alloc
-    ) {
-        for &(_, ref cb) in fixtures.values() {           
-            if let Some(index) = cb.first() {
-                if !self.unsafe_vars.contains_key(&index.get().norm()) {
-                    self.unsafe_vars.insert(index.get().norm(), false);
-                }
-            }
-        }
-
-        for var in fixtures.last_chunk_temp_vars.iter().cloned() {
-            let r = marker.get(var);
-            self.unsafe_vars.insert(r, false);
+    pub(crate) fn from_safe_vars(safe_vars: IndexSet<RegType>) -> Self {
+        UnsafeVarMarker {
+            unsafe_vars: IndexMap::new(),
+            safe_vars,
         }
     }
 
-    pub fn mark_safe_vars(&mut self, query_instr: &QueryInstruction) {
+    pub(crate) fn mark_safe_vars(&mut self, query_instr: &Instruction) -> bool {
         match query_instr {
-            QueryInstruction::PutVariable(RegType::Temp(r), _) => {
-                if let Some(found) = self.unsafe_vars.get_mut(&RegType::Temp(*r)) {
-                    *found = true;
-                }
+            &Instruction::PutVariable(r @ RegType::Temp(_), _) |
+            &Instruction::SetVariable(r) => {
+                self.safe_vars.insert(r);
+                true
             }
-            QueryInstruction::SetVariable(reg) => {
-                if let Some(found) = self.unsafe_vars.get_mut(reg) {
-                    *found = true;
-                }
+            _ => false,
+        }
+    }
+
+    pub(crate) fn mark_phase(&mut self, query_instr: &Instruction, phase: usize) {
+        match query_instr {
+            &Instruction::PutValue(r @ RegType::Perm(_), _) |
+            &Instruction::SetValue(r) => {
+                let p = self.unsafe_vars.entry(r).or_insert(0);
+                *p = phase;
             }
             _ => {}
         }
     }
 
-    pub fn mark_unsafe_vars(&mut self, query_instr: &mut QueryInstruction) {
+    pub(crate) fn mark_unsafe_vars(&mut self, query_instr: &mut Instruction, phase: usize) {
         match query_instr {
-            &mut QueryInstruction::PutValue(RegType::Perm(i), arg) => {
-                if let Some(found) = self.unsafe_vars.get_mut(&RegType::Perm(i)) {
-                    if !*found {
-                        *found = true;
-                        *query_instr = QueryInstruction::PutUnsafeValue(i, arg);
+            &mut Instruction::PutValue(RegType::Perm(i), arg) => {
+                if let Some(p) = self.unsafe_vars.swap_remove(&RegType::Perm(i)) {
+                    if p == phase {
+                        *query_instr = Instruction::PutUnsafeValue(i, arg);
+                        self.safe_vars.insert(RegType::Perm(i));
+                    } else {
+                        self.unsafe_vars.insert(RegType::Perm(i), p);
                     }
                 }
             }
-            &mut QueryInstruction::SetValue(reg) => {
-                if let Some(found) = self.unsafe_vars.get_mut(&reg) {
-                    if !*found {
-                        *found = true;
-                        *query_instr = QueryInstruction::SetLocalValue(reg);
-                    }
+            &mut Instruction::SetValue(r) => {
+                if !self.safe_vars.contains(&r) {
+                    *query_instr = Instruction::SetLocalValue(r);
+
+                    self.safe_vars.insert(r);
+                    self.unsafe_vars.remove(&r);
                 }
             }
             _ => {}

src/forms.rs

@@ -0,0 +1,920 @@
+use crate::arena::*;
+use crate::atom_table::*;
+use crate::instructions::*;
+use crate::machine::heap::*;
+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::rug::{Integer, Rational};
+use crate::types::*;
+
+use fxhash::FxBuildHasher;
+
+use indexmap::{IndexMap, IndexSet};
+use ordered_float::OrderedFloat;
+
+use std::cell::Cell;
+use std::collections::VecDeque;
+use std::convert::TryFrom;
+use std::fmt;
+use std::ops::AddAssign;
+use std::path::PathBuf;
+use std::rc::Rc;
+
+use crate::{is_infix, is_postfix};
+
+pub type PredicateKey = (Atom, usize); // name, arity.
+
+pub type Predicate = Vec<PredicateClause>;
+
+// vars of predicate, toplevel offset.  Vec<Term> is always a vector
+// of vars (we get their adjoining cells this way).
+pub type JumpStub = Vec<Term>;
+
+#[derive(Debug, Clone)]
+pub enum TopLevel {
+    Fact(Term), // Term, line_num, col_num
+    Predicate(Predicate),
+    Query(Vec<QueryTerm>),
+    Rule(Rule), // Rule, line_num, col_num
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum AppendOrPrepend {
+    Append,
+    Prepend,
+}
+
+impl AppendOrPrepend {
+    #[inline]
+    pub(crate) fn is_append(self) -> bool {
+        match self {
+            AppendOrPrepend::Append => true,
+            AppendOrPrepend::Prepend => false,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Level {
+    Deep,
+    Root,
+    Shallow,
+}
+
+impl Level {
+    pub(crate) fn child_level(self) -> Level {
+        match self {
+            Level::Root => Level::Shallow,
+            _ => Level::Deep,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum CallPolicy {
+    Default,
+    Counted,
+}
+
+#[derive(Debug, Clone)]
+pub enum QueryTerm {
+    // register, clause type, subterms, clause call policy.
+    Clause(Cell<RegType>, ClauseType, Vec<Term>, CallPolicy),
+    BlockedCut, // a cut which is 'blocked by letters', like the P term in P -> Q.
+    UnblockedCut(Cell<VarReg>),
+    GetLevelAndUnify(Cell<VarReg>, Rc<String>),
+    Jump(JumpStub),
+}
+
+impl QueryTerm {
+    pub(crate) fn set_call_policy(&mut self, cp: CallPolicy) {
+        match self {
+            &mut QueryTerm::Clause(_, _, _, ref mut clause_cp) => *clause_cp = cp,
+            _ => {}
+        }
+    }
+
+    pub(crate) fn arity(&self) -> usize {
+        match self {
+            &QueryTerm::Clause(_, _, ref subterms, ..) => subterms.len(),
+            &QueryTerm::BlockedCut | &QueryTerm::UnblockedCut(..) => 0,
+            &QueryTerm::Jump(ref vars) => vars.len(),
+            &QueryTerm::GetLevelAndUnify(..) => 1,
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct Rule {
+    pub(crate) head: (Atom, Vec<Term>, QueryTerm),
+    pub(crate) clauses: Vec<QueryTerm>,
+}
+
+#[derive(Clone, Debug, Hash)]
+pub enum ListingSource {
+    DynamicallyGenerated,
+    File(Atom, PathBuf), // filename, path
+    User,
+}
+
+impl ListingSource {
+    pub(crate) fn from_file_and_path(filename: Atom, path_buf: PathBuf) -> Self {
+        ListingSource::File(filename, path_buf)
+    }
+}
+
+pub trait ClauseInfo {
+    fn is_consistent(&self, clauses: &PredicateQueue) -> bool {
+        match clauses.first() {
+            Some(cl) => {
+                self.name() == ClauseInfo::name(cl) && self.arity() == ClauseInfo::arity(cl)
+            }
+            None => true,
+        }
+    }
+
+    fn name(&self) -> Option<Atom>;
+    fn arity(&self) -> usize;
+}
+
+impl ClauseInfo for PredicateKey {
+    #[inline]
+    fn name(&self) -> Option<Atom> {
+        Some(self.0)
+    }
+
+    #[inline]
+    fn arity(&self) -> usize {
+        self.1
+    }
+}
+
+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.
+                            2 => terms[0].name(),
+                            _ => Some(*name),
+                        }
+                    }
+                    _ => Some(*name), //str_buf),
+                }
+            }
+            Term::Literal(_, Literal::Atom(name)) => Some(*name),
+            _ => None,
+        }
+    }
+
+    fn arity(&self) -> usize {
+        match self {
+            Term::Clause(_, name, terms) => match name.as_str() {
+                ":-" => match terms.len() {
+                    1 => 0,
+                    2 => terms[0].arity(),
+                    _ => terms.len(),
+                },
+                _ => terms.len(),
+            },
+            _ => 0,
+        }
+    }
+}
+
+impl ClauseInfo for Rule {
+    fn name(&self) -> Option<Atom> {
+        Some(self.head.0)
+    }
+
+    fn arity(&self) -> usize {
+        self.head.1.len()
+    }
+}
+
+impl ClauseInfo for PredicateClause {
+    fn name(&self) -> Option<Atom> {
+        match self {
+            &PredicateClause::Fact(ref term, ..) => term.name(),
+            &PredicateClause::Rule(ref rule, ..) => rule.name(),
+        }
+    }
+
+    fn arity(&self) -> usize {
+        match self {
+            &PredicateClause::Fact(ref term, ..) => term.arity(),
+            &PredicateClause::Rule(ref rule, ..) => rule.arity(),
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub enum PredicateClause {
+    Fact(Term),
+    Rule(Rule),
+}
+
+impl PredicateClause {
+    pub(crate) fn args(&self) -> Option<&[Term]> {
+        match self {
+            PredicateClause::Fact(term, ..) => match term {
+                Term::Clause(_, _, args) => Some(&args),
+                _ => None,
+            },
+            PredicateClause::Rule(rule, ..) => {
+                if rule.head.1.is_empty() {
+                    None
+                } else {
+                    Some(&rule.head.1)
+                }
+            }
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct ClauseSpan {
+    pub left: usize,
+    pub right: usize,
+    pub instantiated_arg_index: usize,
+}
+
+#[derive(Debug, Clone)]
+pub enum ModuleSource {
+    Library(Atom),
+    File(Atom),
+}
+
+impl ModuleSource {
+    pub(crate) fn as_functor_stub(&self) -> MachineStub {
+        match self {
+            ModuleSource::Library(name) => {
+                functor!(atom!("library"), [atom(name)])
+            }
+            ModuleSource::File(name) => {
+                functor!(name)
+            }
+        }
+    }
+}
+
+#[derive(Clone, Copy, Hash, Debug)]
+pub enum MetaSpec {
+    Minus,
+    Plus,
+    Either,
+    Colon,
+    RequiresExpansionWithArgument(usize),
+}
+
+#[derive(Debug, Clone)]
+pub enum Declaration {
+    Dynamic(Atom, usize),
+    MetaPredicate(Atom, Atom, Vec<MetaSpec>), // module name, name, meta-specs
+    Module(ModuleDecl),
+    NonCountedBacktracking(Atom, usize), // name, arity
+    Op(OpDecl),
+    UseModule(ModuleSource),
+    UseQualifiedModule(ModuleSource, IndexSet<ModuleExport>),
+}
+
+#[derive(Debug, Clone, Copy, Eq, Hash, PartialEq, Ord, PartialOrd)]
+pub struct OpDecl {
+    pub(crate) op_desc: OpDesc,
+    pub(crate) name: Atom,
+}
+
+#[inline(always)]
+pub(crate) fn fixity(spec: u32) -> Fixity {
+    match spec {
+        XFY | XFX | YFX => Fixity::In,
+        XF | YF => Fixity::Post,
+        FX | FY => Fixity::Pre,
+        _ => unreachable!(),
+    }
+}
+
+
+impl OpDecl {
+    #[inline]
+    pub(crate) fn new(op_desc: OpDesc, name: Atom) -> Self {
+        Self { op_desc, name }
+    }
+
+    #[inline]
+    pub(crate) fn remove(&mut self, op_dir: &mut OpDir) {
+        let prec = self.op_desc.get_prec();
+        self.op_desc.set(0, self.op_desc.get_spec());
+
+        self.insert_into_op_dir(op_dir);
+        self.op_desc.set(prec, self.op_desc.get_spec());
+    }
+
+    pub(crate) fn insert_into_op_dir(&self, op_dir: &mut OpDir) -> Option<OpDesc> {
+        let key = (self.name, fixity(self.op_desc.get_spec() as u32));
+
+        match op_dir.get_mut(&key) {
+            Some(cell) => {
+                let (old_prec, old_spec) = cell.get();
+                cell.set(self.op_desc.get_prec(), self.op_desc.get_spec());
+                return Some(OpDesc::build_with(old_prec, old_spec));
+            }
+            None => {}
+        }
+
+        op_dir.insert(key, self.op_desc)
+    }
+
+    pub(crate) fn submit(
+        &self,
+        existing_desc: Option<CompositeOpDesc>,
+        op_dir: &mut OpDir,
+    ) -> Result<(), SessionError> {
+        let (spec, name) = (self.op_desc.get_spec(), self.name.clone());
+
+        if is_infix!(spec as u32) {
+            if let Some(desc) = existing_desc {
+                if desc.post > 0 {
+                    return Err(SessionError::OpIsInfixAndPostFix(name));
+                }
+            }
+        }
+
+        if is_postfix!(spec as u32) {
+            if let Some(desc) = existing_desc {
+                if desc.inf > 0 {
+                    return Err(SessionError::OpIsInfixAndPostFix(name));
+                }
+            }
+        }
+
+        self.insert_into_op_dir(op_dir);
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+pub enum AtomOrString {
+    Atom(Atom),
+    String(String),
+}
+
+impl AtomOrString {
+    #[inline]
+    pub fn as_atom(&self, atom_tbl: &mut AtomTable) -> Atom {
+        match self {
+            &AtomOrString::Atom(atom) => {
+                atom
+            }
+            AtomOrString::String(string) => {
+                atom_tbl.build_with(&string)
+            }
+        }
+    }
+
+    #[inline]
+    pub fn as_str(&self) -> &str {
+        match self {
+            AtomOrString::Atom(atom) if atom == &atom!("[]") => "",
+            AtomOrString::Atom(atom) => atom.as_str(),
+            AtomOrString::String(string) => string.as_str(),
+        }
+    }
+
+    #[inline]
+    pub fn to_string(self) -> String {
+        match self {
+            AtomOrString::Atom(atom) => {
+                atom.as_str().to_owned()
+            }
+            AtomOrString::String(string) => {
+                string
+            }
+        }
+    }
+}
+
+pub(crate) fn fetch_atom_op_spec(
+    name: Atom,
+    spec: Option<OpDesc>,
+    op_dir: &OpDir,
+) -> Option<OpDesc> {
+    fetch_op_spec_from_existing(name, 2, spec, op_dir)
+        .or_else(|| fetch_op_spec_from_existing(name, 1, spec, op_dir))
+}
+
+pub(crate) fn fetch_op_spec_from_existing(
+    name: Atom,
+    arity: usize,
+    op_desc: Option<OpDesc>,
+    op_dir: &OpDir,
+) -> Option<OpDesc> {
+    if let Some(ref op_desc) = &op_desc {
+        if op_desc.arity() != arity {
+            /* it's possible to extend operator functors with
+             * additional terms. When that happens,
+             * void the op_spec by returning None. */
+            return None;
+        }
+    }
+
+    op_desc.or_else(|| fetch_op_spec(name, arity, op_dir))
+}
+
+pub(crate) fn fetch_op_spec(name: Atom, arity: usize, op_dir: &OpDir) -> Option<OpDesc> {
+    match arity {
+        2 => op_dir.get(&(name, Fixity::In)).and_then(|op_desc| {
+            if op_desc.get_prec() > 0 {
+                Some(*op_desc)
+            } else {
+                None
+            }
+        }),
+        1 => {
+            if let Some(op_desc) = op_dir.get(&(name.clone(), Fixity::Pre)) {
+                if op_desc.get_prec() > 0 {
+                    return Some(*op_desc);
+                }
+            }
+
+            op_dir.get(&(name, Fixity::Post)).and_then(|op_desc| {
+                if op_desc.get_prec() > 0 {
+                    Some(*op_desc)
+                } else {
+                    None
+                }
+            })
+        }
+        0 => {
+            fetch_atom_op_spec(name, None, op_dir)
+        }
+        _ => None,
+    }
+}
+
+pub(crate) type ModuleDir = IndexMap<Atom, Module, FxBuildHasher>;
+
+#[derive(Debug, Clone, Eq, Hash, PartialEq)]
+pub enum ModuleExport {
+    OpDecl(OpDecl),
+    PredicateKey(PredicateKey),
+}
+
+#[derive(Debug, Clone)]
+pub struct ModuleDecl {
+    pub(crate) name: Atom,
+    pub(crate) exports: Vec<ModuleExport>,
+}
+
+#[derive(Debug)]
+pub struct Module {
+    pub(crate) module_decl: ModuleDecl,
+    pub(crate) code_dir: CodeDir,
+    pub(crate) op_dir: OpDir,
+    pub(crate) meta_predicates: MetaPredicateDir,
+    pub(crate) extensible_predicates: ExtensiblePredicates,
+    pub(crate) local_extensible_predicates: LocalExtensiblePredicates,
+    pub(crate) listing_src: ListingSource,
+}
+
+// Module's and related types are defined in forms.
+impl Module {
+    pub(crate) fn new(
+        module_decl: ModuleDecl,
+        listing_src: ListingSource,
+    ) -> Self {
+        Module {
+            module_decl,
+            code_dir: CodeDir::with_hasher(FxBuildHasher::default()),
+            op_dir: default_op_dir(),
+            meta_predicates: MetaPredicateDir::with_hasher(FxBuildHasher::default()),
+            extensible_predicates: ExtensiblePredicates::with_hasher(FxBuildHasher::default()),
+            local_extensible_predicates: LocalExtensiblePredicates::with_hasher(
+                FxBuildHasher::default(),
+            ),
+            listing_src,
+        }
+    }
+
+    pub(crate) fn new_in_situ(module_decl: ModuleDecl) -> Self {
+        Module {
+            module_decl,
+            code_dir: CodeDir::with_hasher(FxBuildHasher::default()),
+            op_dir: OpDir::with_hasher(FxBuildHasher::default()),
+            meta_predicates: MetaPredicateDir::with_hasher(FxBuildHasher::default()),
+            extensible_predicates: ExtensiblePredicates::with_hasher(FxBuildHasher::default()),
+            local_extensible_predicates: LocalExtensiblePredicates::with_hasher(
+                FxBuildHasher::default()
+            ),
+            listing_src: ListingSource::DynamicallyGenerated,
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub enum Number {
+    Float(OrderedFloat<f64>),
+    Integer(TypedArenaPtr<Integer>),
+    Rational(TypedArenaPtr<Rational>),
+    Fixnum(Fixnum),
+}
+
+impl Default for Number {
+    fn default() -> Self {
+        Number::Fixnum(Fixnum::build_with(0))
+    }
+}
+
+impl fmt::Display for Number {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Number::Float(fl) => write!(f, "{}", fl),
+            Number::Integer(n) => write!(f, "{}", n),
+            Number::Rational(r) => write!(f, "{}", r),
+            Number::Fixnum(n) => write!(f, "{}", n.get_num()),
+        }
+    }
+}
+
+pub trait ArenaFrom<T> {
+    fn arena_from(value: T, arena: &mut Arena) -> Self;
+}
+
+impl ArenaFrom<Integer> for Number {
+    #[inline]
+    fn arena_from(value: Integer, arena: &mut Arena) -> Number {
+        Number::Integer(arena_alloc!(value, arena))
+    }
+}
+
+impl ArenaFrom<Rational> for Number {
+    #[inline]
+    fn arena_from(value: Rational, arena: &mut Arena) -> Number {
+        Number::Rational(arena_alloc!(value, arena))
+    }
+}
+
+impl ArenaFrom<usize> for Number {
+    #[inline]
+    fn arena_from(value: usize, arena: &mut Arena) -> Number {
+        match i64::try_from(value) {
+            Ok(value) => Fixnum::build_with_checked(value)
+                .map(Number::Fixnum)
+                .unwrap_or_else(|_| Number::Integer(arena_alloc!(Integer::from(value), arena))),
+            Err(_) => Number::Integer(arena_alloc!(Integer::from(value), arena)),
+        }
+    }
+}
+
+impl ArenaFrom<u64> for Number {
+    #[inline]
+    fn arena_from(value: u64, arena: &mut Arena) -> Number {
+        match i64::try_from(value) {
+            Ok(value) => Fixnum::build_with_checked(value)
+                .map(Number::Fixnum)
+                .unwrap_or_else(|_| Number::Integer(arena_alloc!(Integer::from(value), arena))),
+            Err(_) => Number::Integer(arena_alloc!(Integer::from(value), arena)),
+        }
+    }
+}
+
+impl ArenaFrom<i64> for Number {
+    #[inline]
+    fn arena_from(value: i64, arena: &mut Arena) -> Number {
+        Fixnum::build_with_checked(value)
+            .map(Number::Fixnum)
+            .unwrap_or_else(|_| Number::Integer(arena_alloc!(Integer::from(value), arena)))
+    }
+}
+
+impl ArenaFrom<isize> for Number {
+    #[inline]
+    fn arena_from(value: isize, arena: &mut Arena) -> Number {
+        Fixnum::build_with_checked(value as i64)
+            .map(Number::Fixnum)
+            .unwrap_or_else(|_| Number::Integer(arena_alloc!(Integer::from(value), arena)))
+    }
+}
+
+impl ArenaFrom<u32> for Number {
+    #[inline]
+    fn arena_from(value: u32, _arena: &mut Arena) -> Number {
+        Number::Fixnum(Fixnum::build_with(value as i64))
+    }
+}
+
+impl ArenaFrom<i32> for Number {
+    #[inline]
+    fn arena_from(value: i32, _arena: &mut Arena) -> Number {
+        Number::Fixnum(Fixnum::build_with(value as i64))
+    }
+}
+
+impl ArenaFrom<Number> for Literal {
+    #[inline]
+    fn arena_from(value: Number, arena: &mut Arena) -> Literal {
+        match value {
+            Number::Fixnum(n) => Literal::Fixnum(n),
+            Number::Integer(n) => Literal::Integer(n),
+            Number::Float(OrderedFloat(f)) => Literal::from(float_alloc!(f, arena)),
+            Number::Rational(r) => Literal::Rational(r),
+        }
+    }
+}
+
+impl ArenaFrom<Number> for HeapCellValue {
+    #[inline]
+    fn arena_from(value: Number, arena: &mut Arena) -> HeapCellValue {
+        match value {
+            Number::Fixnum(n) => fixnum_as_cell!(n),
+            Number::Integer(n) => typed_arena_ptr_as_cell!(n),
+            Number::Float(OrderedFloat(n)) => HeapCellValue::from(float_alloc!(n, arena)),
+            Number::Rational(n) => typed_arena_ptr_as_cell!(n),
+        }
+    }
+}
+
+impl Number {
+    pub(crate) fn sign(&self) -> Number {
+        match self {
+            &Number::Float(f) if f == 0.0 => Number::Float(OrderedFloat(0f64)),
+            &Number::Float(f) => Number::Float(OrderedFloat(f.signum())),
+            _ => {
+                if self.is_positive() {
+                    Number::Fixnum(Fixnum::build_with(1))
+                } else if self.is_negative() {
+                    Number::Fixnum(Fixnum::build_with(-1))
+                } else {
+                    Number::Fixnum(Fixnum::build_with(0))
+                }
+            }
+        }
+    }
+
+    #[inline]
+    pub(crate) fn is_positive(&self) -> bool {
+        match self {
+            &Number::Fixnum(n) => n.get_num() > 0,
+            &Number::Integer(ref n) => &**n > &0,
+            &Number::Float(f) => f.is_sign_positive(),
+            &Number::Rational(ref r) => &**r > &0,
+        }
+    }
+
+    #[inline]
+    pub(crate) fn is_negative(&self) -> bool {
+        match self {
+            &Number::Fixnum(n) => n.get_num() < 0,
+            &Number::Integer(ref n) => &**n < &0,
+            &Number::Float(OrderedFloat(f)) => f.is_sign_negative() && OrderedFloat(f) != -0f64,
+            &Number::Rational(ref r) => &**r < &0,
+        }
+    }
+
+    #[inline]
+    pub(crate) fn is_zero(&self) -> bool {
+        match self {
+            &Number::Fixnum(n) => n.get_num() == 0,
+            &Number::Integer(ref n) => &**n == &0,
+            &Number::Float(f) => f == OrderedFloat(0f64) || f == OrderedFloat(-0f64),
+            &Number::Rational(ref r) => &**r == &0,
+        }
+    }
+
+    #[inline]
+    pub(crate) fn is_integer(&self) -> bool {
+        match self {
+            Number::Fixnum(_) | Number::Integer(_) => true,
+            _ => false,
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub(crate) enum OptArgIndexKey {
+    Literal(usize, usize, Literal, Vec<Literal>), // index, IndexingCode location, opt arg, alternatives
+    List(usize, usize),                           // index, IndexingCode location
+    None,
+    Structure(usize, usize, Atom, usize), // index, IndexingCode location, name, arity
+}
+
+impl OptArgIndexKey {
+    #[inline]
+    pub(crate) fn take(&mut self) -> OptArgIndexKey {
+        std::mem::replace(self, OptArgIndexKey::None)
+    }
+
+    #[inline]
+    pub(crate) fn arg_num(&self) -> usize {
+        match &self {
+            OptArgIndexKey::Literal(arg_num, ..)
+            | OptArgIndexKey::Structure(arg_num, ..)
+            | OptArgIndexKey::List(arg_num, _) => {
+                // these are always at least 1.
+                *arg_num
+            }
+            OptArgIndexKey::None => 0,
+        }
+    }
+
+    #[inline]
+    pub(crate) fn is_some(&self) -> bool {
+        self.switch_on_term_loc().is_some()
+    }
+
+    #[inline]
+    pub(crate) fn switch_on_term_loc(&self) -> Option<usize> {
+        match &self {
+            OptArgIndexKey::Literal(_, loc, ..)
+            | OptArgIndexKey::Structure(_, loc, ..)
+            | OptArgIndexKey::List(_, loc) => Some(*loc),
+            OptArgIndexKey::None => None,
+        }
+    }
+
+    #[inline]
+    pub(crate) fn set_switch_on_term_loc(&mut self, value: usize) {
+        match self {
+            OptArgIndexKey::Literal(_, ref mut loc, ..)
+            | OptArgIndexKey::Structure(_, ref mut loc, ..)
+            | OptArgIndexKey::List(_, ref mut loc) => {
+                *loc = value;
+            }
+            OptArgIndexKey::None => {}
+        }
+    }
+}
+
+impl AddAssign<usize> for OptArgIndexKey {
+    #[inline]
+    fn add_assign(&mut self, n: usize) {
+        match self {
+            OptArgIndexKey::Literal(_, ref mut o, ..)
+            | OptArgIndexKey::List(_, ref mut o)
+            | OptArgIndexKey::Structure(_, ref mut o, ..) => {
+                *o += n;
+            }
+            OptArgIndexKey::None => {}
+        }
+    }
+}
+
+#[derive(Clone, Debug)]
+pub(crate) struct ClauseIndexInfo {
+    pub(crate) clause_start: usize,
+    pub(crate) opt_arg_index_key: OptArgIndexKey,
+}
+
+impl ClauseIndexInfo {
+    #[inline]
+    pub(crate) fn new(clause_start: usize) -> Self {
+        Self {
+            clause_start,
+            opt_arg_index_key: OptArgIndexKey::None,
+            // index_locs: vec![],
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct PredicateInfo {
+    pub(crate) is_extensible: bool,
+    pub(crate) is_discontiguous: bool,
+    pub(crate) is_dynamic: bool,
+    pub(crate) is_multifile: bool,
+    pub(crate) has_clauses: bool,
+}
+
+impl Default for PredicateInfo {
+    #[inline]
+    fn default() -> Self {
+        PredicateInfo {
+            is_extensible: false,
+            is_discontiguous: false,
+            is_dynamic: false,
+            is_multifile: false,
+            has_clauses: false,
+        }
+    }
+}
+
+impl PredicateInfo {
+    #[inline]
+    pub(crate) fn compile_incrementally(&self) -> bool {
+        let base = self.is_extensible && self.has_clauses;
+        base && (self.is_discontiguous || self.is_multifile)
+    }
+
+    #[inline]
+    pub(crate) fn must_retract_local_clauses(&self) -> bool {
+        self.is_extensible && self.has_clauses && !self.is_discontiguous
+    }
+}
+
+#[derive(Clone, Debug)]
+pub(crate) struct LocalPredicateSkeleton {
+    pub(crate) is_discontiguous: bool,
+    pub(crate) is_dynamic: bool,
+    pub(crate) is_multifile: bool,
+    pub(crate) clause_clause_locs: VecDeque<usize>,
+    pub(crate) clause_assert_margin: usize,
+    pub(crate) retracted_dynamic_clauses: Option<Vec<ClauseIndexInfo>>, // always None if non-dynamic.
+}
+
+impl LocalPredicateSkeleton {
+    #[inline]
+    pub(crate) fn new() -> Self {
+        Self {
+            is_discontiguous: false,
+            is_dynamic: false,
+            is_multifile: false,
+            clause_clause_locs: VecDeque::new(),
+            clause_assert_margin: 0,
+            retracted_dynamic_clauses: Some(vec![]),
+        }
+    }
+
+    #[inline]
+    pub(crate) fn predicate_info(&self) -> PredicateInfo {
+        PredicateInfo {
+            is_extensible: true,
+            is_discontiguous: self.is_discontiguous,
+            is_dynamic: self.is_dynamic,
+            is_multifile: self.is_multifile,
+            has_clauses: !self.clause_clause_locs.is_empty(),
+        }
+    }
+
+    #[inline]
+    pub(crate) fn reset(&mut self) {
+        self.clause_clause_locs.clear();
+        self.clause_assert_margin = 0;
+    }
+
+    #[inline]
+    pub(crate) fn add_retracted_dynamic_clause_info(&mut self, clause_info: ClauseIndexInfo) {
+        debug_assert_eq!(self.is_dynamic, true);
+
+        if self.retracted_dynamic_clauses.is_none() {
+            self.retracted_dynamic_clauses = Some(vec![]);
+        }
+
+        self.retracted_dynamic_clauses
+            .as_mut()
+            .unwrap()
+            .push(clause_info);
+    }
+}
+
+#[derive(Clone, Debug)]
+pub(crate) struct PredicateSkeleton {
+    pub(crate) core: LocalPredicateSkeleton,
+    pub(crate) clauses: VecDeque<ClauseIndexInfo>,
+}
+
+impl PredicateSkeleton {
+    #[inline]
+    pub(crate) fn new() -> Self {
+        PredicateSkeleton {
+            core: LocalPredicateSkeleton::new(),
+            clauses: VecDeque::new(),
+        }
+    }
+
+    #[inline]
+    pub(crate) fn predicate_info(&self) -> PredicateInfo {
+        PredicateInfo {
+            is_extensible: true,
+            is_discontiguous: self.core.is_discontiguous,
+            is_dynamic: self.core.is_dynamic,
+            is_multifile: self.core.is_multifile,
+            has_clauses: !self.clauses.is_empty(),
+        }
+    }
+
+    pub(crate) fn target_pos_of_clause_clause_loc(
+        &mut self,
+        clause_clause_loc: usize,
+    ) -> Option<usize> {
+        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()
+            }
+        }
+    }
+}

src/http.rs

@@ -0,0 +1,25 @@
+use std::sync::Arc;
+use std::convert::Infallible;
+
+use hyper::{Response, Request, Body};
+use tokio::sync::Mutex;
+use tokio::sync::mpsc::{channel, Receiver, Sender};
+
+pub struct HttpListener {
+    pub incoming: Receiver<HttpRequest>
+}
+
+#[derive(Debug)]
+pub struct HttpRequest {
+    pub request: Request<Body>,
+    pub response: HttpResponse,
+}
+
+pub type HttpResponse = Sender<Response<Body>>;
+
+pub async fn serve_req(req: Request<Body>, tx: Arc<Mutex<Sender<HttpRequest>>>) -> Result<Response<Body>, Infallible> {
+    let (response_tx, mut rx) = channel(1);
+    let http_request = HttpRequest { request: req, response: response_tx };
+    tx.lock().await.send(http_request).await.unwrap();
+    Ok(rx.recv().await.unwrap())
+}

src/iterators.rs

@@ -1,74 +1,77 @@
-use prolog_parser::ast::*;
-
-use crate::prolog::clause_types::*;
-use crate::prolog::forms::*;
-use crate::prolog::machine::machine_indices::*;
+use crate::atom_table::*;
+use crate::forms::*;
+use crate::instructions::*;
+use crate::parser::ast::*;
 
 use std::cell::Cell;
 use std::collections::VecDeque;
+use std::fmt;
 use std::iter::*;
 use std::rc::Rc;
 use std::vec::Vec;
 
-#[derive(Clone)]
-pub enum TermRef<'a> {
+#[derive(Debug, Clone)]
+pub(crate) enum TermRef<'a> {
     AnonVar(Level),
     Cons(Level, &'a Cell<RegType>, &'a Term, &'a Term),
-    Constant(Level, &'a Cell<RegType>, &'a Constant),
-    Clause(Level, &'a Cell<RegType>, ClauseType, &'a Vec<Box<Term>>),
-    Var(Level, &'a Cell<VarReg>, Rc<Var>),
+    Literal(Level, &'a Cell<RegType>, &'a Literal),
+    Clause(Level, &'a Cell<RegType>, Atom, &'a Vec<Term>),
+    PartialString(Level, &'a Cell<RegType>, &'a String, &'a Box<Term>),
+    CompleteString(Level, &'a Cell<RegType>, Atom),
+    Var(Level, &'a Cell<VarReg>, Rc<String>),
 }
 
 impl<'a> TermRef<'a> {
-    pub fn level(self) -> Level {
+    pub(crate) fn level(self) -> Level {
         match self {
             TermRef::AnonVar(lvl)
-          | TermRef::Cons(lvl, ..)
-          | TermRef::Constant(lvl, ..)
-          | TermRef::Var(lvl, ..)
-          | TermRef::Clause(lvl, ..) => lvl,
+            | TermRef::Cons(lvl, ..)
+            | TermRef::Literal(lvl, ..)
+            | TermRef::Var(lvl, ..)
+            | TermRef::Clause(lvl, ..)
+            | TermRef::CompleteString(lvl, ..)
+            | TermRef::PartialString(lvl, ..) => lvl,
         }
     }
 }
 
-pub enum TermIterState<'a> {
+#[derive(Debug)]
+pub(crate) enum TermIterState<'a> {
     AnonVar(Level),
-    Constant(Level, &'a Cell<RegType>, &'a Constant),
-    Clause(
-        Level,
-        usize,
-        &'a Cell<RegType>,
-        ClauseType,
-        &'a Vec<Box<Term>>,
-    ),
+    Literal(Level, &'a Cell<RegType>, &'a Literal),
+    Clause(Level, usize, &'a Cell<RegType>, Atom, &'a Vec<Term>),
     InitialCons(Level, &'a Cell<RegType>, &'a Term, &'a Term),
     FinalCons(Level, &'a Cell<RegType>, &'a Term, &'a Term),
-    Var(Level, &'a Cell<VarReg>, Rc<Var>),
+    InitialPartialString(Level, &'a Cell<RegType>, &'a String, &'a Box<Term>),
+    FinalPartialString(Level, &'a Cell<RegType>, &'a String, &'a Box<Term>),
+    CompleteString(Level, &'a Cell<RegType>, Atom),
+    Var(Level, &'a Cell<VarReg>, Rc<String>),
 }
 
 impl<'a> TermIterState<'a> {
-    pub fn subterm_to_state(lvl: Level, term: &'a Term) -> TermIterState<'a> {
+    pub(crate) fn subterm_to_state(lvl: Level, term: &'a Term) -> TermIterState<'a> {
         match term {
-            &Term::AnonVar => TermIterState::AnonVar(lvl),
-            &Term::Clause(ref cell, ref name, ref subterms, ref spec) => {
-                let ct = if let Some(spec) = spec {
-                    ClauseType::Op(name.clone(), spec.clone(), CodeIndex::default())
-                } else {
-                    ClauseType::Named(name.clone(), subterms.len(), CodeIndex::default())
-                };
-
-                TermIterState::Clause(lvl, 0, cell, ct, subterms)
+            Term::AnonVar => TermIterState::AnonVar(lvl),
+            Term::Clause(cell, name, subterms) => {
+                TermIterState::Clause(lvl, 0, cell, *name, subterms)
             }
-            &Term::Cons(ref cell, ref head, ref tail) => {
+            Term::Cons(cell, head, tail) => {
                 TermIterState::InitialCons(lvl, cell, head.as_ref(), tail.as_ref())
             }
-            &Term::Constant(ref cell, ref constant) => TermIterState::Constant(lvl, cell, constant),
-            &Term::Var(ref cell, ref var) => TermIterState::Var(lvl, cell, var.clone()),
+            Term::Literal(cell, constant) => TermIterState::Literal(lvl, cell, constant),
+            Term::PartialString(cell, string_buf, tail) => {
+                TermIterState::InitialPartialString(lvl, cell, string_buf, tail)
+            }
+            Term::CompleteString(cell, atom) => {
+                TermIterState::CompleteString(lvl, cell, *atom)
+            }
+            Term::Var(cell, var) => TermIterState::Var(lvl, cell, var.clone()),
         }
     }
 }
 
-pub struct QueryIterator<'a> {
+#[derive(Debug)]
+pub(crate) struct QueryIterator<'a> {
     state_stack: Vec<TermIterState<'a>>,
 }
 
@@ -78,11 +81,11 @@ impl<'a> QueryIterator<'a> {
             .push(TermIterState::subterm_to_state(lvl, term));
     }
 
-    fn from_rule_head_clause(terms: &'a Vec<Box<Term>>) -> Self {
+    fn from_rule_head_clause(terms: &'a Vec<Term>) -> Self {
         let state_stack = terms
             .iter()
             .rev()
-            .map(|bt| TermIterState::subterm_to_state(Level::Shallow, bt.as_ref()))
+            .map(|bt| TermIterState::subterm_to_state(Level::Shallow, bt))
             .collect();
 
         QueryIterator { state_stack }
@@ -90,30 +93,20 @@ impl<'a> QueryIterator<'a> {
 
     fn from_term(term: &'a Term) -> Self {
         let state = match term {
-            &Term::AnonVar => {
+            Term::AnonVar | Term::Cons(..) | Term::Literal(..) |
+            Term::PartialString(..) | Term::CompleteString(..) => {
                 return QueryIterator {
                     state_stack: vec![],
                 }
             }
-            &Term::Clause(ref r, ref name, ref terms, ref fixity) => TermIterState::Clause(
+            Term::Clause(r, name, terms) => TermIterState::Clause(
                 Level::Root,
                 0,
                 r,
-                ClauseType::from(name.clone(), terms.len(), fixity.clone()),
+                *name,
                 terms,
             ),
-            &Term::Cons(..) => {
-                return QueryIterator {
-                    state_stack: vec![],
-                }
-            }
-            &Term::Constant(_, _) => {
-                return QueryIterator {
-                    state_stack: vec![],
-                }
-            }
-            &Term::Var(ref cell, ref var) =>
-                TermIterState::Var(Level::Root, cell, (*var).clone()),
+            Term::Var(cell, var) => TermIterState::Var(Level::Root, cell, var.clone()),
         };
 
         QueryIterator {
@@ -123,20 +116,20 @@ impl<'a> QueryIterator<'a> {
 
     fn new(term: &'a QueryTerm) -> Self {
         match term {
-            &QueryTerm::Clause(ref cell, ClauseType::CallN, ref terms, _) => {
-                let state = TermIterState::Clause(Level::Root, 1, cell, ClauseType::CallN, terms);
+            &QueryTerm::Clause(ref cell, ClauseType::CallN(_), ref terms, _) => {
+                let state = TermIterState::Clause(Level::Root, 1, cell, atom!("$call"), terms);
                 QueryIterator {
                     state_stack: vec![state],
                 }
             }
             &QueryTerm::Clause(ref cell, ref ct, ref terms, _) => {
-                let state = TermIterState::Clause(Level::Root, 0, cell, ct.clone(), terms);
+                let state = TermIterState::Clause(Level::Root, 0, cell, ct.name(), terms);
                 QueryIterator {
                     state_stack: vec![state],
                 }
             }
             &QueryTerm::UnblockedCut(ref cell) => {
-                let state = TermIterState::Var(Level::Root, cell, rc_atom!("!"));
+                let state = TermIterState::Var(Level::Root, cell, Rc::new("!".to_string()));
                 QueryIterator {
                     state_stack: vec![state],
                 }
@@ -169,46 +162,59 @@ impl<'a> Iterator for QueryIterator<'a> {
     fn next(&mut self) -> Option<Self::Item> {
         while let Some(iter_state) = self.state_stack.pop() {
             match iter_state {
-                TermIterState::AnonVar(lvl) => return Some(TermRef::AnonVar(lvl)),
-                TermIterState::Clause(lvl, child_num, cell, ct, child_terms) => {
+                TermIterState::AnonVar(lvl) => {
+                    return Some(TermRef::AnonVar(lvl));
+                }
+                TermIterState::Clause(lvl, child_num, cell, name, child_terms) => {
                     if child_num == child_terms.len() {
-                        match ct {
-                            ClauseType::CallN => {
-                                self.push_subterm(Level::Shallow, child_terms[0].as_ref())
+                        match name {
+                            atom!("$call") if lvl == Level::Root => {
+                                self.push_subterm(Level::Shallow, &child_terms[0]);
                             }
-                            ClauseType::Named(..) | ClauseType::Op(..) => {
+                            _ => {
                                 return match lvl {
                                     Level::Root => None,
-                                    lvl => Some(TermRef::Clause(lvl, cell, ct, child_terms)),
+                                    lvl => Some(TermRef::Clause(lvl, cell, name, child_terms)),
                                 }
                             }
-                            _ => return None,
                         };
                     } else {
                         self.state_stack.push(TermIterState::Clause(
                             lvl,
                             child_num + 1,
                             cell,
-                            ct,
+                            name,
                             child_terms,
                         ));
-                        self.push_subterm(lvl.child_level(), child_terms[child_num].as_ref());
+
+                        self.push_subterm(lvl.child_level(), &child_terms[child_num]);
                     }
                 }
                 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.push_subterm(lvl.child_level(), tail);
+                }
+                TermIterState::FinalPartialString(lvl, cell, atom, tail) => {
+                    return Some(TermRef::PartialString(lvl, cell, atom, tail));
+                }
+                TermIterState::CompleteString(lvl, cell, atom) => {
+                    return Some(TermRef::CompleteString(lvl, cell, atom));
+                }
                 TermIterState::FinalCons(lvl, cell, head, tail) => {
-                    return Some(TermRef::Cons(lvl, cell, head, tail))
+                    return Some(TermRef::Cons(lvl, cell, head, tail));
                 }
-                TermIterState::Constant(lvl, cell, constant) => {
-                    return Some(TermRef::Constant(lvl, cell, constant))
+                TermIterState::Literal(lvl, cell, constant) => {
+                    return Some(TermRef::Literal(lvl, cell, constant));
+                }
+                TermIterState::Var(lvl, cell, var) => {
+                    return Some(TermRef::Var(lvl, cell, var));
                 }
-                TermIterState::Var(lvl, cell, var) => return Some(TermRef::Var(lvl, cell, var)),
             };
         }
 
@@ -216,7 +222,8 @@ impl<'a> Iterator for QueryIterator<'a> {
     }
 }
 
-pub struct FactIterator<'a> {
+#[derive(Debug)]
+pub(crate) struct FactIterator<'a> {
     state_queue: VecDeque<TermIterState<'a>>,
     iterable_root: bool,
 }
@@ -227,10 +234,10 @@ impl<'a> FactIterator<'a> {
             .push_back(TermIterState::subterm_to_state(lvl, term));
     }
 
-    pub fn from_rule_head_clause(terms: &'a Vec<Box<Term>>) -> Self {
+    pub(crate) fn from_rule_head_clause(terms: &'a Vec<Term>) -> Self {
         let state_queue = terms
             .iter()
-            .map(|bt| TermIterState::subterm_to_state(Level::Shallow, bt.as_ref()))
+            .map(|bt| TermIterState::subterm_to_state(Level::Shallow, bt))
             .collect();
 
         FactIterator {
@@ -241,21 +248,37 @@ impl<'a> FactIterator<'a> {
 
     fn new(term: &'a Term, iterable_root: bool) -> Self {
         let states = match term {
-            &Term::AnonVar => vec![TermIterState::AnonVar(Level::Root)],
-            &Term::Clause(ref cell, ref name, ref terms, ref fixity) => {
-                let ct = ClauseType::from(name.clone(), terms.len(), fixity.clone());
-                vec![TermIterState::Clause(Level::Root, 0, cell, ct, terms)]
+            Term::AnonVar => {
+                vec![TermIterState::AnonVar(Level::Root)]
             }
-            &Term::Cons(ref cell, ref head, ref tail) => vec![TermIterState::InitialCons(
+            Term::Clause(cell, name, terms) => {
+                vec![TermIterState::Clause(Level::Root, 0, cell, *name, terms)]
+            }
+            Term::Cons(cell, head, tail) => vec![TermIterState::InitialCons(
                 Level::Root,
                 cell,
                 head.as_ref(),
                 tail.as_ref(),
             )],
-            &Term::Constant(ref cell, ref constant) => {
-                vec![TermIterState::Constant(Level::Root, cell, constant)]
+            Term::PartialString(cell, string_buf, tail) => {
+                vec![TermIterState::InitialPartialString(
+                    Level::Root,
+                    cell,
+                    string_buf,
+                    tail,
+                )]
             }
-            &Term::Var(ref cell, ref var) => {
+            Term::CompleteString(cell, atom) => {
+                vec![TermIterState::CompleteString(
+                    Level::Root,
+                    cell,
+                    *atom,
+                )]
+            }
+            Term::Literal(cell, constant) => {
+                vec![TermIterState::Literal(Level::Root, cell, constant)]
+            }
+            Term::Var(cell, var) => {
                 vec![TermIterState::Var(Level::Root, cell, var.clone())]
             }
         };
@@ -273,15 +296,17 @@ impl<'a> Iterator for FactIterator<'a> {
     fn next(&mut self) -> Option<Self::Item> {
         while let Some(state) = self.state_queue.pop_front() {
             match state {
-                TermIterState::AnonVar(lvl) => return Some(TermRef::AnonVar(lvl)),
-                TermIterState::Clause(lvl, _, cell, ct, child_terms) => {
+                TermIterState::AnonVar(lvl) => {
+                    return Some(TermRef::AnonVar(lvl));
+                }
+                TermIterState::Clause(lvl, _, cell, name, child_terms) => {
                     for child_term in child_terms {
                         self.push_subterm(lvl.child_level(), child_term);
                     }
 
                     match lvl {
                         Level::Root if !self.iterable_root => continue,
-                        _ => return Some(TermRef::Clause(lvl, cell, ct, child_terms)),
+                        _ => return Some(TermRef::Clause(lvl, cell, name, child_terms)),
                     };
                 }
                 TermIterState::InitialCons(lvl, cell, head, tail) => {
@@ -290,10 +315,19 @@ impl<'a> Iterator for FactIterator<'a> {
 
                     return Some(TermRef::Cons(lvl, cell, head, tail));
                 }
-                TermIterState::Constant(lvl, cell, constant) => {
-                    return Some(TermRef::Constant(lvl, cell, constant))
+                TermIterState::InitialPartialString(lvl, cell, string_buf, tail) => {
+                    self.push_subterm(Level::Deep, tail);
+                    return Some(TermRef::PartialString(lvl, cell, string_buf, tail));
+                }
+                TermIterState::CompleteString(lvl, cell, atom) => {
+                    return Some(TermRef::CompleteString(lvl, cell, atom));
+                }
+                TermIterState::Literal(lvl, cell, constant) => {
+                    return Some(TermRef::Literal(lvl, cell, constant))
+                }
+                TermIterState::Var(lvl, cell, var) => {
+                    return Some(TermRef::Var(lvl, cell, var));
                 }
-                TermIterState::Var(lvl, cell, var) => return Some(TermRef::Var(lvl, cell, var)),
                 _ => {}
             }
         }
@@ -302,27 +336,28 @@ impl<'a> Iterator for FactIterator<'a> {
     }
 }
 
