reconcile '[]' and [] (#644), solve remaining conformity issues (#648), move (-->) from dcgs.pl to builtins.pl (#649)

Improved readline

.dockerignore

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

.travis.yml

@@ -1,14 +1,31 @@
 language: rust
-rust:
-    - stable
-    - beta
-    - nightly
-matrix:
-    allow_failures:
-        - rust: nightly
-    fast_finish: true
+cache: cargo
+os: linux
+dist: xenial
 
-script:
-    - cargo build --verbose --all
-    - cargo test --verbose --all
-    - cargo test --verbose --all --no-default-features --features num
+before_script:
+  - cargo fetch
+
+jobs:
+  allow_failures:
+    env:
+      - CAN_FAIL=true
+  include:
+  - stage: "Stable: Build"
+    rust: stable
+    script: cargo rustc --verbose -- -D warnings
+    name: "Build Stable"
+  - stage: "Stable: Tests"
+    rust: stable
+    script: cargo test --verbose --all
+    name: "Tests Stable"
+  - stage: "Features"
+    rust: stable
+    script: cargo test --verbose --all --no-default-features --features num
+    name: "num Tests"
+    env: CAN_FAIL=true
+  - stage: "Beta: Build"
+  # - #
+    rust: beta
+    script: cargo rustc --verbose -- -D warnings
+    name: "Build Beta"

Cargo.toml

@@ -1,12 +1,15 @@
 [package]
 name = "scryer-prolog"
-version = "0.8.118"
+version = "0.8.127"
 authors = ["Mark Thom <markjordanthom@gmail.com>"]
-build = "build.rs"
-repository = "https://github.com/mthom/scryer-prolog"
-description = "A modern Prolog implementation written mostly in Rust."
-license = "BSD-3-Clause"
 edition = "2018"
+description = "A modern Prolog implementation written mostly in Rust."
+readme = "README.md"
+repository = "https://github.com/mthom/scryer-prolog"
+license = "BSD-3-Clause"
+keywords = ["prolog", "prolog-interpreter", "prolog-system"]
+categories = ["command-line-utilities"]
+build = "build.rs"
 
 [build-dependencies]
 indexmap = "1.0.2"
@@ -16,16 +19,32 @@ default = ["rug", "prolog_parser/rug"]
 num = ["num-rug-adapter", "prolog_parser/num"]
 
 [dependencies]
+cpu-time = "1.0.0"
+crossterm = "0.16.0"
 dirs = "2.0.2"
+divrem = "0.1.0"
 downcast = "0.10.0"
+git-version = "0.3.4"
+hostname = "0.3.1"
 indexmap = "1.0.2"
 lazy_static = "1.4.0"
 libc = "0.2.62"
 nix = "0.15.0"
-num-rug-adapter = { optional = true, version = "0.1.1" }
+num-rug-adapter = { optional = true, version = "0.1.3" }
 ordered-float = "0.5.0"
-prolog_parser = { version = "0.8.40", default-features = false }
+prolog_parser = { version = "0.8.65", default-features = false }
 ref_thread_local = "0.0.0"
 rug = { version = "1.4.0", optional = true }
-rustyline = "5.0.3"
-termion = "1.4.0"
+rustyline = "6.0.0"
+unicode_reader = "1.0.0"
+ring = "0.16.13"
+ripemd160 = "0.8.0"
+sha3 = "0.8.2"
+blake2 = "0.8.1"
+openssl = { version = "0.10.29", features = ["vendored"] }
+native-tls = "0.2.4"
+chrono = "0.4.11"
+select = "0.4.3"
+roxmltree = "0.11.0"
+base64 = "0.12.3"
+sodiumoxide = "0.2.6"

Dockerfile

@@ -0,0 +1,30 @@
+# Based on https://hub.docker.com/_/rust?tab=description and https://blog.sedrik.se/posts/my-docker-setup-for-rust/
+
+# The first container is for build purposes only.
+FROM rust as builder
+
+WORKDIR /usr/src/scryer-prolog
+
+# Using a dummy build.rs and src/main.rs with your Cargo.toml lets Docker cache your Rust dependencies and not rebuild
+# them every time.
+COPY Cargo.toml .
+COPY Cargo.lock .
+RUN mkdir -p src
+RUN echo "fn main() {}" > src/main.rs
+RUN echo "fn main() {}" > build.rs
+RUN cargo build --release
+
+# We need to touch our real main.rs and build.rs files or else
+# docker will use the cached ones.
+COPY . .
+RUN touch src/main.rs
+RUN touch build.rs
+
+RUN cargo build --release
+
+RUN ls ./target/release
+
+# Finally, copy the scryer-prolog executable to a slimmer container.
+FROM debian:buster-slim
+COPY --from=builder /usr/src/scryer-prolog/target/release/scryer-prolog /usr/local/bin/scryer-prolog
+CMD ["scryer-prolog"]