-pub fn post_order_iter(term: &Term) -> QueryIterator {
+pub(crate) fn post_order_iter<'a>(term: &'a Term) -> QueryIterator<'a> {
     QueryIterator::from_term(term)
 }
 
-pub fn breadth_first_iter(term: &Term, iterable_root: bool) -> FactIterator {
+pub(crate) fn breadth_first_iter<'a>(term: &'a Term, iterable_root: bool) -> FactIterator<'a> {
     FactIterator::new(term, iterable_root)
 }
 
-pub enum ChunkedTerm<'a> {
-    HeadClause(ClauseName, &'a Vec<Box<Term>>),
+#[derive(Debug)]
+pub(crate) enum ChunkedTerm<'a> {
+    HeadClause(Atom, &'a Vec<Term>),
     BodyTerm(&'a QueryTerm),
 }
 
-pub fn query_term_post_order_iter<'a>(query_term: &'a QueryTerm) -> QueryIterator<'a> {
+pub(crate) fn query_term_post_order_iter<'a>(query_term: &'a QueryTerm) -> QueryIterator<'a> {
     QueryIterator::new(query_term)
 }
 
 impl<'a> ChunkedTerm<'a> {
-    pub fn post_order_iter(&self) -> QueryIterator<'a> {
+    pub(crate) fn post_order_iter(&self) -> QueryIterator<'a> {
         match self {
-            &ChunkedTerm::BodyTerm(ref qt) => QueryIterator::new(qt),
+            &ChunkedTerm::BodyTerm(qt) => QueryIterator::new(qt),
             &ChunkedTerm::HeadClause(_, terms) => QueryIterator::from_rule_head_clause(terms),
         }
     }
@@ -340,18 +375,30 @@ fn contains_cut_var<'a, Iter: Iterator<Item = &'a Term>>(terms: Iter) -> bool {
     false
 }
 
-pub struct ChunkedIterator<'a> {
-    pub chunk_num: usize,
+pub(crate) struct ChunkedIterator<'a> {
+    pub(crate) chunk_num: usize,
     iter: Box<dyn Iterator<Item = ChunkedTerm<'a>> + 'a>,
     deep_cut_encountered: bool,
     cut_var_in_head: bool,
 }
 
+impl<'a> fmt::Debug for ChunkedIterator<'a> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("ChunkedIterator")
+            .field("chunk_num", &self.chunk_num)
+            // Hacky solution.
+            .field("iter", &"Box<dyn Iterator<Item = ChunkedTerm<'a>> + 'a>")
+            .field("deep_cut_encountered", &self.deep_cut_encountered)
+            .field("cut_var_in_head", &self.cut_var_in_head)
+            .finish()
+    }
+}
+
 type ChunkedIteratorItem<'a> = (usize, usize, Vec<ChunkedTerm<'a>>);
 type RuleBodyIteratorItem<'a> = (usize, usize, Vec<&'a QueryTerm>);
 
 impl<'a> ChunkedIterator<'a> {
-    pub fn rule_body_iter(self) -> Box<dyn Iterator<Item = RuleBodyIteratorItem<'a>> + 'a> {
+    pub(crate) fn rule_body_iter(self) -> Box<dyn Iterator<Item = RuleBodyIteratorItem<'a>> + 'a> {
         Box::new(self.filter_map(|(cn, lt_arity, terms)| {
             let filtered_terms: Vec<_> = terms
                 .into_iter()
@@ -369,16 +416,7 @@ impl<'a> ChunkedIterator<'a> {
         }))
     }
 
-    pub fn from_term_sequence(terms: &'a [QueryTerm]) -> Self {
-        ChunkedIterator {
-            chunk_num: 0,
-            iter: Box::new(terms.iter().map(|t| ChunkedTerm::BodyTerm(t))),
-            deep_cut_encountered: false,
-            cut_var_in_head: false,
-        }
-    }
-
-    pub fn from_rule_body(p1: &'a QueryTerm, clauses: &'a Vec<QueryTerm>) -> Self {
+    pub(crate) fn from_rule_body(p1: &'a QueryTerm, clauses: &'a Vec<QueryTerm>) -> Self {
         let inner_iter = Box::new(once(ChunkedTerm::BodyTerm(p1)));
         let iter = inner_iter.chain(clauses.iter().map(|t| ChunkedTerm::BodyTerm(t)));
 
@@ -390,7 +428,7 @@ impl<'a> ChunkedIterator<'a> {
         }
     }
 
-    pub fn from_rule(rule: &'a Rule) -> Self {
+    pub(crate) fn from_rule(rule: &'a Rule) -> Self {
         let &Rule {
             head: (ref name, ref args, ref p1),
             ref clauses,
@@ -408,7 +446,7 @@ impl<'a> ChunkedIterator<'a> {
         }
     }
 
-    pub fn encountered_deep_cut(&self) -> bool {
+    pub(crate) fn encountered_deep_cut(&self) -> bool {
         self.deep_cut_encountered
     }
 
@@ -420,7 +458,7 @@ impl<'a> ChunkedIterator<'a> {
         while let Some(term) = item {
             match term {
                 ChunkedTerm::HeadClause(_, terms) => {
-                    if contains_cut_var(terms.iter().map(|t| t.as_ref())) {
+                    if contains_cut_var(terms.iter()) {
                         self.cut_var_in_head = true;
                     }
 
@@ -450,13 +488,16 @@ impl<'a> ChunkedIterator<'a> {
                     arity = 1;
                     break;
                 }
-                ChunkedTerm::BodyTerm(&QueryTerm::UnblockedCut(..)) => result.push(term),
+                ChunkedTerm::BodyTerm(&QueryTerm::UnblockedCut(..)) => {
+                    self.deep_cut_encountered = true;
+                    result.push(term);
+                }
                 ChunkedTerm::BodyTerm(&QueryTerm::Clause(_, ClauseType::Inlined(_), ..)) => {
                     result.push(term)
                 }
                 ChunkedTerm::BodyTerm(&QueryTerm::Clause(
                     _,
-                    ClauseType::CallN,
+                    ClauseType::CallN(_),
                     ref subterms,
                     _,
                 )) => {

src/l0/ast.rs

@@ -1,51 +0,0 @@
-use std::cell::{Cell};
-use std::vec::{Vec};
-
-pub type Var = String;
-
-pub type Atom = String;
-
-#[derive(Debug)]
-pub enum TopLevel {
-    Fact(Term),
-    Query(Term)
-}
-
-#[derive(Debug)]
-pub enum Term {
-    Atom(Cell<usize>, Atom),
-    Clause(Cell<usize>, Atom, Vec<Box<Term>>),
-    Var(Cell<usize>, Var)
-}
-
-pub enum FactInstruction {
-    GetStructure(Atom, usize, usize),
-    UnifyVariable(usize),
-    UnifyValue(usize)
-}
-
-pub enum QueryInstruction {    
-    PutStructure(Atom, usize, usize),
-    SetVariable(usize),
-    SetValue(usize),    
-}
-
-pub type CompiledFact = Vec<FactInstruction>;
-
-pub type CompiledQuery = Vec<QueryInstruction>;
-
-#[derive(Clone, Copy, PartialEq)]
-pub enum Addr {
-    HeapCell(usize),
-    RegNum(usize)
-}
-
-impl Term {
-    pub fn set_cell(&self, cell_num: usize) {
-        match self {
-            &Term::Atom(ref cell, _) => cell.set(cell_num),
-            &Term::Clause(ref cell, _, _) => cell.set(cell_num),
-            &Term::Var(ref cell, _) => cell.set(cell_num)
-        };
-    }
-}

src/l0/codegen.rs

@@ -1,126 +0,0 @@
-use l0::ast::{Atom, Term, FactInstruction, QueryInstruction, Var};
-use l0::iterators::{BreadthFirstIterator, PostOrderIterator};
-
-use std::collections::{HashSet};
-use std::fmt;
-use std::vec::{Vec};
-
-impl fmt::Display for QueryInstruction {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &QueryInstruction::PutStructure(ref a, ref s, ref r) =>
-                write!(f, "put_structure {}/{}, X{}", a, s, r),
-            &QueryInstruction::SetVariable(ref r) =>
-                write!(f, "set_variable X{}", r),
-            &QueryInstruction::SetValue(ref r) =>
-                write!(f, "set_value X{}", r),
-        }
-    }
-}
-
-impl fmt::Display for FactInstruction {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &FactInstruction::GetStructure(ref a, ref s, ref r) =>
-                write!(f, "get_structure {}/{}, X{}", a, s, r),
-            &FactInstruction::UnifyVariable(ref r) =>
-                write!(f, "unify_variable X{}", r),
-            &FactInstruction::UnifyValue(ref r) =>
-                write!(f, "unify_value X{}", r)
-        }
-    }
-}
-
-pub trait CompilationTarget<'a> {
-    type Iterator : Iterator<Item=&'a Term>;
-    
-    fn iter(term: &'a Term) -> Self::Iterator;
-
-    fn to_structure(name: Atom, arity: usize, cell_num: usize) -> Self;
-    fn to_value(cell_num: usize) -> Self;
-    fn to_variable(cell_num: usize) -> Self;
-}
-
-impl<'a> CompilationTarget<'a> for FactInstruction {
-    type Iterator = BreadthFirstIterator<'a>;
-    
-    fn iter(term: &'a Term) -> Self::Iterator {
-        term.breadth_first_iter()
-    }
-
-    fn to_structure(name: Atom, arity: usize, cell_num: usize) -> Self {
-        FactInstruction::GetStructure(name, arity, cell_num)
-    }
-
-    fn to_value(cell_num: usize) -> Self {
-        FactInstruction::UnifyValue(cell_num)
-    }
-
-    fn to_variable(cell_num: usize) -> Self {
-        FactInstruction::UnifyVariable(cell_num)
-    }
-}
-
-impl<'a> CompilationTarget<'a> for QueryInstruction {
-    type Iterator = PostOrderIterator<'a>;
-
-    fn iter(term: &'a Term) -> Self::Iterator {
-        term.post_order_iter()
-    }
-
-    fn to_structure(name: Atom, arity: usize, cell_num: usize) -> Self {
-        QueryInstruction::PutStructure(name, arity, cell_num)
-    }
-
-    fn to_value(cell_num: usize) -> Self {
-        QueryInstruction::SetValue(cell_num)
-    }
-
-    fn to_variable(cell_num: usize) -> Self {
-        QueryInstruction::SetVariable(cell_num)
-    }
-}
-
-fn subterm_to_instr<'a, Target>(subterm:  &'a Term,
-                                bindings: &mut HashSet<&'a Var>)
-                                -> Target
-    where Target: CompilationTarget<'a>
-{
-    match subterm {
-        &Term::Atom(ref cell_num, _) =>
-            Target::to_value(cell_num.get()),
-        &Term::Var(ref cell_num, ref atom) if bindings.contains(atom) =>
-            Target::to_value(cell_num.get()),
-        &Term::Var(ref cell_num, ref atom) => {
-            bindings.insert(atom);
-            Target::to_variable(cell_num.get())
-        },
-        &Term::Clause(ref cell_num, _, _) =>
-            Target::to_value(cell_num.get())
-    }
-}
-
-pub fn compile_target<'a, Target>(term: &'a Term) -> Vec<Target>
-    where Target: CompilationTarget<'a>
-{
-    let mut iter     = Target::iter(term);
-    let mut target   = Vec::<Target>::new();
-    let mut bindings = HashSet::new();
-
-    while let Some(term) = iter.next() {
-        match term {
-            &Term::Atom(ref cell_num, ref atom) =>
-                target.push(Target::to_structure(atom.clone(), 0, cell_num.get())),
-            &Term::Clause(ref cell_num, ref atom, ref terms) => {
-                target.push(Target::to_structure(atom.clone(), 0, cell_num.get()));
-
-                for subterm in terms {
-                    target.push(subterm_to_instr(subterm.as_ref(), &mut bindings));
-                }
-            },
-            _ => {},
-        };
-    }
-
-    target
-}

src/l0/iterators.rs

@@ -1,98 +0,0 @@
-use l0::ast::{Term};
-
-use std::collections::{VecDeque};
-use std::vec::{Vec};
-
-enum DepthFirstIteratorState<'a> {        
-    // child no., the containing clause, its vector.
-    Clause(usize, &'a Term, &'a Vec<Box<Term>>),
-    NonClause(&'a Term)
-}
-
-pub struct PostOrderIterator<'a> {
-    state_stack: Vec<DepthFirstIteratorState<'a>>        
-}
-
-impl<'a> PostOrderIterator<'a> {
-    fn push_clause(&mut self,
-                   child_num: usize,
-                   term: &'a Term,
-                   child_terms: &'a Vec<Box<Term>>)
-    {
-        self.state_stack.push(DepthFirstIteratorState::Clause(child_num,
-                                                              term,
-                                                              child_terms));
-    }
-
-    fn render_new_state(term: &'a Term) -> DepthFirstIteratorState<'a> {
-        match term {
-            &Term::Clause(_, _, ref child_terms) =>
-                DepthFirstIteratorState::Clause(0, term, child_terms),
-            _ => DepthFirstIteratorState::NonClause(term)
-        }
-    }
-
-    fn push_term(&mut self, term: &'a Term) {
-        self.state_stack.push(Self::render_new_state(term));
-    }
-}
-
-impl<'a> Iterator for PostOrderIterator<'a> {
-    type Item = &'a Term;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        while let Some(iter_state) = self.state_stack.pop() {
-            match iter_state {
-                DepthFirstIteratorState::Clause(child_num, term, child_terms) => {                    
-                    if child_num == child_terms.len() {
-                        return Some(term);
-                    } else {
-                        self.push_clause(child_num + 1, term, child_terms);
-                        self.push_term(child_terms[child_num].as_ref());
-                    }
-                },
-                DepthFirstIteratorState::NonClause(term) => return Some(term),
-            };
-        }
-
-        None
-    }
-}
-
-pub struct BreadthFirstIterator<'a> {
-    state_queue : VecDeque<&'a Term>
-}
-
-impl<'a> Iterator for BreadthFirstIterator<'a> {
-    type Item = &'a Term;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        if let Some(term) = self.state_queue.pop_front() {            
-            if let &Term::Clause(_, _, ref child_terms) = term {
-                for term in child_terms {
-                    self.state_queue.push_back(term);
-                }
-
-                return Some(term);
-            }
-
-            return Some(term);
-        }
-
-        None
-    }
-}
-    
-impl<'a> Term {
-    pub fn post_order_iter(&'a self) -> PostOrderIterator<'a> {
-        let initial_state = PostOrderIterator::render_new_state(self);
-        PostOrderIterator { state_stack: vec![initial_state] }
-    }
-
-    pub fn breadth_first_iter(&'a self) -> BreadthFirstIterator<'a> {
-        let mut queue = VecDeque::new();
-        queue.push_back(self);
-        
-        BreadthFirstIterator { state_queue: queue }
-    }
-}

src/l0/l0_parser.lalrpop

@@ -1,31 +0,0 @@
-use std::cell::{Cell};
-use l0::ast::{Atom, Term, TopLevel, Var};
-
-grammar;
-
-pub TopLevel: TopLevel = {
-    "?-" <t:Term> "." => TopLevel::Query(t),
-    <t:Term> "."      => TopLevel::Fact(t),
-};
-
-Atom : Atom = {
-     r"[a-z][a-z0-9_]*" => <>.trim().to_string(),
-};
-
-Var : Var = {
-     r"[A-Z][a-z0-9_]*" => <>.trim().to_string(),
-};	
-
-BoxedTerm : Box<Term> = {
-     <t:Term> => Box::new(t),
-};
-
-Term : Term = {
-     <a:Atom> "(" <ts: (<BoxedTerm> ",")*> <t:BoxedTerm> ")" => {
-     	      let mut ts = ts;
-     	      ts.push(t);
-	      Term::Clause(Cell::new(0), a, ts)
-     },
-     <Atom> => Term::Atom(Cell::new(0), <>),
-     <Var>  => Term::Var(Cell::new(0), <>),
-};

src/l0/machine.rs

@@ -1,238 +0,0 @@
-use l0::ast::{Addr, Atom, CompiledFact, FactInstruction, QueryInstruction};
-
-use std::vec::{Vec};
-
-#[derive(Clone)]
-enum HeapCell {
-    NamedStr(usize, Atom),
-    Ref(usize),
-    Str(usize),
-}
-
-#[derive(Clone, Copy)]
-enum MachineMode {
-    Read,
-    Write
-}
-
-type Heap = Vec<HeapCell>;
-
-type Registers = Vec<HeapCell>;
-
-pub struct Machine {
-    h : usize,
-    s : usize,
-    pub fail : bool,
-    heap : Heap,
-    mode : MachineMode,
-    pub program : Option<CompiledFact>,
-    registers : Registers
-}
-
-impl Machine {
-    pub fn new() -> Machine {
-        Machine { h : 0,
-                  s : 0,
-                  fail : false,
-                  heap : Vec::with_capacity(256),
-                  mode : MachineMode::Write,
-                  program : None,
-                  registers : vec![HeapCell::Ref(0); 33] }
-    }
-    
-    fn lookup(&self, a: Addr) -> &HeapCell {
-        match a {
-            Addr::HeapCell(hc) => &self.heap[hc],
-            Addr::RegNum(reg)  => &self.registers[reg]
-        }
-    }
-
-    fn deref(&self, a: Addr) -> Addr {
-        let mut a = a;
-
-        loop {
-            if let &HeapCell::Ref(value) = self.lookup(a) {
-                if let Addr::HeapCell(av) = a {
-                    if value != av {
-                        a = Addr::HeapCell(value);
-                        continue;
-                    }
-                }
-            }
-
-            return a;
-        };
-    }
-
-    fn is_unbound(hc: &HeapCell, index: usize) -> bool {
-        match hc {
-            &HeapCell::Ref(r) => r == index,
-            _ => false
-        }
-    }
-    
-    //TODO: try to compress this function. currently it is dog shit.
-    fn bind(&mut self, a: Addr, val: usize) {
-        let mut a = a;
-        
-        loop {
-            match a {
-                Addr::RegNum(reg) => {
-                    if let HeapCell::Ref(hc) = self.registers[reg] {
-                        a = Addr::HeapCell(hc);
-                    } else if Machine::is_unbound(&self.heap[val], val) {
-                        self.heap[val] = self.registers[reg].clone();
-                        break;
-                    } else {
-                        self.fail = true;
-                        break;
-                    }                        
-                },
-                Addr::HeapCell(hc) if Machine::is_unbound(&self.heap[hc], hc) => {
-                    self.heap[hc] = HeapCell::Ref(val);
-                    break;
-                },
-                Addr::HeapCell(hc) if Machine::is_unbound(&self.heap[val], val) => {                
-                    self.heap[val] = HeapCell::Ref(hc);
-                    break;
-                },
-                _ => {
-                    self.fail = true;                    
-                    break;
-                }
-            };
-        }
-    }
-
-    fn unify(&mut self, a1: Addr, a2: Addr) {
-        let mut pdl : Vec<Addr> = vec![a1, a2];
-
-        self.fail = false;
-
-        while !(pdl.is_empty() || self.fail) {
-            let d1 = self.deref(pdl.pop().unwrap());
-            let d2 = self.deref(pdl.pop().unwrap());
-
-            if d1 != d2 {
-                match (self.lookup(d1), self.lookup(d2)) {
-                    (&HeapCell::Ref(hc), _) =>
-                        self.bind(d2, hc),
-                    (_, &HeapCell::Ref(hc)) =>
-                        self.bind(d1, hc),
-                    (&HeapCell::Str(a1), &HeapCell::Str(a2)) => {
-                        let r1 = &self.heap[a1];
-                        let r2 = &self.heap[a2];
-
-                        if let &HeapCell::NamedStr(n1, ref f1) = r1 {
-                            if let &HeapCell::NamedStr(n2, ref f2) = r2 {
-                                if n1 == n2 && *f1 == *f2 {
-                                    for i in 1 .. n1 {
-                                        pdl.push(Addr::HeapCell(a1 + i));
-                                        pdl.push(Addr::HeapCell(a2 + i));
-                                    }
-
-                                    continue;
-                                }
-                            }
-                        }
-
-                        self.fail = true;
-                    },
-                    _ => self.fail = true,
-                };
-            }
-        }
-    }    
-
-    pub fn execute_query_instr<'a, 'b : 'a>(&'a mut self, instr: &'b QueryInstruction) {
-        match instr {
-            &QueryInstruction::PutStructure(ref name, arity, reg) => {
-                self.heap.push(HeapCell::Str(self.h + 1));
-                self.heap.push(HeapCell::NamedStr(arity, name.clone()));
-
-                self.registers[reg] = self.heap[self.h].clone();
-
-                self.h += 2;
-            },
-            &QueryInstruction::SetVariable(reg) => {
-                self.heap.push(HeapCell::Ref(self.h));
-                self.registers[reg] = self.heap[self.h].clone();
-
-                self.h += 1;
-            },
-            &QueryInstruction::SetValue(reg) => {
-                self.heap.push(self.registers[reg].clone());
-                self.h += 1;
-            },
-        }
-    }
-    
-    pub fn execute_fact_instr<'a, 'b : 'a>(&'a mut self, instr: &'b FactInstruction) {
-        match instr {
-            &FactInstruction::GetStructure(ref name, arity, reg) => {
-                let addr = self.deref(Addr::RegNum(reg));
-
-                match self.lookup(addr) {
-                    &HeapCell::Str(a) => {
-                        let result = &self.heap[a];
-
-                        if let &HeapCell::NamedStr(named_arity, ref named_str) = result {
-                            if arity == named_arity && *name == *named_str {
-                                self.s = a + 1;
-                                self.mode = MachineMode::Read;
-                            } else {
-                                self.fail = true;
-                            }
-                        }
-                    },
-                    &HeapCell::Ref(r) => {
-                        self.heap.push(HeapCell::Str(self.h + 1));
-                        self.heap.push(HeapCell::NamedStr(arity, name.clone()));
-
-                        let h = self.h;
-
-                        self.bind(Addr::HeapCell(r), h);
-
-                        self.h += 2;
-                        self.mode = MachineMode::Write;
-                    },
-                    _ => {
-                        self.fail = true;
-                    }
-                };
-            },
-            &FactInstruction::UnifyVariable(reg) => {
-                match self.mode {
-                    MachineMode::Read  => self.registers[reg] = self.heap[self.s].clone(),
-                    MachineMode::Write => {
-                        self.heap.push(HeapCell::Ref(self.h));
-                        self.registers[reg] = self.heap[self.h].clone();
-                        self.h += 1;
-                    }
-                };
-
-                self.s += 1;
-            },
-            &FactInstruction::UnifyValue(reg) => {
-                let s = self.s;
-
-                match self.mode {
-                    MachineMode::Read  => self.unify(Addr::RegNum(reg), Addr::HeapCell(s)),
-                    MachineMode::Write => {
-                        self.heap.push(self.registers[reg].clone());
-                        self.h += 1;
-                    }
-                };
-                
-                self.s += 1;
-            }
-        }
-    }
-    
-    pub fn reset_heap(&mut self) {
-        let program = self.program.take();
-
-        *self = Machine::new();
-        self.program = program;
-    }    
-}

src/l0/mod.rs

@@ -1,7 +0,0 @@
-mod l0_parser;
-
-pub mod ast;
-pub mod iterators;
-pub mod parser;
-pub mod codegen;
-pub mod machine;

src/l0/parser.rs

@@ -1,52 +0,0 @@
-use l0::ast::{Term, TopLevel, Var};
-use l0::l0_parser::{parse_TopLevel};
-
-use std::collections::{HashMap};
-
-extern crate lalrpop_util as __lalrpop_util;
-
-pub type ParseResult<'a> =
-    Result<TopLevel, __lalrpop_util::ParseError<usize,(usize, &'a str),()>>;
-
-pub fn parse_top_level<'a>(input: &'a str) -> ParseResult {
-    let result = parse_TopLevel(&*input);
-    
-    if let Ok(result) = result {
-        return Ok(mark_cells(result));
-    }
-
-    result
-}
-
-#[inline]
-fn mark_cells(tl: TopLevel) -> TopLevel {
-    match tl {
-        TopLevel::Fact(term) => TopLevel::Fact(mark_term_cells(term)),
-        TopLevel::Query(term) => TopLevel::Query(mark_term_cells(term))            
-    }
-}
-    
-fn mark_term_cells(term: Term) -> Term {
-    let mut cell_num = 1;    
-    
-    {
-        let mut bindings: HashMap<&Var, usize> = HashMap::new();
-        let mut iter = term.breadth_first_iter();
-    
-        while let Some(term) = iter.next() {
-            if let &Term::Var(ref cell, ref var) = term {
-                let cell_num_in_map = bindings.entry(var).or_insert(cell_num);
-                
-                if *cell_num_in_map != cell_num {                    
-                    cell.set(*cell_num_in_map);
-                    continue;
-                }
-            }
-
-            term.set_cell(cell_num);
-            cell_num += 1;
-        }
-    }
-
-    term
-}

src/l1/ast.rs

@@ -1,123 +0,0 @@
-use std::cell::Cell;
-use std::fmt;
-use std::vec::Vec;
-
-pub type Var = String;
-
-pub type Atom = String;
-
-pub enum TopLevel {
-    Fact(Term),
-    Query(Term)
-}
-
-#[derive(Clone, Copy)]
-pub enum Level {
-    Shallow, Deep
-}
-
-impl fmt::Display for Level {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &Level::Shallow => write!(f, "A"),
-            &Level::Deep => write!(f, "X")
-        }
-    }
-}
-
-#[derive(Clone, Copy)]
-pub enum Reg {
-    ArgAndNorm(usize, usize),
-    Norm(usize)
-}
-
-impl Reg {
-    pub fn has_arg(&self) -> bool {
-        match self {
-            &Reg::ArgAndNorm(_, _) => true,
-            _ => false
-        }
-    }
-
-    pub fn norm(&self) -> usize {
-        match self {
-            &Reg::ArgAndNorm(_, norm) | &Reg::Norm(norm) => norm
-        }
-    }
-}
-
-pub enum Term {
-    Atom(Cell<usize>, Atom),
-    Clause(Cell<usize>, Atom, Vec<Box<Term>>),
-    Var(Cell<Reg>, Var)
-}
-
-pub enum TermRef<'a> {
-    Atom(Level, &'a Cell<usize>, &'a Atom),
-    Clause(Level, &'a Cell<usize>, &'a Atom, &'a Vec<Box<Term>>),
-    Var(Level, &'a Cell<Reg>, &'a Var)
-}
-
-#[derive(Clone)]
-pub enum FactInstruction {
-    GetStructure(Level, Atom, usize, usize),
-    GetValue(usize, usize),
-    GetVariable(usize, usize),
-    Proceed,
-    UnifyVariable(usize),
-    UnifyValue(usize)
-}
-
-pub enum QueryInstruction {
-    Call(Atom, usize),
-    PutStructure(Level, Atom, usize, usize),
-    PutValue(usize, usize),
-    PutVariable(usize, usize),
-    SetVariable(usize),
-    SetValue(usize),
-}
-
-pub type CompiledFact = Vec<FactInstruction>;
-
-pub type CompiledQuery = Vec<QueryInstruction>;
-
-#[derive(Clone, Copy, PartialEq)]
-pub enum Addr {
-    HeapCell(usize),
-    RegNum(usize)
-}
-
-#[derive(Clone)]
-pub enum HeapCellValue {
-    NamedStr(usize, Atom),
-    Ref(usize),
-    Str(usize),
-}
-
-pub type Heap = Vec<HeapCellValue>;
-
-pub type Registers = Vec<HeapCellValue>;
-
-impl Term {
-    pub fn subterms(&self) -> usize {
-        match self {
-            &Term::Clause(_, _, ref terms) => terms.len(),
-            _ => 1
-        }
-    }
-
-    pub fn name(&self) -> &Atom {
-        match self {
-            &Term::Atom(_, ref atom)
-            | &Term::Var(_, ref atom)
-            | &Term::Clause(_, ref atom, _) => atom
-        }
-    }
-
-    pub fn arity(&self) -> usize {
-        match self {
-            &Term::Atom(_, _) | &Term::Var(_, _) => 0,
-            &Term::Clause(_, _, ref child_terms) => child_terms.len()
-        }
-    }
-}

src/l1/codegen.rs

@@ -1,312 +0,0 @@
-use l1::ast::{Atom, CompiledFact, CompiledQuery, FactInstruction,
-              Level, QueryInstruction, Reg, Term, TermRef, Var};
-use l1::iterators::{FactIterator, QueryIterator};
-
-use std::cell::Cell;
-use std::collections::HashMap;
-use std::fmt;
-use std::vec::Vec;
-
-impl fmt::Display for QueryInstruction {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &QueryInstruction::Call(ref name, ref arity) =>
-                write!(f, "call {}/{}", name, arity),
-            &QueryInstruction::PutStructure(ref lvl, ref a, ref s, ref r) =>
-                write!(f, "put_structure {}/{}, {}{}", a, s, lvl, r),
-            &QueryInstruction::PutValue(ref a, ref x) =>
-                write!(f, "put_value X{}, A{}", x, a),
-            &QueryInstruction::PutVariable(ref a, ref x) =>
-                write!(f, "put_variable X{}, A{}", x, a),
-            &QueryInstruction::SetVariable(ref r) =>
-                write!(f, "set_variable X{}", r),
-            &QueryInstruction::SetValue(ref r) =>
-                write!(f, "set_value X{}", r),
-        }
-    }
-}
-
-impl fmt::Display for FactInstruction {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &FactInstruction::GetStructure(ref lvl, ref a, ref s, ref r) =>
-                write!(f, "get_structure {}/{}, {}{}", a, s, lvl, r),
-            &FactInstruction::GetValue(ref a, ref x) =>
-                write!(f, "get_value X{}, A{}", x, a),
-            &FactInstruction::GetVariable(ref a, ref x) =>
-                write!(f, "get_variable X{}, A{}", x, a),
-            &FactInstruction::Proceed =>
-                write!(f, "proceed"),
-            &FactInstruction::UnifyVariable(ref r) =>
-                write!(f, "unify_variable X{}", r),
-            &FactInstruction::UnifyValue(ref r) =>
-                write!(f, "unify_value X{}", r)
-        }
-    }
-}
-
-struct TermMarker<'a> {    
-    bindings: HashMap<&'a Var, Reg>,
-    arg_c:    usize,
-    norm_c:   usize
-}
-
-impl<'a> TermMarker<'a> {
-    fn new(term: &'a Term) -> TermMarker<'a> {
-        TermMarker { bindings: HashMap::new(),
-                     arg_c:    1,
-                     norm_c:   term.subterms() + 1 }
-    }
-
-    fn contains_var(&self, var: &'a Var) -> bool {
-        self.bindings.contains_key(var)
-    }
-
-    fn get(&self, var: &'a Var) -> Reg {
-        *self.bindings.get(var).unwrap()
-    }
-
-    fn insert(&mut self, var: &'a Var, r: Reg) {
-        self.bindings.insert(var, r);
-    }
-    
-    fn mark_non_var(&mut self, lvl: Level, cell: &Cell<usize>) {
-        if cell.get() == 0 {            
-            match lvl {
-                Level::Deep => {
-                    let norm = self.norm_c;
-                    self.norm_c += 1;
-                    cell.set(norm);
-                },            
-                Level::Shallow => {
-                    let arg = self.arg_c;
-                    self.arg_c += 1;
-                    cell.set(arg);
-                }
-            };
-        }
-    }
-
-    fn mark_var(&mut self, lvl: Level, var: &'a Var) -> Reg {
-        if self.contains_var(var) {
-            let reg = self.get(var);
-
-            match lvl {
-                Level::Deep => Reg::Norm(reg.norm()),
-                Level::Shallow if reg.has_arg() => {
-                    let arg = self.arg_c;
-                    self.arg_c += 1;
-                    
-                    Reg::ArgAndNorm(arg, reg.norm())
-                },
-                Level::Shallow => {
-                    let norm = reg.norm();
-                    let reg  = Reg::ArgAndNorm(self.arg_c, norm);
-
-                    self.arg_c += 1;
-                    self.insert(var, reg);
-
-                    reg
-                }
-            }
-        } else {
-            let reg = match lvl {
-                Level::Deep    => Reg::Norm(self.norm_c),
-                Level::Shallow => {
-                    let reg = Reg::ArgAndNorm(self.arg_c, self.norm_c);
-                    self.arg_c += 1;
-                    reg
-                }
-            };
-
-            self.norm_c += 1;
-            self.insert(var, reg);
-            reg
-        }
-    }
-}
-
-trait CompilationTarget<'a> {
-    type Iterator : Iterator<Item=TermRef<'a>>;
-
-    fn iter(&'a Term) -> Self::Iterator;
-
-    fn to_structure(Level, Atom, usize, usize) -> Self;
-
-    fn argument_to_variable(usize, usize) -> Self;
-    fn argument_to_value(usize, usize) -> Self;
-    fn subterm_to_variable(usize) -> Self;
-    fn subterm_to_value(usize) -> Self;
-
-    fn clause_arg_to_instr(usize) -> Self;
-}
-
-impl<'a> CompilationTarget<'a> for FactInstruction {
-    type Iterator = FactIterator<'a>;
-
-    fn iter(term: &'a Term) -> Self::Iterator {
-        term.breadth_first_iter()
-    }
-
-    fn to_structure(lvl: Level, atom: Atom, arity: usize, cell_num: usize) -> Self {        
-        FactInstruction::GetStructure(lvl, atom, arity, cell_num)
-    }
-
-    fn argument_to_variable(arg: usize, val: usize) -> Self {
-        FactInstruction::GetVariable(arg, val)
-    }
-
-    fn argument_to_value(arg: usize, val: usize) -> Self {
-        FactInstruction::GetValue(arg, val)
-    }
-
-    fn subterm_to_variable(val: usize) -> Self {
-        FactInstruction::UnifyVariable(val)
-    }
-
-    fn subterm_to_value(val: usize) -> Self {
-        FactInstruction::UnifyValue(val)
-    }
-
-    fn clause_arg_to_instr(val: usize) -> Self {
-        FactInstruction::UnifyVariable(val)
-    }
-}
-
-impl<'a> CompilationTarget<'a> for QueryInstruction {
-    type Iterator = QueryIterator<'a>;
-
-    fn iter(term: &'a Term) -> Self::Iterator {
-        term.post_order_iter()
-    }
-
-    fn to_structure(lvl: Level, atom: Atom, arity: usize, cell_num: usize) -> Self {
-        QueryInstruction::PutStructure(lvl, atom, arity, cell_num)
-    }
-
-    fn argument_to_variable(arg: usize, val: usize) -> Self {
-        QueryInstruction::PutVariable(arg, val)
-    }
-
-    fn argument_to_value(arg: usize, val: usize) -> Self {
-        QueryInstruction::PutValue(arg, val)
-    }
-
-    fn subterm_to_variable(val: usize) -> Self {
-        QueryInstruction::SetVariable(val)
-    }
-
-    fn subterm_to_value(val: usize) -> Self {
-        QueryInstruction::SetValue(val)
-    }
-    
-    fn clause_arg_to_instr(val: usize) -> Self {
-        QueryInstruction::SetValue(val)
-    }
-}
-
-fn to_structure<'a, Target>(tm: &mut TermMarker<'a>,
-                            lvl: Level,
-                            name: &'a Atom,
-                            cell: &'a Cell<usize>,
-                            arity: usize)
-                            -> Target
-    where Target: CompilationTarget<'a>
-{
-    tm.mark_non_var(lvl, cell);
-    Target::to_structure(lvl, name.clone(), arity, cell.get())
-}
-
-fn non_var_subterm<'a, Target>(tm: &mut TermMarker<'a>, cell: &'a Cell<usize>)
-                               -> Target
-    where Target: CompilationTarget<'a>
-{
-    tm.mark_non_var(Level::Deep, cell);
-    Target::clause_arg_to_instr(cell.get())
-}
-
-fn var_term<'a, Target>(tm: &mut TermMarker<'a>,
-                        lvl: Level,
-                        cell: &'a Cell<Reg>,
-                        var: &'a Var)
-                        -> Target
-    where Target: CompilationTarget<'a>
-{
-    if !tm.contains_var(var) {
-        let reg = tm.mark_var(lvl, var);
-        cell.set(reg);
-        
-        match reg {
-            Reg::ArgAndNorm(arg, norm) =>
-                Target::argument_to_variable(arg, norm),
-            Reg::Norm(norm) =>
-                Target::subterm_to_variable(norm)
-        }
-    } else {
-        let reg = tm.mark_var(lvl, var);
-        cell.set(reg);
-        
-        match reg {
-            Reg::ArgAndNorm(arg, norm) =>
-                Target::argument_to_value(arg, norm),
-            Reg::Norm(norm) =>
-                Target::subterm_to_value(norm)
-        }
-    }
-}
-
-fn subterm_to_instr<'a, Target>(tm: &mut TermMarker<'a>, subterm: &'a Term)
-                                -> Target
-    where Target: CompilationTarget<'a>
-{
-    match subterm {
-        &Term::Atom(ref cell, _) | &Term::Clause(ref cell, _, _) =>
-            non_var_subterm(tm, cell),
-        &Term::Var(ref cell, ref var) =>
-            var_term(tm, Level::Deep, cell, var)
-    }
-}
-
-fn compile_target<'a, Target>(term: &'a Term) -> Vec<Target>
-    where Target: CompilationTarget<'a>
-{
-    let iter       = Target::iter(term);
-    let mut target = Vec::<Target>::new();
-    let mut marker = TermMarker::new(term);
-    
-    for term in iter {
-        match term {
-            TermRef::Atom(lvl, term, atom) =>
-                target.push(to_structure(&mut marker, lvl, atom, term, 0)),
-            TermRef::Clause(lvl, term, atom, terms) => {
-                target.push(to_structure(&mut marker, lvl, atom, term, terms.len()));
-
-                for subterm in terms {
-                    target.push(subterm_to_instr(&mut marker, subterm.as_ref()));
-                }
-            },
-            TermRef::Var(lvl @ Level::Shallow, ref cell, ref var) =>
-                target.push(var_term(&mut marker, lvl, cell, var)),
-            _ => {}
-        };
-    }
-
-    target
-}
-
-pub fn compile_fact(term: &Term) -> CompiledFact {
-    let mut compiled_fact = compile_target(term);
-
-    compiled_fact.push(FactInstruction::Proceed);
-    compiled_fact
-}
-
-pub fn compile_query<'a>(term: &'a Term) -> CompiledQuery {
-    let mut compiled_query = compile_target(term);
-
-    if let &Term::Clause(_, ref atom, ref terms) = term {
-        compiled_query.push(QueryInstruction::Call(atom.clone(), terms.len()));
-    }
-
-    compiled_query
-}

src/l1/iterators.rs

@@ -1,175 +0,0 @@
-use l1::ast::{Atom, Level, Reg, Term, TermRef, Var};
-
-use std::cell::Cell;
-use std::collections::VecDeque;
-use std::vec::Vec;
-
-enum IteratorState<'a> {
-    Atom(Level, &'a Cell<usize>, &'a Atom),
-    Clause(Level, usize, &'a Cell<usize>, &'a Atom, &'a Vec<Box<Term>>),
-    IsolatedAtom(&'a Cell<usize>, &'a Atom),
-    IsolatedVar(&'a Cell<Reg>, &'a Var),
-    RootClause(usize, &'a Vec<Box<Term>>),
-    Var(Level, &'a Cell<Reg>, &'a Var)
-}
-
-impl<'a> IteratorState<'a> {
-    fn to_state(lvl: Level, term: &'a Term) -> IteratorState<'a>
-    {
-        match term {
-            &Term::Atom(ref cell, ref atom) =>
-                IteratorState::Atom(lvl, cell, atom),
-            &Term::Clause(ref cell, ref atom, ref child_terms) =>
-                IteratorState::Clause(lvl, 0, cell, atom, child_terms),
-            &Term::Var(ref cell, ref var) =>
-                IteratorState::Var(lvl, cell, var)
-        }
-    }
-}
-
-pub struct QueryIterator<'a> {
-    state_stack: Vec<IteratorState<'a>>
-}
-
-impl<'a> QueryIterator<'a> {
-    fn push_clause(&mut self,
-                   lvl: Level,
-                   child_num: usize,
-                   cell: &'a Cell<usize>,
-                   name: &'a Atom,
-                   child_terms: &'a Vec<Box<Term>>)
-    {
-        self.state_stack.push(IteratorState::Clause(lvl,
-                                                    child_num,
-                                                    cell,
-                                                    name,
-                                                    child_terms));
-    }
-
-    fn push_root_clause(&mut self,
-                        child_num: usize,                        
-                        child_terms: &'a Vec<Box<Term>>)
-    {
-        self.state_stack.push(IteratorState::RootClause(child_num, child_terms));
-    }
-
-    fn push_subterm(&mut self, lvl: Level, term: &'a Term) {
-        self.state_stack.push(IteratorState::to_state(lvl, term));
-    }
-
-    fn new(term: &'a Term) -> QueryIterator<'a> {
-        let state = match term {
-            &Term::Atom(ref cell, ref atom) =>
-                IteratorState::IsolatedAtom(cell, atom),
-            &Term::Clause(_, _, ref terms) =>
-                IteratorState::RootClause(0, terms),
-            &Term::Var(ref cell, ref var) =>
-                IteratorState::IsolatedVar(cell, var)
-        };
-        
-        QueryIterator { state_stack: vec![state] }
-    }
-}
-
-impl<'a> Iterator for QueryIterator<'a> {
-    type Item = TermRef<'a>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        while let Some(iter_state) = self.state_stack.pop() {
-            match iter_state {
-                IteratorState::Atom(lvl, cell, atom) =>
-                    return Some(TermRef::Atom(lvl, cell, atom)),
-                IteratorState::Clause(lvl, child_num, cell, atom, child_terms) => {
-                    if child_num == child_terms.len() {
-                        return Some(TermRef::Clause(lvl, cell, atom, child_terms));
-                    } else {
-                        self.push_clause(lvl, child_num + 1, cell, atom, child_terms);
-                        self.push_subterm(Level::Deep, child_terms[child_num].as_ref());
-                    }
-                },
-                IteratorState::IsolatedAtom(cell, atom) =>
-                    return Some(TermRef::Atom(Level::Shallow, cell, atom)),
-                IteratorState::IsolatedVar(cell, var) =>
-                    return Some(TermRef::Var(Level::Shallow, cell, var)),
-                IteratorState::RootClause(child_num, child_terms) => {
-                    if child_num == child_terms.len() {
-                        return None;
-                    } else {
-                        self.push_root_clause(child_num + 1, child_terms);
-                        self.push_subterm(Level::Shallow, child_terms[child_num].as_ref());
-                    }
-                },
-                IteratorState::Var(lvl, cell, var) =>
-                    return Some(TermRef::Var(lvl, cell, var))
-            };
-        }
-
-        None
-    }
-}
-
-pub struct FactIterator<'a> {
-    state_queue: VecDeque<IteratorState<'a>>,
-}
-
-impl<'a> FactIterator<'a> {
-    fn push_subterm(&mut self, lvl: Level, term: &'a Term) {
-        self.state_queue.push_back(IteratorState::to_state(lvl, term));
-    }
-
-    fn new(term: &'a Term) -> FactIterator<'a> {
-        let states = match term {
-            &Term::Atom(ref cell, ref atom) =>
-                vec![IteratorState::IsolatedAtom(cell, atom)],
-            &Term::Clause(_, _, ref terms) =>
-                vec![IteratorState::RootClause(0, terms)],
-            &Term::Var(ref cell, ref var) =>
-                vec![IteratorState::IsolatedVar(cell, var)]
-        };
-
-        FactIterator { state_queue:  VecDeque::from(states) }
-    }
-}
-
-impl<'a> Iterator for FactIterator<'a> {
-    type Item = TermRef<'a>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        while let Some(state) = self.state_queue.pop_front() {
-            match state {
-                IteratorState::Atom(lvl, cell, atom) =>
-                    return Some(TermRef::Atom(lvl, cell, atom)),
-                IteratorState::Clause(lvl, _, cell, atom, child_terms) => {
-                    for child_term in child_terms {
-                        self.push_subterm(Level::Deep, child_term);
-                    }
-
-                    return Some(TermRef::Clause(lvl, cell, atom, child_terms));
-                },
-                IteratorState::IsolatedAtom(cell, atom) =>
-                    return Some(TermRef::Atom(Level::Shallow, cell, atom)),
-                IteratorState::IsolatedVar(cell, var) =>
-                    return Some(TermRef::Var(Level::Shallow, cell, var)),
-                IteratorState::RootClause(_, child_terms) => {
-                    for child_term in child_terms {
-                        self.push_subterm(Level::Shallow, child_term);
-                    }
-                },
-                IteratorState::Var(lvl, cell, var) =>
-                    return Some(TermRef::Var(lvl, cell, var))
-            }
-        }
-
-        None
-    }
-}
-
-impl Term {
-    pub fn post_order_iter(&self) -> QueryIterator {
-        QueryIterator::new(self)
-    }
-
-    pub fn breadth_first_iter(&self) -> FactIterator {
-        FactIterator::new(self)
-    }
-}

src/l1/l1_parser.lalrpop

@@ -1,32 +0,0 @@
-use std::cell::Cell;
-
-use l1::ast::{Atom, Reg, Term, TopLevel, Var};
-
-grammar;
-
-pub TopLevel: TopLevel = {
-    "?-" <t:Term> "." => TopLevel::Query(t),
-    <t:Term> "."      => TopLevel::Fact(t),
-};
-
-Atom : Atom = {
-    r"[a-z][a-z0-9_]*" => <>.trim().to_string(),
-};
-
-Var : Var = {
-    r"[A-Z][a-z0-9_]*" => <>.trim().to_string(),
-};
-
-BoxedTerm : Box<Term> = {
-    <t:Term> => Box::new(t),
-};
-
-Term : Term = {
-    <a:Atom> "(" <ts: (<BoxedTerm> ",")*> <t:BoxedTerm> ")" => {
-     	let mut ts = ts;
-     	ts.push(t);
-	Term::Clause(Cell::new(0), a, ts)
-    },
-    <Atom> => Term::Atom(Cell::new(0), <>),
-    <Var>  => Term::Var(Cell::new(Reg::Norm(0)), <>)
-};

src/l1/machine.rs

@@ -1,309 +0,0 @@
-use l1::ast::{Addr, Atom, CompiledFact, CompiledQuery,
-              FactInstruction, Heap, HeapCellValue, QueryInstruction,
-              Registers};
-
-use std::collections::HashMap;
-use std::vec::Vec;
-
-#[derive(Clone, Copy)]
-enum MachineMode {
-    Read,
-    Write
-}
-
-pub struct Machine {
-    h : usize,
-    s : usize,
-    p : usize,
-    code : CompiledFact,
-    code_dir : HashMap<(Atom, usize), usize>,
-    fail : bool,
-    heap : Heap,
-    mode : MachineMode,
-    registers : Registers
-}
-
-impl Machine {
-    pub fn new() -> Machine {
-        Machine { h : 0,
-                  s : 0,
-                  p : 0,
-                  code : Vec::new(),
-                  code_dir : HashMap::new(),
-                  fail : false,
-                  heap : Vec::with_capacity(256),
-                  mode : MachineMode::Write,
-                  registers : vec![HeapCellValue::Ref(0); 32] }
-    }
-
-    pub fn add_fact(&mut self, mut fact: CompiledFact, name: Atom, arity: usize)
-    {
-        let index = self.code.len();
-
-        self.code.append(&mut fact);
-        self.code_dir.insert((name, arity), index);
-    }
-
-    pub fn failed(&self) -> bool {
-        self.fail
-    }
-
-    fn lookup(&self, a: Addr) -> &HeapCellValue {
-        match a {
-            Addr::HeapCell(hc) => &self.heap[hc],
-            Addr::RegNum(reg)  => &self.registers[reg]
-        }
-    }
-
-    fn deref(&self, a: Addr) -> Addr {
-        let mut a = a;
-
-        loop {
-            if let &HeapCellValue::Ref(value) = self.lookup(a) {
-                if let Addr::HeapCell(av) = a {
-                    if value != av {
-                        a = Addr::HeapCell(value);
-                        continue;
-                    }
-                } else {
-                    a = Addr::HeapCell(value);
-                    continue;
-                }
-            }
-
-            return a;
-        };
-    }
-
-    fn is_unbound(hc: &HeapCellValue, index: usize) -> bool {
-        match hc {
-            &HeapCellValue::Ref(r) => r == index,
-            _ => false
-        }
-    }
-
-    //TODO: try to compress this function.
-    fn bind(&mut self, a: Addr, val: usize) {
-        let mut a = a;
-
-        loop {
-            match a {
-                Addr::RegNum(reg) => {
-                    if let HeapCellValue::Ref(hc) = self.registers[reg] {
-                        a = Addr::HeapCell(hc);
-                    } else if Machine::is_unbound(&self.heap[val], val) {
-                        self.heap[val] = self.registers[reg].clone();
-                        break;
-                    } else {
-                        self.fail = true;
-                        break;
-                    }
-                },
-                Addr::HeapCell(hc) if Machine::is_unbound(&self.heap[hc], hc) => {
-                    self.heap[hc] = HeapCellValue::Ref(val);
-                    break;
-                },
-                Addr::HeapCell(hc) if Machine::is_unbound(&self.heap[val], val) => {
-                    self.heap[val] = HeapCellValue::Ref(hc);
-                    break;
-                },
-                _ => {
-                    self.fail = true;
-                    break;
-                }
-            };
-        }
-    }
-
-    fn unify(&mut self, a1: Addr, a2: Addr) {
-        let mut pdl = vec![a1, a2];
-
-        self.fail = false;
-
-        while !(pdl.is_empty() || self.fail) {
-            let d1 = self.deref(pdl.pop().unwrap());
-            let d2 = self.deref(pdl.pop().unwrap());
-
-            if d1 != d2 {
-                match (self.lookup(d1), self.lookup(d2)) {
-                    (&HeapCellValue::Ref(hc), _) =>
-                        self.bind(d2, hc),
-                    (_, &HeapCellValue::Ref(hc)) =>
-                        self.bind(d1, hc),
-                    (&HeapCellValue::Str(a1), &HeapCellValue::Str(a2)) => {
-                        let r1 = &self.heap[a1];
-                        let r2 = &self.heap[a2];
-
-                        if let &HeapCellValue::NamedStr(n1, ref f1) = r1 {
-                            if let &HeapCellValue::NamedStr(n2, ref f2) = r2 {
-                                if n1 == n2 && *f1 == *f2 {
-                                    for i in 1 .. n1 {
-                                        pdl.push(Addr::HeapCell(a1 + i));
-                                        pdl.push(Addr::HeapCell(a2 + i));
-                                    }
-
-                                    continue;
-                                }
-                            }
-                        }
-
-                        self.fail = true;
-                    },
-                    _ => self.fail = true,
-                };
-            }
-        }
-    }
-
-    pub fn execute_fact(&mut self) {
-        loop {
-            if let &FactInstruction::Proceed = &self.code[self.p] {
-                break;
-            } else if self.fail {
-                break;
-            }
-
-            let fact_instr = self.code[self.p].clone();
-            self.execute_fact_instr(fact_instr);
-        }
-    }
-
-    pub fn execute_query(&mut self, query: &CompiledQuery) {
-        for instr in query {
-            self.execute_query_instr(instr);
-
-            if self.fail {
-                break;
-            }
-        }
-    }
-
-    fn execute_query_instr<'a, 'b: 'a>(&'a mut self, instr: &'b QueryInstruction) {
-        match instr {
-            &QueryInstruction::Call(ref name, arity) => {
-                // why is Option<&T> not Deref?!?!?
-                // is it because if the value is None, there's nothing to
-                // dereference?
-                let compiled_fact_index =
-                    self.code_dir.get(&(name.clone(), arity))
-                        .map(|index| *index);
-
-                match compiled_fact_index {
-                    Some(compiled_fact_index) => {
-                        self.p = compiled_fact_index;
-                        self.execute_fact();
-                    },
-                    None => self.fail = true,
-                };
-            }
-            &QueryInstruction::PutStructure(_, ref name, arity, reg) => {
-                self.heap.push(HeapCellValue::Str(self.h + 1));
-                self.heap.push(HeapCellValue::NamedStr(arity, name.clone()));
-
-                self.registers[reg] = self.heap[self.h].clone();
-
-                self.h += 2;
-            },
-            &QueryInstruction::PutValue(arg, norm) =>
-                self.registers[arg] = self.registers[norm].clone(),
-            &QueryInstruction::PutVariable(arg, norm) => {
-                self.heap.push(HeapCellValue::Ref(self.h));
-
-                self.registers[norm] = self.heap[self.h].clone();
-                self.registers[arg]  = self.heap[self.h].clone();
-
-                self.h += 1;
-            },
-            &QueryInstruction::SetVariable(reg) => {
-                self.heap.push(HeapCellValue::Ref(self.h));
-                self.registers[reg] = self.heap[self.h].clone();
-
-                self.h += 1;
-            },
-            &QueryInstruction::SetValue(reg) => {
-                self.heap.push(self.registers[reg].clone());
-                self.h += 1;
-            },
-        }
-    }
-
-    fn execute_fact_instr(&mut self, instr: FactInstruction) {
-        match instr {
-            FactInstruction::Proceed => return,
-            FactInstruction::GetStructure(_, name, arity, reg) => {
-                let addr = self.deref(Addr::RegNum(reg));
-
-                match self.lookup(addr) {
-                    &HeapCellValue::Str(a) => {
-                        let result = &self.heap[a];
-
-                        if let &HeapCellValue::NamedStr(named_arity, ref named_str) = result {
-                            if arity == named_arity && *name == *named_str {
-                                self.s = a + 1;
-                                self.mode = MachineMode::Read;
-                            } else {
-                                self.fail = true;
-                            }
-                        }
-                    },
-                    &HeapCellValue::Ref(r) => {
-                        self.heap.push(HeapCellValue::Str(self.h + 1));
-                        self.heap.push(HeapCellValue::NamedStr(arity, name));
-
-                        let h = self.h;
-
-                        self.bind(Addr::HeapCell(r), h);
-
-                        self.h += 2;
-                        self.mode = MachineMode::Write;
-                    },
-                    _ => {
-                        self.fail = true;
-                    }
-                };
-            },
-            FactInstruction::GetVariable(arg, norm) =>
-                self.registers[norm] = self.registers[arg].clone(),
-            FactInstruction::GetValue(arg, norm) =>
-                self.unify(Addr::RegNum(norm), Addr::RegNum(arg)),
-            FactInstruction::UnifyVariable(reg) => {
-                match self.mode {
-                    MachineMode::Read  => self.registers[reg] = self.heap[self.s].clone(),
-                    MachineMode::Write => {
-                        self.heap.push(HeapCellValue::Ref(self.h));
-                        self.registers[reg] = self.heap[self.h].clone();
-                        self.h += 1;
-                    }
-                };
-
-                self.s += 1;
-            },
-            FactInstruction::UnifyValue(reg) => {
-                let s = self.s;
-
-                match self.mode {
-                    MachineMode::Read  => self.unify(Addr::RegNum(reg), Addr::HeapCell(s)),
-                    MachineMode::Write => {
-                        self.heap.push(self.registers[reg].clone());
-                        self.h += 1;
-                    }
-                };
-
-                self.s += 1;
-            }
-        }
-
-        self.p += 1;
-    }
-
-    pub fn reset_machine_state(&mut self) {
-        self.h = 0;
-        self.s = 0;
-        self.p = 0;
-
-        self.fail = false;
-        self.heap = Vec::with_capacity(256);
-        self.mode = MachineMode::Write;
-        self.registers = vec![HeapCellValue::Ref(0); 32];
-    }
-}

src/l1/mod.rs

@@ -1,5 +0,0 @@
-pub mod ast;
-pub mod iterators;
-pub mod l1_parser;
-pub mod codegen;
-pub mod machine;

src/l2/ast.rs

@@ -1,253 +0,0 @@
-use std::cell::Cell;
-use std::fmt;
-use std::ops::{Add, AddAssign};
-use std::vec::Vec;
-
-pub type Var = String;
-
-pub type Atom = String;
-
-pub enum TopLevel {
-    Fact(Term),
-    Rule(Rule),
-    Query(Term)
-}
-
-#[derive(Clone, Copy)]
-pub enum Level {
-    Shallow, Deep
-}
-
-impl fmt::Display for Level {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &Level::Shallow => write!(f, "A"),
-            &Level::Deep => write!(f, "X")
-        }
-    }
-}
-
-#[derive(Clone, Copy)]
-pub enum RegType {
-    Perm(usize),
-    Temp(usize)
-}
-
-impl RegType {
-    pub fn reg_num(self) -> usize {
-        match self {
-            RegType::Perm(reg_num) | RegType::Temp(reg_num) => reg_num
-        }
-    }
-
-    pub fn is_perm(self) -> bool {
-        match self {
-            RegType::Perm(_) => true,
-            _ => false
-        }
-    }
-}
-
-impl fmt::Display for VarReg {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &VarReg::Norm(RegType::Perm(reg)) => write!(f, "Y{}", reg),
-            &VarReg::Norm(RegType::Temp(reg)) => write!(f, "X{}", reg),
-            &VarReg::ArgAndNorm(RegType::Perm(reg), arg) =>
-                write!(f, "Y{} A{}", reg, arg),
-            &VarReg::ArgAndNorm(RegType::Temp(reg), arg) =>
-                write!(f, "X{} A{}", reg, arg)
-        }
-    }
-}
-
-impl From<RegType> for Addr {
-    fn from(reg: RegType) -> Addr {
-        match reg {
-            RegType::Perm(reg) => Addr::StackCell(reg),
-            RegType::Temp(reg) => Addr::RegNum(reg)
-        }
-    }
-}
-
-impl fmt::Display for RegType {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &RegType::Perm(val) => write!(f, "Y{}", val),
-            &RegType::Temp(val) => write!(f, "X{}", val)
-        }
-    }
-}
-
-#[derive(Clone, Copy)]
-pub enum VarReg {
-    ArgAndNorm(RegType, usize),
-    Norm(RegType)
-}
-
-impl VarReg {
-    pub fn norm(self) -> RegType {
-        match self {
-            VarReg::ArgAndNorm(reg, _) | VarReg::Norm(reg) => reg
-        }
-    }
-
-    pub fn root_register(self) -> usize {
-        match self {
-            VarReg::ArgAndNorm(_, root) => root,
-            VarReg::Norm(root) => root.reg_num()
-        }
-    }
-}
-
-pub enum Term {
-    Atom(Cell<RegType>, Atom),
-    Clause(Cell<RegType>, Atom, Vec<Box<Term>>),
-    Var(Cell<VarReg>, Var)
-}
-
-pub struct Rule {
-    pub head: (Term, Term),
-    pub clauses: Vec<Term>
-}
-
-pub enum TermRef<'a> {
-    Atom(Level, &'a Cell<RegType>, &'a Atom),
-    Clause(Level, &'a Cell<RegType>, &'a Atom, &'a Vec<Box<Term>>),
-    Var(Level, &'a Cell<VarReg>, &'a Var)
-}
-
-pub enum FactInstruction {
-    GetStructure(Level, Atom, usize, RegType),
-    GetValue(RegType, usize),
-    GetVariable(RegType, usize),
-    UnifyVariable(RegType),
-    UnifyValue(RegType)
-}
-
-pub enum QueryInstruction {
-    PutStructure(Level, Atom, usize, RegType),
-    PutValue(RegType, usize),
-    PutVariable(RegType, usize),
-    SetVariable(RegType),
-    SetValue(RegType)
-}
-
-pub enum ControlInstruction {
-    Allocate(usize),
-    Call(Atom, usize),
-    Deallocate,
-    Proceed
-}
-
-pub type CompiledFact = Vec<FactInstruction>;
-
-pub type CompiledQuery = Vec<QueryInstruction>;
-
-pub enum Line {
-    Control(ControlInstruction),    
-    Fact(CompiledFact),
-    Query(CompiledQuery)
-}
-
-pub type Code = Vec<Line>;
-
-#[derive(Clone, Copy, PartialEq)]
-pub enum Addr {
-    HeapCell(usize),
-    RegNum(usize),
-    StackCell(usize),
-}
-
-#[derive(Clone, PartialEq)]
-pub enum HeapCellValue {
-    NamedStr(usize, Atom),
-    Ref(usize),
-    Str(usize)
-}
-
-impl HeapCellValue {
-    pub fn as_ref(&self, focus: usize) -> HeapCellRef {
-        match self {
-            &HeapCellValue::Ref(r) => HeapCellRef::Ref(r),
-            &HeapCellValue::Str(s) => HeapCellRef::Str(s),
-            &HeapCellValue::NamedStr(_, _) => HeapCellRef::Str(focus)
-        }
-    }
-}
-
-#[derive(Copy, Clone)]
-pub enum HeapCellRef {
-    Ref(usize),
-    Str(usize)
-}
-
-impl HeapCellRef {
-    pub fn heap_offset(&self) -> usize {
-        match self {
-            &HeapCellRef::Ref(r) | &HeapCellRef::Str(r) => r
-        }
-    }        
-}
-
-impl From<HeapCellRef> for HeapCellValue {
-    fn from(hcr: HeapCellRef) -> HeapCellValue {
-        match hcr {
-            HeapCellRef::Ref(r) => HeapCellValue::Ref(r),
-            HeapCellRef::Str(s) => HeapCellValue::Str(s)
-        }
-    }
-}
-
-#[derive(Clone, Copy)]
-pub enum CodePtr {
-    DirEntry(usize),
-    TopLevel
-}
-
-impl Add<usize> for CodePtr {
-    type Output = CodePtr;
-    fn add(self, rhs: usize) -> Self::Output {
-        match self {
-            CodePtr::DirEntry(p) => CodePtr::DirEntry(p + rhs),
-            CodePtr::TopLevel => CodePtr::TopLevel
-        }
-    }
-}
-
-impl AddAssign<usize> for CodePtr {
-    fn add_assign(&mut self, rhs: usize) {
-        match self {
-            &mut CodePtr::DirEntry(ref mut p) => *p += rhs,
-            _ => {}
-        }
-    }
-}
-
-pub type Heap = Vec<HeapCellValue>;
-
-pub type Registers = Vec<HeapCellRef>;
-
-impl Term {
-    pub fn subterms(&self) -> usize {
-        match self {
-            &Term::Clause(_, _, ref terms) => terms.len(),
-            _ => 1
-        }
-    }
-
-    pub fn name(&self) -> &Atom {
-        match self {
-            &Term::Atom(_, ref atom)
-            | &Term::Var(_, ref atom)
-            | &Term::Clause(_, ref atom, _) => atom
-        }
-    }
-
-    pub fn arity(&self) -> usize {
-        match self {
-            &Term::Atom(_, _) | &Term::Var(_, _) => 0,
-            &Term::Clause(_, _, ref child_terms) => child_terms.len()
-        }
-    }
-}

src/l2/codegen.rs

@@ -1,469 +0,0 @@
-use l2::ast::*;
-use l2::iterators::{FactIterator, QueryIterator};
-
-use std::cell::Cell;
-use std::cmp::max;
-use std::collections::HashMap;
-use std::fmt;
-use std::vec::Vec;
-
-impl fmt::Display for FactInstruction {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &FactInstruction::GetStructure(Level::Deep, ref name, ref arity, ref r) =>
-                write!(f, "get_structure {}/{}, {}", name, arity, r),
-            &FactInstruction::GetStructure(Level::Shallow, ref name, ref arity, ref r) =>
-                write!(f, "get_structure {}/{}, A{}", name, arity, r.reg_num()),
-            &FactInstruction::GetValue(ref x, ref a) =>
-                write!(f, "get_value {}, A{}", x, a),
-            &FactInstruction::GetVariable(ref x, ref a) =>
-                write!(f, "get_variable {}, A{}", x, a),
-            &FactInstruction::UnifyVariable(ref r) =>
-                write!(f, "unify_variable {}", r),
-            &FactInstruction::UnifyValue(ref r) =>
-                write!(f, "unify_value {}", r)
-        }
-    }
-}
-
-impl fmt::Display for QueryInstruction {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &QueryInstruction::PutStructure(Level::Deep, ref name, ref arity, ref r) =>
-                write!(f, "put_structure {}/{}, A{}", name, arity, r.reg_num()),
-            &QueryInstruction::PutStructure(Level::Shallow, ref name, ref arity, ref r) =>
-                write!(f, "put_structure {}/{}, {}", name, arity, r),
-            &QueryInstruction::PutValue(ref x, ref a) =>
-                write!(f, "put_value {}, A{}", x, a),
-            &QueryInstruction::PutVariable(ref x, ref a) =>
-                write!(f, "put_variable {}, A{}", x, a),
-            &QueryInstruction::SetVariable(ref r) =>
-                write!(f, "set_variable {}", r),
-            &QueryInstruction::SetValue(ref r) =>
-                write!(f, "set_value {}", r),
-        }
-    }
-}
-
-impl fmt::Display for ControlInstruction {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &ControlInstruction::Allocate(num_cells) =>
-                write!(f, "allocate {}", num_cells),
-            &ControlInstruction::Call(ref name, ref arity) =>
-                write!(f, "call {}/{}", name, arity),
-            &ControlInstruction::Deallocate =>
-                write!(f, "deallocate"),
-            &ControlInstruction::Proceed =>
-                write!(f, "proceed")
-        }
-    }
-}
-
-trait CompilationTarget<'a> {
-    type Iterator : Iterator<Item=TermRef<'a>>;
-
-    fn iter(&'a Term) -> Self::Iterator;
-
-    fn to_structure(Level, Atom, usize, RegType) -> Self;
-
-    fn argument_to_variable(RegType, usize) -> Self;
-    fn argument_to_value(RegType, usize) -> Self;
-    fn subterm_to_variable(RegType) -> Self;
-    fn subterm_to_value(RegType) -> Self;
-
-    fn clause_arg_to_instr(RegType) -> Self;
-}
-
-impl<'a> CompilationTarget<'a> for FactInstruction {
-    type Iterator = FactIterator<'a>;
-
-    fn iter(term: &'a Term) -> Self::Iterator {
-        term.breadth_first_iter()
-    }
-
-    fn to_structure(lvl: Level, atom: Atom, arity: usize, reg: RegType) -> Self {
-        FactInstruction::GetStructure(lvl, atom, arity, reg)
-    }
-
-    fn argument_to_variable(arg: RegType, val: usize) -> Self {
-        FactInstruction::GetVariable(arg, val)
-    }
-
-    fn argument_to_value(arg: RegType, val: usize) -> Self {
-        FactInstruction::GetValue(arg, val)
-    }
-
-    fn subterm_to_variable(val: RegType) -> Self {
-        FactInstruction::UnifyVariable(val)
-    }
-
-    fn subterm_to_value(val: RegType) -> Self {
-        FactInstruction::UnifyValue(val)
-    }
-
-    fn clause_arg_to_instr(val: RegType) -> Self {
-        FactInstruction::UnifyVariable(val)
-    }
-}
-
-impl<'a> CompilationTarget<'a> for QueryInstruction {
-    type Iterator = QueryIterator<'a>;
-
-    fn iter(term: &'a Term) -> Self::Iterator {
-        term.post_order_iter()
-    }
-
-    fn to_structure(lvl: Level, atom: Atom, arity: usize, reg: RegType) -> Self {
-        QueryInstruction::PutStructure(lvl, atom, arity, reg)
-    }
-
-    fn argument_to_variable(arg: RegType, val: usize) -> Self {
-        QueryInstruction::PutVariable(arg, val)
-    }
-
-    fn argument_to_value(arg: RegType, val: usize) -> Self {
-        QueryInstruction::PutValue(arg, val)
-    }
-
-    fn subterm_to_variable(val: RegType) -> Self {
-        QueryInstruction::SetVariable(val)
-    }
-
-    fn subterm_to_value(val: RegType) -> Self {
-        QueryInstruction::SetValue(val)
-    }
-
-    fn clause_arg_to_instr(val: RegType) -> Self {
-        QueryInstruction::SetValue(val)
-    }
-}
-
-struct TermMarker<'a> {
-    bindings: HashMap<&'a Var, VarReg>,
-    arg_c:    usize,
-    perm_c:   usize,
-    temp_c:   usize
-}
-
-impl<'a> TermMarker<'a> {
-    fn new() -> TermMarker<'a> {
-        TermMarker { bindings: HashMap::new(),
-                     arg_c:    1,
-                     perm_c:   1,
-                     temp_c:   1 }
-    }
-
-    fn contains_var(&self, var: &'a Var) -> bool {
-        self.bindings.contains_key(var)
-    }
-
-    fn get(&self, var: &'a Var) -> VarReg {
-        *self.bindings.get(var).unwrap()
-    }
-
-    fn insert(&mut self, var: &'a Var, r: VarReg) {
-        self.bindings.insert(var, r);
-    }
-
-    fn mark_non_var(&mut self, lvl: Level, cell: &Cell<RegType>) {
-        let reg_type = cell.get();
-
-        if reg_type.reg_num() == 0 {
-            match lvl {
-                Level::Deep if reg_type.is_perm() => {
-                    let perm = self.perm_c;
-                    self.perm_c += 1;
-                    cell.set(RegType::Perm(perm));
-                },
-                Level::Deep => {
-                    let temp = self.temp_c;
-                    self.temp_c += 1;
-                    cell.set(RegType::Temp(temp));
-                },
-                Level::Shallow if reg_type.is_perm() => {
-                    let arg = self.arg_c;
-                    self.arg_c += 1;
-                    cell.set(RegType::Perm(arg));
-                },
-                Level::Shallow => {
-                    let arg = self.arg_c;
-                    self.arg_c += 1;
-                    cell.set(RegType::Temp(arg));
-                }
-            };
-        }
-    }
-
-    fn mark_old_var(&mut self, lvl: Level, var: &'a Var) -> VarReg
-    {
-        let reg = self.get(var);
-
-        match lvl {
-            Level::Deep => VarReg::Norm(reg.norm()),
-            Level::Shallow => {
-                let reg = VarReg::ArgAndNorm(reg.norm(), self.arg_c);
-
-                self.arg_c += 1;
-                self.insert(var, reg);
-
-                reg
-            }
-        }
-    }
-
-    fn mark_new_var(&mut self, lvl: Level, var: &'a Var, reg: RegType) -> VarReg
-    {
-        let inner_reg = if reg.is_perm() {
-            let perm = self.perm_c;
-            self.perm_c += 1;
-            RegType::Perm(perm)
-        } else {
-            let temp = self.temp_c;
-            self.temp_c += 1;
-            RegType::Temp(temp)
-        };
-
-        let reg = match lvl {
-            Level::Deep => VarReg::Norm(inner_reg),
-            Level::Shallow => {
-                let reg = VarReg::ArgAndNorm(inner_reg, self.arg_c);
-                self.arg_c += 1;
-                reg
-            }
-        };
-
-        self.insert(var, reg);
-        reg
-    }
-
-    fn advance_at_header(&mut self, term: &'a Term) {
-        self.arg_c = 1;
-        self.temp_c = max(term.subterms(), self.temp_c) + 1;
-    }
-
-    fn advance(&mut self, term: &'a Term) {
-        self.arg_c = 1;
-        self.temp_c = term.subterms() + 1;
-    }
-}
-
-#[derive(Copy, Clone)]
-enum TermStatus {
-    New, Old, Recurrent
-}
-
-pub struct CodeGenerator<'a> {
-    marker: TermMarker<'a>
-}
-
-type VariableFixture<'a>  = (TermStatus, Vec<&'a Cell<VarReg>>);
-type VariableFixtures<'a> = HashMap<&'a Var, VariableFixture<'a>>;
-
-impl<'a> CodeGenerator<'a> {
-    pub fn new() -> Self {
-        CodeGenerator { marker: TermMarker::new() }
-    }
-
-    pub fn vars(&self) -> &HashMap<&Var, VarReg> {
-        &self.marker.bindings
-    }
-
-    fn to_structure<Target>(&mut self,
-                            lvl: Level,
-                            name: &'a Atom,
-                            cell: &'a Cell<RegType>,
-                            arity: usize)
-                            -> Target
-        where Target: CompilationTarget<'a>
-    {
-        self.marker.mark_non_var(lvl, cell);
-        Target::to_structure(lvl, name.clone(), arity, cell.get())
-    }
-
-    fn var_term<Target>(&mut self,
-                        lvl: Level,
-                        cell: &'a Cell<VarReg>,
-                        var: &'a Var)
-                        -> Target
-        where Target: CompilationTarget<'a>
-    {
-        if !self.marker.contains_var(var) {
-            let reg = self.marker.mark_new_var(lvl, var, cell.get().norm());
-            cell.set(reg);
-
-            match reg {
-                VarReg::ArgAndNorm(arg, norm) =>
-                    Target::argument_to_variable(arg, norm),
-                VarReg::Norm(norm) =>
-                    Target::subterm_to_variable(norm)
-            }
-        } else {
-            let reg = self.marker.mark_old_var(lvl, var);
-            cell.set(reg);
-
-            match reg {
-                VarReg::ArgAndNorm(arg, norm) =>
-                    Target::argument_to_value(arg, norm),
-                VarReg::Norm(norm) =>
-                    Target::subterm_to_value(norm)
-            }
-        }
-    }
-
-    fn non_var_subterm<Target>(&mut self, cell: &'a Cell<RegType>) -> Target
-        where Target: CompilationTarget<'a>
-    {
-        self.marker.mark_non_var(Level::Deep, cell);
-        Target::clause_arg_to_instr(cell.get())
-    }
-
-    fn subterm_to_instr<Target>(&mut self, subterm: &'a Term) -> Target
-        where Target: CompilationTarget<'a>
-    {
-        match subterm {
-            &Term::Atom(ref cell, _) | &Term::Clause(ref cell, _, _) =>
-                self.non_var_subterm(cell),
-            &Term::Var(ref cell, ref var) =>
-                self.var_term(Level::Deep, cell, var)
-        }
-    }
-
-    fn compile_target<Target>(&mut self, term: &'a Term) -> Vec<Target>
-        where Target: CompilationTarget<'a>
-    {
-        let iter       = Target::iter(term);
-        let mut target = Vec::new();
-
-        for term in iter {
-            match term {
-                TermRef::Atom(lvl, term, atom) =>
-                    target.push(self.to_structure(lvl, atom, term, 0)),
-                TermRef::Clause(lvl, term, atom, terms) => {
-                    target.push(self.to_structure(lvl, atom, term, terms.len()));
-
-                    for subterm in terms {
-                        target.push(self.subterm_to_instr(subterm.as_ref()));
-                    }
-                },
-                TermRef::Var(lvl @ Level::Shallow, ref cell, ref var) =>
-                    target.push(self.var_term(lvl, cell, var)),
-                _ => {}
-            };
-        }
-
-        target
-    }
-
-    fn mark_vars_in_term<Iter>(iter: Iter, vs: &mut VariableFixtures<'a>)
-        where Iter : Iterator<Item=TermRef<'a>>
-    {
-        for term in iter {
-            if let TermRef::Var(_, reg_cell, var) = term {
-                let mut status = vs.entry(var)
-                                   .or_insert((TermStatus::New, Vec::new()));
-
-                status.1.push(reg_cell);
-
-                match status.0 {
-                    TermStatus::Old => status.0 = TermStatus::Recurrent,
-                    _ => {}
-                };
-            }
-        }
-
-        for &mut (ref mut term_status, ref mut cb) in vs.values_mut() {
-            match *term_status {
-                TermStatus::New => *term_status = TermStatus::Old,
-                TermStatus::Recurrent => {
-                    for cell_reg in cb.drain(0..) {
-                        cell_reg.set(VarReg::Norm(RegType::Perm(0)));
-                    }
-                },
-                _ => {}
-            }
-        }
-    }
-
-    fn mark_perm_vars(rule: &'a Rule) -> VariableFixtures {
-        let &Rule { head: (ref p0, ref p1), ref clauses } = rule;
-        let mut vfs = HashMap::new();
-
-        let iter = p0.breadth_first_iter().chain(p1.breadth_first_iter());
-
-        Self::mark_vars_in_term(iter, &mut vfs);
-
-        for term in clauses {
-            Self::mark_vars_in_term(term.breadth_first_iter(), &mut vfs);
-        }
-
-        vfs
-    }
-
-    fn add_conditional_call(compiled_query: &mut Code, term: &Term) {
-        match term {
-            &Term::Atom(_, ref atom) => {
-                let call = ControlInstruction::Call(atom.clone(), 0);
-                compiled_query.push(Line::Control(call));
-            },
-            &Term::Clause(_, ref atom, ref terms) => {
-                let call = ControlInstruction::Call(atom.clone(), terms.len());
-                compiled_query.push(Line::Control(call));
-            },
-            _ => {}
-        }
-    }
-
-    pub fn compile_rule(&mut self, rule: &'a Rule) -> Code {
-        let vfs = Self::mark_perm_vars(&rule);
-        let &Rule { head: (ref p0, ref p1), ref clauses } = rule;
-        let mut perm_vars = 0;
-
-        for &(term_status, _) in vfs.values() {
-            if let TermStatus::Recurrent = term_status {
-                perm_vars += 1;
-            }
-        }
-
-        let mut body = Vec::new();
-
-        body.push(Line::Control(ControlInstruction::Allocate(perm_vars)));
-
-        self.marker.advance(p0);
-        body.push(Line::Fact(self.compile_target(p0)));
-
-        self.marker.advance_at_header(p1);
-        body.push(Line::Query(self.compile_target(p1)));
-        Self::add_conditional_call(&mut body, p1);
-
-        body = clauses.iter()
-            .map(|ref term| self.compile_query(term))
-            .fold(body, |mut body, ref mut cqs| {
-                body.append(cqs);
-                body
-            });
-
-        body.push(Line::Control(ControlInstruction::Deallocate));
-
-        body
-    }
-
-    pub fn compile_fact(&mut self, term: &'a Term) -> Code {
-        self.marker.advance(term);
-
-        let mut compiled_fact = vec![Line::Fact(self.compile_target(term))];
-        let proceed = Line::Control(ControlInstruction::Proceed);
-
-        compiled_fact.push(proceed);
-        compiled_fact
-    }
-
-    pub fn compile_query(&mut self, term: &'a Term) -> Code {
-        self.marker.advance(term);
-
-        let mut compiled_query = vec![Line::Query(self.compile_target(term))];
-        Self::add_conditional_call(&mut compiled_query, term);
-
-        compiled_query
-    }
-}

src/l2/heapview.rs

@@ -1,64 +0,0 @@
-use l2::ast::*;
-
-use std::vec::Vec;
-
-#[derive(Clone, Copy)]
-pub enum HeapCellView<'a> {
-    Str(usize, &'a Atom),
-    Var(usize)
-}
-
-pub struct HeapCellViewer<'a> {
-    heap: &'a Heap,
-    state_stack: Vec<(usize, &'a HeapCellValue)>
-}
-
-impl<'a> HeapCellViewer<'a> {
-    pub fn new(heap: &'a Heap, focus: usize) -> Self {
-        HeapCellViewer {
-            heap: heap,
-            state_stack: vec![(focus, &heap[focus])]
-        }
-    }
-
-    fn follow(&self, value: &'a HeapCellValue) -> &'a HeapCellValue {
-        match value {
-            &HeapCellValue::NamedStr(_, _) => value,
-            &HeapCellValue::Ref(cell_num) | &HeapCellValue::Str(cell_num) =>
-                &self.heap[cell_num],
-        }
-    }
-}
-
-impl<'a> Iterator for HeapCellViewer<'a> {
-    type Item = HeapCellView<'a>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        while let Some(hcv) = self.state_stack.pop() {
-            match hcv {
-                (focus, &HeapCellValue::NamedStr(arity, ref name)) => {
-                    for i in (1 .. arity + 1).rev() {
-                        self.state_stack.push((focus + i, &self.heap[focus + i]));
-                    }                            
-                    
-                    return Some(HeapCellView::Str(arity, name));
-                },
-                (_, &HeapCellValue::Ref(cell_num)) => {
-                    let new_hcv = self.follow(hcv.1);
-
-                    if hcv.1 == new_hcv {
-                        return Some(HeapCellView::Var(cell_num));
-                    } else {
-                        self.state_stack.push((cell_num, new_hcv));
-                    }
-                },
-                (_, &HeapCellValue::Str(cell_num)) => {
-                    let new_hcv = self.follow(hcv.1);
-                    self.state_stack.push((cell_num, new_hcv));
-                }
-            }
-        }
-
-        None
-    }
-}

src/l2/iterators.rs

@@ -1,175 +0,0 @@
-use l2::ast::*;
-
-use std::cell::Cell;
-use std::collections::VecDeque;
-use std::vec::Vec;
-
-enum IteratorState<'a> {
-    Atom(Level, &'a Cell<RegType>, &'a Atom),
-    Clause(Level, usize, &'a Cell<RegType>, &'a Atom, &'a Vec<Box<Term>>),
-    IsolatedAtom(&'a Cell<RegType>, &'a Atom),
-    IsolatedVar(&'a Cell<VarReg>, &'a Var),
-    RootClause(usize, &'a Vec<Box<Term>>),
-    Var(Level, &'a Cell<VarReg>, &'a Var)
-}
-
-impl<'a> IteratorState<'a> {
-    fn to_state(lvl: Level, term: &'a Term) -> IteratorState<'a>
-    {
-        match term {
-            &Term::Atom(ref cell, ref atom) =>
-                IteratorState::Atom(lvl, cell, atom),
-            &Term::Clause(ref cell, ref atom, ref child_terms) =>
-                IteratorState::Clause(lvl, 0, cell, atom, child_terms),
-            &Term::Var(ref cell, ref var) =>
-                IteratorState::Var(lvl, cell, var)
-        }
-    }
-}
-
-pub struct QueryIterator<'a> {
-    state_stack: Vec<IteratorState<'a>>
-}
-
-impl<'a> QueryIterator<'a> {
-    fn push_clause(&mut self,
-                   lvl: Level,
-                   child_num: usize,
-                   cell: &'a Cell<RegType>,
-                   name: &'a Atom,
-                   child_terms: &'a Vec<Box<Term>>)
-    {
-        self.state_stack.push(IteratorState::Clause(lvl,
-                                                    child_num,
-                                                    cell,
-                                                    name,
-                                                    child_terms));
-    }
-
-    fn push_root_clause(&mut self,
-                        child_num: usize,
-                        child_terms: &'a Vec<Box<Term>>)
-    {
-        self.state_stack.push(IteratorState::RootClause(child_num, child_terms));
-    }
-
-    fn push_subterm(&mut self, lvl: Level, term: &'a Term) {
-        self.state_stack.push(IteratorState::to_state(lvl, term));
-    }
-
-    fn new(term: &'a Term) -> QueryIterator<'a> {
-        let state = match term {
-            &Term::Atom(ref cell, ref atom) =>
-                IteratorState::IsolatedAtom(cell, atom),
-            &Term::Clause(_, _, ref terms) =>
-                IteratorState::RootClause(0, terms),
-            &Term::Var(ref cell, ref var) =>
-                IteratorState::IsolatedVar(cell, var)
-        };
-
-        QueryIterator { state_stack: vec![state] }
-    }
-}
-
-impl<'a> Iterator for QueryIterator<'a> {
-    type Item = TermRef<'a>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        while let Some(iter_state) = self.state_stack.pop() {
-            match iter_state {
-                IteratorState::Atom(lvl, cell, atom) =>
-                    return Some(TermRef::Atom(lvl, cell, atom)),
-                IteratorState::Clause(lvl, child_num, cell, atom, child_terms) => {
-                    if child_num == child_terms.len() {
-                        return Some(TermRef::Clause(lvl, cell, atom, child_terms));
-                    } else {
-                        self.push_clause(lvl, child_num + 1, cell, atom, child_terms);
-                        self.push_subterm(Level::Deep, child_terms[child_num].as_ref());
-                    }
-                },
-                IteratorState::IsolatedAtom(cell, atom) =>
-                    return Some(TermRef::Atom(Level::Shallow, cell, atom)),
-                IteratorState::IsolatedVar(cell, var) =>
-                    return Some(TermRef::Var(Level::Shallow, cell, var)),
-                IteratorState::RootClause(child_num, child_terms) => {
-                    if child_num == child_terms.len() {
-                        return None;
-                    } else {
-                        self.push_root_clause(child_num + 1, child_terms);
-                        self.push_subterm(Level::Shallow, child_terms[child_num].as_ref());
-                    }
-                },
-                IteratorState::Var(lvl, cell, var) =>
-                    return Some(TermRef::Var(lvl, cell, var))
-            };
-        }
-
-        None
-    }
-}
-
-pub struct FactIterator<'a> {
-    state_queue: VecDeque<IteratorState<'a>>,
-}
-
-impl<'a> FactIterator<'a> {
-    fn push_subterm(&mut self, lvl: Level, term: &'a Term) {
-        self.state_queue.push_back(IteratorState::to_state(lvl, term));
-    }
-
-    fn new(term: &'a Term) -> FactIterator<'a> {
-        let states = match term {
-            &Term::Atom(ref cell, ref atom) =>
-                vec![IteratorState::IsolatedAtom(cell, atom)],
-            &Term::Clause(_, _, ref terms) =>
-                vec![IteratorState::RootClause(0, terms)],
-            &Term::Var(ref cell, ref var) =>
-                vec![IteratorState::IsolatedVar(cell, var)]
-        };
-
-        FactIterator { state_queue:  VecDeque::from(states) }
-    }
-}
-
-impl<'a> Iterator for FactIterator<'a> {
-    type Item = TermRef<'a>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        while let Some(state) = self.state_queue.pop_front() {
-            match state {
-                IteratorState::Atom(lvl, cell, atom) =>
-                    return Some(TermRef::Atom(lvl, cell, atom)),
-                IteratorState::Clause(lvl, _, cell, atom, child_terms) => {
-                    for child_term in child_terms {
-                        self.push_subterm(Level::Deep, child_term);
-                    }
-
-                    return Some(TermRef::Clause(lvl, cell, atom, child_terms));
-                },
-                IteratorState::IsolatedAtom(cell, atom) =>
-                    return Some(TermRef::Atom(Level::Shallow, cell, atom)),
-                IteratorState::IsolatedVar(cell, var) =>
-                    return Some(TermRef::Var(Level::Shallow, cell, var)),
-                IteratorState::RootClause(_, child_terms) => {
-                    for child_term in child_terms {
-                        self.push_subterm(Level::Shallow, child_term);
-                    }
-                },
-                IteratorState::Var(lvl, cell, var) =>
-                    return Some(TermRef::Var(lvl, cell, var))
-            }
-        }
-
-        None
-    }
-}
-
-impl Term {
-    pub fn post_order_iter(&self) -> QueryIterator {
-        QueryIterator::new(self)
-    }
-
-    pub fn breadth_first_iter(&self) -> FactIterator {
-        FactIterator::new(self)
-    }
-}

src/l2/l2_parser.lalrpop

@@ -1,45 +0,0 @@
-use l2::ast::*;
-
-use std::cell::Cell;
-
-grammar;
-
-pub TopLevel: TopLevel = {
-    "?-" <t:Term> "." => TopLevel::Query(t),
-    <r:Rule> "."      => TopLevel::Rule(r),
-    <t:Term> "."      => TopLevel::Fact(t),
-};
-
-Atom : Atom = {
-    r"[a-z][a-z0-9_]*" => <>.trim().to_string(),
-};
-
-BoxedTerm : Box<Term> = {
-    <t:Term> => Box::new(t),
-};
-
-Clause : Term = {
-    <a:Atom> "(" <ts: (<BoxedTerm> ",")*> <t:BoxedTerm> ")" => {
-     	let mut ts = ts;
-     	ts.push(t);
-	Term::Clause(Cell::new(RegType::Temp(0)), a, ts)
-    },
-};
-
-Rule : Rule = {
-    <c:Clause> ":-" <h:Term> <cs: ("," <Term>)*> =>
-         Rule { head: (c, h), clauses: cs },
-    <a:Atom> ":-" <h:Term> <cs: ("," <Term>)*> =>
-         Rule { head: (Term::Atom(Cell::new(RegType::Temp(0)), a), h),
-	        clauses: cs }
-};
-
-Term : Term = {
-    <Clause> => <>,
-    <Atom> => Term::Atom(Cell::new(RegType::Temp(0)), <>),
-    <Var>  => Term::Var(Cell::new(VarReg::Norm(RegType::Temp(0))), <>),
-};
-
-Var : Var = {
-    r"[A-Z][a-z0-9_]*" => <>.trim().to_string(),
-};