README.md

@@ -5,6 +5,8 @@ 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
@@ -30,7 +32,7 @@ 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
+- [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.
@@ -40,7 +42,7 @@ 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`,
@@ -51,12 +53,15 @@ Extend Scryer Prolog to include the following, among other features:
 - [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 list of
-      chars, using a packed internal representation.
-- [ ] clp(B) and clp(ℤ) as builtin libraries (_in progress_).
-- [ ] Streams and predicates for stream control (_in progress_).
-- [ ] An incremental compacting garbage collector satisfying the five
+      (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.  
+- [ ] Incremental compilation and loading process, newly written,
+      primarily in Prolog. (_in progress_)
+- [ ] A compacting garbage collector satisfying the five
       properties of "Precise Garbage Collection in Prolog."
 - [ ] Mode declarations.
 
@@ -90,10 +95,18 @@ strings.
 
 ## Installing Scryer Prolog
 
+### Native Install (Unix Only)
+
 First, install the latest stable version of
 [Rust](https://www.rust-lang.org/en-US/install.html) using your
-preferred method. Then install 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.
+
+Scryer Prolog can be installed with cargo, like so:
 
 ```
 $> cargo install scryer-prolog
@@ -117,69 +130,85 @@ $> cargo run [--release]
 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 presently the case.
+### Docker Install (All Platforms)
+
+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 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 input and consults the entered Prolog text.
+
+After a program is consulted, you can ask *queries* about the
+predicates it defines. For example, with the program shown above:
+
+```
+?- hello(What).
+   What = declarative_world
+;  What = pure_world.
+```
+
+Press `SPACE` to show further answers, if any exist. Press `RETURN` or
+ `.` to abort the search and return to the toplevel prompt.
+Press `h` to show a help message.
+
+To quit Scryer Prolog, use the standard predicate `halt/0`:
 
-To quit scryer-prolog, type
 ```
 ?- halt.
 ```
@@ -190,46 +219,247 @@ 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
+### Strings and partial strings
 
-Scryer has three specialized non-ISO predicates for handling so-called
-"partial strings." Partial strings imitate difference lists of
-characters, but their characters are packed in UTF-8 format, a much
-more efficient alternative to how lists of characters are represented
-in many other Prologs.
+In Scryer Prolog, the default value of the Prolog flag `double_quotes`
+is `chars`, which is also the recommended setting. This means that
+double-quoted strings are interpreted as lists of *characters*, in the
+tradition of Marseille Prolog.
 
-To use partial strings, the `non_iso` library must be loaded:
+For example, the following query succeeds:
 
-`?- use_module(library(non_iso)).`
+```
+?- "abc" = [a,b,c].
+   true.
+```
 
-If `X` is a free variable, the query
+Internally, strings are represented very compactly in packed
+UTF-8 encoding. A naive representation of strings as lists of
+characters would use one memory cell per character, one
+memory cell per list constructor, and one memory cell for
+each tail that occurs in the list. Since one memory cell takes
+8 bytes on 64-bit machines, the packed representation used by
+Scryer Prolog yields an up to **24-fold reduction** of
+memory usage, and corresponding reduction of memory accesses when
+creating and processing strings.
 
-`?- partial_string("abc", X, _), X = [a, b, c | Y], partial_string(X),
-partial_string_tail(X, Tail), Tail == Y.`
+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 strings explicitly. For example:
 
-will succeed, posting:
+```
+?- partial_string("abc", Ls0, Ls).
+   Ls0 = [a,b,c|Ls].
+```
 
-`Tail = Y, X = [a,b,c|Y].`
+In this case, and as the answer illustrates, `Ls0` is
+indistinguishable from a partial list with tail `Ls`, while
+the efficient packed representation is used internally.
 
-By all appearances, partial strings are plain Prolog lists.
+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.
+
+Definite clause grammars as provided by
+[`library(dcgs)`](src/lib/lists.pl), and the predicates from
+[`library(lists)`](src/lib/lists.pl), are ideally suited for reasoning
+about strings.
+
+Partial strings were first proposed by Ulrich Neumerkel in issue
+[#95](https://github.com/mthom/scryer-prolog/issues/95).
+
+### 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.
+* [`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.
+* [`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
+* [`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.
+  TLS negotiation is performed via the option `tls(true)` in
+  `socket_client_open/3`, yielding secure encrypted connections.
+* [`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` 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.
+
+To use predicates provided by the `lists` library, write:
 