src/l2/machine.rs

@@ -1,456 +0,0 @@
-use l2::ast::*;
-use l2::codegen::*;
-use l2::heapview::*;
-use l2::stack::*;
-
-use std::collections::HashMap;
-use std::vec::Vec;
-
-#[derive(Clone, Copy)]
-enum MachineMode {
-    Read,
-    Write
-}
-
-struct MachineState {
-    h: usize,
-    s: usize,
-    p: CodePtr,
-    cp: CodePtr,
-    fail: bool,
-    heap: Heap,
-    mode: MachineMode,
-    stack: Stack,
-    registers: Registers
-}
-
-type CodeDir = HashMap<(Atom, usize), usize>;
-
-pub struct Machine {
-    ms: MachineState,
-    code: Code,
-    code_dir: CodeDir
-}
-
-impl Machine {
-    pub fn new() -> Self {
-        Machine {
-            ms: MachineState::new(),
-            code: Vec::new(),
-            code_dir: HashMap::new()
-        }
-    }
-
-    pub fn failed(&self) -> bool {
-        self.ms.fail
-    }
-
-    pub fn add_fact(&mut self, fact: &Term, mut code: Code) {
-        let p = self.code.len();
-        let name  = fact.name().clone();
-        let arity = fact.arity();
-
-        self.code.append(&mut code);
-        self.code_dir.insert((name, arity), p);
-    }
-
-    pub fn add_rule(&mut self, rule: &Rule, mut code: Code) {
-        let p = self.code.len();
-        let name  = rule.head.0.name().clone();
-        let arity = rule.head.0.arity();
-
-        self.code.append(&mut code);
-        self.code_dir.insert((name, arity), p);
-    }
-
-    fn execute_instr(&mut self, instr: &Line) -> bool {
-        let mut instr = instr;
-
-        loop {
-            match instr {
-                &Line::Fact(ref fact) => {
-                    for fact_instr in fact {
-                        self.ms.execute_fact_instr(&fact_instr);
-                    }
-                    self.ms.p += 1;
-                },
-                &Line::Query(ref query) => {
-                    for query_instr in query {
-                        self.ms.execute_query_instr(&query_instr);
-                    }
-                    self.ms.p += 1;
-                },
-                &Line::Control(ref control_instr) =>
-                    self.ms.execute_ctrl_instr(&self.code_dir, control_instr),
-            }
-
-            if self.failed() {
-                return false;
-            }
-
-            match self.ms.p {
-                CodePtr::DirEntry(p) if p < self.code.len() =>
-                    instr = &self.code[p],
-                _ => break
-            }
-        }
-
-        true
-    }
-
-    fn heap_view(&self, var_dir: HashMap<&Var, HeapCellRef>) -> String {
-        let mut result = String::new();
-
-        for (var, hcr) in var_dir {
-            let mut arities = Vec::new();
-            let viewer = HeapCellViewer::new(&self.ms.heap, hcr.heap_offset());
-
-            if result != "" {
-                result += "\n";
-            }
-
-            result += var.as_str();
-            result += " = ";
-
-            for view in viewer {
-                match arities.pop() {
-                    Some(n) => arities.push(n-1),
-                    None => {}
-                }
-
-                if !(arities.is_empty() || result.ends_with("(")) {
-                    result += ", ";
-                }
-
-                match view {
-                    HeapCellView::Str(arity, ref name) => {
-                        result += name.as_str();
-
-                        if arity > 0 {
-                            arities.push(arity);
-                            result += "(";
-                        }
-                    },
-                    HeapCellView::Var(cell_num) => {
-                        result += "_";
-                        result += cell_num.to_string().as_str();
-                    }
-                }
-
-                while let Some(&0) = arities.last() {
-                    result += ")";
-                    arities.pop();
-                }
-            }
-        }
-
-        result
-    }
-
-    pub fn run_query(&mut self, code: Code, cg: &CodeGenerator) -> Option<String>
-    {
-        let mut succeeded = true;
-
-        for instr in code.iter().take(1) {
-            succeeded = self.execute_instr(&instr);
-        }
-
-        let mut heap_locs = HashMap::new();
-
-        if succeeded {            
-            for (var, vr) in cg.vars() {
-                let hcr = self.ms.registers[vr.root_register()];
-                heap_locs.insert(*var, hcr);
-            }
-
-            for instr in code.iter().skip(1) {
-                succeeded = self.execute_instr(&instr);
-                if !succeeded {
-                    break;
-                }
-            }
-        }
-        
-        if succeeded {
-            Some(self.heap_view(heap_locs))
-        } else {
-            None
-        }   
-    }
-
-    pub fn reset(&mut self) {
-        self.ms.reset();
-    }
-}
-
-impl MachineState {
-    fn new() -> MachineState {
-        MachineState { h: 0,
-                       s: 0,
-                       p: CodePtr::TopLevel,
-                       cp: CodePtr::TopLevel,
-                       fail: false,
-                       heap: Vec::with_capacity(256),
-                       mode: MachineMode::Write,
-                       stack: Stack::new(),
-                       registers: vec![HeapCellRef::Ref(0); 32] }
-    }
-
-    fn register_mut(&mut self, r: RegType) -> &mut HeapCellRef {
-        match r {
-            RegType::Temp(r) => &mut self.registers[r],
-            RegType::Perm(r) => &mut self.stack[r]
-        }
-    }
-
-    fn lookup(&self, a: Addr) -> HeapCellRef {
-        match a {
-            Addr::HeapCell(r)  => self.heap[r].as_ref(r),
-            Addr::RegNum(r)    => self.registers[r],
-            Addr::StackCell(s) => self.stack[s]
-        }
-    }
-
-    fn deref(&self, a: Addr) -> Addr {
-        let mut a = a;
-
-        loop {
-            if let HeapCellRef::Ref(value) = self.lookup(a) {
-                if let Addr::HeapCell(av) = a {
-                    if value != av {
-                        a = Addr::HeapCell(value);
-                        continue;
-                    }
-                } else {
-                    a = Addr::HeapCell(value);
-                    continue;
-                }
-            }
-
-            return a;
-        };
-    }
-
-    fn is_unbound(hc: &HeapCellValue, index: usize) -> bool {
-        match hc {
-            &HeapCellValue::Ref(r) => r == index,
-            _ => false
-        }
-    }
-
-    fn bind(&mut self, a: Addr, val: usize) {
-        let mut a = a;
-
-        loop {
-            match a {
-                addr @ Addr::RegNum(_) | addr @ Addr::StackCell(_) => {
-                    if let HeapCellRef::Ref(hc) = self.lookup(addr) {
-                        a = Addr::HeapCell(hc);
-                    } else if Self::is_unbound(&self.heap[val], val) {
-                        self.heap[val] = HeapCellValue::from(self.lookup(addr));
-                        break;
-                    } else {
-                        self.fail = true;
-                        break;
-                    }
-                },
-                Addr::HeapCell(hc) => {
-                    if Self::is_unbound(&self.heap[hc], hc) {
-                        self.heap[hc] = HeapCellValue::Ref(val);
-                        break;
-                    } else if Self::is_unbound(&self.heap[val], val) {
-                        self.heap[val] = HeapCellValue::Ref(hc);
-                        break;
-                    } else {
-                        self.fail = true;
-                        break;
-                    }
-                }
-            };
-        }
-    }
-
-    fn unify(&mut self, a1: Addr, a2: Addr) {
-        let mut pdl = vec![a1, a2];
-
-        self.fail = false;
-
-        while !(pdl.is_empty() || self.fail) {
-            let d1 = self.deref(pdl.pop().unwrap());
-            let d2 = self.deref(pdl.pop().unwrap());
-
-            if d1 != d2 {
-                match (self.lookup(d1), self.lookup(d2)) {
-                    (HeapCellRef::Ref(hc), _) =>
-                        self.bind(d2, hc),
-                    (_, HeapCellRef::Ref(hc)) =>
-                        self.bind(d1, hc),
-                    (HeapCellRef::Str(a1), HeapCellRef::Str(a2)) => {
-                        let r1 = &self.heap[a1];
-                        let r2 = &self.heap[a2];
-
-                        if let &HeapCellValue::NamedStr(n1, ref f1) = r1 {
-                            if let &HeapCellValue::NamedStr(n2, ref f2) = r2 {
-                                if n1 == n2 && *f1 == *f2 {
-                                    for i in 1 .. n1 + 1 {
-                                        pdl.push(Addr::HeapCell(a1 + i));
-                                        pdl.push(Addr::HeapCell(a2 + i));
-                                    }
-
-                                    continue;
-                                }
-                            }
-                        }
-
-                        self.fail = true;
-                    },
-                };
-            }
-        }
-    }
-
-    fn execute_query_instr(&mut self, instr: &QueryInstruction) {
-        match instr {
-            &QueryInstruction::PutStructure(_, ref name, arity, reg) => {
-                self.heap.push(HeapCellValue::Str(self.h + 1));
-                self.heap.push(HeapCellValue::NamedStr(arity, name.clone()));
-
-                *self.register_mut(reg) = HeapCellRef::Str(self.h + 1);
-
-                self.h += 2;
-            },
-            &QueryInstruction::PutValue(norm, arg) =>
-                self.registers[arg] = match norm {
-                    RegType::Temp(reg) => self.registers[reg],
-                    RegType::Perm(reg) => self.stack[reg]
-                },
-            &QueryInstruction::PutVariable(norm, arg) => {
-                self.heap.push(HeapCellValue::Ref(self.h));
-
-                *self.register_mut(norm) = HeapCellRef::Ref(self.h);
-                self.registers[arg] = HeapCellRef::Ref(self.h);
-
-                self.h += 1;
-            },
-            &QueryInstruction::SetVariable(reg) => {
-                self.heap.push(HeapCellValue::Ref(self.h));
-                *self.register_mut(reg) = HeapCellRef::Ref(self.h);
-
-                self.h += 1;
-            },
-            &QueryInstruction::SetValue(reg) => {
-                let heap_val = self.lookup(Addr::from(reg));
-                self.heap.push(HeapCellValue::from(heap_val));
-
-                self.h += 1;
-            },
-        }
-    }
-
-    fn execute_fact_instr(&mut self, instr: &FactInstruction) {
-        match instr {
-            &FactInstruction::GetStructure(_, ref name, arity, reg) => {
-                let addr = self.deref(Addr::from(reg));
-
-                match self.lookup(addr) {
-                    HeapCellRef::Str(a) => {
-                        let result = &self.heap[a];
-
-                        if let &HeapCellValue::NamedStr(narity, ref str) = result {
-                            if narity == arity && *name == *str {
-                                self.s = a + 1;
-                                self.mode = MachineMode::Read;
-                            } else {
-                                self.fail = true;
-                            }
-                        }
-                    },
-                    HeapCellRef::Ref(_) => {
-                        self.heap.push(HeapCellValue::Str(self.h + 1));
-                        self.heap.push(HeapCellValue::NamedStr(arity, name.clone()));
-
-                        let h = self.h;
-
-                        self.bind(addr, h);
-
-                        self.h += 2;
-                        self.mode = MachineMode::Write;
-                    }
-                };
-            },
-            &FactInstruction::GetVariable(norm, arg) =>
-                *self.register_mut(norm) = self.registers[arg],
-            &FactInstruction::GetValue(norm, arg) =>
-                self.unify(Addr::from(norm), Addr::RegNum(arg)),
-            &FactInstruction::UnifyVariable(reg) => {
-                match self.mode {
-                    MachineMode::Read  =>
-                        *self.register_mut(reg) = self.heap[self.s].as_ref(self.s),
-                    MachineMode::Write => {
-                        self.heap.push(HeapCellValue::Ref(self.h));
-                        *self.register_mut(reg) = HeapCellRef::Ref(self.h);
-                        self.h += 1;
-                    }
-                };
-
-                self.s += 1;
-            },
-            &FactInstruction::UnifyValue(reg) => {
-                let s = self.s;
-
-                match self.mode {
-                    MachineMode::Read  =>
-                        self.unify(Addr::from(reg), Addr::HeapCell(s)),
-                    MachineMode::Write => {
-                        let heap_val = self.lookup(Addr::from(reg));
-                        self.heap.push(HeapCellValue::from(heap_val));
-                        self.h += 1;
-                    }
-                };
-
-                self.s += 1;
-            }
-        }
-    }
-
-    fn execute_ctrl_instr(&mut self, code_dir: &CodeDir, instr: &ControlInstruction)
-    {
-        match instr {
-            &ControlInstruction::Allocate(num_cells) => {
-                self.stack.push(self.cp, num_cells);
-                self.p += 1;
-            },
-            &ControlInstruction::Call(ref name, arity) => {
-                let compiled_tl_index = code_dir.get(&(name.clone(), arity))
-                                                .map(|index| *index);
-
-                match compiled_tl_index {
-                    Some(compiled_tl_index) => {
-                        self.cp = self.p + 1;
-                        self.p  = CodePtr::DirEntry(compiled_tl_index);
-                    },
-                    None => self.fail = true
-                };
-            },
-            &ControlInstruction::Deallocate => {
-                self.p = self.stack.get_cp();
-                self.stack.pop();
-            },
-            &ControlInstruction::Proceed =>
-                self.p = self.cp,
-        };
-    }
-
-    fn reset(&mut self) {
-        self.h = 0;
-        self.s = 0;
-        self.p = CodePtr::TopLevel;
-        self.cp = CodePtr::TopLevel;
-
-        self.fail = false;
-        self.heap.clear();
-        self.mode = MachineMode::Write;
-        self.stack = Stack::new();
-        self.registers = vec![HeapCellRef::Ref(0); 32];
-    }
-}

src/l2/mod.rs

@@ -1,7 +0,0 @@
-pub mod ast;
-pub mod heapview;
-pub mod iterators;
-pub mod l2_parser;
-pub mod codegen;
-pub mod machine;
-pub mod stack;

src/l2/stack.rs

@@ -1,60 +0,0 @@
-use l2::ast::*;
-
-use std::ops::{Index, IndexMut};
-use std::vec::Vec;
-
-struct Frame {
-    cp: CodePtr,
-    perms: Vec<HeapCellRef>
-}
-
-impl Frame {
-    fn new(cp: CodePtr, n: usize) -> Self {
-        Frame {
-            cp: cp,
-            perms: vec![HeapCellRef::Ref(0); n]
-        }
-    }
-
-    fn read_pv(&self, i: usize) -> &HeapCellRef {
-        self.perms.index(i)
-    }
-
-    fn read_pv_mut(&mut self, i: usize) -> &mut HeapCellRef {
-        self.perms.index_mut(i)
-    }
-}
-
-pub struct Stack(Vec<Frame>);
-
-impl Stack {
-    pub fn new() -> Self {
-        Stack(Vec::new())
-    }
-    
-    pub fn push(&mut self, cp: CodePtr, n: usize) {
-        self.0.push(Frame::new(cp, n));
-    }
-
-    pub fn get_cp(&self) -> CodePtr {
-        self.0.last().unwrap().cp
-    }
-    
-    pub fn pop(&mut self) {
-        self.0.pop();
-    }
-}
-
-impl Index<usize> for Stack {
-    type Output = HeapCellRef;
-
-    fn index(&self, index: usize) -> &Self::Output {
-        self.0.last().unwrap().read_pv(index - 1)
-    }
-}
-
-impl IndexMut<usize> for Stack {
-    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
-        self.0.last_mut().unwrap().read_pv_mut(index - 1)
-    }
-}

src/l3/and_stack.rs

@@ -1,80 +0,0 @@
-use l3::ast::*;
-
-use std::ops::{Index, IndexMut};
-use std::vec::Vec;
-
-pub struct Frame {
-    pub global_index: usize,
-    pub e: usize,
-    pub cp: CodePtr,
-    perms: Vec<Addr>
-}
-
-impl Frame {
-    fn new(global_index: usize, e: usize, cp: CodePtr, n: usize) -> Self {
-        Frame {
-            global_index: global_index,
-            e: e,
-            cp: cp,
-            perms: vec![Addr::HeapCell(0); n]
-        }
-    }
-}
-
-pub struct AndStack(Vec<Frame>);
-
-impl AndStack {
-    pub fn new() -> Self {
-        AndStack(Vec::new())
-    }
-
-    pub fn push(&mut self, global_index: usize, e: usize, cp: CodePtr, n: usize) {
-        self.0.push(Frame::new(global_index, e, cp, n));
-    }
-
-    pub fn top(&self) -> Option<&Frame> {
-        self.0.last()
-    }
-
-    pub fn len(&self) -> usize {
-        self.0.len()
-    }
-
-    pub fn clear(&mut self) {
-        self.0.clear()
-    }
-
-    // drop the last n frames.
-    pub fn drop_frames(&mut self, n: usize) {
-        let len = self.0.len();
-        self.0.truncate(len - n);
-    }
-}
-
-impl Index<usize> for AndStack {
-    type Output = Frame;
-
-    fn index(&self, index: usize) -> &Self::Output {
-        self.0.index(index)
-    }
-}
-
-impl IndexMut<usize> for AndStack {
-    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
-        self.0.index_mut(index)
-    }
-}
-
-impl Index<usize> for Frame {
-    type Output = Addr;
-
-    fn index(&self, index: usize) -> &Self::Output {
-        self.perms.index(index - 1)
-    }
-}
-
-impl IndexMut<usize> for Frame {
-    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
-        self.perms.index_mut(index - 1)
-    }
-}

src/l3/ast.rs

@@ -1,303 +0,0 @@
-use std::cell::Cell;
-use std::collections::HashMap;
-use std::ops::{Add, AddAssign};
-use std::vec::Vec;
-
-pub type Var = String;
-
-pub type Atom = String;
-
-pub enum PredicateClause {
-    Fact(Term),
-    Rule(Rule)
-}
-
-impl PredicateClause {
-    pub fn name(&self) -> &Atom {
-        match self {
-            &PredicateClause::Fact(ref t) => t.name(),
-            &PredicateClause::Rule(ref rule) => rule.head.0.name()
-        }
-    }
-
-    pub fn arity(&self) -> usize {
-        match self {
-            &PredicateClause::Fact(ref t) => t.arity(),
-            &PredicateClause::Rule(ref rule) => rule.head.0.arity()
-        }
-    }
-}
-
-pub enum TopLevel {
-    Fact(Term),
-    Predicate(Vec<PredicateClause>),
-    Query(Term),
-    Rule(Rule)
-}
-
-#[derive(Clone, Copy)]
-pub enum Level {
-    Deep, Shallow
-}
-
-#[derive(Clone, Copy)]
-pub enum RegType {
-    Perm(usize),
-    Temp(usize)
-}
-
-impl RegType {
-    pub fn reg_num(self) -> usize {
-        match self {
-            RegType::Perm(reg_num) | RegType::Temp(reg_num) => reg_num
-        }
-    }
-
-    pub fn is_perm(self) -> bool {
-        match self {
-            RegType::Perm(_) => true,
-            _ => false
-        }
-    }
-}
-
-#[derive(Clone, Copy)]
-pub enum VarReg {
-    ArgAndNorm(RegType, usize),
-    Norm(RegType)
-}
-
-impl VarReg {
-    pub fn norm(self) -> RegType {
-        match self {
-            VarReg::ArgAndNorm(reg, _) | VarReg::Norm(reg) => reg
-        }
-    }
-
-    pub fn root_register(self) -> usize {
-        match self {
-            VarReg::ArgAndNorm(_, root) => root,
-            VarReg::Norm(root) => root.reg_num()
-        }
-    }
-}
-
-pub enum Term {
-    Atom(Cell<RegType>, Atom),
-    Clause(Cell<RegType>, Atom, Vec<Box<Term>>),
-    Var(Cell<VarReg>, Var)
-}
-
-pub struct Rule {
-    pub head: (Term, Term),
-    pub clauses: Vec<Term>
-}
-
-pub enum TermRef<'a> {
-    Atom(Level, &'a Cell<RegType>, &'a Atom),
-    Clause(Level, &'a Cell<RegType>, &'a Atom, &'a Vec<Box<Term>>),
-    Var(Level, &'a Cell<VarReg>, &'a Var)
-}
-
-pub enum FactInstruction {
-    GetStructure(Level, Atom, usize, RegType),
-    GetValue(RegType, usize),
-    GetVariable(RegType, usize),
-    UnifyVariable(RegType),
-    UnifyValue(RegType)
-}
-
-pub enum QueryInstruction {
-    PutStructure(Level, Atom, usize, RegType),
-    PutValue(RegType, usize),
-    PutVariable(RegType, usize),
-    SetVariable(RegType),
-    SetValue(RegType)
-}
-
-pub enum ChoiceInstruction {
-    RetryMeElse(usize),
-    TrustMe,
-    TryMeElse(usize)
-}
-
-pub enum ControlInstruction {
-    Allocate(usize),
-    Call(Atom, usize),
-    Deallocate,
-    Proceed
-}
-
-pub type CompiledFact = Vec<FactInstruction>;
-
-pub type CompiledQuery = Vec<QueryInstruction>;
-
-pub enum Line {
-    Choice(ChoiceInstruction),
-    Control(ControlInstruction),
-    Fact(CompiledFact),
-    Query(CompiledQuery)
-}
-
-pub enum LineOrCodeOffset<'a> {
-    Instruction(&'a Line),
-    Offset(usize)
-}
-
-impl<'a> From<&'a Line> for LineOrCodeOffset<'a> {
-    fn from(line: &'a Line) -> Self {
-        LineOrCodeOffset::Instruction(line)
-    }
-}
-
-pub type Code = Vec<Line>;
-
-#[derive(Clone, Copy, PartialEq)]
-pub enum Addr {
-    HeapCell(usize),
-    StackCell(usize, usize),
-    Str(usize)
-}
-
-impl Addr {
-    pub fn is_ref(self) -> bool {
-        match self {
-            Addr::HeapCell(_) | Addr::StackCell(_, _) => true,
-            _ => false
-        }
-    }
-
-    pub fn as_ref(self) -> Option<Ref> {
-        match self {
-            Addr::HeapCell(hc) => Some(Ref::HeapCell(hc)),
-            Addr::StackCell(fr, sc) => Some(Ref::StackCell(fr, sc)),
-            _ => None
-        }
-    }
-}
-
-impl From<Ref> for Addr {
-    fn from(r: Ref) -> Self {
-        match r {
-            Ref::HeapCell(hc) => Addr::HeapCell(hc),
-            Ref::StackCell(fr, sc) => Addr::StackCell(fr, sc)
-        }
-    }
-}
-
-#[derive(Clone, Copy, PartialEq)]
-pub enum Ref {
-    HeapCell(usize),
-    StackCell(usize, usize)
-}
-
-#[derive(Clone, PartialEq)]
-pub enum HeapCellValue {
-    NamedStr(usize, Atom),
-    Ref(Ref),
-    Str(usize)
-}
-
-impl From<Addr> for HeapCellValue {
-    fn from(addr: Addr) -> HeapCellValue {
-        match addr {
-            Addr::HeapCell(hc) =>
-                HeapCellValue::Ref(Ref::HeapCell(hc)),
-            Addr::StackCell(fr, sc) =>
-                HeapCellValue::Ref(Ref::StackCell(fr, sc)),
-            Addr::Str(hc) =>
-                HeapCellValue::Str(hc)
-        }
-    }
-}
-
-impl HeapCellValue {
-    pub fn as_addr(&self, focus: usize) -> Addr {
-        match self {           
-            &HeapCellValue::Ref(r) => Addr::from(r),
-            &HeapCellValue::Str(s) => Addr::Str(s),
-            &HeapCellValue::NamedStr(_, _) => Addr::Str(focus)
-        }
-    }
-}
-
-#[derive(Clone, Copy)]
-pub enum CodePtr {
-    DirEntry(usize),
-    TopLevel
-}
-
-impl Default for CodePtr {
-    fn default() -> Self {
-        CodePtr::TopLevel
-    }
-}
-
-impl Add<usize> for CodePtr {
-    type Output = CodePtr;
-
-    fn add(self, rhs: usize) -> Self::Output {
-        match self {
-            CodePtr::DirEntry(p) => CodePtr::DirEntry(p + rhs),
-            CodePtr::TopLevel => CodePtr::TopLevel
-        }
-    }
-}
-
-impl AddAssign<usize> for CodePtr {
-    fn add_assign(&mut self, rhs: usize) {
-        match self {
-            &mut CodePtr::DirEntry(ref mut p) => *p += rhs,
-            _ => {}
-        }
-    }
-}
-
-pub type Heap = Vec<HeapCellValue>;
-
-pub type Registers = Vec<Addr>;
-
-impl Term {
-    pub fn subterms(&self) -> usize {
-        match self {
-            &Term::Clause(_, _, ref terms) => terms.len(),
-            _ => 1
-        }
-    }
-
-    pub fn name(&self) -> &Atom {
-        match self {
-            &Term::Atom(_, ref atom)
-            | &Term::Var(_, ref atom)
-            | &Term::Clause(_, ref atom, _) => atom
-        }
-    }
-
-    pub fn arity(&self) -> usize {
-        match self {
-            &Term::Atom(_, _) | &Term::Var(_, _) => 0,
-            &Term::Clause(_, _, ref child_terms) => child_terms.len()
-        }
-    }
-}
-
-pub type HeapVarDict = HashMap<Var, Addr>;
-
-pub enum EvalResult {
-    EntryFailure,
-    EntrySuccess,
-    InitialQuerySuccess(HeapVarDict),
-    QueryFailure,
-    SubsequentQuerySuccess,
-}
-
-impl EvalResult {
-    #[allow(dead_code)]
-    pub fn failed_query(&self) -> bool {
-        if let &EvalResult::QueryFailure = self {
-            true
-        } else {
-            false
-        }
-    }
-}

src/l3/codegen.rs

@@ -1,447 +0,0 @@
-use l3::ast::*;
-use l3::iterators::{FactIterator, QueryIterator};
-
-use std::cell::Cell;
-use std::cmp::max;
-use std::collections::HashMap;
-use std::vec::Vec;
-
-trait CompilationTarget<'a> {
-    type Iterator : Iterator<Item=TermRef<'a>>;
-
-    fn iter(&'a Term) -> Self::Iterator;
-
-    fn to_structure(Level, Atom, usize, RegType) -> Self;
-
-    fn argument_to_variable(RegType, usize) -> Self;
-    fn argument_to_value(RegType, usize) -> Self;
-    fn subterm_to_variable(RegType) -> Self;
-    fn subterm_to_value(RegType) -> Self;
-
-    fn clause_arg_to_instr(RegType) -> Self;
-}
-
-impl<'a> CompilationTarget<'a> for FactInstruction {
-    type Iterator = FactIterator<'a>;
-
-    fn iter(term: &'a Term) -> Self::Iterator {
-        term.breadth_first_iter()
-    }
-
-    fn to_structure(lvl: Level, atom: Atom, arity: usize, reg: RegType) -> Self {
-        FactInstruction::GetStructure(lvl, atom, arity, reg)
-    }
-
-    fn argument_to_variable(arg: RegType, val: usize) -> Self {
-        FactInstruction::GetVariable(arg, val)
-    }
-
-    fn argument_to_value(arg: RegType, val: usize) -> Self {
-        FactInstruction::GetValue(arg, val)
-    }
-
-    fn subterm_to_variable(val: RegType) -> Self {
-        FactInstruction::UnifyVariable(val)
-    }
-
-    fn subterm_to_value(val: RegType) -> Self {
-        FactInstruction::UnifyValue(val)
-    }
-
-    fn clause_arg_to_instr(val: RegType) -> Self {
-        FactInstruction::UnifyVariable(val)
-    }
-}
-
-impl<'a> CompilationTarget<'a> for QueryInstruction {
-    type Iterator = QueryIterator<'a>;
-
-    fn iter(term: &'a Term) -> Self::Iterator {
-        term.post_order_iter()
-    }
-
-    fn to_structure(lvl: Level, atom: Atom, arity: usize, reg: RegType) -> Self {
-        QueryInstruction::PutStructure(lvl, atom, arity, reg)
-    }
-
-    fn argument_to_variable(arg: RegType, val: usize) -> Self {
-        QueryInstruction::PutVariable(arg, val)
-    }
-
-    fn argument_to_value(arg: RegType, val: usize) -> Self {
-        QueryInstruction::PutValue(arg, val)
-    }
-
-    fn subterm_to_variable(val: RegType) -> Self {
-        QueryInstruction::SetVariable(val)
-    }
-
-    fn subterm_to_value(val: RegType) -> Self {
-        QueryInstruction::SetValue(val)
-    }
-
-    fn clause_arg_to_instr(val: RegType) -> Self {
-        QueryInstruction::SetValue(val)
-    }
-}
-
-struct TermMarker<'a> {
-    bindings: HashMap<&'a Var, VarReg>,
-    arg_c:    usize,
-    perm_c:   usize,
-    temp_c:   usize
-}
-
-impl<'a> TermMarker<'a> {
-    fn new() -> TermMarker<'a> {
-        TermMarker { bindings: HashMap::new(),
-                     arg_c:    1,
-                     perm_c:   1,
-                     temp_c:   1 }
-    }
-
-    fn reset(&mut self) {
-        self.bindings.clear();
-        self.perm_c = 1;
-    }
-    
-    fn contains_var(&self, var: &'a Var) -> bool {
-        self.bindings.contains_key(var)
-    }
-
-    fn get(&self, var: &'a Var) -> VarReg {
-        *self.bindings.get(var).unwrap()
-    }
-
-    fn insert(&mut self, var: &'a Var, r: VarReg) {
-        self.bindings.insert(var, r);
-    }
-
-    fn mark_non_var(&mut self, lvl: Level, cell: &Cell<RegType>) {
-        let reg_type = cell.get();
-
-        if reg_type.reg_num() == 0 {
-            match lvl {
-                Level::Deep if reg_type.is_perm() => {
-                    let perm = self.perm_c;
-                    self.perm_c += 1;
-                    cell.set(RegType::Perm(perm));
-                },
-                Level::Deep => {
-                    let temp = self.temp_c;
-                    self.temp_c += 1;
-                    cell.set(RegType::Temp(temp));
-                },
-                Level::Shallow if reg_type.is_perm() => {
-                    let arg = self.arg_c;
-                    self.arg_c += 1;
-                    cell.set(RegType::Perm(arg));
-                },
-                Level::Shallow => {
-                    let arg = self.arg_c;
-                    self.arg_c += 1;
-                    cell.set(RegType::Temp(arg));
-                }
-            };
-        }
-    }
-
-    fn mark_old_var(&mut self, lvl: Level, var: &'a Var) -> VarReg
-    {
-        let reg = self.get(var);
-
-        match lvl {
-            Level::Deep => VarReg::Norm(reg.norm()),
-            Level::Shallow => {
-                let reg = VarReg::ArgAndNorm(reg.norm(), self.arg_c);
-
-                self.arg_c += 1;
-                self.insert(var, reg);
-
-                reg
-            }
-        }
-    }
-
-    fn mark_new_var(&mut self, lvl: Level, var: &'a Var, reg: RegType) -> VarReg
-    {
-        let inner_reg = if reg.is_perm() {
-            let perm = self.perm_c;
-            self.perm_c += 1;
-            RegType::Perm(perm)
-        } else {
-            let temp = self.temp_c;
-            self.temp_c += 1;
-            RegType::Temp(temp)
-        };
-
-        let reg = match lvl {
-            Level::Deep => VarReg::Norm(inner_reg),
-            Level::Shallow => {
-                let reg = VarReg::ArgAndNorm(inner_reg, self.arg_c);
-                self.arg_c += 1;
-                reg
-            }
-        };
-
-        self.insert(var, reg);
-        reg
-    }
-
-    fn advance_at_head(&mut self, term: &'a Term) {
-        self.arg_c = 1;
-        self.temp_c = max(term.subterms(), self.temp_c) + 1;
-    }
-
-    fn advance(&mut self, term: &'a Term) {
-        self.arg_c = 1;
-        self.temp_c = term.subterms() + 1;
-    }
-}
-
-#[derive(Copy, Clone)]
-enum TermStatus {
-    New, Old, Recurrent
-}
-
-pub struct CodeGenerator<'a> {
-    marker: TermMarker<'a>
-}
-
-type VariableFixture<'a>  = (TermStatus, Vec<&'a Cell<VarReg>>);
-type VariableFixtures<'a> = HashMap<&'a Var, VariableFixture<'a>>;
-
-impl<'a> CodeGenerator<'a> {
-    pub fn new() -> Self {
-        CodeGenerator { marker: TermMarker::new() }
-    }
-
-    pub fn vars(&self) -> &HashMap<&Var, VarReg> {
-        &self.marker.bindings
-    }
-
-    fn to_structure<Target>(&mut self,
-                            lvl: Level,
-                            name: &'a Atom,
-                            cell: &'a Cell<RegType>,
-                            arity: usize)
-                            -> Target
-        where Target: CompilationTarget<'a>
-    {
-        self.marker.mark_non_var(lvl, cell);
-        Target::to_structure(lvl, name.clone(), arity, cell.get())
-    }
-
-    fn var_term<Target>(&mut self,
-                        lvl: Level,
-                        cell: &'a Cell<VarReg>,
-                        var: &'a Var)
-                        -> Target
-        where Target: CompilationTarget<'a>
-    {
-        if !self.marker.contains_var(var) {
-            let reg = self.marker.mark_new_var(lvl, var, cell.get().norm());
-            cell.set(reg);
-
-            match reg {
-                VarReg::ArgAndNorm(arg, norm) =>
-                    Target::argument_to_variable(arg, norm),
-                VarReg::Norm(norm) =>
-                    Target::subterm_to_variable(norm)
-            }
-        } else {
-            let reg = self.marker.mark_old_var(lvl, var);
-            cell.set(reg);
-
-            match reg {
-                VarReg::ArgAndNorm(arg, norm) =>
-                    Target::argument_to_value(arg, norm),
-                VarReg::Norm(norm) =>
-                    Target::subterm_to_value(norm)
-            }
-        }
-    }
-
-    fn non_var_subterm<Target>(&mut self, cell: &'a Cell<RegType>) -> Target
-        where Target: CompilationTarget<'a>
-    {
-        self.marker.mark_non_var(Level::Deep, cell);
-        Target::clause_arg_to_instr(cell.get())
-    }
-
-    fn subterm_to_instr<Target>(&mut self, subterm: &'a Term) -> Target
-        where Target: CompilationTarget<'a>
-    {
-        match subterm {
-            &Term::Atom(ref cell, _) | &Term::Clause(ref cell, _, _) =>
-                self.non_var_subterm(cell),
-            &Term::Var(ref cell, ref var) =>
-                self.var_term(Level::Deep, cell, var)
-        }
-    }
-
-    fn compile_target<Target>(&mut self, term: &'a Term) -> Vec<Target>
-        where Target: CompilationTarget<'a>
-    {
-        let iter       = Target::iter(term);
-        let mut target = Vec::new();
-
-        for term in iter {
-            match term {
-                TermRef::Atom(lvl, term, atom) =>
-                    target.push(self.to_structure(lvl, atom, term, 0)),
-                TermRef::Clause(lvl, term, atom, terms) => {
-                    target.push(self.to_structure(lvl, atom, term, terms.len()));
-
-                    for subterm in terms {
-                        target.push(self.subterm_to_instr(subterm.as_ref()));
-                    }
-                },
-                TermRef::Var(lvl @ Level::Shallow, ref cell, ref var) =>
-                    target.push(self.var_term(lvl, cell, var)),
-                _ => {}
-            };
-        }
-
-        target
-    }
-
-    fn mark_vars_in_term<Iter>(iter: Iter, vs: &mut VariableFixtures<'a>)
-        where Iter : Iterator<Item=TermRef<'a>>
-    {
-        for term in iter {
-            if let TermRef::Var(_, reg_cell, var) = term {
-                let mut status = vs.entry(var)
-                                   .or_insert((TermStatus::New, Vec::new()));
-
-                status.1.push(reg_cell);
-
-                match status.0 {
-                    TermStatus::Old => status.0 = TermStatus::Recurrent,
-                    _ => {}
-                };
-            }
-        }
-
-        for &mut (ref mut term_status, ref mut cb) in vs.values_mut() {
-            match *term_status {
-                TermStatus::New => *term_status = TermStatus::Old,
-                TermStatus::Recurrent => {
-                    for cell_reg in cb.drain(0..) {
-                        cell_reg.set(VarReg::Norm(RegType::Perm(0)));
-                    }
-                },
-                _ => {}
-            }
-        }
-    }
-
-    fn mark_perm_vars(rule: &'a Rule) -> VariableFixtures {
-        let &Rule { head: (ref p0, ref p1), ref clauses } = rule;
-        let mut vfs = HashMap::new();
-
-        let iter = p0.breadth_first_iter().chain(p1.breadth_first_iter());
-
-        Self::mark_vars_in_term(iter, &mut vfs);
-
-        for term in clauses {
-            Self::mark_vars_in_term(term.breadth_first_iter(), &mut vfs);
-        }
-
-        vfs
-    }
-
-    fn add_conditional_call(compiled_query: &mut Code, term: &Term) {
-        match term {
-            &Term::Atom(_, ref atom) => {
-                let call = ControlInstruction::Call(atom.clone(), 0);
-                compiled_query.push(Line::Control(call));
-            },
-            &Term::Clause(_, ref atom, ref terms) => {
-                let call = ControlInstruction::Call(atom.clone(), terms.len());
-                compiled_query.push(Line::Control(call));
-            },
-            _ => {}
-        }
-    }
-
-    pub fn compile_rule(&mut self, rule: &'a Rule) -> Code {
-        let vfs = Self::mark_perm_vars(&rule);
-        let &Rule { head: (ref p0, ref p1), ref clauses } = rule;
-        let mut perm_vars = 0;
-
-        for &(term_status, _) in vfs.values() {
-            if let TermStatus::Recurrent = term_status {
-                perm_vars += 1;
-            }
-        }
-
-        let mut body = Vec::new();
-
-        body.push(Line::Control(ControlInstruction::Allocate(perm_vars)));
-
-        self.marker.advance(p0);
-        body.push(Line::Fact(self.compile_target(p0)));
-
-        self.marker.advance_at_head(p1);
-        body.push(Line::Query(self.compile_target(p1)));
-        
-        Self::add_conditional_call(&mut body, p1);
-
-        body = clauses.iter()
-            .map(|ref term| self.compile_query(term))
-            .fold(body, |mut body, ref mut cqs| {
-                body.append(cqs);
-                body
-            });
-
-        body.push(Line::Control(ControlInstruction::Deallocate));
-        body
-    }
-
-    pub fn compile_fact(&mut self, term: &'a Term) -> Code {
-        self.marker.advance(term);
-
-        let mut compiled_fact = vec![Line::Fact(self.compile_target(term))];
-        let proceed = Line::Control(ControlInstruction::Proceed);
-
-        compiled_fact.push(proceed);
-        compiled_fact
-    }
-
-    pub fn compile_query(&mut self, term: &'a Term) -> Code {
-        self.marker.advance(term);
-
-        let mut compiled_query = vec![Line::Query(self.compile_target(term))];
-        Self::add_conditional_call(&mut compiled_query, term);
-
-        compiled_query
-    }
-
-    pub fn compile_predicate(&mut self, clauses: &'a Vec<PredicateClause>) -> Code
-    {
-        let mut code = Vec::new();
-        
-        for (i, clause) in clauses.iter().enumerate() {
-            self.marker.reset();
-            
-            let mut clause_code = match clause {
-                &PredicateClause::Fact(ref fact) =>
-                    self.compile_fact(fact),
-                &PredicateClause::Rule(ref rule) =>
-                    self.compile_rule(rule)
-            };
-
-            let choice = match i {
-                0 => ChoiceInstruction::TryMeElse(clause_code.len() + 1),
-                _ if i == clauses.len() - 1 => ChoiceInstruction::TrustMe,
-                _ => ChoiceInstruction::RetryMeElse(clause_code.len() + 1)
-            };
-
-            code.push(Line::Choice(choice));
-            code.append(&mut clause_code);
-        }
-
-        code
-    }
-}

src/l3/heapview.rs

@@ -1,86 +0,0 @@
-use l3::and_stack::*;
-use l3::ast::*;
-
-use std::vec::Vec;
-
-#[derive(Clone, Copy)]
-pub enum HeapCellView<'a> {
-    Str(usize, &'a Atom),
-    HeapVar(usize),
-    StackVar(usize, usize)
-}
-
-pub struct HeapCellViewer<'a> {
-    heap: &'a Heap,
-    and_stack: &'a AndStack,
-    state_stack: Vec<Addr>
-}
-
-impl<'a> HeapCellViewer<'a> {
-    pub fn new(heap: &'a Heap, and_stack: &'a AndStack, focus: Addr) -> Self {
-        HeapCellViewer {
-            heap: heap,
-            and_stack: and_stack,
-            state_stack: vec![focus]
-        }
-    }
-
-    fn follow_stack_ref(&mut self, mut fr: usize, mut sc: usize) -> HeapCellView<'a>
-    {
-        loop {
-            match self.and_stack[fr][sc] {
-                Addr::HeapCell(hc) | Addr::Str(hc) =>
-                    return self.follow_heap_ref(hc),
-                Addr::StackCell(fr1, sc1) => {
-                    if fr1 == fr && sc1 == sc {
-                        return HeapCellView::StackVar(fr, sc);
-                    }
-
-                    fr = fr1; sc = sc1;
-                }
-            }
-        }
-    }
-
-    fn follow_heap_ref(&mut self, mut focus: usize) -> HeapCellView<'a> {
-        loop {
-            match &self.heap[focus] {
-                &HeapCellValue::NamedStr(arity, ref name) => {
-                    for i in (1 .. arity + 1).rev() {
-                        self.state_stack.push(Addr::HeapCell(focus + i));
-                    }
-
-                    return HeapCellView::Str(arity, name);
-                },
-                &HeapCellValue::Ref(Ref::HeapCell(hc)) => {
-                    if focus == hc {
-                        return HeapCellView::HeapVar(hc);
-                    } else {
-                        focus = hc;
-                    }
-                },
-                &HeapCellValue::Ref(Ref::StackCell(fr, sc)) =>
-                    return self.follow_stack_ref(fr, sc),
-                &HeapCellValue::Str(cell_num) =>
-                    focus = cell_num,
-            }
-        }
-    }
-}
-
-impl<'a> Iterator for HeapCellViewer<'a> {
-    type Item = HeapCellView<'a>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        if let Some(addr) = self.state_stack.pop() {
-            match addr {
-                Addr::HeapCell(hc) | Addr::Str(hc) =>
-                    return Some(self.follow_heap_ref(hc)),
-                Addr::StackCell(fr, sc) =>
-                    return Some(self.follow_stack_ref(fr, sc))
-            }
-        }
-
-        None
-    }
-}

src/l3/io.rs

@@ -1,255 +0,0 @@
-use l3::ast::*;
-use l3::codegen::*;
-use l3::l3_parser::*;
-use l3::machine::*;
-
-use termion::raw::IntoRawMode;
-use termion::input::TermRead;
-use termion::event::Key;
-
-use std::io::{Write, stdin, stdout};
-use std::fmt;
-
-impl fmt::Display for FactInstruction {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &FactInstruction::GetStructure(Level::Deep, ref name, ref arity, ref r) =>
-                write!(f, "get_structure {}/{}, {}", name, arity, r),
-            &FactInstruction::GetStructure(Level::Shallow, ref name, ref arity, ref r) =>
-                write!(f, "get_structure {}/{}, A{}", name, arity, r.reg_num()),
-            &FactInstruction::GetValue(ref x, ref a) =>
-                write!(f, "get_value {}, A{}", x, a),
-            &FactInstruction::GetVariable(ref x, ref a) =>
-                write!(f, "get_variable {}, A{}", x, a),
-            &FactInstruction::UnifyVariable(ref r) =>
-                write!(f, "unify_variable {}", r),
-            &FactInstruction::UnifyValue(ref r) =>
-                write!(f, "unify_value {}", r)
-        }
-    }
-}
-
-impl fmt::Display for QueryInstruction {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &QueryInstruction::PutStructure(Level::Deep, ref name, ref arity, ref r) =>
-                write!(f, "put_structure {}/{}, {}", name, arity, r.reg_num()),
-            &QueryInstruction::PutStructure(Level::Shallow, ref name, ref arity, ref r) =>
-                write!(f, "put_structure {}/{}, A{}", name, arity, r.reg_num()),
-            &QueryInstruction::PutValue(ref x, ref a) =>
-                write!(f, "put_value {}, A{}", x, a),
-            &QueryInstruction::PutVariable(ref x, ref a) =>
-                write!(f, "put_variable {}, A{}", x, a),
-            &QueryInstruction::SetVariable(ref r) =>
-                write!(f, "set_variable {}", r),
-            &QueryInstruction::SetValue(ref r) =>
-                write!(f, "set_value {}", r),
-        }
-    }
-}
-
-impl fmt::Display for ControlInstruction {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &ControlInstruction::Allocate(num_cells) =>
-                write!(f, "allocate {}", num_cells),
-            &ControlInstruction::Call(ref name, ref arity) =>
-                write!(f, "call {}/{}", name, arity),
-            &ControlInstruction::Deallocate =>
-                write!(f, "deallocate"),
-            &ControlInstruction::Proceed =>
-                write!(f, "proceed")
-        }
-    }
-}
-
-impl fmt::Display for ChoiceInstruction {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &ChoiceInstruction::TryMeElse(offset) =>
-                write!(f, "try_me_else {}", offset),
-            &ChoiceInstruction::RetryMeElse(offset) =>
-                write!(f, "retry_me_else {}", offset),
-            &ChoiceInstruction::TrustMe =>
-                write!(f, "trust_me")
-        }
-    }
-}
-
-impl fmt::Display for Level {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &Level::Shallow => write!(f, "A"),
-            &Level::Deep => write!(f, "X")
-        }
-    }
-}
-
-impl fmt::Display for VarReg {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &VarReg::Norm(RegType::Perm(reg)) => write!(f, "Y{}", reg),
-            &VarReg::Norm(RegType::Temp(reg)) => write!(f, "X{}", reg),
-            &VarReg::ArgAndNorm(RegType::Perm(reg), arg) =>
-                write!(f, "Y{} A{}", reg, arg),
-            &VarReg::ArgAndNorm(RegType::Temp(reg), arg) =>
-                write!(f, "X{} A{}", reg, arg)
-        }
-    }
-}
-
-impl fmt::Display for RegType {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            &RegType::Perm(val) => write!(f, "Y{}", val),
-            &RegType::Temp(val) => write!(f, "X{}", val)
-        }
-    }
-}
-
-
-fn is_consistent(predicate: &Vec<PredicateClause>) -> bool {
-    let name  = predicate.first().unwrap().name();
-    let arity = predicate.first().unwrap().arity();
-
-    for clause in predicate.iter().skip(1) {
-        if !(name == clause.name() && arity == clause.arity()) {
-            return false;
-        }
-    }
-
-    true
-}
-
-#[allow(dead_code)]
-pub fn print_code(code: &Code) {
-    for clause in code {
-        match clause {
-            &Line::Fact(ref fact) =>
-                for fact_instr in fact {
-                    println!("{}", fact_instr);
-                },
-            &Line::Choice(ref choice) =>
-                println!("{}", choice),
-            &Line::Control(ref control) =>
-                println!("{}", control),
-            &Line::Query(ref query) =>
-                for query_instr in query {
-                    println!("{}", query_instr);
-                }
-        }
-    }
-}
-
-pub fn read() -> String {
-    let _ = stdout().flush();
-
-    let mut buffer = String::new();
-    let mut result = String::new();
-
-    let stdin = stdin();
-    stdin.read_line(&mut buffer).unwrap();
-
-    if &*buffer.trim() == ":{" {
-        buffer.clear();
-
-        stdin.read_line(&mut buffer).unwrap();
-
-        while &*buffer.trim() != "}:" {
-            result += buffer.as_str();
-            buffer.clear();
-            stdin.read_line(&mut buffer).unwrap();
-        }
-    } else {
-        result = buffer;
-    }
-
-    result
-}
-
-pub fn eval(wam: &mut Machine, buffer: &str) -> EvalResult
-{
-    let result = parse_TopLevel(buffer);
-    let mut cg = CodeGenerator::new();
-
-    match &result {
-        &Ok(TopLevel::Predicate(ref clauses)) => {
-            if is_consistent(clauses) {
-                let compiled_pred = cg.compile_predicate(clauses);
-                wam.add_predicate(clauses, compiled_pred);
-
-                EvalResult::EntrySuccess
-            } else {
-                let msg = r"Error: predicate is inconsistent.
-Each predicate must have the same name and arity.";
-
-                println!("{}", msg);
-                EvalResult::EntryFailure
-            }
-        },
-        &Ok(TopLevel::Fact(ref fact)) => {
-            let compiled_fact = cg.compile_fact(&fact);
-            wam.add_fact(fact, compiled_fact);
-            EvalResult::EntrySuccess
-        },
-        &Ok(TopLevel::Rule(ref rule)) => {
-            let compiled_rule = cg.compile_rule(&rule);
-            wam.add_rule(rule, compiled_rule);
-            EvalResult::EntrySuccess
-        },
-        &Ok(TopLevel::Query(ref query)) => {
-            let compiled_query = cg.compile_query(&query);
-            wam.run_query(compiled_query, &cg)
-        },
-        &Err(_) => {
-            println!("Grammatical error of some kind!");
-            EvalResult::EntryFailure
-        }
-    }
-}
-
-pub fn print(wam: &mut Machine, result: EvalResult) {
-    match result {
-        EvalResult::InitialQuerySuccess(heap_locs) => {
-            println!("yes");
-
-            'outer: loop {
-                let mut result = EvalResult::QueryFailure;
-                let bindings = wam.heap_view(&heap_locs);
-
-                let stdin  = stdin();
-                let mut stdout = stdout().into_raw_mode().unwrap();
-
-                write!(stdout, "{}\n\r", bindings).unwrap();
-                stdout.flush().unwrap();
-
-                if !wam.or_stack_is_empty() {
-                    write!(stdout, "Press ; to continue or A to abort.\n\r").unwrap();
-                    stdout.flush().unwrap();
-
-                    for c in stdin.keys() {
-                        match c.unwrap() {
-                            Key::Char(';') => {
-                                result = wam.continue_query();
-                                break;
-                            },
-                            Key::Char('a') | Key::Char('A') =>
-                                break 'outer,
-                            _ => {}
-                        }
-                    };
-
-                    if let &EvalResult::QueryFailure = &result {
-                        write!(stdout, "no\n\r").unwrap();
-                        stdout.flush().unwrap();
-                        break;
-                    }
-                } else {
-                    break;
-                }
-            }
-        },
-        EvalResult::QueryFailure => println!("no"),
-        _ => {}
-    };
-}

src/l3/iterators.rs

@@ -1,175 +0,0 @@
-use l3::ast::*;
-
-use std::cell::Cell;
-use std::collections::VecDeque;
-use std::vec::Vec;
-
-enum IteratorState<'a> {
-    Atom(Level, &'a Cell<RegType>, &'a Atom),
-    Clause(Level, usize, &'a Cell<RegType>, &'a Atom, &'a Vec<Box<Term>>),
-    IsolatedAtom(&'a Cell<RegType>, &'a Atom),
-    IsolatedVar(&'a Cell<VarReg>, &'a Var),
-    RootClause(usize, &'a Vec<Box<Term>>),
-    Var(Level, &'a Cell<VarReg>, &'a Var)
-}
-
-impl<'a> IteratorState<'a> {
-    fn to_state(lvl: Level, term: &'a Term) -> IteratorState<'a>
-    {
-        match term {
-            &Term::Atom(ref cell, ref atom) =>
-                IteratorState::Atom(lvl, cell, atom),
-            &Term::Clause(ref cell, ref atom, ref child_terms) =>
-                IteratorState::Clause(lvl, 0, cell, atom, child_terms),
-            &Term::Var(ref cell, ref var) =>
-                IteratorState::Var(lvl, cell, var)
-        }
-    }
-}
-
-pub struct QueryIterator<'a> {
-    state_stack: Vec<IteratorState<'a>>
-}
-
-impl<'a> QueryIterator<'a> {
-    fn push_clause(&mut self,
-                   lvl: Level,
-                   child_num: usize,
-                   cell: &'a Cell<RegType>,
-                   name: &'a Atom,
-                   child_terms: &'a Vec<Box<Term>>)
-    {
-        self.state_stack.push(IteratorState::Clause(lvl,
-                                                    child_num,
-                                                    cell,
-                                                    name,
-                                                    child_terms));
-    }
-
-    fn push_root_clause(&mut self,
-                        child_num: usize,
-                        child_terms: &'a Vec<Box<Term>>)
-    {
-        self.state_stack.push(IteratorState::RootClause(child_num, child_terms));
-    }
-
-    fn push_subterm(&mut self, lvl: Level, term: &'a Term) {
-        self.state_stack.push(IteratorState::to_state(lvl, term));
-    }
-
-    fn new(term: &'a Term) -> QueryIterator<'a> {
-        let state = match term {
-            &Term::Atom(ref cell, ref atom) =>
-                IteratorState::IsolatedAtom(cell, atom),
-            &Term::Clause(_, _, ref terms) =>
-                IteratorState::RootClause(0, terms),
-            &Term::Var(ref cell, ref var) =>
-                IteratorState::IsolatedVar(cell, var)
-        };
-
-        QueryIterator { state_stack: vec![state] }
-    }
-}
-
-impl<'a> Iterator for QueryIterator<'a> {
-    type Item = TermRef<'a>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        while let Some(iter_state) = self.state_stack.pop() {
-            match iter_state {
-                IteratorState::Atom(lvl, cell, atom) =>
-                    return Some(TermRef::Atom(lvl, cell, atom)),
-                IteratorState::Clause(lvl, child_num, cell, atom, child_terms) => {
-                    if child_num == child_terms.len() {
-                        return Some(TermRef::Clause(lvl, cell, atom, child_terms));
-                    } else {
-                        self.push_clause(lvl, child_num + 1, cell, atom, child_terms);
-                        self.push_subterm(Level::Deep, child_terms[child_num].as_ref());
-                    }
-                },
-                IteratorState::IsolatedAtom(cell, atom) =>
-                    return Some(TermRef::Atom(Level::Shallow, cell, atom)),
-                IteratorState::IsolatedVar(cell, var) =>
-                    return Some(TermRef::Var(Level::Shallow, cell, var)),
-                IteratorState::RootClause(child_num, child_terms) => {
-                    if child_num == child_terms.len() {
-                        return None;
-                    } else {
-                        self.push_root_clause(child_num + 1, child_terms);
-                        self.push_subterm(Level::Shallow, child_terms[child_num].as_ref());
-                    }
-                },
-                IteratorState::Var(lvl, cell, var) =>
-                    return Some(TermRef::Var(lvl, cell, var))
-            };
-        }
-
-        None
-    }
-}
-
-pub struct FactIterator<'a> {
-    state_queue: VecDeque<IteratorState<'a>>,
-}
-
-impl<'a> FactIterator<'a> {
-    fn push_subterm(&mut self, lvl: Level, term: &'a Term) {
-        self.state_queue.push_back(IteratorState::to_state(lvl, term));
-    }
-
-    fn new(term: &'a Term) -> FactIterator<'a> {
-        let states = match term {
-            &Term::Atom(ref cell, ref atom) =>
-                vec![IteratorState::IsolatedAtom(cell, atom)],
-            &Term::Clause(_, _, ref terms) =>
-                vec![IteratorState::RootClause(0, terms)],
-            &Term::Var(ref cell, ref var) =>
-                vec![IteratorState::IsolatedVar(cell, var)]
-        };
-
-        FactIterator { state_queue:  VecDeque::from(states) }
-    }
-}
-
-impl<'a> Iterator for FactIterator<'a> {
-    type Item = TermRef<'a>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        while let Some(state) = self.state_queue.pop_front() {
-            match state {
-                IteratorState::Atom(lvl, cell, atom) =>
-                    return Some(TermRef::Atom(lvl, cell, atom)),
-                IteratorState::Clause(lvl, _, cell, atom, child_terms) => {
-                    for child_term in child_terms {
-                        self.push_subterm(Level::Deep, child_term);
-                    }
-
-                    return Some(TermRef::Clause(lvl, cell, atom, child_terms));
-                },
-                IteratorState::IsolatedAtom(cell, atom) =>
-                    return Some(TermRef::Atom(Level::Shallow, cell, atom)),
-                IteratorState::IsolatedVar(cell, var) =>
-                    return Some(TermRef::Var(Level::Shallow, cell, var)),
-                IteratorState::RootClause(_, child_terms) => {
-                    for child_term in child_terms {
-                        self.push_subterm(Level::Shallow, child_term);
-                    }
-                },
-                IteratorState::Var(lvl, cell, var) =>
-                    return Some(TermRef::Var(lvl, cell, var))
-            }
-        }
-
-        None
-    }
-}
-
-impl Term {
-    pub fn post_order_iter(&self) -> QueryIterator {
-        QueryIterator::new(self)
-    }
-
-    pub fn breadth_first_iter(&self) -> FactIterator {
-        FactIterator::new(self)
-    }
-}

src/l3/l3_parser.lalrpop

@@ -1,59 +0,0 @@
-use l3::ast::*;
-
-use std::cell::Cell;
-
-grammar;
-
-pub TopLevel: TopLevel = {
-    "?-" <t:Term> "." => TopLevel::Query(t),
-    <Predicate> => TopLevel::Predicate(<>),
-    <Rule>  "." => TopLevel::Rule(<>),
-    <Term>  "." => TopLevel::Fact(<>)    
-};
-
-Atom : Atom = {
-    r"[a-z][a-z0-9_]*" => <>.trim().to_string(),
-};
-
-BoxedTerm : Box<Term> = {
-    <t:Term> => Box::new(t)
-};
-
-Clause : Term = {
-    <a:Atom> "(" <ts: (<BoxedTerm> ",")*> <t:BoxedTerm> ")" => {
-     	let mut ts = ts;
-     	ts.push(t);
-	Term::Clause(Cell::new(RegType::Temp(0)), a, ts)
-    }
-};
-
-Predicate : Vec<PredicateClause> = {
-    <pcs: (<PredicateClause>)+> <pc: PredicateClause> => {
-        let mut pcs = pcs;
-	pcs.push(pc);
-	pcs
-    }  
-};
-
-PredicateClause : PredicateClause = {
-    <Rule> "." => PredicateClause::Rule(<>),
-    <Term> "." => PredicateClause::Fact(<>)
-};
-
-Rule : Rule = {
-    <c:Clause> ":-" <h:Term> <cs: ("," <Term>)*> =>
-         Rule { head: (c, h), clauses: cs },
-    <a:Atom> ":-" <h:Term> <cs: ("," <Term>)*> =>
-         Rule { head: (Term::Atom(Cell::new(RegType::Temp(0)), a), h),
-	        clauses: cs }
-};
-
-Term : Term = {
-    <Clause> => <>,
-    <Atom>   => Term::Atom(Cell::new(RegType::Temp(0)), <>),
-    <Var>    => Term::Var(Cell::new(VarReg::Norm(RegType::Temp(0))), <>)
-};
-
-Var : Var = {
-    r"[A-Z][a-z0-9_]*" => <>.trim().to_string(),
-};

src/l3/machine.rs

@@ -1,677 +0,0 @@
-use l3::ast::*;
-use l3::codegen::*;
-use l3::heapview::*;
-use l3::and_stack::*;
-use l3::or_stack::*;
-
-use std::collections::HashMap;
-use std::ops::{Index, IndexMut};
-use std::vec::Vec;
-
-#[derive(Clone, Copy)]
-enum MachineMode {
-    Read,
-    Write
-}
-
-struct MachineState {
-    h: usize,
-    s: usize,
-    p: CodePtr,
-    b: usize,
-    e: usize,
-    num_of_args: usize,
-    cp: CodePtr,
-    fail: bool,
-    heap: Heap,
-    mode: MachineMode,
-    and_stack: AndStack,
-    or_stack: OrStack,
-    registers: Registers,
-    trail: Vec<Ref>,
-    tr: usize,
-    hb: usize
-}
-
-type CodeDir = HashMap<(Atom, usize), usize>;
-
-impl Index<RegType> for MachineState {
-    type Output = Addr;
-
-    fn index(&self, reg: RegType) -> &Self::Output {
-        match reg {
-            RegType::Temp(temp) => &self.registers[temp],
-            RegType::Perm(perm) => {
-                let e = self.e;
-                &self.and_stack[e][perm]
-            }
-        }
-    }
-}
-
-impl IndexMut<RegType> for MachineState {
-    fn index_mut(&mut self, reg: RegType) -> &mut Self::Output {
-        match reg {
-            RegType::Temp(temp) => &mut self.registers[temp],
-            RegType::Perm(perm) => {
-                let e = self.e;
-                &mut self.and_stack[e][perm]
-            }
-        }
-    }
-}
-
-pub struct Machine {
-    ms: MachineState,
-    code: Code,
-    code_dir: CodeDir
-}
-
-impl Machine {
-    pub fn new() -> Self {
-        Machine {
-            ms: MachineState::new(),
-            code: Vec::new(),
-            code_dir: HashMap::new()
-        }
-    }
-
-    pub fn failed(&self) -> bool {
-        self.ms.fail
-    }
-
-    pub fn add_fact(&mut self, fact: &Term, mut code: Code) {
-        let p = self.code.len();
-        let name  = fact.name().clone();
-        let arity = fact.arity();
-
-        self.code.append(&mut code);
-        self.code_dir.insert((name, arity), p);
-    }
-
-    pub fn add_rule(&mut self, rule: &Rule, mut code: Code) {
-        let p = self.code.len();
-        let name  = rule.head.0.name().clone();
-        let arity = rule.head.0.arity();
-
-        self.code.append(&mut code);
-        self.code_dir.insert((name, arity), p);
-    }
-
-    pub fn add_predicate(&mut self, pred: &Vec<PredicateClause>, mut code: Code)
-    {
-        let p = self.code.len();
-        let name  = pred.first().unwrap().name().clone();
-        let arity = pred.first().unwrap().arity();
-
-        self.code.append(&mut code);
-        self.code_dir.insert((name, arity), p);
-    }
-
-    fn execute_instr<'a>(&mut self, instr_src: LineOrCodeOffset<'a>) -> bool
-    {
-        let mut instr = match instr_src {
-            LineOrCodeOffset::Instruction(instr) => instr,
-            LineOrCodeOffset::Offset(p) => &self.code[p]
-        };
-
-        loop {
-            match instr {
-                &Line::Choice(ref choice_instr) =>
-                    self.ms.execute_choice_instr(choice_instr),
-                &Line::Fact(ref fact) => {
-                    for fact_instr in fact {
-                        self.ms.execute_fact_instr(&fact_instr);
-                    }
-                    self.ms.p += 1;
-                },
-                &Line::Query(ref query) => {
-                    for query_instr in query {
-                        self.ms.execute_query_instr(&query_instr);
-                    }
-                    self.ms.p += 1;
-                },
-                &Line::Control(ref control_instr) =>
-                    self.ms.execute_ctrl_instr(&self.code_dir, control_instr),
-            }
-
-            if self.failed() {
-                let p = self.ms
-                            .or_stack
-                            .top()
-                            .map(|fr| fr.bp)
-                            .unwrap_or_default();
-
-                if let CodePtr::TopLevel = p {
-                    return false;
-                } else {
-                    self.ms.fail = false;
-                    self.ms.p = p;
-                }
-            }
-
-            match self.ms.p {
-                CodePtr::DirEntry(p) if p < self.code.len() =>
-                    instr = &self.code[p],
-                _ => break
-            }
-        }
-
-        true
-    }
-
-    pub fn heap_view(&self, var_dir: &HeapVarDict) -> String {
-        let mut result = String::new();
-
-        for (var, addr) in var_dir {
-            let mut arities = Vec::new();
-            let viewer = HeapCellViewer::new(&self.ms.heap,
-                                             &self.ms.and_stack,
-                                             *addr);
-
-            if result != "" {
-                result += "\n\r";
-            }
-
-            result += var.as_str();
-            result += " = ";
-
-            for view in viewer {
-                match arities.pop() {
-                    Some(n) => arities.push(n-1),
-                    None => {}
-                }
-
-                if !(arities.is_empty() || result.ends_with("(")) {
-                    result += ", ";
-                }
-
-                match view {
-                    HeapCellView::Str(arity, ref name) => {
-                        result += name.as_str();
-
-                        if arity > 0 {
-                            arities.push(arity);
-                            result += "(";
-                        }
-                    },
-                    HeapCellView::HeapVar(cell_num) => {
-                        result += "_";
-                        result += cell_num.to_string().as_str();
-                    },
-                    HeapCellView::StackVar(fr, sc) => {
-                        result += "_s_";
-                        result += fr.to_string().as_str();
-                        result += "_";
-                        result += sc.to_string().as_str();
-                    }
-                }
-
-                while let Some(&0) = arities.last() {
-                    result += ")";
-                    arities.pop();
-                }
-            }
-        }
-
-        result
-    }
-
-    pub fn run_query(&mut self, code: Code, cg: &CodeGenerator) -> EvalResult
-    {
-        let mut succeeded = true;
-        let mut heap_locs = HashMap::new();
-
-        for instr in code.iter().take(1) {
-            succeeded = self.execute_instr(LineOrCodeOffset::from(instr));
-        }
-
-        if succeeded {
-            for (var, vr) in cg.vars() {
-                let addr = self.ms.registers[vr.root_register()];
-                heap_locs.insert((*var).clone(), addr);
-            }
-
-            for instr in code.iter().skip(1) {
-                succeeded = self.execute_instr(LineOrCodeOffset::from(instr));
-                if !succeeded {
-                    break;
-                }
-            }
-        }
-
-        if succeeded {
-            EvalResult::InitialQuerySuccess(heap_locs)
-        } else {
-            EvalResult::QueryFailure
-        }
-    }
-
-    pub fn or_stack_is_empty(&self) -> bool {
-        self.ms.or_stack.is_empty()
-    }
-
-    pub fn continue_query(&mut self) -> EvalResult
-    {
-        if !self.or_stack_is_empty() {
-            let b = self.ms.b;
-            self.ms.p = self.ms.or_stack[b].bp;
-
-            let succeeded = if let CodePtr::DirEntry(p) = self.ms.p {
-                self.execute_instr(LineOrCodeOffset::Offset(p))
-            } else {
-                false
-            };
-
-            if succeeded {
-                EvalResult::SubsequentQuerySuccess
-            } else {
-                EvalResult::QueryFailure
-            }
-        } else {
-            EvalResult::QueryFailure
-        }
-    }
-
-    pub fn reset(&mut self) {
-        self.ms.reset();
-    }
-}
-
-impl MachineState {
-    fn new() -> MachineState {
-        MachineState { h: 0,
-                       s: 0,
-                       p: CodePtr::TopLevel,
-                       b: 0,
-                       e: 0,
-                       num_of_args: 0,
-                       cp: CodePtr::TopLevel,
-                       fail: false,
-                       heap: Vec::with_capacity(256),
-                       mode: MachineMode::Write,
-                       and_stack: AndStack::new(),
-                       or_stack: OrStack::new(),
-                       registers: vec![Addr::HeapCell(0); 32],
-                       trail: Vec::new(),
-                       tr: 0,
-                       hb: 0
-        }
-    }
-
-    fn num_frames(&self) -> usize {
-        self.and_stack.len() + self.or_stack.len()
-    }
-
-    fn store(&self, a: Addr) -> Addr {
-        match a {
-            Addr::HeapCell(r)       => self.heap[r].as_addr(r),
-            Addr::StackCell(fr, sc) => self.and_stack[fr][sc],
-            addr                    => addr
-        }
-    }
-
-    fn deref(&self, a: Addr) -> Addr {
-        let mut a = a;
-
-        loop {
-            let value = self.store(a);
-
-            if value.is_ref() && value != a {
-                a = value;
-                continue;
-            }
-
-            return a;
-        };
-    }
-
-    fn bind(&mut self, r1: Ref, a2: Addr) {
-        let t2 = self.store(a2);
-
-        match r1 {
-            Ref::StackCell(fr, sc) =>
-                self.and_stack[fr][sc] = t2,
-            Ref::HeapCell(hc) =>
-                self.heap[hc] = HeapCellValue::from(t2)
-        };
-
-        self.trail(r1);
-    }
-
-    fn unify(&mut self, a1: Addr, a2: Addr) {
-        let mut pdl = vec![a1, a2];
-
-        self.fail = false;
-
-        while !(pdl.is_empty() || self.fail) {
-            let d1 = self.deref(pdl.pop().unwrap());
-            let d2 = self.deref(pdl.pop().unwrap());
-
-            if d1 != d2 {
-                match (self.store(d1), self.store(d2)) {
-                    (Addr::HeapCell(hc), _) =>
-                        self.bind(Ref::HeapCell(hc), d2),
-                    (_, Addr::HeapCell(hc)) =>
-                        self.bind(Ref::HeapCell(hc), d1),
-                    (Addr::StackCell(fr, sc), _) =>
-                        self.bind(Ref::StackCell(fr, sc), d2),
-                    (_, Addr::StackCell(fr, sc)) =>
-                        self.bind(Ref::StackCell(fr, sc), d1),
-                    (Addr::Str(a1), Addr::Str(a2)) => {
-                        let r1 = &self.heap[a1];
-                        let r2 = &self.heap[a2];
-
-                        if let &HeapCellValue::NamedStr(n1, ref f1) = r1 {
-                            if let &HeapCellValue::NamedStr(n2, ref f2) = r2 {
-                                if n1 == n2 && *f1 == *f2 {
-                                    for i in 1 .. n1 + 1 {
-                                        pdl.push(Addr::HeapCell(a1 + i));
-                                        pdl.push(Addr::HeapCell(a2 + i));
-                                    }
-
-                                    continue;
-                                }
-                            }
-                        }
-
-                        self.fail = true;
-                    }
-                };
-            }
-        }
-    }
-
-    fn trail(&mut self, r: Ref) {
-        match r {
-            Ref::HeapCell(hc) => {
-                if hc < self.hb {
-                    self.trail.push(r);
-                    self.tr += 1;
-                }
-            },
-            Ref::StackCell(fr, _) => {
-                let fr_gi = self.and_stack[fr].global_index;
-                let b_gi  = if !self.or_stack.is_empty() {
-                    self.or_stack[self.b].global_index
-                } else {
-                    0
-                };
-
-                if fr_gi < b_gi {
-                    self.trail.push(r);
-                    self.tr += 1;
-                }
-            }
-        }
-    }
-
-    fn unwind_trail(&mut self, a1: usize, a2: usize) {
-        for i in a1 .. a2 {
-            match self.trail[i] {
-                Ref::HeapCell(r) =>
-                    self.heap[r] = HeapCellValue::Ref(self.trail[i]),
-                Ref::StackCell(fr, sc) =>
-                    self.and_stack[fr][sc] = Addr::StackCell(fr, sc)
-            }
-        }
-    }
-
-    fn execute_query_instr(&mut self, instr: &QueryInstruction) {
-        match instr {
-            &QueryInstruction::PutStructure(_, ref name, arity, reg) => {
-                self.heap.push(HeapCellValue::Str(self.h + 1));
-                self.heap.push(HeapCellValue::NamedStr(arity, name.clone()));
-
-                self[reg] = Addr::Str(self.h + 1);
-
-                self.h += 2;
-            },
-            &QueryInstruction::PutValue(norm, arg) =>
-                self.registers[arg] = self[norm],
-            &QueryInstruction::PutVariable(norm, arg) => {
-                self.heap.push(HeapCellValue::Ref(Ref::HeapCell(self.h)));
-
-                self[norm] = Addr::HeapCell(self.h);
-                self.registers[arg] = Addr::HeapCell(self.h);
-
-                self.h += 1;
-            },
-            &QueryInstruction::SetVariable(reg) => {
-                self.heap.push(HeapCellValue::Ref(Ref::HeapCell(self.h)));
-                self[reg] = Addr::HeapCell(self.h);
-
-                self.h += 1;
-            },
-            &QueryInstruction::SetValue(reg) => {
-                let heap_val = self[reg];
-                self.heap.push(HeapCellValue::from(heap_val));
-
-                self.h += 1;
-            },
-        }
-    }
-
-    fn execute_fact_instr(&mut self, instr: &FactInstruction) {
-        match instr {
-            &FactInstruction::GetStructure(_, ref name, arity, reg) => {
-                let addr = self.deref(self[reg]);
-
-                match self.store(addr) {
-                    Addr::Str(a) => {
-                        let result = &self.heap[a];
-
-                        if let &HeapCellValue::NamedStr(narity, ref str) = result {
-                            if narity == arity && *name == *str {
-                                self.s = a + 1;
-                                self.mode = MachineMode::Read;
-                            } else {
-                                self.fail = true;
-                            }
-                        }
-                    },
-                    Addr::HeapCell(_) | Addr::StackCell(_, _) => {
-                        self.heap.push(HeapCellValue::Str(self.h + 1));
-                        self.heap.push(HeapCellValue::NamedStr(arity, name.clone()));
-
-                        let h = self.h;
-
-                        self.bind(addr.as_ref().unwrap(), Addr::HeapCell(h));
-
-                        self.h += 2;
-                        self.mode = MachineMode::Write;
-                    }
-                };
-            },
-            &FactInstruction::GetVariable(norm, arg) =>
-                self[norm] = self.registers[arg],
-            &FactInstruction::GetValue(norm, arg) => {
-                let norm_addr = self[norm];
-                let reg_addr  = self.registers[arg];
-
-                self.unify(norm_addr, reg_addr);
-            },
-            &FactInstruction::UnifyVariable(reg) => {
-                match self.mode {
-                    MachineMode::Read  =>
-                        self[reg] = self.heap[self.s].as_addr(self.s),
-                    MachineMode::Write => {
-                        self.heap.push(HeapCellValue::Ref(Ref::HeapCell(self.h)));
-                        self[reg] = Addr::HeapCell(self.h);
-                        self.h += 1;
-                    }
-                };
-
-                self.s += 1;
-            },
-            &FactInstruction::UnifyValue(reg) => {
-                let s = self.s;
-
-                match self.mode {
-                    MachineMode::Read  => {
-                        let reg_addr = self[reg];
-                        self.unify(reg_addr, Addr::HeapCell(s));
-                    },
-                    MachineMode::Write => {
-                        let heap_val = self.store(self[reg]);
-                        self.heap.push(HeapCellValue::from(heap_val));
-                        self.h += 1;
-                    }
-                };
-
-                self.s += 1;
-            }
-        };
-    }
-
-    fn execute_ctrl_instr(&mut self, code_dir: &CodeDir, instr: &ControlInstruction)
-    {
-        match instr {
-            &ControlInstruction::Allocate(num_cells) => {
-                let num_frames = self.num_frames();
-
-                self.and_stack.push(num_frames + 1, self.e, self.cp, num_cells);
-
-                self.e = self.and_stack.len() - 1;
-                self.p += 1;
-            },
-            &ControlInstruction::Call(ref name, arity) => {
-                let compiled_tl_index = code_dir.get(&(name.clone(), arity))
-                                                .map(|index| *index);
-
-                match compiled_tl_index {
-                    Some(compiled_tl_index) => {
-                        self.cp = self.p + 1;
-                        self.num_of_args = arity;
-                        self.p  = CodePtr::DirEntry(compiled_tl_index);
-                    },
-                    None => self.fail = true
-                };
-            },
-            &ControlInstruction::Deallocate => {
-                let e = self.e;
-
-                let num_frame_e = self.and_stack.top().unwrap().global_index;
-                let num_frame_b = self.or_stack
-                                      .top()
-                                      .map(|fr| fr.global_index)
-                                      .unwrap_or(0);
-
-                self.p = self.and_stack[e].cp;
-                self.e = self.and_stack[e].e;
-
-                if num_frame_e > num_frame_b {
-                    let top_e = self.and_stack.top().unwrap().e;
-                    self.and_stack.drop_frames(top_e - self.e + 1);
-                }
-            },
-            &ControlInstruction::Proceed =>
-                self.p = self.cp,
-        };
-    }
-
-    fn execute_choice_instr(&mut self, instr: &ChoiceInstruction)
-    {
-        match instr {
-            &ChoiceInstruction::TryMeElse(offset) => {
-                let n = self.num_of_args;
-                let num_frames = self.num_frames();
-
-                self.or_stack.push(num_frames + 1,
-                                   self.e,
-                                   self.cp,
-                                   self.b,
-                                   self.p + offset,
-                                   self.tr,
-                                   self.h,
-                                   self.num_of_args);
-
-                self.b = self.or_stack.len() - 1;
-                let b = self.b;
-
-                for i in 1 .. n + 1 {
-                    self.or_stack[b][i] = self.registers[i];
-                }
-
-                self.hb = self.h;
-                self.p += 1;
-            },
-            &ChoiceInstruction::RetryMeElse(offset) => {
-                let b = self.b;
-                let n = self.or_stack[b].num_args();
-
-                for i in 1 .. n + 1 {
-                    self.registers[i] = self.or_stack[b][i];
-                }
-
-                self.e = self.or_stack[b].e;
-                self.cp = self.or_stack[b].cp;
-
-                self.or_stack[b].bp = self.p + offset;
-
-                let old_tr  = self.or_stack[b].tr;
-                let curr_tr = self.tr;
-
-                self.unwind_trail(old_tr, curr_tr);
-                self.tr = self.or_stack[b].tr;
-
-                self.trail.truncate(self.tr);
-                self.heap.truncate(self.or_stack[b].h);
-
-                self.h  = self.or_stack[b].h;
-                self.hb = self.h;
-
-                self.p += 1;
-            },
-            &ChoiceInstruction::TrustMe => {
-                let b = self.b;
-                let n = self.or_stack[b].num_args();
-
-                for i in 1 .. n + 1 {
-                    self.registers[i] = self.or_stack[b][i];
-                }
-
-                self.e  = self.or_stack[b].e;
-                self.cp = self.or_stack[b].cp;
-
-                let old_tr  = self.or_stack[b].tr;
-                let curr_tr = self.tr;
-
-                self.unwind_trail(old_tr, curr_tr);
-
-                self.tr = self.or_stack[b].tr;
-                self.trail.truncate(self.tr);
-
-                self.h = self.or_stack[b].h;
-                self.heap.truncate(self.h);
-
-                self.b = self.or_stack[b].b;
-
-                self.or_stack.pop();
-
-                self.hb = self.h;
-                self.p += 1;
-            }
-        }
-    }
-
-    fn reset(&mut self) {
-        self.h = 0;
-        self.hb = 0;
-        self.e = 0;
-        self.b = 0;
-        self.s = 0;
-        self.tr = 0;
-        self.p = CodePtr::TopLevel;
-        self.cp = CodePtr::TopLevel;
-        self.num_of_args = 0;
-
-        self.fail = false;
-        self.trail.clear();
-        self.heap.clear();
-        self.mode = MachineMode::Write;
-        self.and_stack.clear();
-        self.or_stack.clear();
-        self.registers = vec![Addr::HeapCell(0); 32];
-    }
-}

src/l3/mod.rs

@@ -1,9 +0,0 @@
-pub mod and_stack;
-pub mod ast;
-pub mod codegen;
-pub mod heapview;
-pub mod io;
-pub mod iterators;
-pub mod l3_parser;
-pub mod machine;
-pub mod or_stack;

src/l3/or_stack.rs

@@ -1,112 +0,0 @@
-use l3::ast::*;
-
-use std::ops::{Index, IndexMut};
-use std::vec::Vec;
-
-pub struct Frame {
-    pub global_index: usize,
-    pub e: usize,
-    pub cp: CodePtr,
-    pub b: usize,
-    pub bp: CodePtr,
-    pub tr: usize,
-    pub h: usize,
-    args: Vec<Addr>
-}
-
-impl Frame {
-    fn new(global_index: usize,
-           e: usize,
-           cp: CodePtr,
-           b: usize,
-           bp: CodePtr,
-           tr: usize,
-           h: usize,
-           n: usize)
-           -> Self
-    {
-        Frame {
-            global_index: global_index,
-            e: e,
-            cp: cp,
-            b: b,
-            bp: bp,
-            tr: tr,
-            h: h,
-            args: vec![Addr::HeapCell(0); n]
-        }
-    }
-
-    pub fn num_args(&self) -> usize {
-        self.args.len()
-    }
-}
-
-pub struct OrStack(Vec<Frame>);
-
-impl OrStack {
-    pub fn new() -> Self {
-        OrStack(Vec::new())
-    }
-
-    pub fn push(&mut self,
-                global_index: usize,
-                e: usize,
-                cp: CodePtr,
-                b: usize,
-                bp: CodePtr,
-                tr: usize,
-                h: usize,
-                n: usize)
-    {
-        self.0.push(Frame::new(global_index, e, cp, b, bp, tr, h, n));
-    }
-
-    pub fn len(&self) -> usize {
-        self.0.len()
-    }
-
-    pub fn clear(&mut self) {
-        self.0.clear()
-    }
-
-    pub fn top(&self) -> Option<&Frame> {
-        self.0.last()
-    }
-
-    pub fn pop(&mut self) {
-        self.0.pop();
-    }
-
-    pub fn is_empty(&self) -> bool {
-        self.0.is_empty()
-    }
-}
-
-impl Index<usize> for OrStack {
-    type Output = Frame;
-
-    fn index(&self, index: usize) -> &Self::Output {
-        self.0.index(index)
-    }
-}
-
-impl IndexMut<usize> for OrStack {
-    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
-        self.0.index_mut(index)
-    }
-}
-
-impl Index<usize> for Frame {
-    type Output = Addr;
-
-    fn index(&self, index: usize) -> &Self::Output {
-        self.args.index(index - 1)
-    }
-}
-
-impl IndexMut<usize> for Frame {
-    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
-        self.args.index_mut(index - 1)
-    }
-}

src/lib.rs

@@ -0,0 +1,36 @@
+#![recursion_limit = "4112"]
+
+#[macro_use]
+extern crate static_assertions;
+
+#[macro_use]
+pub mod macros;
+#[macro_use]
+pub mod atom_table;
+#[macro_use]
+pub mod arena;
+#[macro_use]
+pub mod parser;
+mod allocator;
+mod arithmetic;
+pub mod codegen;
+mod debray_allocator;
+mod fixtures;
+mod forms;
+mod heap_iter;
+pub mod heap_print;
+mod http;
+mod indexing;
+#[macro_use]
+pub mod instructions {
+    include!(concat!(env!("OUT_DIR"), "/instructions.rs"));
+}
+mod iterators;
+pub mod machine;
+mod raw_block;
+pub mod read;
+mod repl_helper;
+mod targets;
+pub mod types;
+
+use instructions::instr;

src/lib/arithmetic.pl

@@ -0,0 +1,121 @@
+:- module(arithmetic, [expmod/4, lsb/2, msb/2, number_to_rational/2,
+                       number_to_rational/3, popcount/2,
+                       rational_numerator_denominator/3]).
+
+:- use_module(library(charsio), [write_term_to_chars/3]).
+:- use_module(library(error)).
+:- use_module(library(lists), [append/3, member/2]).
+
+expmod(Base, Expo, Mod, R) :-
+    (   member(N, [Base, Expo, Mod]), var(N) -> instantiation_error(expmod/4)
+    ;   member(N, [Base, Expo, Mod]), \+ integer(N) ->
+        type_error(integer, N, expmod/4)
+    ;   Expo < 0 -> domain_error(not_less_than_zero, Expo, expmod/4)
+    ;   expmod_(Base, Expo, Mod, 1, R)
+    ).
+
+expmod_(_, _, 1, _, 0) :- !.
+expmod_(_, 0, _, R, R) :- !.
+expmod_(Base0, Expo0, Mod, C0, R) :-
+    Expo0 /\ 1 =:= 1,
+    C is (C0 * Base0) mod Mod,
+    !,
+    Expo is Expo0 >> 1,
+    Base is (Base0 * Base0) mod Mod,
+    expmod_(Base, Expo, Mod, C, R).
+expmod_(Base0, Expo0, Mod, C, R) :-
+    Expo is Expo0 >> 1,
+    Base is (Base0 * Base0) mod Mod,
+    expmod_(Base, Expo, Mod, C, R).
+
+lsb(X, N) :-
+    builtins:must_be_number(X, lsb/2),
+    (   \+ integer(X) -> type_error(integer, X, lsb/2)
+    ;   X < 1 -> domain_error(not_less_than_one, X, lsb/2)
+    ;   builtins:can_be_number(N, lsb/2),
+        X1 is X /\ (-X),
+        msb_(X1, -1, N)
+    ).
+
+msb(X, N) :-
+    builtins:must_be_number(X, msb/2),
+    (   \+ integer(X) -> type_error(integer, X, msb/2)
+    ;   X < 1 -> domain_error(not_less_than_one, X, msb/2)
+    ;   builtins:can_be_number(N, msb/2),
+        X1 is X >> 1,
+        msb_(X1, 0, N)
+    ).
+
+msb_(0, N, N) :- !.
+msb_(X, M, N) :-
+    X1 is X >> 1,
+    M1 is M + 1,
+    msb_(X1, M1, N).
+
+number_to_rational(Real, Fraction) :-
+    (   var(Real) -> instantiation_error(number_to_rational/2)
+    ;   integer(Real) -> Fraction is Real rdiv 1
+    ;   (rational(Real) ; float(Real)) ->
+            number_to_rational(1.0e-6, Real, Fraction)
+    ;   type_error(number, Real, number_to_rational/2)
+    ).
+
+% If 0 <= Eps0 <= 1e-16 then the search is for "infinite" precision.
+number_to_rational(Eps0, Real0, Fraction) :-
+    (   var(Eps0) -> instantiation_error(number_to_rational/3)
+    ;   \+ number(Eps0) -> type_error(number, Eps0, number_to_rational/3)
+    ;   Eps0 < 0 -> domain_error(not_less_than_zero, Eps0, number_to_rational/3)
+    ;   Eps_ is Eps0 rdiv 1,
+        rational_numerator_denominator(Eps_, EpsN, EpsD),
+        Eps = EpsN/EpsD
+    ),
+    (   var(Real0) -> instantiation_error(number_to_rational/3)
+    ;   \+ number(Real0) -> type_error(number, Eps0, number_to_rational/3)
+    ;   Real_ is Real0 rdiv 1,
+        rational_numerator_denominator(Real_, RealN, RealD),
+        Real = RealN/RealD
+    ),
+    E0/E1 = Eps,
+    P0/Q0 = Real,
+    (   P0 < 0 -> I1 is -1 + P0 // Q0
+    ;   I1 is P0 // Q0
+    ),
+    P1 is P0 mod Q0,
+    Q1 = Q0,
+    (   P1 =:= 0 -> Fraction is I1 + 0 rdiv 1
+    ;   Qn1n is max(P1 * E1 - Q1 * E0, 0),
+        Qn1d is Q1 * E1,
+        Qn1 = Qn1n/Qn1d,
+        Qp1n is P1 * E1 + Q1 * E0,
+        Qp1d = Qn1d,
+        Qp1 = Qp1n/Qp1d,
+        stern_brocot_(Qn1, Qp1, 0/1, 1/0, P2/Q2),
+        Fraction is I1 + P2 rdiv Q2
+    ),
+    !.
+
+stern_brocot_(Qnn/Qnd, Qpn/Qpd, A/B, C/D, Fraction) :-
+    Fn1 is A + C,
+    Fd1 is B + D,
+    simplify_fraction(Fn1/Fd1, Fn/Fd),
+    S1 is sign(Fn * Qnd - Fd * Qnn),
+    S2 is sign(Fn * Qpd - Fd * Qpn),
+    (   S1 < 0 -> stern_brocot_(Qnn/Qnd, Qpn/Qpd, Fn/Fd, C/D, Fraction)
+    ;   S2 > 0 -> stern_brocot_(Qnn/Qnd, Qpn/Qpd, A/B, Fn/Fd, Fraction)
+    ;   Fraction = Fn/Fd
+    ).
+
+simplify_fraction(A0/B0, A/B) :-
+    G is gcd(A0, B0),
+    A is A0 // G,
+    B is B0 // G.
+
+rational_numerator_denominator(R, N, D) :-
+    write_term_to_chars(R, [], Cs),
+    append(Ns, [' ', r, d, i, v, ' '|Ds], Cs),
+    number_chars(N, Ns),
+    number_chars(D, Ds).
+
+popcount(X, N) :-
+    must_be(integer, X),
+    '$popcount'(X, N).

src/lib/assoc.pl

@@ -63,12 +63,9 @@ Assocs are Key-Value associations implemented as  a balanced binary tree
 @author         R.A.O'Keefe, L.Damas, V.S.Costa and Jan Wielemaker
 */
 
-/*					  
-:- meta_predicate
-    map_assoc(1, ?),
-    map_assoc(2, ?, ?).
-*/
-					  
+:- meta_predicate map_assoc(1, ?).
+:- meta_predicate map_assoc(2, ?, ?).
+
 %!  empty_assoc(?Assoc) is semidet.
 %
 %   Is true if Assoc is the empty association list.

src/lib/atts.pl

@@ -0,0 +1,196 @@
+:- module(atts, [op(1199, fx, attribute),
+                 call_residue_vars/2,
+                 term_attributed_variables/2]).
+
+:- use_module(library(dcgs)).
+:- use_module(library(terms)).
+
+/* represent the list of attributes belonging to a variable,
+   of a particular module, as a list of terms of the form
+   Module:put_atts(V, ListOfAtts). */
+'$default_attr_list'(Module, V) -->
+    (  { Module:get_atts(V, Attributes) } ->
+       '$default_attr_list'(Attributes, Module, V)
+    ;  []
+    ).
+
+'$default_attr_list'([PG | PGs], Module, AttrVar) -->
+    [Module:put_atts(AttrVar, PG)],
+    '$default_attr_list'(PGs, Module, AttrVar).
+'$default_attr_list'([], _, _) --> [].
+
+'$absent_attr'(V, Attr) :-
+    '$get_attr_list'(V, Ls),
+    '$absent_from_list'(Ls, Attr).
+
+'$absent_from_list'(X, Attr) :-
+    (  var(X) ->
+       true
+    ;  X = [L|Ls],
+       L \= Attr ->
+       '$absent_from_list'(Ls, Attr)
+    ).
+
+'$get_attr'(V, Attr) :-
+    '$get_attr_list'(V, Ls),
+    nonvar(Ls),
+    '$get_from_list'(Ls, V, Attr).
+
+'$get_from_list'([L|Ls], V, Attr) :-
+    nonvar(L),
+    (  L \= Attr ->
+       nonvar(Ls),
+       '$get_from_list'(Ls, V, Attr)
+    ;  L = Attr,
+       '$enqueue_attr_var'(V)
+    ).
+
+'$put_attr'(V, Attr) :-
+    '$get_attr_list'(V, Ls),
+    '$add_to_list'(Ls, V, Attr).
+
+'$add_to_list'(Ls, V, Attr) :-
+    (  var(Ls) ->
+       Ls = [Attr | _],
+       '$enqueue_attr_var'(V)
+    ;  Ls = [_ | Ls0],
+       '$add_to_list'(Ls0, V, Attr)
+    ).
+
+'$del_attr'(Ls0, _, _) :-
+    var(Ls0),
+    !.
+'$del_attr'(Ls0, V, Attr) :-
+    Ls0 = [Att | Ls1],
+    nonvar(Att),
+    (  Att \= Attr ->
+       '$del_attr_buried'(Ls0, Ls1, V, Attr)
+    ;  '$enqueue_attr_var'(V),
+       '$del_attr_head'(V),
+       '$del_attr'(Ls1, V, Attr)
+    ).
+
+'$del_attr_step'(Ls1, V, Attr) :-
+    (  nonvar(Ls1) ->
+       Ls1 = [_ | Ls2],
+       '$del_attr_buried'(Ls1, Ls2, V, Attr)
+    ;  true
+    ).
+
+%% assumptions: Ls0 is a list, Ls1 is its tail;
+%%              the head of Ls0 can be ignored.
+'$del_attr_buried'(Ls0, Ls1, V, Attr) :-
+    (  var(Ls1) -> true
+    ;  Ls1 = [Att | Ls2] ->
+       (  Att \= Attr ->
+          '$del_attr_buried'(Ls1, Ls2, V, Attr)
+       ;  '$enqueue_attr_var'(V),
+	      '$del_attr_non_head'(Ls0), %% set tail of Ls0 = tail of Ls1. can be undone by backtracking.
+	      '$del_attr_step'(Ls1, V, Attr)
+       )
+    ).
+
+'$copy_attr_list'(L, _Module, []) :- var(L), !.
+'$copy_attr_list'([Module0:Att|Atts], Module, CopiedAtts) :-
+    (  Module0 == Module ->
+       CopiedAtts = [Att|CopiedAtts0],
+       '$copy_attr_list'(Atts, Module, CopiedAtts0)
+    ;  '$copy_attr_list'(Atts, Module, CopiedAtts)
+    ).
+
+user:term_expansion(Term0, Terms) :-
+    nonvar(Term0),
+    Term0 = (:- attribute Atts),
+    nonvar(Atts),
+    prolog_load_context(module, Module),
+    phrase(expand_terms(Atts, Module), Terms).
+
+expand_terms(Atts, Module) -->
+    put_attrs_var_check,
+    put_attrs(Atts, Module),
+    get_attrs_var_check(Module),
+    get_attrs(Atts, Module).
+
+put_attrs_var_check -->
+    [(put_atts(Var, Attr) :- nonvar(Var),
+                             throw(error(uninstantiation_error(Var), put_atts/2))),
+     (put_atts(Var, Attr) :- var(Attr),
+                             throw(error(instantiation_error, put_atts/2)))].
+
+get_attrs_var_check(Module) -->
+    [(get_atts(Var, Attr) :- nonvar(Var),
+                             throw(error(uninstantiation_error(Var), get_atts/2))),
+     (get_atts(Var, Attr) :- var(Attr),
+                             !,
+                             '$get_attr_list'(Var, Ls),
+                             nonvar(Ls),
+			                 atts:'$copy_attr_list'(Ls, Module, Attr))].
+
+put_attrs(Name/Arity, Module) -->
+    put_attr(Name, Arity, Module),
+    [(put_atts(Var, Attr) :- lists:maplist(Module:put_atts(Var), Attr), !)].
+put_attrs((Name/Arity, Atts), Module) -->
+    { nonvar(Atts) },
+    put_attr(Name, Arity, Module),
+    put_attrs(Atts, Module).
+
+get_attrs(Name/Arity, Module) -->
+    get_attr(Name, Arity, Module).
+get_attrs((Name/Arity, Atts), Module) -->
+    { nonvar(Atts) },
+    get_attr(Name, Arity, Module),
+    get_attrs(Atts, Module).
+
+put_attr(Name, Arity, Module) -->
+    { functor(Attr, Name, Arity) },
+    [(put_atts(V, +Attr) :-
+          !,
+          functor(Attr, Head, Arity),
+	      functor(AttrForm, Head, Arity),
+	      '$get_attr_list'(V, Ls),
+	      atts:'$del_attr'(Ls, V, Module:AttrForm),
+	      atts:'$put_attr'(V, Module:Attr)),
+     (put_atts(V,  Attr) :-
+          !,
+          functor(Attr, Head, Arity),
+	      functor(AttrForm, Head, Arity),
+	      '$get_attr_list'(V, Ls),
+	      atts:'$del_attr'(Ls, V, Module:AttrForm),
+	      atts:'$put_attr'(V, Module:Attr)),
+     (put_atts(V, -Attr) :-
+          !,
+          functor(Attr, _, _),
+	      '$get_attr_list'(V, Ls),
+	      atts:'$del_attr'(Ls, V, Module:Attr))].
+
+get_attr(Name, Arity, Module) -->
+    { functor(Attr, Name, Arity) },
+    [(get_atts(V, +Attr) :-
+          !,
+          functor(Attr, _, _),
+          atts:'$get_attr'(V, Module:Attr)),
+     (get_atts(V,  Attr) :-
+          !,
+          functor(Attr, _, _),
+          atts:'$get_attr'(V, Module:Attr)),
+     (get_atts(V, -Attr) :-
+          !,
+          functor(Attr, _, _),
+          atts:'$absent_attr'(V, Module:Attr))].
+
+user:goal_expansion(Term, M:put_atts(Var, Attr)) :-
+    nonvar(Term),
+    Term = put_atts(Var, M, Attr).
+user:goal_expansion(Term, M:get_atts(Var, Attr)) :-
+    nonvar(Term),
+    Term = get_atts(Var, M, Attr).
+
+:- meta_predicate call_residue_vars(0, ?).
+
+call_residue_vars(Goal, Vars) :-
+    '$get_attr_var_queue_delim'(B),
+    call(Goal),
+    '$get_attr_var_queue_beyond'(B, Vars).
+
+term_attributed_variables(Term, Vars) :-
+    '$term_attributed_variables'(Term, Vars).

src/lib/between.pl

@@ -9,14 +9,21 @@ between(Lower, Upper, X) :-
     must_be(integer, Lower),
     must_be(integer, Upper),
     can_be(integer, X),
-    between_(Lower, Upper, X).
+    (   nonvar(X) ->
+        Lower =< X,
+        X =< Upper
+    ;   Lower =< Upper,
+        between_(Lower, Upper, X)
+    ).
 
-between_(Lower, Upper, Lower) :-
-    Lower =< Upper.
-between_(Lower1, Upper, X) :-
-    Lower1 < Upper,
-    Lower2 is Lower1 + 1,
-    between_(Lower2, Upper, X).
+between_(Lower, Upper, Lower1) :-
+   Lower < Upper,
+   !,
+   (  Lower1 = Lower
+   ;  Lower0 is Lower + 1,
+      between_(Lower0, Upper, Lower1)
+   ).
+between_(Lower, Lower, Lower).
 
 enumerate_nats(I, I).
 enumerate_nats(I0, N) :-

src/lib/charsio.pl

@@ -0,0 +1,257 @@
+:- module(charsio, [char_type/2,
+                    chars_utf8bytes/2,
+                    get_single_char/1,
+                    get_n_chars/3,
+                    read_line_to_chars/3,
+                    read_from_chars/2,
+                    write_term_to_chars/3,
+                    chars_base64/3]).
+
+:- use_module(library(dcgs)).
+:- use_module(library(iso_ext)).
+:- use_module(library(error)).
+:- use_module(library(lists)).
+:- use_module(library(iso_ext), [partial_string/1,partial_string/3]).
+
+fabricate_var_name(VarType, VarName, N) :-
+    char_code('A', AC),
+    LN is N mod 26 + AC,
+    char_code(LC, LN),
+    NN is N // 26,
+    (  NN =:= 0 ->
+       (  VarType == fabricated ->
+          atom_chars(VarName, ['_', LC])
+       ;  VarType == numbervars ->
+          atom_chars(VarName, [LC])
+       )
+    ;  number_chars(NN, NNChars),
+       (  VarType == fabricated ->
+          atom_chars(VarName, ['_', LC | NNChars])
+       ;  VarType == numbervars ->
+          atom_chars(VarName, [LC | NNChars])
+       )
+    ).
+
+var_list_contains_name([VarName = _ | VarList], VarName0) :-
+    (  VarName == VarName0 -> true
+    ;  var_list_contains_name(VarList, VarName0)
+    ).
+
+var_list_contains_variable([_ = Var | VarList], Var0) :-
+    (  Var == Var0 -> true
+    ;  var_list_contains_variable(VarList, Var0)
+    ).
+
+make_new_var_name(VarType, V, VarName, N, N1, VarList) :-
+    fabricate_var_name(VarType, VarName0, N),
+    (  var_list_contains_name(VarList, VarName0) ->
+       N0 is N + 1,
+       make_new_var_name(VarType, V, VarName, N0, N1, VarList)
+    ;  VarName = VarName0,
+       N1 is N + 1
+    ).
+
+extend_var_list(Vars, VarList, NewVarList, VarType) :-
+    extend_var_list_(Vars, 0, VarList, NewVarList0, VarType),
+    append(VarList, NewVarList0, NewVarList).
+
+extend_var_list_([], _, _, [], _).
+extend_var_list_([V|Vs], N, VarList, NewVarList, VarType) :-
+    (  var_list_contains_variable(VarList, V) ->
+       extend_var_list_(Vs, N, VarList, NewVarList, VarType)
+    ;  make_new_var_name(VarType, V, VarName, N, N1, VarList),
+       NewVarList = [VarName = V | NewVarList0],
+       extend_var_list_(Vs, N1, VarList, NewVarList0, VarType)
+    ).
+
+
+char_type(Char, Type) :-
+        must_be(character, Char),
+        (   ground(Type) ->
+            (   ctype(Type) ->
+                '$char_type'(Char, Type)
+            ;   domain_error(char_type, Type, char_type/2)
+            )
+        ;   ctype(Type),
+            '$char_type'(Char, Type)
+        ).
+
+
+ctype(alnum).
+ctype(alpha).
+ctype(alphabetic).
+ctype(alphanumeric).
+ctype(ascii).
+ctype(ascii_graphic).
+ctype(ascii_punctuation).
+ctype(binary_digit).
+ctype(control).
+ctype(decimal_digit).
+ctype(exponent).
+ctype(graphic).
+ctype(graphic_token).
+ctype(hexadecimal_digit).
+ctype(layout).
+ctype(lower).
+ctype(meta).
+ctype(numeric).
+ctype(octal_digit).
+ctype(octet).
+ctype(prolog).
+ctype(sign).
+ctype(solo).
+ctype(symbolic_control).
+ctype(symbolic_hexadecimal).
+ctype(upper).
+ctype(whitespace).
+
+
+get_single_char(C) :-
+    (  var(C) -> '$get_single_char'(C)
+    ;  atom_length(C, 1) -> '$get_single_char'(C)
+    ;  type_error(in_character, C, get_single_char/1)
+    ).
+
+
+read_from_chars(Chars, Term) :-
+    must_be(chars, Chars),
+    '$read_term_from_chars'(Chars, Term).
+
+
+write_term_to_chars(_, Options, _) :-
+    var(Options), instantiation_error(write_term_to_chars/3).
+write_term_to_chars(Term, Options, Chars) :-
+    builtins:parse_write_options(Options,
+                                 [IgnoreOps, MaxDepth, NumberVars, Quoted, VNNames],
+                                 write_term_to_chars/3),
+    (  nonvar(Chars)  ->
+       throw(error(uninstantiation_error(Chars), write_term_to_chars/3))
+    ;
+       true
+    ),
+    term_variables(Term, Vars),
+    extend_var_list(Vars, VNNames, NewVarNames, numbervars),
+    '$write_term_to_chars'(Chars, Term, IgnoreOps, NumberVars, Quoted, NewVarNames, MaxDepth).
+
+% Encodes Ch character to list of Bytes.
+char_utf8bytes(Ch, Bytes) :-
+  char_code(Ch, Code),
+  phrase(code_to_utf8(Code), Bytes).
+
+code_to_utf8(Code) --> {Code @< 0x80},     [Code], !.
+code_to_utf8(Code) --> {Code @< 0x800},    encode(Code, 0xC0, 2), !.
+code_to_utf8(Code) --> {Code @< 0x10000},  encode(Code, 0xE0, 3), !.
+code_to_utf8(Code) --> {Code @< 0x110000}, encode(Code, 0xF0, 4), !.
+
+encode(_, _, 0) --> !.
+encode(Code, Prefix, Nb) -->
+  { Nb1 is Nb - 1, Byte is Prefix \/ ((Code >> (6 * Nb1)) /\ 0x3F) },
+  [Byte], encode(Code, 0x80, Nb1).
+
+% Maps characters and UTF-8 bytes.
+% If Cs is a variable, parses Bs as a list of UTF-8 bytes.
+% Otherwise, transform the list of characters Cs to UTF-8 bytes.
+chars_utf8bytes(Cs, Bs) :-
+  var(Cs), must_be(list, Bs) ->
+    once(phrase(decode_utf8(Cs), Bs))
+  ; (must_be(list, Cs),
+     maplist(must_be(atom), Cs),
+     maplist(char_utf8bytes, Cs, Bss),
+     append(Bss, Bs)).
+
+decode_utf8([]) --> [].
+decode_utf8(Chars) --> leading(Nb, Code), continuation(Code, Chars, Nb).
+
+leading(1, Byte) --> [Byte], {Byte /\ 0x80 =:= 0}.
+leading(2, Code) --> [Byte], {Byte /\ 0xE0 =:= 0xC0, Code is Byte - 0xC0}.
+leading(3, Code) --> [Byte], {Byte /\ 0xF0 =:= 0xE0, Code is Byte - 0xE0}.
+leading(4, Code) --> [Byte], {Byte /\ 0xF8 =:= 0xF0, Code is Byte - 0xF0}.
+leading(1, 0xFFFD) --> [_]. % invalid first byte
+
+continuation(Code, [H|T], 1) --> {char_code(H, Code)}, decode_utf8(T).
+continuation(Code, Chars, Nb) --> [Byte],
+  {Nb1 is Nb - 1, Byte /\ 0xC0 =:= 0x80, NextCode is (Code << 6) \/ (Byte - 0x80)},
+  continuation(NextCode, Chars, Nb1).
+
+% invalid continuation byte
+% each remaining continuation byte (if any) will raise 0xFFFD too
+continuation(_, ['\xFFFD\'|T], _) --> [_], decode_utf8(T).
+
+
+read_line_to_chars(Stream, Cs0, Cs) :-
+        '$get_n_chars'(Stream, 1, Char), % this also works for binary streams
+        (   Char == [] -> Cs0 = Cs
+        ;   Char = [C],
+            Cs0 = [C|Rest],
+            (   C == '\n' -> Rest = Cs
+            ;   read_line_to_chars(Stream, Rest, Cs)
+            )
+        ).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Read N characters from Stream.
+
+   If N is a variable, read until EOF, unifying N with the number of
+   characters read.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+get_n_chars(Stream, N, Cs) :-
+        can_be(integer, N),
+        (   var(N) ->
+            read_to_eof(Stream, Cs),
+            length(Cs, N)
+        ;   N >= 0,
+            '$get_n_chars'(Stream, N, Cs)
+        ).
+
+read_to_eof(Stream, Cs) :-
+        '$get_n_chars'(Stream, 512, Cs0),
+        (   Cs0 == [] -> Cs = []
+        ;   partial_string(Cs0, Cs, Rest),
+            read_to_eof(Stream, Rest)
+        ).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Relation between a list of characters Cs and its Base64 encoding Bs,
+   also a list of characters.
+
+   At least one of the arguments must be instantiated.
+
+   Options are:
+
+      - padding(Boolean)
+        Whether to use padding: true (the default) or false.
+      - charset(C)
+        Either 'standard' (RFC 4648 §4, the default) or 'url' (RFC 4648 §5).
+
+   Example:
+
+      ?- chars_base64("hello", Bs, []).
+         Bs = "aGVsbG8=".
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+chars_base64(Cs, Bs, Options) :-
+        must_be(list, Options),
+        (   member(O, Options), var(O) ->
+            instantiation_error(chars_base64/3)
+        ;   (   member(padding(Padding), Options) -> true
+            ;   Padding = true
+            ),
+            (   member(charset(Charset), Options) -> true
+            ;   Charset = standard
+            )
+        ),
+        must_be(boolean, Padding),
+        must_be(atom, Charset),
+        (   member(Charset, [standard,url]) -> true
+        ;   domain_error(charset, Charset, chars_base64/3)
+        ),
+        (   var(Cs) ->
+            must_be(chars, Bs),
+            '$chars_base64'(Cs, Bs, Padding, Charset)
+        ;   must_be(chars, Cs),
+            (   '$first_non_octet'(Cs, N) ->
+                domain_error(octet_character, N, chars_base64/3)
+            ;   '$chars_base64'(Cs, Bs, Padding, Charset)
+            )
+        ).

src/lib/clpb.pl

@@ -16,11 +16,9 @@
    Public operators.
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
-:- op(300, fy, ~).
-:- op(500, yfx, #).
-
-:- module(clpb, [
-                 sat/1,
+:- module(clpb, [op(300, fy, ~),
+		         op(500, yfx, #),
+		         sat/1,
                  taut/2,
                  labeling/1,
                  sat_count/2,
@@ -32,9 +30,11 @@
 :- use_module(library(between)).
 :- use_module(library(atts)).
 :- use_module(library(lists)).
-:- use_module(library(non_iso)).
+:- use_module(library(iso_ext)).
+:- use_module(library(random)).
+:- use_module(library(pairs)).
 :- use_module(library(dcgs)).
-:- use_module(library(error), []).
+:- use_module(library(error), [domain_error/3, type_error/3]).
 
 :- attribute
         clpb/1,
@@ -49,17 +49,6 @@
    Compatibility predicates.
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
-group_pairs_by_key([], []).
-group_pairs_by_key([M-N|T0], [M-[N|TN]|T]) :-
-    same_key(M, T0, TN, T1),
-    group_pairs_by_key(T1, T).
-
-same_key(M0, [M-N|T0], [N|TN], T) :-
-    M0 == M,
-    !,
-    same_key(M, T0, TN, T).
-same_key(_, L, [], L).
-
 must_be(What, Term) :- must_be(What, unknown(Term)-1, Term).
 
 must_be(acyclic, Where, Term) :- !,
@@ -98,75 +87,14 @@ instantiation_error(_, Goal-Arg) :-
 domain_error(Expectation, Term) :-
         domain_error(Expectation, Term, unknown(Term)-1).
 
-domain_error(Expectation, Term, Goal-Arg) :-
-        throw(error(domain_error(Expectation, Term), domain_error(Goal, Arg, Expectation, Term))).
-
 
 type_error(Expectation, Term) :-
         type_error(Expectation, Term, unknown(Term)-1).
 
-type_error(Expectation, Term, Goal-Arg) :-
-        throw(error(type_error(Expectation, Term), type_error(Goal, Arg, Expectation, Term))).
-
-
-/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-   foldl/4
-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
-
-foldl(Goal_3, Ls, A0, A) :-
-        foldl_(Ls, Goal_3, A0, A).
-
-foldl_([], _, A, A).
-foldl_([L|Ls], G_3, A0, A) :-
-        call(G_3, L, A0, A1),
-        foldl_(Ls, G_3, A1, A).
-
-/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-   foldl/5
-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
-
-foldl(Goal_4, Xs, Ys, A0, A) :-
-        foldl_(Xs, Ys, Goal_4, A0, A).
-
-foldl_([], [], _, A, A).
-foldl_([X|Xs], [Y|Ys], G_4, A0, A) :-
-        call(G_4, X, Y, A0, A1),
-        foldl_(Xs, Ys, G_4, A1, A).
-
-
 partition(Pred, Ls0, As, Bs) :-
         include(Pred, Ls0, As),
         exclude(Pred, Ls0, Bs).
 
-sum_list(Ls, S) :-
-        foldl(sum_, Ls, 0, S).
-
-sum_(L, S0, S) :- S is S0 + L.
-
-/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-  Pairs.
-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
-
-pairs_keys_values([], [], []).
-pairs_keys_values([A-B|ABs], [A|As], [B|Bs]) :-
-        pairs_keys_values(ABs, As, Bs).
-
-pairs_keys(Ps, Ks) :- pairs_keys_values(Ps, Ks, _).
-
-pairs_values(Ps, Vs) :- pairs_keys_values(Ps, _, Vs).
-
-map_list_to_pairs(Pred, Ls, Ps) :-
-        map_list_to_pairs2(Ls, Pred, Ps).
-
-map_list_to_pairs2([], _, []).
-map_list_to_pairs2([H|T0], Pred, [K-H|T]) :-
-        call(Pred, H, K),
-        map_list_to_pairs2(T0, Pred, T).
-
-
-
-
-
 goal_expansion(get_attr(Var, Module, Value), (var(Var),get_atts(Var, Access))) :-
         Access =.. [Module,Value].
 
@@ -730,10 +658,6 @@ existential(V, BDD, Node) :-
    Counter network for card(Is,Fs).
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
-same_length([], []).
-same_length([_|As], [_|Bs]) :-
-        same_length(As, Bs).
-
 counter_network(Cs, Fs, Node) :-
         same_length([_|Fs], Indicators),
         fill_indicators(Indicators, 0, Cs),
@@ -907,9 +831,8 @@ verify_attributes(Var, Other, Gs) :-
             (   integer(Other) ->
                 (   between(0, 1, Other) ->
                     root_get_formula_bdd(Root, Sat, BDD0),
-                    bdd_restriction(BDD0, I, Other, BDD),
                     root_put_formula_bdd(Root, Sat, BDD),
-                    Gs = [satisfiable_bdd(BDD)]
+                    Gs = [bdd_restriction(BDD0,I,Other,BDD),satisfiable_bdd(BDD)]
                 ;   no_truth_value(Other)
                 )
             ;   atom(Other) ->
@@ -1199,6 +1122,8 @@ indomain(1).
 % CountAnd = 1.
 % ==
 
+
+
 sat_count(Sat0, N) :-
         catch((parse_sat(Sat0, Sat),
                sat_bdd(Sat, BDD),
@@ -1244,8 +1169,7 @@ bdd_count(Node, VNum, Count) :-
                 bdd_count(High, VNum, HCount),
                 bdd_pow(Low, V, VNum, LPow),
                 bdd_pow(High, V, VNum, HPow),
-                Count0 is LPow*LCount + HPow*HCount,
-                Count = Count0
+                Count is LPow*LCount + HPow*HCount
             )
         ).
 
@@ -1354,13 +1278,18 @@ weighted_maximum(Ws, Vars, Max) :-
         maplist(var_with_index, Vars, IVs),
         pairs_keys_values(Pairs0, IVs, Ws),
         keysort(Pairs0, Pairs1),
-        pairs_keys_values(Pairs1, IVs1, WeightsIndexOrder),
+        % sum linear combinations of repeated variables
+        group_pairs_by_key(Pairs1, Groups),
+        maplist(group_sumweights_pair, Groups, Pairs2),
+        pairs_keys_values(Pairs2, IVs1, WeightsIndexOrder),
         pairs_values(IVs1, VarsIndexOrder),
         % Pairs is a list of Var-Weight terms, in index order of Vars
         pairs_keys_values(Pairs, VarsIndexOrder, WeightsIndexOrder),
         bdd_maximum(BDD, Pairs, Max),
         max_labeling(BDD, Pairs).
 
+group_sumweights_pair((I-V)-Ws, (I-V)-W) :- sum_list(Ws, W).
+
 max_labeling(1, Pairs) :- max_upto(Pairs, _, _).
 max_labeling(node(_,Var,Low,High,Aux), Pairs0) :-
         max_upto(Pairs0, Var, Pairs),
@@ -1595,8 +1524,8 @@ pairs_([], _) --> [].
 pairs_([B|Bs], A) --> [A-B], pairs_(Bs, A).
 
 /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-   Set the Prolog flag clpb_residuals to bdd to obtain the BDD nodes
-   as residuals. Note that they cannot be used as regular goals.
+   Assert clpb:clpb_residuals(bdd) to obtain the BDD nodes as
+   residuals. Note that they cannot be used as regular goals.
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
 nodes([]) --> [].
@@ -1624,9 +1553,10 @@ sats([]) --> [].
 sats([A|As]) --> [clpb:sat(A)], sats(As).
 
 booleans([]) --> [].
-booleans([B|Bs]) --> boolean(B), { del_clpb(B) }, booleans(Bs).
+booleans([B|Bs]) --> boolean(B), booleans(Bs).
 
 boolean(Var) -->
+        { del_clpb(Var) },
         (   { get_attr(Var, clpb_omit_boolean, true) } -> []
         ;   [clpb:sat(Var =:= Var)]
         ).

src/lib/cont.pl

@@ -0,0 +1,32 @@
+:- module(cont, [reset/3, shift/1]).
+
+:- meta_predicate reset(0, ?, ?).
+
+reset(Goal, Ball, Cont) :-
+    call(Goal),
+    '$reset_cont_marker',
+    '$bind_from_register'(Cont, 3),
+    '$bind_from_register'(Ball, 4).
+
+shift(Ball) :-
+    '$nextEP'(first, E, P),
+    get_chunks(E, P, L),
+    (  L == [] ->
+       Cont = cont(true)
+    ;  Cont = cont(cont:call_continuation(L))
+    ),
+    '$write_cont_and_term'(_, _, Cont, Ball),
+    '$unwind_environments'.
+
+get_chunks(E, P, L) :-
+    (  '$points_to_cont_reset_marker'(P) ->
+       L = []
+    ;  '$get_cont_chunk'(E,P,TB),
+       L = [TB|Rest],
+       '$nextEP'(E, NextE, NextP),
+       get_chunks(NextE, NextP, Rest)
+    ).
+
+call_continuation(L) :- '$call_continuation'(L).
+
+'$write_cont_and_term'(_, _, _, _).

src/lib/crypto.pl

@@ -0,0 +1,838 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written 2020, 2021, 2022 by Markus Triska (triska@metalevel.at)
+   Part of Scryer Prolog.
+
+   Predicates for cryptographic applications.
+
+   This library assumes that the Prolog flag double_quotes is set to chars.
+   In Scryer Prolog, lists of characters are very efficiently represented,
+   and strings have the advantage that the atom table remains unmodified.
+
+   Especially for cryptographic applications, it is an advantage that
+   using strings leaves little trace of what was processed in the system.
+
+   For predicates that accept an encoding/1 option to specify the encoding
+   of the input data, if encoding(octet) is used, then the input can also
+   be specified as a list of bytes, i.e., integers between 0 and 255.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(crypto,
+          [hex_bytes/2,                  % ?Hex, ?Bytes
+           crypto_n_random_bytes/2,      % +N, -Bytes
+           crypto_data_hash/3,           % +Data, -Hash, +Options
+           crypto_data_hkdf/4,           % +Data, +Length, -Bytes, +Options
+           crypto_password_hash/2,       % +Password, ?Hash
+           crypto_password_hash/3,       % +Password, -Hash, +Options
+           crypto_data_encrypt/6,        % +PlainText, +Algorithm, +Key, +IV, -CipherText, +Options
+           crypto_data_decrypt/6,        % +CipherText, +Algorithm, +Key, +IV, -PlainText, +Options
+           ed25519_new_keypair/1,        % -KeyPair
+           ed25519_keypair_public_key/2, % +KeyPair, +PublicKey
+           ed25519_sign/4,               % +KeyPair, +Data, -Signature, +Options
+           ed25519_verify/4,             % +PublicKey, +Data, +Signature, +Options
+           curve25519_generator/1,       % -Generator
+           curve25519_scalar_mult/3,     % +Scalar, +Point, -Result
+           crypto_name_curve/2,          % +Name, -Curve
+           crypto_curve_order/2,         % +Curve, -Order
+           crypto_curve_generator/2,     % +Curve, -Generator
+           crypto_curve_scalar_mult/4    % +Curve, +Scalar, +Point, -Result
+          ]).
+
+:- use_module(library(error)).
+:- use_module(library(lists)).
+:- use_module(library(between)).
+:- use_module(library(dcgs)).
+:- use_module(library(clpz)).
+:- use_module(library(arithmetic)).
+:- use_module(library(format)).
+:- use_module(library(charsio)).
+:- use_module(library(si)).
+:- use_module(library(iso_ext), [partial_string/3]).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   hex_bytes(?Hex, ?Bytes) is det.
+
+   Relation between a hexadecimal sequence and a list of bytes. Hex
+   is a string of hexadecimal numbers. Bytes is a list of *integers*
+   between 0 and 255 that represent the sequence as a list of bytes.
+   At least one of the arguments must be instantiated.
+
+   Example:
+
+   ?- hex_bytes("501ACE", Bs).
+      Bs = [80,26,206].
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+
+hex_bytes(Hs, Bytes) :-
+        (   ground(Hs) ->
+            must_be(chars, Hs),
+            (   phrase(hex_bytes(Hs), Bytes) ->
+                true
+            ;   domain_error(hex_encoding, Hs, hex_bytes/2)
+            )
+        ;   must_be_bytes(Bytes, hex_bytes/2),
+            phrase(bytes_hex(Bytes), Hs)
+        ).
+
+hex_bytes([]) --> [].
+hex_bytes([H1,H2|Hs]) --> [Byte],
+        { char_hexval(H1, High),
+          char_hexval(H2, Low),
+          Byte #= High*16 + Low },
+        hex_bytes(Hs).
+
+bytes_hex([]) --> [].
+bytes_hex([B|Bs]) --> [C0,C1],
+        { High #= B>>4,
+          Low #= B /\ 0xf,
+          char_hexval(C0, High),
+          char_hexval(C1, Low)
+        },
+        bytes_hex(Bs).
+
+char_hexval(C, H) :- nth0(H, "0123456789abcdef", C), !.
+char_hexval(C, H) :- nth0(H, "0123456789ABCDEF", C), !.
+
+
+must_be_bytes(Bytes, Context) :-
+        must_be(list, Bytes),
+        maplist(must_be(integer), Bytes),
+        (   member(B, Bytes), \+ between(0, 255, B) ->
+            type_error(byte, B, Context)
+        ;   true
+        ).
+
+
+must_be_octet_chars(Chars, Context) :-
+        must_be(chars, Chars),
+        (   '$first_non_octet'(Chars, F) ->
+            domain_error(octet_character, F, Context)
+        ;   true
+        ).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Cryptographically secure random numbers
+   =======================================
+
+   crypto_n_random_bytes(+N, -Bytes) is det
+
+   Bytes is unified with a list of N cryptographically secure
+   pseudo-random bytes. Each byte is an integer between 0 and 255. If
+   the internal pseudo-random number generator (PRNG) has not been
+   seeded with enough entropy to ensure an unpredictable byte
+   sequence, an exception is thrown.
+
+   One way to relate such a list of bytes to an _integer_ is to use
+   CLP(ℤ) constraints as follows:
+
+   :- use_module(library(clpz)).
+   :- use_module(library(lists)).
+
+   bytes_integer(Bs, N) :-
+           foldl(pow, Bs, 0-0, N-_).
+
+   pow(B, N0-I0, N-I) :-
+           B in 0..255,
+           N #= N0 + B*256^I0,
+           I #= I0 + 1.
+
+   With this definition, we can generate a random 256-bit integer
+   _from_ a list of 32 random _bytes_:
+
+   ?- crypto_n_random_bytes(32, Bs),
+      bytes_integer(Bs, I).
+      Bs = [146,166,162,210,242,7,25,132,64,94|...],
+      I = 337420085690608915485...(56 digits omitted).
+
+   The above relation also works in the other direction, letting you
+   translate an integer _to_ a list of bytes. In addition, you can
+   use hex_bytes/2 to convert bytes to _tokens_ that can be easily
+   exchanged in your applications.
+
+   ?- crypto_n_random_bytes(12, Bs),
+      hex_bytes(Hex, Bs).
+      Bs = [34,25,50,72,58,63,50,172,32,46|...], Hex = "221932483a3f32ac202 ...".
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+
+crypto_n_random_bytes(N, Bs) :-
+        must_be(integer, N),
+        length(Bs, N),
+        maplist(crypto_random_byte, Bs).
+
+crypto_random_byte(B) :- '$crypto_random_byte'(B).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Hashing
+   =======
+
+   crypto_data_hash(+Data, -Hash, +Options)
+
+   Where Data is a list of characters, and Hash is the computed hash
+   as a list of hexadecimal characters.
+
+   Options is a list of:
+
+     - algorithm(+A)
+       where A is one of ripemd160, sha256, sha384, sha512, sha512_256,
+       sha3_224, sha3_256, sha3_384, sha3_512, blake2s256, blake2b512,
+       or a variable. If A is a variable, then it is unified with the
+       default algorithm, which is an algorithm that is considered
+       cryptographically secure at the time of this writing.
+     - encoding(+Encoding)
+       The default encoding is utf8. The alternative is octet,
+       to treat the input as a list of raw bytes.
+
+   Example:
+
+   ?- crypto_data_hash("abc", Hs, [algorithm(sha256)]).
+      Hs = "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad".
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   SHA256 is the current default for several hash-related predicates.
+   It is deemed sufficiently secure for the foreseeable future.  Yet,
+   application programmers must be aware that the default may change in
+   future versions. The hash predicates all yield the algorithm they
+   used if a Prolog variable is used for the pertaining option.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+crypto_data_hash(Data0, Hash, Options0) :-
+        must_be(list, Options0),
+        options_data_chars(Options0, Data0, Data, Encoding),
+        functor_hash_options(algorithm, A, Options0, _),
+        (   hash_algorithm(A) -> true
+        ;   domain_error(hash_algorithm, A, crypto_data_hash/3)
+        ),
+        '$crypto_data_hash'(Data, Encoding, HashBytes, A),
+        hex_bytes(Hash, HashBytes).
+
+options_data_chars(Options, Data, Chars, Encoding) :-
+        option(encoding(Encoding), Options, utf8),
+        must_be(atom, Encoding),
+        encoding_chars(Encoding, Data, Chars).
+
+default_hash(sha256).
+
+functor_hash_options(F, Hash, Options0, [Option|Options]) :-
+        Option =.. [F,Hash],
+        (   select(Option, Options0, Options) ->
+            (   var(Hash) ->
+                default_hash(Hash)
+            ;   must_be(atom, Hash)
+            )
+        ;   Options = Options0,
+            default_hash(Hash)
+        ).
+
+hash_algorithm(ripemd160).
+hash_algorithm(sha256).
+hash_algorithm(sha512).
+hash_algorithm(sha384).
+hash_algorithm(sha512_256).
+hash_algorithm(sha3_224).
+hash_algorithm(sha3_256).
+hash_algorithm(sha3_384).
+hash_algorithm(sha3_512).
+hash_algorithm(blake2s256).
+hash_algorithm(blake2b512).
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   crypto_data_hkdf(+Data, +Length, -Bytes, +Options) is det.
+
+   Concentrate possibly dispersed entropy of Data and then expand it
+   to the desired length. Data is a list of characters.
+
+   Bytes is unified with a list of bytes of length Length, and is
+   suitable as input keying material and initialization vectors to
+   symmetric encryption algorithms.
+
+   Admissible options are:
+
+     - algorithm(+Algorithm)
+       One of sha256, sha384 or sha512. If you specify a variable,
+       then it is unified with the algorithm that was used, which is a
+       cryptographically secure algorithm by default.
+     - info(+Info)
+       Optional context and application specific information,
+       specified as a list of characters. The default is [].
+     - salt(+List)
+       Optionally, a list of bytes that are used as salt. The
+       default is all zeroes.
+     - encoding(+Encoding)
+       The default encoding is utf8. The alternative is octet,
+       to treat the input as a list of raw bytes.
+
+   The `info/1`  option can be  used to  generate multiple keys  from a
+   single  master key,  using for  example values  such as  "key" and
+   "iv", or the name of a file that is to be encrypted.
+
+   See crypto_n_random_bytes/2 to obtain a suitable salt.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+crypto_data_hkdf(Data0, L, Bytes, Options0) :-
+        functor_hash_options(algorithm, Algorithm, Options0, Options),
+        (   hkdf_algorithm(Algorithm) -> true
+        ;   domain_error(hkdf_algorithm, Algorithm, crypto_data_hkdf/4)
+        ),
+        must_be(integer, L),
+        L #>= 0,
+        options_data_chars(Options, Data0, Data, Encoding),
+        option(salt(SaltBytes), Options, []),
+        must_be_bytes(SaltBytes, crypto_data_hkdf/4),
+        option(info(Info0), Options, []),
+        chars_bytes_(Info0, Info, crypto_data_hkdf/4),
+        '$crypto_data_hkdf'(Data, Encoding, SaltBytes, Info, Algorithm, L, Bytes).
+
+hkdf_algorithm(sha256).
+hkdf_algorithm(sha384).
+hkdf_algorithm(sha512).
+
+option(What, Options, Default) :-
+        (   member(V, Options), var(V) ->
+            instantiation_error(option/3)
+        ;   true
+        ),
+        (   member(What, Options) -> true
+        ;   What =.. [_,Default]
+        ).
+
+chars_bytes_(Cs, Bytes, Context) :-
+        must_be(list, Cs),
+        (   maplist(integer, Cs) -> Bytes = Cs
+        ;   chars_utf8bytes(Cs, Bytes)
+        ),
+        must_be_bytes(Bytes, Context).
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   The so-called modular crypt format (MCF) is a standard for encoding
+   password hash strings. However, there's no official specification
+   document describing it. Nor is there a central registry of
+   identifiers or rules. This page describes what is known about it:
+
+   https://pythonhosted.org/passlib/modular_crypt_format.html
+
+   As of 2016, the MCF is deprecated in favor of the PHC String Format:
+
+   https://github.com/P-H-C/phc-string-format/blob/master/phc-sf-spec.md
+
+   This is what we are using below. For the time being, it is best to
+   treat these hashes as opaque terms in applications. Please let me
+   know if you need to rely on any specifics of this format.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   crypto_password_hash(+Password, ?Hash) is semidet.
+
+   If Hash is instantiated, the predicate succeeds _iff_ the hash
+   matches the given password. Otherwise, the call is equivalent to
+   crypto_password_hash(Password, Hash, []) and computes a
+   password-based hash using the default options.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+crypto_password_hash(Password0, Hash) :-
+        (   nonvar(Hash) ->
+            chars_bytes_(Password0, Password, crypto_password_hash/2),
+            must_be(list, Hash),
+            dollar_segments(Hash, [[],"pbkdf2-sha512",[t,=|CsIterations],SaltB64,HashB64]),
+            number_chars(Iterations, CsIterations),
+            bytes_base64(SaltBytes, SaltB64),
+            bytes_base64(HashBytes, HashB64),
+            '$crypto_password_hash'(Password, SaltBytes, Iterations, HashBytes)
+        ;   crypto_password_hash(Password0, Hash, [])
+        ).
+
+
+dollar_segments(Ls, Segments) :-
+        (   append(Front, [$|Ds], Ls) ->
+            Segments = [Front|Rest],
+            dollar_segments(Ds, Rest)
+        ;   Segments = [Ls]
+        ).
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   crypto_password_hash(+Password, -Hash, +Options) is det.
+
+   Derive Hash based on Password. This predicate is similar to
+   crypto_data_hash/3 in that it derives a hash from given data.
+   However, it is tailored for the specific use case of _passwords_.
+   One essential distinction is that for this use case, the derivation
+   of a hash should be _as slow as possible_ to counteract brute-force
+   attacks over possible passwords.
+
+   Another important distinction is that equal passwords must yield,
+   with very high probability, _different_ hashes. For this reason,
+   cryptographically strong random numbers are automatically added to
+   the password before a hash is derived.
+
+   Hash is unified with a string that contains the computed hash and
+   all parameters that were used, except for the password. Instead of
+   storing passwords, store these hashes. Later, you can verify the
+   validity of a password with crypto_password_hash/2, comparing the
+   then entered password to the stored hash. If you need to export this
+   atom, you should treat it as opaque ASCII data with up to 255 bytes
+   of length. The maximal length may increase in the future.
+
+   Admissible options are:
+
+     - algorithm(+Algorithm)
+       The algorithm to use. Currently, the only available algorithm
+       is 'pbkdf2-sha512', which is therefore also the default.
+     - cost(+C)
+       C is an integer, denoting the binary logarithm of the number
+       of _iterations_ used for the derivation of the hash. This
+       means that the number of iterations is set to 2^C. Currently,
+       the default is 17, and thus more than one hundred _thousand_
+       iterations. You should set this option as high as your server
+       and users can tolerate. The default is subject to change and
+       will likely increase in the future or adapt to new algorithms.
+     - salt(+Salt)
+       Use the given list of bytes as salt. By default,
+       cryptographically secure random numbers are generated for this
+       purpose. The default is intended to be secure, and constitutes
+       the typical use case of this predicate.
+
+   Currently, PBKDF2 with SHA-512 is used as the hash derivation
+   function, using 128 bits of salt. All default parameters, including
+   the algorithm, are subject to change, and other algorithms will also
+   become available in the future. Since computed hashes store all
+   parameters that were used during their derivation, such changes will
+   not affect the operation of existing deployments. Note though that
+   new hashes will then be computed with the new default parameters.
+
+   See crypto_data_hkdf/4 for generating keys from Hash.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+crypto_password_hash(Password0, Hash, Options) :-
+        chars_bytes_(Password0, Password, crypto_password_hash/3),
+        must_be(list, Options),
+        option(cost(C), Options, 17),
+        Iterations #= 2^C,
+        Algorithm = 'pbkdf2-sha512', % current default and only option
+        option(algorithm(Algorithm), Options, Algorithm),
+        (   member(salt(SaltBytes), Options) ->
+            must_be_bytes(SaltBytes, crypto_password_hash/2)
+        ;   crypto_n_random_bytes(16, SaltBytes)
+        ),
+        '$crypto_password_hash'(Password, SaltBytes, Iterations, HashBytes),
+        bytes_base64(HashBytes, HashB64),
+        bytes_base64(SaltBytes, SaltB64),
+        phrase(format_("$pbkdf2-sha512$t=~d$~s$~s", [Iterations,SaltB64,HashB64]), Hash).
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Bidirectional Bytes <-> Base64 conversion *without padding*.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+bytes_base64(Bytes, Base64) :-
+        (   var(Bytes) ->
+            chars_base64(Chars, Base64, [padding(false)]),
+            maplist(char_code, Chars, Bytes)
+        ;   maplist(char_code, Chars, Bytes),
+            chars_base64(Chars, Base64, [padding(false)])
+        ).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   crypto_data_encrypt(+PlainText,
+                       +Algorithm,
+                       +Key,
+                       +IV,
+                       -CipherText,
+                       +Options).
+
+   Encrypt the given PlainText, using the symmetric algorithm
+   Algorithm, key Key, and initialization vector (or nonce) IV, to
+   give CipherText.
+
+   PlainText must be a list of characters, Key and IV must be lists of
+   bytes, and CipherText is created as a list of characters.
+
+   Keys and IVs can be chosen at random (using for example
+   crypto_n_random_bytes/2) or derived from input keying material (IKM)
+   using for example crypto_data_hkdf/4. This input is often a shared
+   secret, such as a negotiated point on an elliptic curve, or the hash
+   that was computed from a password via crypto_password_hash/3 with a
+   freshly generated and specified _salt_.
+
+   Reusing the same combination of Key and IV typically leaks at least
+   _some_ information about the plaintext. For example, identical
+   plaintexts will then correspond to identical ciphertexts. For some
+   algorithms, reusing an IV with the same Key has disastrous results
+   and can cause the loss of all properties that are otherwise
+   guaranteed. Especially in such cases, an IV is also called a
+   _nonce_ (number used once).
+
+   It is safe to store and  transfer the used initialization vector (or
+   nonce) in plain text, but the key _must be kept secret_.
+
+   Currently, the only supported algorithm is 'chacha20-poly1305', a
+   powerful and efficient _authenticated_ encryption scheme, providing
+   secrecy and at the same time reliable protection against undetected
+   _modifications_ of the encrypted data. This is a very good choice
+   for virtually all use cases. It is a stream cipher and can encrypt
+   data of any length up to 256 GB. Further, the encrypted data has
+   exactly the same length as the original, and no padding is used.
+
+   Options:
+
+      - encoding(+Encoding)
+      Encoding to use for PlainText. Default is utf8. The alternative
+      is octet to treat PlainText as raw bytes.
+
+      - tag(-List)
+      For authenticated encryption schemes, List is unified with a
+      list of _bytes_ holding the tag. This tag must be provided for
+      decryption.
+
+      - aad(+Data)
+      Data is additional authenticated data (AAD), a list of
+      characters. It is authenticated in that it influences the tag,
+      but it is not encrypted. The encoding/1 option also specifies
+      the encoding of Data.
+
+   Here is an example encryption and decryption, using the ChaCha20
+   stream cipher with the Poly1305 authenticator. This cipher uses a
+   256-bit key and a 96-bit nonce, i.e., 32 and 12 _bytes_,
+   respectively:
+
+    ?- Algorithm = 'chacha20-poly1305',
+       crypto_n_random_bytes(32, Key),
+       crypto_n_random_bytes(12, IV),
+       crypto_data_encrypt("this text is to be encrypted", Algorithm,
+                   Key, IV, CipherText, [tag(Tag)]),
+       crypto_data_decrypt(CipherText, Algorithm,
+                   Key, IV, RecoveredText, [tag(Tag)]).
+
+   Yielding:
+
+       Algorithm = 'chacha20-poly1305',
+       Key = [113,247,153,134,177,220,13,193,50,150|...],
+       IV = [135,20,149,153,63,35,68,114,247,171|...],
+       CipherText = "\x94\0Ej\x94\®Â\x95\óÑÆXÃn¾ð©b\x1c\ ...",
+       RecoveredText = "this text is to be  ...",
+       Tag = [152,117,152,17,162,75,150,206,144,40|...]
+
+   In this example, we use crypto_n_random_bytes/2 to generate a key
+   and nonce from cryptographically secure random numbers. For
+   repeated applications, you must ensure that a nonce is only used
+   _once_ together with the same key. Note that for _authenticated_
+   encryption schemes, the _tag_ that was computed during encryption
+   is necessary for decryption. It is safe to store and transfer the
+   tag in plain text.
+
+   See also crypto_data_decrypt/6, and hex_bytes/2 for conversion
+   between bytes and hex encoding.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+crypto_data_encrypt(PlainText0, Algorithm, Key, IV, CipherText, Options) :-
+        options_data_chars(Options, PlainText0, PlainText, Encoding),
+        option(tag(Tag), Options, _),
+        (   nonvar(Tag) ->
+            must_be_bytes(Tag, crypto_data_encrypt/6)
+        ;   true
+        ),
+        option(aad(AAD0), Options, []),
+        encoding_chars(Encoding, AAD0, AAD),
+        must_be_bytes(Key, crypto_data_encrypt/6),
+        must_be_bytes(IV, crypto_data_encrypt/6),
+        must_be(atom, Algorithm),
+        (   Algorithm = 'chacha20-poly1305' -> true
+        ;   domain_error('chacha20-poly1305', Algorithm, crypto_data_encrypt/6)
+        ),
+        algorithm_key_iv(Algorithm, Key, IV),
+        '$crypto_data_encrypt'(PlainText, AAD, Encoding, Key, IV, Tag, CipherText).
+
+algorithm_key_iv('chacha20-poly1305', Key, IV) :-
+        length(Key, 32),
+        length(IV, 12).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+  crypto_data_decrypt(+CipherText,
+                      +Algorithm,
+                      +Key,
+                      +IV,
+                      -PlainText,
+                      +Options).
+
+   Decrypt the given CipherText, using the symmetric algorithm
+   Algorithm, key Key, and initialization vector IV, to give
+   PlainText. CipherText must be a list of characters, and Key and IV
+   must be lists of bytes. PlainText is created as a list of
+   characters.
+
+   Currently, the only supported algorithm is 'chacha20-poly1305',
+   a very secure, fast and versatile authenticated encryption method.
+
+   Options is a list of:
+
+    - encoding(+Encoding)
+    Encoding to use for PlainText. The default is utf8. The
+    alternative is octet, which is used if the data are raw bytes.
+
+    - tag(+Tag)
+    For authenticated encryption schemes, the tag must be specified as
+    a list of bytes exactly as they were generated upon encryption.
+
+    - aad(+Data)
+    Any additional authenticated data (AAD) must be specified. The
+    encoding/1 option also specifies the encoding of Data.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+crypto_data_decrypt(CipherText0, Algorithm, Key, IV, PlainText, Options) :-
+        option(tag(Tag), Options, []),
+        must_be_bytes(Tag, crypto_data_decrypt/6),
+        must_be_bytes(Key, crypto_data_decrypt/6),
+        must_be_bytes(IV, crypto_data_decrypt/6),
+        must_be(atom, Algorithm),
+        option(encoding(Encoding), Options, utf8),
+        option(aad(AAD0), Options, []),
+        encoding_chars(Encoding, AAD0, AAD),
+        must_be(atom, Encoding),
+        member(Encoding, [utf8,octet]),
+        encoding_chars(octet, CipherText0, CipherText1),
+        maplist(char_code, TagChars, Tag),
+        % we append the tag very efficiently, retaining a compact
+        % internal string representation of the ciphertext
+        partial_string(CipherText1, CipherText, TagChars),
+        (   Algorithm = 'chacha20-poly1305' -> true
+        ;   domain_error('chacha20-poly1305', Algorithm, crypto_data_decrypt/6)
+        ),
+        algorithm_key_iv(Algorithm, Key, IV),
+        '$crypto_data_decrypt'(CipherText, AAD, Key, IV, Encoding, PlainText).
+
+
+encoding_chars(octet, Bs, Cs) :-
+        must_be(list, Bs),
+        (   maplist(integer, Bs) ->
+            maplist(char_code, Cs, Bs)
+        ;   Bs = Cs
+        ),
+        must_be_octet_chars(Cs, crypto_encoding).
+encoding_chars(utf8, Cs, Cs) :-
+        must_be(chars, Cs).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Digital signatures with Ed25519
+   ===============================
+
+   - ed25519_new_keypair(-Pair)
+     Yields a new Ed25519 key pair Pair, a list of characters. The
+     pair contains the private key and must be kept absolutely secret.
+     Pair can be used for signing. Its public key can be obtained
+     with ed25519_keypair_public_key/2.
+
+   - ed25519_keypair_public_key(+Pair, -PublicKey)
+     PublicKey is the public key of the given key pair. The public key
+     can be used for signature verification, and can be shared freely.
+     The public key is represented as a list of characters.
+
+   - ed25519_sign(+Key, +Data, -Signature, +Options)
+     Key and Data must be lists of characters. Key is a key pair in
+     PKCS#8 v2 format as generated by ed25519_new_keypair/1. Sign Data
+     with Key, yielding Signature as a list of hexadecimal characters.
+
+   - ed25519_verify(+Key, +Data, +Signature, +Options)
+     Key and Data must be lists of characters. Key is a public key.
+     Succeeds if Data was signed with the private key corresponding to
+     Key, where Signature is a list of hexadecimal characters as
+     generated by ed25519_sign/4. Fails otherwise.
+
+   Currently, the only option for signing and verifying is:
+
+     - encoding(+Encoding)
+       The default encoding of Data is utf8. The alternative is octet,
+       which treats Data as a list of raw bytes.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+ed25519_new_keypair(Pair) :-
+        '$ed25519_new_keypair'(Pair).
+
+ed25519_keypair_public_key(Pair, PublicKey) :-
+        must_be_octet_chars(Pair, ed25519_keypair_public_key),
+        '$ed25519_keypair_public_key'(Pair, PublicKey).
+
+ed25519_sign(Key, Data0, Signature, Options) :-
+        must_be_octet_chars(Key, ed25519_sign),
+        options_data_chars(Options, Data0, Data, Encoding),
+        '$ed25519_sign'(Key, Data, Encoding, Signature0),
+        hex_bytes(Signature, Signature0).
+
+ed25519_verify(Key, Data0, Signature0, Options) :-
+        must_be_octet_chars(Key, ed25519_verify),
+        options_data_chars(Options, Data0, Data, Encoding),
+        hex_bytes(Signature0, Signature),
+        '$ed25519_verify'(Key, Data, Encoding, Signature).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   X25519: ECDH key exchange over Curve25519
+   =========================================
+
+   Points on Curve25519 are represented as lists of characters that denote
+   the u-coordinate of the Montgomery curve.
+
+   - curve25519_generator(-Gs)
+     Gs is the generator point of Curve25519.
+
+   - curve25519_scalar_mult(+Scalar, +Ps, -Rs)
+     Scalar must be an integer between 0 and 2^256-1,
+     or a list of 32 bytes, and Ps must be a point on the curve.
+     Computes the point Rs = Scalar*Ps as mandated by X25519.
+
+   Alice and Bob can use this to establish a shared secret as follows,
+   where Gs is the generator point of Curve25519:
+
+     1. Alice creates a random integer a and sends As = a*Gs to Bob.
+     2. Bob creates a random integer b and sends Bs = b*Gs to Alice.
+     3. Alice computes Rs = a*Bs.
+     4. Bob computes Rs = b*As.
+     5. Alice and Bob use crypto_data_hkdf/4 on Rs with suitable
+        (same) parameters to obtain lists of bytes that can be used as
+        keys and initialization vectors for symmetric encryption.
+
+   If a and b are kept secret, this method is considered very secure.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+curve25519_generator(Gs) :-
+        length(Gs0, 32),
+        Gs0 = [9|Zs],
+        maplist(=(0), Zs),
+        maplist(char_code, Gs, Gs0).
+
+curve25519_scalar_mult(Scalar, Point, Result) :-
+        (   integer_si(Scalar) ->
+            length(ScalarBytes, 32),
+            bytes_integer(ScalarBytes, Scalar)
+        ;   ScalarBytes = Scalar,
+            must_be_bytes(ScalarBytes, curve25519_scalar_mult/3),
+            length(ScalarBytes, 32)
+        ),
+        maplist(char_code, Point, PointBytes),
+        '$curve25519_scalar_mult'(ScalarBytes, PointBytes, Result).
+
+bytes_integer(Bs, N) :-
+        foldl(pow, Bs, t(0,0,N), t(N,_,_)).
+
+pow(B, t(N0,P0,I0), t(N,P,I)) :-
+        (   integer(I0) ->
+            B #= I0 mod 256,
+            I #= I0 >> 8
+        ;   true
+        ),
+        B in 0..255,
+        N #= N0 + B*256^P0,
+        P #= P0 + 1.
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Operations on Elliptic Curves
+   =============================
+
+   Sample use: Establishing a shared secret S, using ECDH key exchange.
+
+    ?- crypto_name_curve(secp256k1, C),
+       crypto_curve_generator(C, Generator),
+       PrivateKey = 10,
+       crypto_curve_scalar_mult(C, PrivateKey, Generator, PublicKey),
+       Random = 12,
+       crypto_curve_scalar_mult(C, Random, Generator, R),
+       crypto_curve_scalar_mult(C, Random, PublicKey, S),
+       crypto_curve_scalar_mult(C, PrivateKey, R, S).
+
+   For better security, new code should use Curve25519 instead.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   An elliptic curve over a prime field F_p is represented as:
+
+   curve(Name,P,A,B,point(X,Y),Order,FieldLength,Cofactor).
+
+   First, we define suitable accessors.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+curve_name(curve(Name,_,_,_,_,_,_,_), Name).
+curve_p(curve(_,P,_,_,_,_,_,_), P).
+curve_a(curve(_,_,A,_,_,_,_,_), A).
+curve_b(curve(_,_,_,B,_,_,_,_), B).
+curve_field_length(curve(_,_,_,_,_,_,FieldLength,_), FieldLength).
+
+crypto_curve_generator(curve(_,_,_,_,G,_,_,_), G).
+crypto_curve_order(curve(_,_,_,_,_,Order,_,_), Order).
+
+crypto_curve_scalar_mult(Curve, Scalar, point(X,Y), point(RX, RY)) :-
+        must_be(integer, Scalar),
+        must_be_on_curve(Curve, point(X,Y)),
+        curve_name(Curve, Name),
+        curve_field_length(Curve, L0),
+        L #= 2*L0, % for hex encoding
+        phrase(format_("04~|~`0t~16r~*+~`0t~16r~*+", [X,L,Y,L]), PointHex),
+        hex_bytes(PointHex, PointBytes),
+        once(bytes_integer(ScalarBytes, Scalar)),
+        '$crypto_curve_scalar_mult'(Name, ScalarBytes, PointBytes, [_|Us]),
+        maplist(char_code, Us, Bs),
+        length(XBs, 32),
+        append(XBs, YBs, Bs),
+        maplist(reverse, [XBs,YBs], RBs),
+        maplist(bytes_integer, RBs, [RX,RY]).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+?- crypto_name_curve(secp256k1, Curve),
+   crypto_curve_generator(Curve, G),
+   crypto_curve_scalar_mult(Curve, 2, G, R).
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Validation.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+curve_contains_point(Curve, point(QX,QY)) :-
+        curve_a(Curve, A),
+        curve_b(Curve, B),
+        curve_p(Curve, P),
+        QY^2 mod P #= (QX^3 + A*QX + B) mod P.
+
+must_be_on_curve(Curve, P) :-
+        \+ curve_contains_point(Curve, P),
+        domain_error(point_on_curve, P, crypto_elliptic_curves).
+must_be_on_curve(Curve, P) :- curve_contains_point(Curve, P).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Predefined curves
+   =================
+
+   List available curves:
+
+   $ openssl ecparam -list_curves
+
+   Show curve parameters for secp256k1:
+
+   $ openssl ecparam -param_enc explicit -conv_form uncompressed \
+                     -text -no_seed -name secp256k1
+
+   You must remove the leading "04:" from the generator.
+
+   The field length depends on the order of the curve and can be computed
+   with order_field_length/2.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+order_field_length(Order, L) :-
+        fitting_exponent(Order, 0, E),
+        L #= (E + 7) // 8.
+
+fitting_exponent(N, E0, E) :-
+        (   2^E0 #>= N -> E #= E0
+        ;   E1 #= E0 + 1,
+            fitting_exponent(N, E1, E)
+        ).
+
+crypto_name_curve(secp256k1,
+                  curve(secp256k1,
+                        0x00fffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2f,
+                        0x0,
+                        0x7,
+                        point(0x79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798,
+                              0x483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8),
+                        0x00fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141,
+                        32,
+                        1)).

src/lib/csv.pl

@@ -0,0 +1,238 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+  Predicates for parsing CSV data
+
+
+  Read csv files
+
+  Only two options with default values :
+  - token_separator(',')
+  - with_header(true)
+
+  Examples
+
+  * parsing a csv string:
+
+  ?- use_module(library(csv)).
+  ?- use_module(library(dcgs)).
+  ?- phrase(parse_csv(Data), "col1,col2,col3,col4\none,2,,three").
+    Data = frame(["col1","col2","col3","col4"],[["one",2,[],"three"]]).
+
+  * with some options:
+
+  ?- phrase(parse_csv(Data, [with_header(false), token_separator(';')]), "one;2;;three").
+    Data = frame([],[["one",2,[],"three"]]).
+
+  * parsing a csv file:
+
+  ?- use_module(library(csv)).
+  ?- use_module(library(pio)).
+  ?- phrase_from_file(parse_csv(frame(Header, Rows)), './test.csv').
+
+
+  Write csv files
+
+  Four options with default values :
+  - line_separator('\n')
+  - token_separator(',')
+  - with_header(true)
+  - null_value(empty)
+
+  Examples
+
+  * writing a csv file:
+
+  ?- use_module(library(csv)).
+  ?- write_csv('./test.csv', frame(["col1","col2","col3","col4"], [["one",2,[],"three"]])).
+
+  * with some options
+
+  ?- use_module(library(csv)).
+  ?- write_csv('./test.csv', frame(["col1","col2","col3","col4"], [["one",2,[],"three"]]), [with_header(false), line_separator('\r\n'), token_separator(';'), null_value('\\N')]).
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(csv, [
+  parse_csv//1,
+  parse_csv//2,
+  write_csv/2,
+  write_csv/3
+]).
+
+:- use_module(library(format)).
+:- use_module(library(dcgs)).
+:- use_module(library(iso_ext)).
+:- use_module(library(lists)).
+
+
+option(W, O) :-
+  ( member(W, O) -> true
+  ; throw(error(domain_error(csv_option, W), option/2))).
+
+
+option_extends([], Opt, Opt).
+option_extends([X | Y], Opt0, Opt) :-
+  functor(X, Name, 1),
+  F0 =.. [Name, _],
+  ( select(F0, Opt0, R) ->
+    option_extends(Y, [X | R], Opt)
+  ; option_extends(Y, [X | Opt0], Opt) ).
+
+
+%% -- write --
+
+
+escaped_field([], []).
+escaped_field(['"' | Y], ['"', '"' | R]) :-
+  escaped_field(Y, R).
+escaped_field([X | Y], [X | R]) :-
+  X \== '"',
+  escaped_field(Y, R).
+
+
+ensure_escaped(Field, Field) :-
+  (atom(Field); integer(Field); float(Field)).
+ensure_escaped([X | Y], Field) :-
+  escaped_field([X | Y], Field).
+
+
+write_field(Out, Field, Opt) :-
+  ( Field \== [] ->
+    ensure_escaped(Field, Field0),
+    format(Out, "~w", [Field0])
+  ; option(null_value(Null_Value), Opt),
+    ( Null_Value == empty -> true
+    ; format(Out, "~w", [Null_Value]))).
+
+
+write_row(Out, [Field], Opt) :-
+  write_field(Out, Field, Opt).
+write_row(Out, [Field, X | Y], Opt) :-
+  write_field(Out, Field, Opt),
+  option(token_separator(Tk_Sep), Opt),
+  format(Out, "~w", [Tk_Sep]),
+  write_row(Out, [X | Y], Opt).
+
+
+write_rows(Out, [Row], Opt) :-
+  write_row(Out, Row, Opt).
+write_rows(Out, [Row, X | Y], Opt) :-
+  option(line_separator(Line_Sep), Opt),
+  write_row(Out, Row, Opt),
+  format(Out, "~w", [Line_Sep]),
+  write_rows(Out, [X | Y], Opt).
+
+
+write_csv_(Out, frame(Header, Rows), Opt) :-
+  option(with_header(With_Header), Opt),
+  ( With_Header == true -> 
+    write_row(Out, Header, Opt),
+    option(line_separator(Line_Sep), Opt),
+    format(Out, "~w", [Line_Sep])
+  ; true),
+  write_rows(Out, Rows, Opt).
+
+
+write_csv(File_Name, Frm, Opt) :-
+  option_extends(Opt, [
+    null_value(empty),
+    token_separator(','),
+    with_header(true),
+    line_separator('\n')
+  ], Opt0),
+  setup_call_cleanup(
+    open(File_Name, write, Out),
+    write_csv_(Out, Frm, Opt0),
+    close(Out)).
+write_csv(File_Name, Frm) :-
+  write_csv(File_Name, Frm, []).
+
+
+%% -- read --
+
+
+tokens([], Opt), [Tk_Sep] -->
+  { option(token_separator(Tk_Sep), Opt) },
+  [Tk_Sep],
+  !.
+tokens([], _), "\r\n" -->
+  "\r\n",
+  !.
+tokens([], _), "\n" -->
+  "\n",
+  !.
+tokens([], _), "\r" -->
+  "\r",
+  !.
+tokens([X | Y], Opt) -->
+  [X],
+  !,
+  tokens(Y, Opt).
+tokens([], _) --> [].
+
+
+field(R, Opt) -->
+  "\"",
+  !,
+  string_tokens(R, Opt).
+field(R, Opt) -->
+  tokens(R0, Opt),
+  { R0 \== [],
+    catch(number_chars(R, R0), _, R = R0)
+  }.
+field([], _) --> [].
+
+
+string_tokens(R, Opt) -->
+  [X],
+  ( { X == '"' } ->
+    ( "\"" ->
+      { R = [X | Y] },
+      string_tokens(Y, Opt)
+    ; { R = [] })
+  ; { R = [X | Y] },
+    string_tokens(Y, Opt)).
+
+
+end_token --> "\r\n".
+end_token --> "\n".
+end_token --> "\r".
+end_token --> [].
+
+
+separator(Opt) -->
+    { option(token_separator(Tk_Sep), Opt) },
+    [Tk_Sep].
+
+
+row([X | Y], Opt) -->
+  field(X, Opt),
+  !,
+  ( separator(Opt) ->
+    row(Y, Opt)
+  ; end_token ->
+    { Y = [] }).
+
+
+rows(R, Opt) -->
+  row(X, Opt),
+  !,
+  ( { X \== [[]] } ->
+    rows(Y, Opt),
+    { R = [X | Y] }
+  ; { R = [] }).
+
+
+parse_csv(frame(Header, Rows), Opt) --> 
+  { option_extends(Opt, [
+      with_header(true),
+      token_separator(',')
+    ], Opt0)
+  },
+  ( { option(with_header(With_Header), Opt0),
+      With_Header == true } ->
+    row(Header, Opt0),
+    { Header \== [[]] },
+    end_token
+  ; { Header = [] }),
+  rows(Rows, Opt0).
+parse_csv(R) -->
+  parse_csv(R, []).

src/lib/dcgs.pl

@@ -1,48 +1,52 @@
-:- op(1200, xfx, -->).
-% :- op(1105, xfy, ('|')).
+:- module(dcgs,
+          [op(1105, xfy, '|'),
+           phrase/2,
+           phrase/3,
+           seq//1,
+           seqq//1,
+           ... //0
+          ]).
 
-:- module(dcgs, [phrase/2, phrase/3]).
+:- use_module(library(error)).
+:- use_module(library(iso_ext)).
+:- use_module(library(lists), [append/3, member/2]).
+:- use_module(library(loader), [strip_module/3]).
 
-:- use_module(library(lists), [append/3]).
+:- meta_predicate phrase(2, ?).
 
-user:term_expansion(Term0, (Head :- Body)) :-
-    dcg_rule(Term0, Term),
-    Term = (Head :- Body).
+:- meta_predicate phrase(2, ?, ?).
 
 phrase(GRBody, S0) :-
     phrase(GRBody, S0, []).
 
 phrase(GRBody, S0, S) :-
-    (  var(GRBody) -> throw(error(instantiation_error, phrase/3))
-    ;  dcg_constr(GRBody) -> phrase_(GRBody, S0, S)
-    ;  functor(GRBody, _, _) -> call(GRBody, S0, S)
-    ;  throw(error(type_error(callable, GRBody), phrase/3))
+    strip_module(GRBody, M, GRBody1),
+    (  var(GRBody) ->
+       instantiation_error(phrase/3)
+    ;  nonvar(GRBody1),
+       dcg_constr(GRBody1),
+       dcg_body(GRBody1, S0, S, GRBody2) ->
+       call(M:GRBody2)
+    ;  call(M:GRBody1, S0, S)
     ).
 
-phrase_([], S, S).
-phrase_(!, S, S).
-phrase_((A, B), S0, S) :-
-    phrase(A, S0, S1), phrase(B, S1, S).
-phrase_((A -> B ; C), S0, S) :-
-    !,
-    (  phrase(A, S0, S1) ->
-       phrase(B, S1, S)
-    ;  phrase(C, S0, S)
+
+module_call_qualified(M, Call, Call1) :-
+    (  nonvar(M) -> Call1 = M:Call
+    ;  Call = Call1
     ).
-phrase_((A ; B), S0, S) :-
-    (  phrase(A, S0, S) ; phrase(B, S0, S)  ).
-%% phrase_((A | B), S0, S) :-
-%%     (  phrase(A, S0, S) ; phrase(B, S0, S)  ).
-phrase_({G}, S0, S) :-
-    (  G, S0 = S  ).
-phrase_(call(G), S0, S) :-
-    call(G, S0, S).
-phrase_((A -> B), S0, S) :-
-    phrase((A -> B ; fail), S0, S).
-phrase_(phrase(NonTerminal), S0, S) :-
-    phrase(NonTerminal, S0, S).
-phrase_([T|Ts], S0, S) :-
-    append([T|Ts], S, S0).
+
+
+% The same version of the below two dcg_rule clauses, but with module scoping.
+dcg_rule(( M:NonTerminal, Terminals --> GRBody ), ( M:Head :- Body )) :-
+    dcg_non_terminal(NonTerminal, S0, S, Head),
+    dcg_body(GRBody, S0, S1, Goal1),
+    dcg_terminals(Terminals, S, S1, Goal2),
+    Body = ( Goal1, Goal2 ).
+dcg_rule(( M:NonTerminal --> GRBody ), ( M:Head :- Body )) :-
+    NonTerminal \= ( _, _ ),
+    dcg_non_terminal(NonTerminal, S0, S, Head),
+    dcg_body(GRBody, S0, S, Body).
 
 % This program uses append/3 as defined in the Prolog prologue.
 % Expands a DCG rule into a Prolog rule, when no error condition applies.
@@ -71,12 +75,14 @@ dcg_body(GRBody, S0, S, Body) :-
     nonvar(GRBody),
     dcg_constr(GRBody),
     dcg_cbody(GRBody, S0, S, Body).
-dcg_body(NonTerminal, S0, S, Goal) :-
+dcg_body(NonTerminal, S0, S, Goal1) :-
     nonvar(NonTerminal),
     \+ dcg_constr(NonTerminal),
     NonTerminal \= ( _ -> _ ),
     NonTerminal \= ( \+ _ ),
-    dcg_non_terminal(NonTerminal, S0, S, Goal).
+    loader:strip_module(NonTerminal, M, NonTerminal0),
+    dcg_non_terminal(NonTerminal0, S0, S, Goal0),
+    module_call_qualified(M, Goal0, Goal1).
 
 % The following constructs in a grammar rule body
 % are defined in the corresponding subclauses.
@@ -84,7 +90,7 @@ dcg_constr([]). % 7.14.1
 dcg_constr([_|_]). % 7.14.2 - terminal sequence
 dcg_constr(( _, _ )). % 7.14.3 - concatenation
 dcg_constr(( _ ; _ )). % 7.14.4 - alternative
-%% dcg_constr(( _'|'_ )). % 7.14.6 - alternative
+dcg_constr(( _'|'_ )). % 7.14.6 - alternative
 dcg_constr({_}). % 7.14.7
 dcg_constr(call(_)). % 7.14.8
 dcg_constr(phrase(_)). % 7.14.9
@@ -96,6 +102,7 @@ dcg_constr((_->_)). % 7.14.12 - if-then (existence implementation dep.)
 % the construct to be expanded.
 dcg_cbody([], S0, S, S0 = S).
 dcg_cbody([T|Ts], S0, S, Goal) :-
+    must_be(list, [T|Ts]),
     dcg_terminals([T|Ts], S0, S, Goal).
 dcg_cbody(( GRFirst, GRSecond ), S0, S, ( First, Second )) :-
     dcg_body(GRFirst, S0, S1, First),
@@ -108,9 +115,9 @@ dcg_cbody(( GRCond ; GRElse ), S0, S, ( Cond ; Else )) :-
     subsumes_term(( _GRIf -> _GRThen ), GRCond),
     dcg_cbody(GRCond, S0, S, Cond),
     dcg_body(GRElse, S0, S, Else).
-%% dcg_cbody(( GREither '|' GROr ), S0, S, ( Either ; Or )) :-
-%%     dcg_body(GREither, S0, S, Either),
-%%     dcg_body(GROr, S0, S, Or).
+dcg_cbody(( GREither '|' GROr ), S0, S, ( Either ; Or )) :-
+    dcg_body(GREither, S0, S, Either),
+    dcg_body(GROr, S0, S, Or).
 dcg_cbody({Goal}, S0, S, ( Goal, S0 = S )).
 dcg_cbody(call(Cont), S0, S, call(Cont, S0, S)).
 dcg_cbody(phrase(Body), S0, S, phrase(Body, S0, S)).
@@ -119,3 +126,43 @@ dcg_cbody(\+ GRBody, S0, S, ( \+ phrase(GRBody,S0,_), S0 = S )).
 dcg_cbody(( GRIf -> GRThen ), S0, S, ( If -> Then )) :-
     dcg_body(GRIf, S0, S1, If),
     dcg_body(GRThen, S1, S, Then).
+
+user:term_expansion(Term0, Term) :-
+    nonvar(Term0),
+    dcg_rule(Term0, Term).
+
+% Describes a sequence
+seq(Xs, Cs0,Cs) :-
+   var(Xs),
+   Cs0 == [],
+   !,
+   Xs = [],
+   Cs0 = Cs.
+seq([]) --> [].
+seq([E|Es]) --> [E], seq(Es).
+
+% Describes a sequence of sequences
+seqq([]) --> [].
+seqq([Es|Ess]) --> seq(Es), seqq(Ess).
+
+% Describes an arbitrary number of elements
+...(Cs0,Cs) :-
+   Cs0 == [],
+   !,
+   Cs0 = Cs.
+... --> [] | [_], ... .
+
+error_goal(error(E, must_be/2), error(E, must_be/2)).
+error_goal(error(E, (=..)/2), error(E, (=..)/2)).
+error_goal(E, _) :- throw(E).
+
+user:goal_expansion(phrase(GRBody, S, S0), GRBody2) :-
+    loader:strip_module(GRBody, M, GRBody0),
+    nonvar(GRBody0),
+    catch(dcgs:dcg_body(GRBody0, S, S0, GRBody1),
+          E,
+          dcgs:error_goal(E, GRBody1)
+         ),
+    module_call_qualified(M, GRBody1, GRBody2).
+
+user:goal_expansion(phrase(GRBody, S), phrase(GRBody, S, [])).

src/lib/debug.pl

@@ -0,0 +1,26 @@
+% Source: https://stackoverflow.com/a/30791637
+
+:- module(debug, [
+    op(900, fx, $),
+    op(900, fx, $-),
+    op(950, fy, *),
+    (*)/1,
+    ($)/1,
+    ($-)/1
+]).
+
+:- use_module(library(format), [portray_clause/1]).
+
+:- meta_predicate *(0).
+:- meta_predicate $(0).
+:- meta_predicate $-(0).
+
+$-(G_0) :-
+   catch(G_0, Ex, ( portray_clause(exception:Ex:G_0), throw(Ex) ) ).
+
+$(G_0) :-
+   portray_clause(call:G_0),
+   $-G_0,
+   portray_clause(exit:G_0).
+
+*(_).

src/lib/diag.pl

@@ -0,0 +1,24 @@
+:- module(diag, [wam_instructions/2]).
+
+:- use_module(library(error)).
+
+
+wam_instructions(Clause, Listing) :-
+    (  nonvar(Clause) ->
+       (  Clause = Name / Arity ->
+          fetch_instructions(user, Name, Arity, Listing)
+       ;  Clause = Module : (Name / Arity) ->
+          fetch_instructions(Module, Name, Arity, Listing)
+       )
+    ;  throw(error(instantiation_error, wam_instructions/2))
+    ).
+
+
+fetch_instructions(Module, Name, Arity, Listing) :-
+    must_be(atom, Module),
+    must_be(atom, Name),
+    must_be(integer, Arity),
+    (  Arity >= 0 ->
+       '$wam_instructions'(Module, Name, Arity, Listing)
+    ;  throw(error(domain_error(not_less_than_zero, Arity), wam_instructions/2))
+    ).

src/lib/dif.pl

@@ -8,8 +8,8 @@
 
 put_dif_att(Var, X, Y) :-
     (   get_atts(Var, +dif(Z)) ->
-	sort([X \== Y | Z], NewZ),
-	put_atts(Var, +dif(NewZ))
+	    sort([X \== Y | Z], NewZ),
+	    put_atts(Var, +dif(NewZ))
     ;   put_atts(Var, +dif([X \== Y]))
     ).
 
@@ -21,8 +21,8 @@ dif_set_variables([Var|Vars], X, Y) :-
 append_goals([], _).
 append_goals([Var|Vars], Goals) :-
     (   get_atts(Var, +dif(VarGoals)) ->
-	append(Goals, VarGoals, NewGoals0),
-	sort(NewGoals0, NewGoals)
+	    append(Goals, VarGoals, NewGoals0),
+	    sort(NewGoals0, NewGoals)
     ;   NewGoals = Goals
     ),
     put_atts(Var, +dif(NewGoals)),
@@ -30,25 +30,30 @@ append_goals([Var|Vars], Goals) :-
 
 verify_attributes(Var, Value, Goals) :-
     (   get_atts(Var, +dif(Goals)) ->
-	term_variables(Value, ValueVars),
-	append_goals(ValueVars, Goals)
+	    term_variables(Value, ValueVars),
+	    append_goals(ValueVars, Goals)
     ;   Goals = []
     ).
 
 % Probably the world's worst dif/2 implementation. I'm open to
 % suggestions for improvement.
 
-dif(X, Y) :- X \== Y,
-             (   term_variables(X, XVars), term_variables(Y, YVars),
-	         dif_set_variables(XVars, X, Y),
-		 dif_set_variables(YVars, X, Y)
-	     ).
+dif(X, Y) :-
+    X \== Y,
+    (   X \= Y -> true
+    ;   (   term_variables(X, XVars),
+            term_variables(Y, YVars),
+            dif_set_variables(XVars, X, Y),
+            dif_set_variables(YVars, X, Y)
+        )
+    ).
 
 gather_dif_goals([]) --> [].
 gather_dif_goals([(X \== Y) | Goals]) -->
-    [dif(X, Y)],
+    [dif:dif(X, Y)],
     gather_dif_goals(Goals).
 
 attribute_goals(X) -->
     { get_atts(X, +dif(Goals)) },
-    gather_dif_goals(Goals).
+    gather_dif_goals(Goals),
+    { put_atts(X, -dif(_)) }.

src/lib/error.pl

@@ -0,0 +1,224 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written 2018-2022 by Markus Triska (triska@metalevel.at)
+   I place this code in the public domain. Use it in any way you want.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(error, [must_be/2,
+                  can_be/2,
+                  instantiation_error/1,
+                  domain_error/3,
+                  type_error/3
+                  ]).
+
+
+:- meta_predicate check_(1, ?, ?).
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   must_be(Type, Term)
+
+   This predicate is intended for type-checks of built-in predicates.
+
+   It asserts that Term is:
+
+       1) instantiated *and*
+       2) instantiated to an instance of the given Type.
+
+   It corresponds to usage mode +Term.
+
+   Currently, the following types are supported:
+
+       - atom
+       - boolean
+       - character
+       - chars
+       - in_character
+       - integer
+       - list
+       - octet_character
+       - octet_chars
+       - term
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+must_be(Type, Term) :-
+        must_be_(type, Type),
+        must_be_(Type, Term).
+
+must_be_(Type, _) :-
+        var(Type),
+        instantiation_error(must_be/2).
+must_be_(var, Term) :-
+        (   var(Term) -> true
+        ;   throw(error(uninstantiation_error(Term), must_be/2))
+        ).
+must_be_(integer, Term) :- check_(integer, integer, Term).
+must_be_(not_less_than_zero, N) :-
+        must_be(integer, N),
+        (   N >= 0 -> true
+        ;   domain_error(not_less_than_zero, N, must_be/2)
+        ).
+must_be_(atom, Term)    :- check_(atom, atom, Term).
+must_be_(character, T)  :- check_(error:character, character, T).
+must_be_(in_character, T) :- check_(error:in_character, in_character, T).
+must_be_(chars, Ls) :-
+        can_be(chars, Ls), % prioritize type errors over instantiation errors
+        must_be(list, Ls),
+        (   '$is_partial_string'(Ls) ->
+            % The expected case (success) uses a very fast test.
+            % We cannot use partial_string/1 from library(iso_ext),
+            % because that library itself imports library(error).
+            true
+        ;   all_characters(Ls)
+        ).
+must_be_(octet_character, C) :-
+        must_be(character, C),
+        (   octet_character(C) -> true
+        ;   domain_error(octet_character, C, must_be/2)
+        ).
+must_be_(octet_chars, Cs) :-
+        must_be(chars, Cs),
+        (   '$first_non_octet'(Cs, C) ->
+            domain_error(octet_character, C, must_be/2)
+        ;   true
+        ).
+must_be_(list, Term)    :- check_(error:ilist, list, Term).
+must_be_(type, Term)    :- check_(error:type, type, Term).
+must_be_(boolean, Term) :- check_(error:boolean, boolean, Term).
+must_be_(term, Term)    :-
+        (   \+ ground(Term) ->
+            instantiation_error(must_be/2)
+        ;   \+ acyclic_term(Term) ->
+            type_error(term, Term, must_be/2)
+        ;   true
+        ).
+
+% We cannot use maplist(must_be(character), Cs), because library(lists)
+% uses library(error), so importing it would create a cyclic dependency.
+
+all_characters([]).
+all_characters([C|Cs]) :-
+        must_be(character, C),
+        all_characters(Cs).
+
+check_(Pred, Type, Term) :-
+        (   var(Term) -> instantiation_error(must_be/2)
+        ;   call(Pred, Term) -> true
+        ;   type_error(Type, Term, must_be/2)
+        ).
+
+boolean(B) :- ( B == true ; B == false ).
+
+character(C) :-
+        atom(C),
+        atom_length(C, 1).
+
+octet_character(C) :-
+        char_code(C, Code),
+        0 =< Code, Code =< 0xff.
+
+in_character(C) :-
+        (   character(C)
+        ;   C == end_of_file
+        ).
+
+ilist(Ls) :-
+        '$skip_max_list'(_, _, Ls, Rs),
+        (   var(Rs) ->
+            instantiation_error(must_be/2)
+        ;   Rs == []
+        ).
+
+type(type).
+type(integer).
+type(atom).
+type(character).
+type(in_character).
+type(octet_character).
+type(octet_chars).
+type(chars).
+type(list).
+type(var).
+type(boolean).
+type(term).
+type(not_less_than_zero).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   can_be(Type, Term)
+
+   This predicate is intended for type-checks of built-in predicates.
+
+   It asserts that there is a substitution which, if applied to Term,
+   makes it an instance of Type.
+
+   It corresponds to usage mode ?Term.
+
+   It supports the same types as must_be/2.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+
+can_be(Type, Term) :-
+        must_be(type, Type),
+        (   var(Term) -> true
+        ;   can_(Type, Term) -> true
+        ;   type_error(Type, Term, can_be/2)
+        ).
+
+can_(integer, Term) :- integer(Term).
+can_(not_less_than_zero, N) :-
+        (   integer(N) ->
+            (   N >= 0 -> true
+            ;   domain_error(not_less_than_zero, N, can_be/2)
+            )
+        ;   type_error(integer, N, can_be/2)
+        ).
+can_(atom, Term)    :- atom(Term).
+can_(character, T)  :- character(T).
+can_(in_character, T) :- in_character(T).
+can_(chars, Ls)     :-
+        (   '$is_partial_string'(Ls) -> true
+        ;   can_be(list, Ls),
+            can_be_chars(Ls)
+        ).
+can_(octet_character, C) :-
+        (   octet_character(C) -> true
+        ;   domain_error(octet_character, C, can_be/2)
+        ).
+can_(octet_chars, Cs) :-
+        can_be(chars, Cs),
+        (   '$skip_max_list'(_, _, Cs, []), % temporarily turn Cs into a list
+            '$first_non_octet'(Cs, C) ->
+            domain_error(octet_character, C, can_be/2)
+        ;   true
+        ).
+can_(list, Term)    :- list_or_partial_list(Term).
+can_(boolean, Term) :- boolean(Term).
+can_(term, Term)    :-
+        (   acyclic_term(Term) ->
+            true
+        ;   type_error(term, Term, can_be/2)
+        ).
+
+can_be_chars(Var) :- var(Var), !.
+can_be_chars([]).
+can_be_chars([X|Xs]) :-
+        can_be(character, X),
+        can_be_chars(Xs).
+
+list_or_partial_list(Ls) :-
+        '$skip_max_list'(_, _, Ls, Rs),
+        (   var(Rs) -> true
+        ;   Rs == []
+        ).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Shorthands for throwing ISO errors.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+instantiation_error(Context) :-
+    throw(error(instantiation_error, Context)).
+
+domain_error(Type, Term, Context) :-
+    throw(error(domain_error(Type, Term), Context)).
+
+type_error(Type, Term, Context) :-
+    throw(error(type_error(Type, Term), Context)).

src/lib/files.pl

@@ -0,0 +1,221 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written 2020, 2022 by Markus Triska (triska@metalevel.at)
+   Part of Scryer Prolog.
+
+   Predicates for reasoning about files and directories.
+
+   In this library, directories and files are represented as
+   *lists of characters*. This is an ideal representation:
+
+   -) Lists of characters can be conveniently reasoned about with DCGs
+      and built-in Prolog predicates from library(lists). This alone
+      is already a very compelling argument to use them.
+   -) Other Scryer libraries such as library(http/http_open) also already
+      use lists of characters to represent paths.
+   -) File names are mostly ephemeral, so it is good for efficiency
+      that they can quickly allocated transiently on the heap, leaving the
+      atom table mostly unaffected. Indexing is almost never needed
+      for file names. If needed, it should be added to the engine.
+   -) The previous point is also good for security, since the system
+      leaves little trace of which files were even accessed.
+   -) Scryer Prolog represents lists of characters extremely compactly.
+
+   Some Prolog programmers will likely find this representation quite
+   unusual, because files are represented as *atoms* in many systems.
+
+   However, the ISO standard only demands that sources and sinks be
+   *ground* terms, so lists of characters are completely admissible:
+
+       A source/sink is specified as an implementation defined
+       ground term in a call of open/4 (8.11.5). All subsequent
+       references to the source/sink are made by referring to a
+       stream-term (7.10.2) or alias (7.10.2.2).
+
+   I believe that with the advent of Scryer Prolog and its efficient
+   representation of strings as lists of characters, we should take
+   this opportunity for improvement, and in fact extend the use of
+   lists of characters also to other predicates like open/3.
+
+   Please note that we *cannot* simply accept *both* representations,
+   because that would invalidate the type errors raised by this library,
+   and make future extensions for type checking impossible.
+
+   So I ask you: Please try out this representation for a few months.
+   It simplifies working with files considerably. Once we have collected
+   more experience with this representations, please let us consider
+   how to proceed in such a way that we can call it an improvement.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(files, [directory_files/2,
+                  file_size/2,
+                  file_exists/1,
+                  directory_exists/1,
+                  delete_file/1,
+				  rename_file/2,
+				  delete_directory/1,
+                  make_directory/1,
+                  make_directory_path/1,
+                  working_directory/2,
+                  path_canonical/2,
+                  path_segments/2,
+                  file_modification_time/2,
+                  file_creation_time/2,
+                  file_access_time/2]).
+
+:- use_module(library(error)).
+:- use_module(library(lists)).
+:- use_module(library(charsio)).
+:- use_module(library(dcgs)).
+
+directory_files(Directory, Files) :-
+        must_be(chars, Directory),
+        can_be(list, Files),
+        '$directory_files'(Directory, Files).
+
+file_size(File, Size) :-
+        file_must_exist(File, file_size/2),
+        can_be(integer, Size),
+        '$file_size'(File, Size).
+
+file_exists(File) :-
+        must_be(chars, File),
+        '$file_exists'(File).
+
+directory_exists(Directory) :-
+        must_be(chars, Directory),
+        '$directory_exists'(Directory).
+
+make_directory(Directory) :-
+        must_be(chars, Directory),
+        '$make_directory'(Directory).
+
+make_directory_path(Directory) :-
+        must_be(chars, Directory),
+        '$make_directory_path'(Directory).
+
+delete_file(File) :-
+        file_must_exist(File, delete_file/1),
+        '$delete_file'(File).
+
+rename_file(File, Renamed) :-
+        file_must_exist(File, rename_file/2),
+        must_be(chars, Renamed),
+        '$rename_file'(File, Renamed).
+
+delete_directory(Directory) :-
+        directory_must_exist(Directory, delete_directory/1),
+        must_be(chars, Directory),
+        '$delete_directory'(Directory).
+
+file_must_exist(File, Context) :-
+        (   file_exists(File) -> true
+        ;   throw(error(existence_error(file, File), Context))
+        ).
+
+directory_must_exist(Directory, Context) :-
+        (   directory_exists(Directory) -> true
+        ;   throw(error(existence_error(directory, Directory), Context))
+        ).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Dir0 is the current working directory, and the working directory
+   is changed to Dir.
+
+   Use working_directory(Ds, Ds) to determine the current working directory,
+   and leave it as is.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+working_directory(Dir0, Dir) :-
+        can_be(list, Dir0),
+        can_be(list, Dir),
+        '$working_directory'(Dir0, Dir).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   True iff Cs is the canonical, absolute path of Ps.
+
+   All intermediate components are normalized, and all symbolic links
+   are resolved.
+
+   The predicate fails in the following situations, though not
+   necessarily *only* in these cases:
+
+      1. Ps is a path that does not exist.
+      2. A non-final component in Ps is not a directory.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+path_canonical(Ps, Cs) :-
+        must_be(chars, Ps),
+        can_be(list, Cs),
+        '$path_canonical'(Ps, Cs).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   T is, respectively, the modification, access or creation time of File.
+   T is a time stamp, suitable for use in format_time//2 in library(time).
+
+   For two time stamps A and B, if A precedes B, then A @< B holds.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+file_modification_time(File, T) :-
+        file_time_(File, modification, T).
+
+file_access_time(File, T) :-
+        file_time_(File, access, T).
+
+file_creation_time(File, T) :-
+        file_time_(File, creation, T).
+
+file_time_(File, Which, T) :-
+        file_must_exist(File, file_time_/3),
+        '$file_time'(File, Which, T0),
+        read_from_chars(T0, T).
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   path_segments(Ps, Segments): True iff Segments are the segments of Ps.
+
+   Segments is the list of components of the path Ps that are
+   separated by the platform-specific directory separator. Each
+   segment is a list of characters.
+
+   At least one of the arguments must be instantiated.
+
+   Examples:
+
+      ?- path_segments("/hello/there", Segments).
+         Segments = [[],"hello","there"].
+
+      ?- path_segments(Path, ["hello","there"]).
+         Path = "hello/there".
+
+
+   To obtain the platform-specific directory separator, you can use:
+
+      ?- path_segments(Separator, ["",""]).
+         Separator = "/".
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+path_segments(Path, Segments) :-
+        '$directory_separator'(Sep),
+        (   var(Path) ->
+            must_be(list, Segments),
+            maplist(must_be(chars), Segments),
+            phrase(append_with_separator(Segments, Sep), Path)
+        ;   must_be(chars, Path),
+            path_to_segments(Path, Sep, Segments)
+        ).
+
+append_with_separator([], _) --> [].
+append_with_separator([Segment|Segments], Sep) -->
+        append_with_separator_(Segments, Segment, Sep).
+
+append_with_separator_([], Segment, _) --> seq(Segment).
+append_with_separator_([Segment|Segments], Prev, Sep) -->
+        seq(Prev), [Sep],
+        append_with_separator_(Segments, Segment, Sep).
+
+path_to_segments(Path, Sep, Segments) :-
+        (   append(Front, [Sep|Ps], Path) ->
+            Segments = [Front|Rest],
+            path_to_segments(Ps, Sep, Rest)
+        ;   Segments = [Path]
+        ).

src/lib/format.pl

@@ -0,0 +1,636 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written 2020, 2021, 2022 by Markus Triska (triska@metalevel.at)
+   Part of Scryer Prolog.
+
+   This library provides the nonterminal format_//2 to describe
+   formatted strings. format/[2,3] are provided for impure output.
+
+   Usage:
+   ======
+
+   phrase(format_(FormatString, Arguments), Ls)
+
+   format_//2 describes a list of characters Ls that are formatted
+   according to FormatString. FormatString is a string (i.e.,
+   a list of characters) that specifies the layout of Ls.
+   The characters in FormatString are used literally, except
+   for the following tokens with special meaning:
+
+     ~w    use the next available argument from Arguments here
+     ~q    use the next argument here, formatted as by writeq/1
+     ~a    use the next argument here, which must be an atom
+     ~s    use the next argument here, which must be a string
+     ~d    use the next argument here, which must be an integer
+     ~f    use the next argument here, a floating point number
+     ~Nf   where N is an integer: format the float argument
+           using N digits after the decimal point
+     ~Nd   like ~d, placing the last N digits after a decimal point;
+           if N is 0 or omitted, no decimal point is used.
+     ~ND   like ~Nd, separating digits to the left of the decimal point
+           in groups of three, using the character "," (comma)
+     ~NU   like ~ND, using "_" (underscore) to separate groups of digits
+     ~NL   format an integer so that at most N digits appear on a line.
+           If N is 0 or omitted, it defaults to 72.
+     ~Nr   where N is an integer between 2 and 36: format the
+           next argument, which must be an integer, in radix N.
+           The characters "a" to "z" are used for radices 10 to 36.
+           If N is omitted, it defaults to 8 (octal).
+     ~NR   like ~Nr, except that "A" to "Z" are used for radices > 9
+     ~|    place a tab stop at this position
+     ~N|   where N is an integer: place a tab stop at text column N
+     ~N+   where N is an integer: place a tab stop N characters
+           after the previous tab stop (or start of line)
+     ~t    distribute spaces evenly between the two closest tab stops
+     ~`Ct  like ~t, use character C instead of spaces to fill the space
+     ~n    newline
+     ~Nn   N newlines
+     ~i    ignore the next argument
+     ~~    the literal ~
+
+   Instead of ~N, you can write ~* to use the next argument from Arguments
+   as the numeric argument.
+
+   The predicate format/2 is like format_//2, except that it outputs
+   the text on the terminal instead of describing it declaratively.
+
+   format/3, used as format(Stream, FormatString, Arguments), outputs
+   the described string to the given Stream. If Stream is a binary
+   stream, then the code of each emitted character must be in 0..255.
+
+   If at all possible, format_//2 should be used, to stress pure parts
+   that enable easy testing etc. If necessary, you can emit the list Ls
+   with maplist(put_char, Ls) or, much faster, with format("~s", [Ls]).
+   Ideally, however, you use phrase_to_file/[2,3] or phrase_to_stream/2
+   from library(pio) to write the described list directly to a file
+   or stream, respectively: phrase_to_stream(format_(..., [...]), S).
+   The advantage of this is that an ideal implementation writes
+   the characters as they become known, without manifesting the list.
+
+   The entire library only works if the Prolog flag double_quotes
+   is set to chars, the default value in Scryer Prolog. This should
+   also stay that way, to encourage a sensible environment.
+
+   Example:
+
+   ?- phrase(format_("~s~n~`.t~w!~12|", ["hello",there]), Cs).
+   %@    Cs = "hello\n......there!".
+
+   I place this code in the public domain. Use it in any way you want.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(format, [format_//2,
+                   format/2,
+                   format/3,
+                   portray_clause_//1,
+                   portray_clause/1,
+                   portray_clause/2,
+                   listing/1
+                  ]).
+
+:- use_module(library(dcgs)).
+:- use_module(library(lists)).
+:- use_module(library(error)).
+:- use_module(library(charsio)).
+:- use_module(library(between)).
+:- use_module(library(pio)).
+
+format_(Fs, Args) -->
+        { must_be(list, Fs),
+          must_be(list, Args),
+          unique_variable_names(Args, VNs),
+          phrase(cells(Fs,Args,0,[],VNs), Cells) },
+        format_cells(Cells).
+
+format_cells([]) --> [].
+format_cells([Cell|Cells]) -->
+        format_cell(Cell),
+        format_cells(Cells).
+
+format_cell(newline) --> "\n".
+format_cell(cell(From,To,Es)) -->
+        % distribute the space between the glue elements
+        { phrase(elements_gluevars(Es, 0, Length), Vs),
+          (   Vs = [] -> true
+          ;   Space is To - From - Length,
+              (   Space =< 0 -> maplist(=(0), Vs)
+              ;   length(Vs, NumGlue),
+                  Distr is Space // NumGlue,
+                  Delta is Space - Distr*NumGlue,
+                  (   Delta =:= 0 ->
+                      maplist(=(Distr), Vs)
+                  ;   BigGlue is Distr + Delta,
+                      reverse(Vs, [BigGlue|Rest]),
+                      maplist(=(Distr), Rest)
+                  )
+              )
+          ) },
+        format_elements(Es).
+
+format_elements([]) --> [].
+format_elements([E|Es]) -->
+        format_element(E),
+        format_elements(Es).
+
+format_element(chars(Cs)) --> seq(Cs).
+format_element(glue(Fill,Num)) -->
+        { length(Ls, Num),
+          maplist(=(Fill), Ls) },
+        seq(Ls).
+
+elements_gluevars([], N, N) --> [].
+elements_gluevars([E|Es], N0, N) -->
+        element_gluevar(E, N0, N1),
+        elements_gluevars(Es, N1, N).
+
+element_gluevar(chars(Cs), N0, N) -->
+        { length(Cs, L),
+          N is N0 + L }.
+element_gluevar(glue(_,V), N, N) --> [V].
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Our key datastructure is a list of cells and newlines.
+   A cell has the shape cell(From,To,Elements), where
+   From and To denote the positions of surrounding tab stops.
+
+   Elements is a list of elements that occur in a cell,
+   namely terms of the form chars(Cs) and glue(Char, Var).
+   "glue" elements (TeX terminology) are evenly stretched
+   to fill the remaining whitespace in the cell. For each
+   glue element, the character Char is used for filling,
+   and Var is a free variable that is used when the
+   available space is distributed.
+
+   newline is used if ~n occurs in a format string.
+   It is used because a newline character does not
+   consume whitespace in the sense of format strings.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+cells([], Args, Tab, Es, _) --> !,
+        (   { Args == [] } -> cell(Tab, Tab, Es)
+        ;   { domain_error(empty_list, Args, format_//2) }
+        ).
+cells([~,~|Fs], Args, Tab, Es, VNs) --> !,
+        cells(Fs, Args, Tab, [chars("~")|Es], VNs).
+cells([~,w|Fs], [Arg|Args], Tab, Es, VNs) --> !,
+        { write_term_to_chars(Arg, [numbervars(true),variable_names(VNs)], Chars) },
+        cells(Fs, Args, Tab, [chars(Chars)|Es], VNs).
+cells([~,q|Fs], [Arg|Args], Tab, Es, VNs) --> !,
+        { write_term_to_chars(Arg, [quoted(true),numbervars(true),variable_names(VNs)], Chars) },
+        cells(Fs, Args, Tab, [chars(Chars)|Es], VNs).
+cells([~,a|Fs], [Arg|Args], Tab, Es, VNs) --> !,
+        { atom_chars(Arg, Chars) },
+        cells(Fs, Args, Tab, [chars(Chars)|Es], VNs).
+cells([~|Fs0], Args0, Tab, Es, VNs) -->
+        { numeric_argument(Fs0, Num, [d|Fs], Args0, [Arg0|Args]) },
+        !,
+        { Arg is Arg0, % evaluate compound expression
+          must_be(integer, Arg),
+          number_chars(Arg, Cs0) },
+        (   { Num =:= 0 } -> { Cs = Cs0 }
+        ;   { length(Cs0, L),
+              (   L =< Num ->
+                  Delta is Num - L,
+                  length(Zs, Delta),
+                  maplist(=('0'), Zs),
+                  phrase(("0.",seq(Zs),seq(Cs0)), Cs)
+              ;   BeforeComma is L - Num,
+                  length(Bs, BeforeComma),
+                  append(Bs, Ds, Cs0),
+                  phrase((seq(Bs),".",seq(Ds)), Cs)
+              ) }
+        ),
+        cells(Fs, Args, Tab, [chars(Cs)|Es], VNs).
+cells([~|Fs0], Args0, Tab, Es, VNs) -->
+        { numeric_argument(Fs0, Num, ['D'|Fs], Args0, [Arg|Args]) },
+        !,
+        { separate_digits_fractional(Arg, ',', Num, Cs) },
+        cells(Fs, Args, Tab, [chars(Cs)|Es], VNs).
+cells([~|Fs0], Args0, Tab, Es, VNs) -->
+        { numeric_argument(Fs0, Num, ['U'|Fs], Args0, [Arg|Args]) },
+        !,
+        { separate_digits_fractional(Arg, '_', Num, Cs) },
+        cells(Fs, Args, Tab, [chars(Cs)|Es], VNs).
+cells([~|Fs0], Args0, Tab, Es, VNs) -->
+        { numeric_argument(Fs0, Num0, ['L'|Fs], Args0, [Arg|Args]) },
+        !,
+        { (   Num0 =:= 0 ->
+              Num = 72
+          ;   Num = Num0
+          ),
+          phrase(format_("~d", [Arg]), Cs0),
+          phrase(split_lines_width(Cs0, Num), Cs) },
+        cells(Fs, Args, Tab, [chars(Cs)|Es], VNs).
+cells([~,i|Fs], [_|Args], Tab, Es, VNs) --> !,
+        cells(Fs, Args, Tab, Es, VNs).
+cells([~,n|Fs], Args, Tab, Es, VNs) --> !,
+        cell(Tab, Tab, Es),
+        n_newlines(1),
+        cells(Fs, Args, 0, [], VNs).
+cells([~|Fs0], Args0, Tab, Es, VNs) -->
+        { numeric_argument(Fs0, Num, [n|Fs], Args0, Args) },
+        !,
+        cell(Tab, Tab, Es),
+        n_newlines(Num),
+        cells(Fs, Args, 0, [], VNs).
+cells([~,s|Fs], [Arg|Args], Tab, Es, VNs) --> !,
+        cells(Fs, Args, Tab, [chars(Arg)|Es], VNs).
+cells([~,f|Fs], [Arg|Args], Tab, Es, VNs) --> !,
+        { format_number_chars(Arg, Chars) },
+        cells(Fs, Args, Tab, [chars(Chars)|Es], VNs).
+cells([~|Fs0], Args0, Tab, Es, VNs) -->
+        { numeric_argument(Fs0, Num, [f|Fs], Args0, [Arg|Args]) },
+        !,
+        { format_number_chars(Arg, Cs0),
+          phrase(upto_what(Bs, .), Cs0, Cs),
+          (   Num =:= 0 -> Chars = Bs
+          ;   (   Cs = ['.'|Rest] ->
+                  length(Rest, L),
+                  (   Num < L ->
+                      length(Ds, Num),
+                      append(Ds, _, Rest)
+                  ;   Num =:= L ->
+                      Ds = Rest
+                  ;   Num > L,
+                      Delta is Num - L,
+                      % we should look into the float with
+                      % greater accuracy here, and use the
+                      % actual digits instead of 0.
+                      length(Zs, Delta),
+                      maplist(=('0'), Zs),
+                      append(Rest, Zs, Ds)
+                  )
+              ;   length(Ds, Num),
+                  maplist(=('0'), Ds)
+              ),
+              append(Bs, ['.'|Ds], Chars)
+          ) },
+        cells(Fs, Args, Tab, [chars(Chars)|Es], VNs).
+cells([~,r|Fs], Args, Tab, Es, VNs) --> !,
+        cells([~,'8',r|Fs], Args, Tab, Es, VNs).
+cells([~|Fs0], Args0, Tab, Es, VNs) -->
+        { numeric_argument(Fs0, Num, [r|Fs], Args0, [Arg|Args]) },
+        !,
+        { integer_to_radix(Arg, Num, lowercase, Cs) },
+        cells(Fs, Args, Tab, [chars(Cs)|Es], VNs).
+cells([~,'R'|Fs], Args, Tab, Es, VNs) --> !,
+        cells([~,'8','R'|Fs], Args, Tab, Es, VNs).
+cells([~|Fs0], Args0, Tab, Es, VNs) -->
+        { numeric_argument(Fs0, Num, ['R'|Fs], Args0, [Arg|Args]) },
+        !,
+        { integer_to_radix(Arg, Num, uppercase, Cs) },
+        cells(Fs, Args, Tab, [chars(Cs)|Es], VNs).
+cells([~,'`',Char,t|Fs], Args, Tab, Es, VNs) --> !,
+        cells(Fs, Args, Tab, [glue(Char,_)|Es], VNs).
+cells([~,t|Fs], Args, Tab, Es, VNs) --> !,
+        cells(Fs, Args, Tab, [glue(' ',_)|Es], VNs).
+cells([~,'|'|Fs], Args, Tab0, Es, VNs) --> !,
+        { phrase(elements_gluevars(Es, 0, Width), _),
+          Tab is Tab0 + Width },
+        cell(Tab0, Tab, Es),
+        cells(Fs, Args, Tab, [], VNs).
+cells([~|Fs0], Args0, Tab, Es, VNs) -->
+        { numeric_argument(Fs0, Num, ['|'|Fs], Args0, Args) },
+        !,
+        cell(Tab, Num, Es),
+        cells(Fs, Args, Num, [], VNs).
+cells([~|Fs0], Args0, Tab0, Es, VNs) -->
+        { numeric_argument(Fs0, Num, [+|Fs], Args0, Args) },
+        !,
+        { Tab is Tab0 + Num },
+        cell(Tab0, Tab, Es),
+        cells(Fs, Args, Tab, [], VNs).
+cells([~|Cs], Args, _, _, _) -->
+        (   { Args == [] } ->
+            { domain_error(non_empty_list, [], format_//2) }
+        ;   { domain_error(format_string, [~|Cs], format_//2) }
+        ).
+cells(Fs0, Args, Tab, Es, VNs) -->
+        { phrase(upto_what(Fs1, ~), Fs0, Fs),
+          Fs1 = [_|_] },
+        cells(Fs, Args, Tab, [chars(Fs1)|Es], VNs).
+
+format_number_chars(N0, Chars) :-
+        N is N0, % evaluate compound expression
+        number_chars(N, Chars).
+
+n_newlines(0) --> !.
+n_newlines(N0) --> { N0 > 0, N is N0 - 1 }, [newline], n_newlines(N).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+?- phrase(upto_what(Cs, ~), "abc~test", Rest).
+Cs = [a,b,c], Rest = [~,t,e,s,t].
+?- phrase(upto_what(Cs, ~), "abc", Rest).
+Cs = [a,b,c], Rest = [].
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+separate_digits_fractional(Arg, Sep, Num, Cs) :-
+        number_chars(Num, NCs),
+        phrase(("~",seq(NCs),"d"), FStr),
+        phrase(format_(FStr, [Arg]), Cs0),
+        phrase(upto_what(Bs0, .), Cs0, Ds),
+        reverse(Bs0, Bs1),
+        phrase(groups_of_three(Bs1,Sep), Bs2),
+        reverse(Bs2, Bs),
+        append(Bs, Ds, Cs).
+
+upto_what([], W), [W] --> [W], !.
+upto_what([C|Cs], W) --> [C], !, upto_what(Cs, W).
+upto_what([], _) --> [].
+
+groups_of_three([A,B,C,D|Rs], Sep) --> !, [A,B,C,Sep], groups_of_three([D|Rs], Sep).
+groups_of_three(Ls, _) --> seq(Ls).
+
+split_lines_width(Cs, Num) -->
+        (   { length(Prefix, Num),
+              append(Prefix, [R|Rs], Cs) } ->
+            seq(Prefix), "_\n",
+            split_lines_width([R|Rs], Num)
+        ;   seq(Cs)
+        ).
+
+cell(From, To, Es0) -->
+        (   { Es0 == [] } -> []
+        ;   { reverse(Es0, Es) },
+            [cell(From,To,Es)]
+        ).
+
+%?- format:numeric_argument("2f", Num, [f|Fs], Args0, Args).
+
+%?- format:numeric_argument("100b", Num, Rs, Args0, Args).
+
+numeric_argument(Ds, Num, Rest, Args0, Args) :-
+        (   Ds = [*|Rest] ->
+            Args0 = [Num|Args]
+        ;   phrase(numeric_argument_(Ds, Rest), Ns),
+            foldl(plus_times10, Ns, 0, Num),
+            Args0 = Args
+        ).
+
+numeric_argument_([D|Ds], Rest) -->
+        (   { member(D, "0123456789") } ->
+            { number_chars(N, [D]) },
+            [N],
+            numeric_argument_(Ds, Rest)
+        ;   { Rest = [D|Ds] }
+        ).
+
+
+plus_times10(D, N0, N) :- N is D + N0*10.
+
+radix_error(lowercase, R) --> format_("~~~dr", [R]).
+radix_error(uppercase, R) --> format_("~~~dR", [R]).
+
+integer_to_radix(I0, R, Which, Cs) :-
+        I is I0, % evaluate compound expression
+        must_be(integer, I),
+        must_be(integer, R),
+        (   \+ between(2, 36, R) ->
+            phrase(radix_error(Which,R), Es),
+            domain_error(format_string, Es, format_//2)
+        ;   true
+        ),
+        digits(Which, Ds),
+        (   I < 0 ->
+            Pos is abs(I),
+            phrase(integer_to_radix_(Pos, R, Ds), Cs0, "-")
+        ;   I =:= 0 -> Cs0 = "0"
+        ;   phrase(integer_to_radix_(I, R, Ds), Cs0)
+        ),
+        reverse(Cs0, Cs).
+
+integer_to_radix_(0, _, _) --> !.
+integer_to_radix_(I0, R, Ds) -->
+        { M is I0 mod R,
+          nth0(M, Ds, D),
+          I is I0 // R },
+        [D],
+        integer_to_radix_(I, R, Ds).
+
+digits(lowercase, "0123456789abcdefghijklmnopqrstuvwxyz").
+digits(uppercase, "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ").
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Impure I/O, implemented as a small wrapper over format_//2.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+format(Fs, Args) :-
+        current_output(Stream),
+        format(Stream, Fs, Args).
+
+format(Stream, Fs, Args) :-
+        phrase_to_stream(format_(Fs, Args), Stream),
+        flush_output(Stream).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+?- phrase(format:cells("hello", [], 0, [], []), Cs).
+
+?- phrase(format:cells("hello~10|", [], 0, [], []), Cs).
+?- phrase(format:cells("~ta~t~10|", [], 0, [], []), Cs).
+
+?- phrase(format_("~`at~50|", []), Ls).
+
+?- phrase(format:cells("~`at~50|", [], 0, [], []), Cs),
+   phrase(format:format_cells(Cs), Ls).
+?- phrase(format:cells("~ta~t~tb~tc~21|", [], 0, [], []), Cs).
+Cs = [cell(0,21,[glue(' ',_A),chars("a"),glue(' ',_B),glue(' ',_C),chars("b"),glue(' ',_D),chars("c ...")])]
+?- phrase(format:cells("~ta~t~4|", [], 0, [], []), Cs).
+Cs = [cell(0,4,[glue(' ',_A),chars("a"),glue(' ',_B)])]
+
+?- phrase(format:format_cell(cell(0,1,[glue(a,_94)])), Ls).
+
+?- phrase(format:format_cell(cell(0,50,[chars("hello")])), Ls).
+
+?- phrase(format_("~`at~50|~n", []), Ls).
+?- phrase(format_("hello~n~tthere~6|", []), Ls).
+
+?- format("~ta~t~4|", []).
+ a     true.
+
+?- format("~ta~tb~tc~10|", []).
+  a  b   c   true.
+
+?- format("~tabc~3|", []).
+
+?- format("~ta~t~4|", []).
+
+?- format("~ta~t~tb~tc~20|", []).
+    a        b     c   true.
+
+?- format("~2f~n", [3]).
+3.00
+   true.
+
+?- format("~20f", [0.1]).
+0.10000000000000000000   true.
+
+?- X is atan(2), format("~7f~n", [X]).
+1.1071487
+   X = 1.1071487177940906.
+
+?- format("~`at~50|~n", []).
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+   true
+
+?- format("~t~N", []).
+
+?- format("~q", [.]).
+'.'   true.
+
+?- format("~12r", [300]).
+210   true.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   We also provide rudimentary versions of portray_clause/1 and listing/1.
+
+   In the eventual library organization, portray_clause/1 and
+   related predicates may be placed in their own dedicated library.
+
+   portray_clause/1 is useful for printing solutions in such a way
+   that they can be read back with read/1.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+portray_clause(Term) :-
+        current_output(Out),
+        portray_clause(Out, Term).
+
+portray_clause(Stream, Term) :-
+        phrase_to_stream(portray_clause_(Term), Stream),
+        flush_output(Stream).
+
+portray_clause_(Term) -->
+        { unique_variable_names(Term, VNs) },
+        portray_(Term, VNs), ".\n".
+
+unique_variable_names(Term, VNs) :-
+        term_variables(Term, Vs),
+        foldl(var_name, Vs, VNs, 0, _).
+
+var_name(V, Name=V, Num0, Num) :-
+        charsio:fabricate_var_name(numbervars, Name, Num0),
+        Num is Num0 + 1.
+
+literal(Lit, VNs) -->
+        { write_term_to_chars(Lit, [quoted(true),variable_names(VNs)], Ls) },
+        seq(Ls).
+
+portray_(Var, VNs) --> { var(Var) }, !, literal(Var, VNs).
+portray_((Head :- Body), VNs) --> !,
+        literal(Head, VNs), " :-\n",
+        body_(Body, 0, 3, VNs).
+portray_((Head --> Body), VNs) --> !,
+        literal(Head, VNs), " -->\n",
+        body_(Body, 0, 3, VNs).
+portray_(Any, VNs) --> literal(Any, VNs).
+
+
+body_(Var, C, I, VNs) --> { var(Var) }, !,
+        indent_to(C, I),
+        literal(Var, VNs).
+body_((A,B), C, I, VNs) --> !,
+        body_(A, C, I, VNs), ",\n",
+        body_(B, 0, I, VNs).
+body_(Body, C, I, VNs) -->
+        { body_if_then_else(Body, If, Then, Else) },
+        !,
+        indent_to(C, I),
+        "(  ",
+        { C1 is I + 3 },
+        body_(If, C1, C1, VNs), " ->\n",
+        body_(Then, 0, C1, VNs), "\n",
+        else_branch(Else, I, VNs).
+body_((A;B), C, I, VNs) --> !,
+        indent_to(C, I),
+        "(  ",
+        { C1 is I + 3 },
+        body_(A, C1, C1, VNs), "\n",
+        else_branch(B, I, VNs).
+body_(Goal, C, I, VNs) -->
+        indent_to(C, I), literal(Goal, VNs).
+
+
+% True iff Body has the shape ( If -> Then ; Else ).
+body_if_then_else(Body, If, Then, Else) :-
+        nonvar(Body),
+        Body = (A ; Else),
+        nonvar(A),
+        A = (If -> Then).
+
+else_branch(Else, I, VNs) -->
+        indent_to(0, I),
+        ";  ",
+        { C is I + 3 },
+        (   { body_if_then_else(Else, If, Then, NextElse) } ->
+            body_(If, C, C, VNs), " ->\n",
+            body_(Then, 0, C, VNs), "\n",
+            else_branch(NextElse, I, VNs)
+        ;   { nonvar(Else), Else = ( A ; B ) } ->
+            body_(A, C, C, VNs), "\n",
+            else_branch(B, I, VNs)
+        ;   body_(Else, C, C, VNs), "\n",
+            indent_to(0, I),
+            ")"
+        ).
+
+indent_to(CurrentColumn, Indent) -->
+        format_("~t~*|", [Indent-CurrentColumn]).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+?- portray_clause(a).
+a.
+
+?- portray_clause((a :- b)).
+a :-
+   b.
+
+?- portray_clause((a :- b, c, d)).
+a :-
+   b,
+   c,
+   d.
+   true.
+
+
+?- portray_clause([a,b,c,d]).
+"abcd".
+
+?- portray_clause(X).
+?- portray_clause((f(X) :- X)).
+
+?- portray_clause((h :- ( a -> b; c))).
+
+?- portray_clause((h :- ( (a -> x ; y) -> b; c))).
+
+?- portray_clause((h(X) :- ( (a(X) ; y(A,B)) -> b; c))).
+
+?- portray_clause((h :- (a,d;b,c) ; (b,e;d))).
+
+?- portray_clause((a :- b ; c ; d)).
+
+?- portray_clause((h :- L = '.')).
+
+?- portray_clause(-->(a, (b, {t}, d))).
+
+?- portray_clause((A :- B)).
+
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+listing(PI) :-
+        nonvar(PI),
+        (   PI = Name/Arity0 ->
+            Arity = Arity0
+        ;   PI = Name//Arity0 ->
+            Arity is Arity0 + 2
+        ;   type_error(predicate_indicator, PI, listing/1)
+        ),
+        functor(Head, Name, Arity),
+        \+ \+ clause(Head, _), % only true if there is at least one clause
+        (   clause(Head, Body),
+            (   Body == true ->
+                portray_clause(Head)
+            ;   portray_clause((Head :- Body))
+            ),
+            false
+        ;   true
+        ).

src/lib/freeze.pl

@@ -3,6 +3,8 @@
 :- use_module(library(atts)).
 :- use_module(library(dcgs)).
 
+:- meta_predicate freeze(-, 0).
+
 :- attribute frozen/1.
 
 verify_attributes(Var, Other, Goals) :-
@@ -21,15 +23,8 @@ freeze(X, Goal) :-
     put_atts(Fresh, frozen(Goal)),
     Fresh = X.
 
-gather_freeze_goals(Attrs, _) -->
-    { var(Attrs) },
-    !.
-gather_freeze_goals([frozen(X) | _], Var) -->
-    [freeze(Var, X)],
-    !.
-gather_freeze_goals([_ | Attrs], Var) -->
-    gather_freeze_goals(Attrs, Var).
+attribute_goals(Var) -->
+    { get_atts(Var, frozen(Goals)),
+      put_atts(Var, -frozen(_)) },
+    [freeze(Var, Goals)].
 
-attribute_goals(X) -->
-    { '$get_attr_list'(X, Attrs) },
-    gather_freeze_goals(Attrs, X).

src/lib/gensym.pl

@@ -0,0 +1,32 @@
+:- module(gensym, [gensym/2,
+		   reset_gensym/1]).
+
+:- use_module(library(error)).
+:- use_module(library(lists)).
+:- use_module(library(iso_ext)).
+:- use_module(library(si)).
+
+gensym_key(Base, BaseKey) :-
+    atom_concat('gensym_', Base, BaseKey).
+
+append_id(Base, UniqueID, Unique) :-
+    atom_chars(Base, BaseChars),
+    number_chars(UniqueID, IDChars),
+    append(BaseChars, IDChars, AtomChars),
+    atom_chars(Unique, AtomChars).
+
+gensym(Base, Unique) :-
+    must_be(var, Unique),
+    atom_si(Base),
+    gensym_key(Base, BaseKey),
+    (  bb_get(BaseKey, UniqueID0) ->
+       UniqueID is UniqueID0 + 1,
+       bb_put(BaseKey, UniqueID),
+       append_id(Base, UniqueID, Unique)
+    ;  bb_put(BaseKey, 1),
+       append_id(Base, 1, Unique)
+    ).
+
+reset_gensym(Base) :-
+    atom_si(Base),
+    bb_put(Base, 0).

src/lib/http/http_open.pl

@@ -0,0 +1,68 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written 2022 by Adrián Arroyo Calle (adrian.arroyocalle@gmail.com)
+   Part of Scryer Prolog.
+
+   http_open(+Address, -Stream, +Options)
+   ======================================
+
+   Yields Stream to read the body of an HTTP reply from Address.
+   Address is a list of characters, and includes the method. Both HTTP
+   and HTTPS are supported.
+
+   Options supported:
+
+     * method(+Method): Sets the HTTP method of the call. Method can be get (default), head, delete, post, put or patch.
+     * data(+Data): Data to be sent in the request. Useful for POST, PUT and PATCH operations.
+     * size(-Size): Unifies with the value of the Content-Length header
+     * request_headers(+RequestHeaders): Headers to be used in the request
+     * headers(-ListHeaders): Unifies with a list with all headers returned in the response
+     * status_code(-Code): Unifies with the status code of the request (200, 201, 404, ...)
+
+   Example:
+
+       ?- http_open("https://github.com/mthom/scryer-prolog", S, []).
+       %@    S = '$stream'(0x7fcfc9e00f00).
+
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(http_open, [http_open/3]).
+
+:- use_module(library(lists)).
+
+http_open(Address, Response, Options) :-
+    parse_http_options(Options, OptionValues),
+    ( member(method(Method), OptionValues) -> true; Method = get),
+    ( member(data(Data), OptionValues) -> true; Data = []),
+    ( member(request_headers(RequestHeaders), OptionValues) -> true; RequestHeaders = ['user-agent'("Scryer Prolog")]),
+    ( member(status_code(Code), OptionValues) -> true; true),
+    ( member(headers(Headers), OptionValues) -> true; true),
+    ( member(size(Size), OptionValues) -> member('content-length'(Size), Headers); true),
+    '$http_open'(Address, Response, Method, Code, Data, Headers, RequestHeaders).
+
+parse_http_options(Options, OptionValues) :-
+    maplist(parse_http_options_, Options, OptionValues).
+
+parse_http_options_(method(Method), method(Method)) :-
+    (  var(Method) ->
+       throw(error(instantiation_error, http_open/3))
+    ;
+       member(Method, [get, post, put, delete, patch, head]) -> true
+    ;
+       throw(error(domain_error(http_option, method(Method)), _))
+    ).
+
+parse_http_options_(data(Data), data(Data)) :-
+    (  var(Data) ->
+       throw(error(instantiation_error, http_open/3))
+    ;  true
+    ).
+
+parse_http_options_(request_headers(Headers), request_headers(Headers)) :-
+    (  var(Headers) ->
+       throw(error(instantiation_error, http_open/3))
+    ;  true
+    ).
+
+parse_http_options_(size(Size), size(Size)).
+parse_http_options_(status_code(Code), status_code(Code)).
+parse_http_options_(headers(Headers), headers(Headers)).

src/lib/http/http_server.pl

@@ -0,0 +1,315 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written in December 2020 by Adrián Arroyo (adrian.arroyocalle@gmail.com)
+   Updated in March 2022 by Adrián Arroyo to use the Hyper backend
+   Part of Scryer Prolog
+
+   This library provides an starting point to build HTTP server based applications.
+   It is based on Hyper, which allows for HTTP/1.0, HTTP/1.1 and HTTP/2. However,
+   some advanced features that Hyper provides are still not accesible.
+
+   Usage
+   ==========
+   The main predicate of the library is http_listen/2, which needs a port number
+    (usually 80) and a list of handlers. A handler is a compound term with the functor
+   as one HTTP method (in lowercase) and followed by a Route Match and a predicate
+   which will handle the call.
+
+   text_handler(Request, Response) :-
+    http_status_code(Response, 200),
+    http_body(Response, text("Welcome to Scryer Prolog!")).
+
+   parameter_handler(User, Request, Response) :-
+    http_body(Response, text(User)).
+
+   http_listen(7890, [
+        get(echo, text_handler),           % GET /echo
+        post(user/User, parameter_handler(User)) % POST /user/<User>
+   ]).
+
+   Every handler predicate will have at least 2-arity, with Request and Response.
+   Although you can work directly with http_request and http_response terms, it is
+   recommeded to use the helper predicates, which are easier to understand and cleaner:
+   - http_headers(Response/Request, Headers)
+   - http_status_code(Responde, StatusCode)
+   - http_body(Response/Request, text(Body))
+   - http_body(Response/Request, binary(Body))
+   - http_body(Request, form(Form))
+   - http_body(Response, file(Filename))
+   - http_redirect(Response, Url)
+   - http_query(Request, QueryName, QueryValue)
+
+   Some things that are still missing:
+   - Read forms in multipart format
+   - HTTP Basic Auth
+   - Session handling via cookies
+   - HTML Templating
+
+   I place this code in the public domain. Use it in any way you want.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+
+:- module(http_server, [
+	      http_listen/2,
+	      http_headers/2,
+	      http_status_code/2,
+	      http_body/2,
+	      http_redirect/2,
+	      http_query/3
+]).
+
+:- meta_predicate http_listen(?, :).
+
+:- use_module(library(charsio)).
+:- use_module(library(crypto)).
+:- use_module(library(error)).
+:- use_module(library(format)).
+:- use_module(library(iso_ext)).
+:- use_module(library(lists)).
+:- use_module(library(pio)).
+:- use_module(library(time)).
+
+http_listen(Port, Module:Handlers0) :-
+    must_be(integer, Port),
+    must_be(list, Handlers0),
+    maplist(module_qualification(Module), Handlers0, Handlers),
+    http_listen_(Port, Handlers).
+
+module_qualification(M, H0, H) :-
+    H0 =.. [Method, Path, Goal],
+    H =.. [Method, Path, M:Goal].
+
+http_listen_(Port, Handlers) :-
+    phrase(format_("0.0.0.0:~d", [Port]), Addr),
+    '$http_listen'(Addr, HttpListener),!,
+    format("Listening at ~s\n", [Addr]),
+    http_loop(HttpListener, Handlers).
+
+http_loop(HttpListener, Handlers) :-
+    '$http_accept'(HttpListener, RequestMethod, RequestPath, RequestHeaders, RequestQuery, RequestStream, ResponseHandle),
+    current_time(Time),
+    phrase(format_time("%Y-%m-%d (%H:%M:%S)", Time), TimeString),
+    format("~s ~w ~s\n", [TimeString, RequestMethod, RequestPath]),
+    maplist(map_header_kv, RequestHeaders, RequestHeadersKV),
+    phrase(parse_queries(RequestQueries), RequestQuery),
+    (
+	match_handler(Handlers, RequestMethod, RequestPath, Handler) ->
+	(
+	    HttpRequest = http_request(RequestHeadersKV, stream(RequestStream), RequestQueries),
+	    HttpResponse = http_response(_, _, _),
+	    (call(Handler, HttpRequest, HttpResponse) ->
+		 send_response(ResponseHandle, HttpResponse)
+	    ;    (
+		'$http_answer'(ResponseHandle, 500, [], ResponseStream),
+		call_cleanup(format(ResponseStream, "Internal Server Error", []), close(ResponseStream)))
+	    )
+	)
+    ; (
+	'$http_answer'(ResponseHandle, 404, [], ResponseStream),
+	call_cleanup(format(ResponseStream, "Not Found"), close(ResponseStream)))
+    ),
+    http_loop(HttpListener, Handlers).
+
+send_response(ResponseHandle, http_response(StatusCode0, text(ResponseText), ResponseHeaders0)) :-
+    default(StatusCode0, 200, StatusCode),
+    maplist(map_header_kv_2, ResponseHeaders, ResponseHeaders0),
+    '$http_answer'(ResponseHandle, StatusCode, ResponseHeaders, ResponseStream),
+    call_cleanup(
+	format(ResponseStream, "~s", [ResponseText]),
+	close(ResponseStream)
+    ).
+
+send_response(ResponseHandle, http_response(StatusCode0, bytes(ResponseBytes), ResponseHeaders0)) :-
+    default(StatusCode0, 200, StatusCode),
+    maplist(map_header_kv_2, ResponseHeaders, ResponseHeaders0),
+    '$http_answer'(ResponseHandle, StatusCode, ResponseHeaders, ResponseStream),
+    call_cleanup(
+	format(ResponseStream, "~s", [ResponseBytes]),
+	close(ResponseStream)
+    ).
+
+send_response(ResponseHandle, http_response(StatusCode0, file(Filename), ResponseHeaders0)) :-
+    default(StatusCode0, 200, StatusCode),
+    maplist(map_header_kv_2, ResponseHeaders, ResponseHeaders0),
+    '$http_answer'(ResponseHandle, StatusCode, ResponseHeaders, ResponseStream),
+    call_cleanup(
+	setup_call_cleanup(
+	    open(Filename, read, FileStream, [type(binary)]),
+	    (
+		get_n_chars(FileStream, _, FileCs),
+		format(ResponseStream, "~s", [FileCs])
+	    ),
+	    close(FileStream)
+	),
+        close(ResponseStream)
+    ).
+    
+
+default(Var, Default, Out) :-
+    (var(Var) -> Out = Default
+    ;   Var = Out  
+    ).
+
+map_header_kv(T, K-V) :-
+    T =.. [K0, V],
+    atom_chars(K0, K).
+
+map_header_kv_2(T, K-V) :-
+    atom_chars(K0, K),
+    T =.. [K0, V].
+
+match_handler(Handlers, Method, "/", Handler) :-
+    member(H, Handlers),
+    H =.. [Method, /, Handler].
+match_handler(Handlers, Method, Path, Handler) :-
+    member(H, Handlers),
+    copy_term(H, H1),
+    H1 =.. [Method, Pattern, Handler],
+    \+ var(Pattern),
+    phrase(path(Pattern), Path).
+match_handler(Handlers, Method, Path, Handler) :-
+    member(H, Handlers),
+    copy_term(H, H1),
+    H1 =.. [Method, Var, Handler],
+    var(Var),
+    Var = Path.
+
+path(Pattern) -->
+    {
+        Pattern =.. Parts,
+        length(Parts, 3),
+        nth0(1, Parts, Pattern0),
+        nth0(2, Parts, PartAtom),
+        (var(PartAtom) -> Part = PartAtom; atom_chars(PartAtom, Part))
+    },
+    path(Pattern0),
+    "/",
+    string_without("/", Part).
+
+path(Pattern) -->
+    {
+        Pattern =.. Parts,
+        Parts = [PartAtom],
+        (var(PartAtom) -> Part = PartAtom; atom_chars(PartAtom, Part))
+    },
+    "/",
+    string_without("/", Part).
+
+path([]) --> [].
+
+string_without(Not, [Char|String]) -->
+    [Char],
+    {
+        \+ member(Char, Not)
+    },
+    string_without(Not, String).
+
+string_without(_, []) -->
+    [].
+
+http_headers(http_request(Headers, _, _), Headers).
+http_headers(http_response(_, _, Headers), Headers).
+
+http_body(http_request(_, stream(StreamBody), _), bytes(BytesBody)) :- get_n_chars(StreamBody, _, BytesBody).
+http_body(http_request(_, stream(StreamBody), _), text(TextBody)) :- get_n_chars(StreamBody, _, TextBody).
+http_body(http_request(Headers, stream(StreamBody), _), form(FormBody)) :- 
+    member("content-type"-"application/x-www-form-urlencoded", Headers),
+    get_n_chars(StreamBody, _, TextBody),
+    phrase(parse_queries(FormBody), TextBody).
+http_body(http_request(_, Body, _), Body).
+http_body(http_response(_, Body, _), Body).
+
+http_status_code(http_response(StatusCode, _, _), StatusCode).
+http_redirect(http_response(307, text("Moved Temporarily"), ["Location"-Uri]), Uri).
+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([Key-Value]) -->
+    string_without("=", Key0),
+    {
+        phrase(url_decode(Key), Key0)
+    },
+    "=",
+    string_without(" ", Value0),
+    {
+        phrase(url_decode(Value), Value0)  
+    }.
+
+parse_queries([]) -->
+    [].
+
+% Decodes a UTF-8 URL Encoded string: RFC-1738
+url_decode([Char|Chars]) -->
+    [Char],
+    {
+        Char \= '%'
+    },
+    url_decode(Chars).
+url_decode([Char|Chars]) -->
+    "%",
+    [A],
+    [B],
+    {
+        hex_bytes([A,B], Bytes),
+        Bytes = [FirstByte|_],
+        FirstByte < 128,
+        chars_utf8bytes(Chars0, Bytes),
+        Chars0 = [Char]
+    },
+    url_decode(Chars).
+url_decode([Char|Chars]) -->
+    "%",
+    [A, B],
+    "%",
+    [C, D],
+    {
+        hex_bytes([A,B,C,D], Bytes),
+        Bytes = [FirstByte|_],
+        FirstByte < 224,
+        chars_utf8bytes(Chars0, Bytes),
+        Chars0 = [Char]
+    },
+    url_decode(Chars).
+url_decode([Char|Chars]) -->
+    "%",
+    [A, B],
+    "%",
+    [C, D],
+    "%",
+    [E, F],
+    {
+        hex_bytes([A,B,C,D,E,F], Bytes),
+        Bytes = [FirstByte|_],
+        FirstByte < 240,
+        chars_utf8bytes(Chars0, Bytes),
+        Chars0 = [Char]
+    },
+    url_decode(Chars).
+url_decode([Char|Chars]) -->
+    "%",
+    [A, B],
+    "%",
+    [C, D],
+    "%",
+    [E, F],
+    "%",
+    [H, I],
+    {
+        hex_bytes([A,B,C,D,E,F,H,I], Bytes),
+        chars_utf8bytes(Chars0, Bytes),
+        Chars0 = [Char]
+    },
+    url_decode(Chars).
+
+url_decode([]) --> [].

src/lib/iso_ext.pl

@@ -0,0 +1,265 @@
+:- module(iso_ext, [bb_b_put/2,
+                    bb_get/2,
+                    bb_put/2,
+                    call_cleanup/2,
+                    call_with_inference_limit/3,
+                    forall/2,
+                    partial_string/1,
+                    partial_string/3,
+                    partial_string_tail/2,
+                    setup_call_cleanup/3,
+                    call_nth/2,
+                    copy_term_nat/2,
+		    asserta/2,
+		    assertz/2]).
+
+:- use_module(library(error), [can_be/2,
+                               domain_error/3,
+                               instantiation_error/1,
+                               type_error/3]).
+
+:- use_module(library(lists), [maplist/3]).
+
+:- meta_predicate(forall(0, 0)).
+
+forall(Generate, Test) :-
+    \+ (Generate, \+ Test).
+
+%% (non-)backtrackable global variables.
+
+bb_put(Key, Value) :-
+    (  atom(Key) ->
+       '$store_global_var'(Key, Value)
+    ;  type_error(atom, Key, bb_put/2)
+    ).
+
+%% backtrackable global variables.
+
+bb_b_put(Key, Value) :-
+    (  atom(Key) ->
+       '$store_backtrackable_global_var'(Key, Value)
+    ;  type_error(atom, Key, bb_b_put/2)
+    ).
+
+bb_get(Key, Value) :-
+    (  atom(Key) ->
+       '$fetch_global_var'(Key, Value)
+    ;  type_error(atom, Key, bb_get/2)
+    ).
+
+
+% setup_call_cleanup.
+
+:- meta_predicate(call_cleanup(0, 0)).
+
+call_cleanup(G, C) :- setup_call_cleanup(true, G, C).
+
+:- meta_predicate(setup_call_cleanup(0, 0, 0)).
+
+:- non_counted_backtracking setup_call_cleanup/3.
+
+setup_call_cleanup(S, G, C) :-
+    '$get_b_value'(B),
+    '$call_with_inference_counting'(call(S)),
+    '$set_cp_by_default'(B),
+    '$get_current_block'(Bb),
+    (  C = _:CC,
+       var(CC) ->
+       instantiation_error(setup_call_cleanup/3)
+    ;  scc_helper(C, G, Bb)
+    ).
+
+:- meta_predicate(scc_helper(?,0,?)).
+
+:- non_counted_backtracking scc_helper/3.
+
+scc_helper(C, G, Bb) :-
+    '$get_cp'(Cp),
+    '$install_scc_cleaner'(C, NBb),
+    '$call_with_inference_counting'(call(G)),
+    (  '$check_cp'(Cp) ->
+       '$reset_block'(Bb),
+       run_cleaners_without_handling(Cp)
+    ;  true
+    ;  '$reset_block'(NBb),
+       '$fail'
+    ).
+scc_helper(_, _, Bb) :-
+    '$reset_block'(Bb),
+    '$push_ball_stack',
+    run_cleaners_with_handling,
+    '$pop_from_ball_stack',
+    '$unwind_stack'.
+scc_helper(_, _, _) :-
+    '$get_cp'(Cp),
+    run_cleaners_without_handling(Cp),
+    '$fail'.
+
+:- non_counted_backtracking run_cleaners_with_handling/0.
+
+run_cleaners_with_handling :-
+    '$get_scc_cleaner'(C),
+    '$get_level'(B),
+    catch(C, _, true),
+    '$set_cp_by_default'(B),
+    run_cleaners_with_handling.
+run_cleaners_with_handling :-
+    '$restore_cut_policy'.
+
+:- non_counted_backtracking run_cleaners_without_handling/1.
+
+run_cleaners_without_handling(Cp) :-
+    '$get_scc_cleaner'(C),
+    '$get_level'(B),
+    call(C),
+    '$set_cp_by_default'(B),
+    run_cleaners_without_handling(Cp).
+run_cleaners_without_handling(Cp) :-
+    '$set_cp_by_default'(Cp),
+    '$restore_cut_policy'.
+
+% call_with_inference_limit
+
+:- non_counted_backtracking end_block/4.
+
+end_block(_, Bb, NBb, _L) :-
+    '$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.
+
+call_with_inference_limit(G, L, R) :-
+    (  integer(L) ->
+       (  L < 0 ->
+          domain_error(not_less_than_zero, L, call_with_inference_limit/3)
+       ;  true
+       )
+    ;  var(L) ->
+       instantiation_error(call_with_inference_limit/3)
+    ;  type_error(integer, L, call_with_inference_limit/3)
+    ),
+    '$get_current_block'(Bb),
+    '$get_b_value'(B),
+    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,?,?,?,?)).
+
+:- non_counted_backtracking call_with_inference_limit/5.
+
+call_with_inference_limit(G, L, R, Bb, B) :-
+    '$install_new_block'(NBb),
+    '$install_inference_counter'(B, L, Count0),
+    '$call_with_inference_counting'(call(G)),
+    '$inference_level'(R, B),
+    '$remove_inference_counter'(B, Count1),
+    Diff is L - (Count1 - Count0),
+    end_block(B, Bb, NBb, Diff).
+call_with_inference_limit(_, _, R, Bb, B) :-
+    '$reset_block'(Bb),
+    '$remove_inference_counter'(B, _),
+    (  '$get_ball'(Ball),
+       '$push_ball_stack',
+       '$get_level'(Cp),
+       '$set_cp_by_default'(Cp)
+    ;  '$remove_call_policy_check'(B),
+       '$fail'
+    ),
+    handle_ile(B, Ball, R).
+
+partial_string(String, L, L0) :-
+    (  String == [] ->
+       L = L0
+    ;  catch(atom_chars(Atom, String),
+             error(E, _),
+             throw(error(E, partial_string/3))),
+       '$create_partial_string'(Atom, L, L0)
+    ).
+
+partial_string(String) :-
+    '$is_partial_string'(String).
+
+partial_string_tail(String, Tail) :-
+    (  partial_string(String) ->
+       '$partial_string_tail'(String, Tail)
+    ;  throw(error(type_error(partial_string, String), partial_string_tail/2))
+    ).
+
+:- dynamic(i_call_nth_nesting/2).
+:- dynamic(i_call_nth_counter/1).
+
+:- meta_predicate(call_nth(0, ?)).
+
+call_nth(Goal, N) :-
+    can_be(integer, N),
+    (   integer(N) ->
+        (   N < 0 ->
+            domain_error(not_less_than_zero, N, call_nth/2)
+        ;   N > 0
+        )
+    ;   true
+    ),
+    setup_call_cleanup(call_nth_nesting(C, ID),
+                       (   Goal,
+                           bb_get(ID, N0),
+                           N1 is N0 + 1,
+                           bb_put(ID, N1),
+                           (   integer(N) ->
+                               N = N1,
+                               !
+                           ;   N = N1
+                           )
+                       ),
+                       (   bb_get(i_call_nth_counter, C) ->
+                           C1 is C - 1,
+                           bb_put(i_call_nth_counter, C1)
+                       ;   true
+                       )).
+
+call_nth_nesting(C, ID) :-
+    (   bb_get(i_call_nth_counter, C0) ->
+        C is C0 + 1
+    ;   C = 0
+    ),
+    number_chars(C, Cs),
+    atom_chars(Atom, Cs),
+    atom_concat(i_call_nth_nesting_, Atom, ID),
+    bb_put(ID, 0),
+    bb_put(i_call_nth_counter, C).
+
+
+copy_term_nat(Source, Dest) :-
+    '$copy_term_without_attr_vars'(Source, Dest).
+
+
+asserta(Module, (Head :- Body)) :-
+    !,
+    '$asserta'(Module, Head, Body).
+asserta(Module, Fact) :-
+    '$asserta'(Module, Fact, true).
+
+assertz(Module, (Head :- Body)) :-
+    !,
+    '$assertz'(Module, Head, Body).
+assertz(Module, Fact) :-
+    '$assertz'(Module, Fact, true).
+