 ```
 ?- use_module(library(lists)).
@@ -264,7 +494,6 @@ REPL:
 
 ```
 ?- [user].
-(type Enter + Ctrl-D to terminate the stream when finished)
 :- module(test, [local_member/2]).
 :- use_module(library(lists)).
 
@@ -273,3 +502,17 @@ 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.
+
+### 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)).
+```

build.rs

@@ -1,56 +1,55 @@
 extern crate indexmap;
 
-use indexmap::IndexSet;
-
 use std::env;
-use std::fs::{File, copy, read_dir};
+use std::fs;
+use std::fs::File;
 use std::io::Write;
 use std::path::Path;
 
-fn main()
-{
+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 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 lib_path = Path::new("src/lib");
 
-    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! {
+    libraries
+        .write_all(
+            b"ref_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();
+        let mut m = IndexMap::new();\n",
+        )
+        .unwrap();
+    find_prolog_files(&mut libraries, "", &lib_path);
+    libraries.write_all(b"\n        m\n    };\n}\n").unwrap();
 }

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+</svg>

src/allocator.rs

@@ -1,9 +1,9 @@
-use prolog_parser::ast::*;
+use crate::prolog_parser::ast::*;
 
-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::machine::machine_indices::*;
+use crate::targets::*;
 
 use std::cell::Cell;
 use std::rc::Rc;

src/arithmetic.rs

@@ -1,26 +1,29 @@
-use prolog_parser::ast::*;
+use crate::prolog_parser::ast::*;
 
-use crate::prolog::clause_types::*;
-use crate::prolog::fixtures::*;
-use crate::prolog::forms::*;
-use crate::prolog::instructions::*;
-use crate::prolog::iterators::*;
+use crate::clause_types::*;
+use crate::fixtures::*;
+use crate::forms::*;
+use crate::instructions::*;
+use crate::iterators::*;
 
-use crate::prolog::machine::machine_errors::*;
-use crate::prolog::machine::machine_indices::*;
+use crate::machine::heap::*;
+use crate::machine::machine_errors::*;
+use crate::machine::machine_indices::*;
 
-use crate::prolog::ordered_float::*;
-use crate::prolog::rug::ops::PowAssign;
-use crate::prolog::rug::{Assign, Integer, Rational};
+use crate::ordered_float::*;
+use crate::rug::ops::PowAssign;
+use crate::rug::{Assign, Integer, Rational};
 
 use std::cell::Cell;
 use std::cmp::{max, min, Ordering};
+use std::convert::TryFrom;
 use std::f64;
 use std::num::FpCategory;
 use std::ops::{Add, Div, Mul, Neg, Sub};
 use std::rc::Rc;
 use std::vec::Vec;
 
+#[derive(Debug)]
 pub struct ArithInstructionIterator<'a> {
     state_stack: Vec<TermIterState<'a>>,
 }
@@ -66,6 +69,7 @@ impl<'a> ArithInstructionIterator<'a> {
     }
 }
 
+#[derive(Debug)]
 pub enum ArithTermRef<'a> {
     Constant(&'a Constant),
     Op(ClauseName, usize), // name, arity.
@@ -107,6 +111,7 @@ impl<'a> Iterator for ArithInstructionIterator<'a> {
     }
 }
 
+#[derive(Debug)]
 pub struct ArithmeticEvaluator<'a> {
     bindings: &'a AllocVarDict,
     interm: Vec<ArithmeticTerm>,
@@ -262,6 +267,9 @@ impl<'a> ArithmeticEvaluator<'a> {
 
     fn push_constant(&mut self, c: &Constant) -> Result<(), ArithmeticError> {
         match c {
+            &Constant::Fixnum(n) => self
+                .interm
+                .push(ArithmeticTerm::Number(Number::Fixnum(n))),
             &Constant::Integer(ref n) => self
                 .interm
                 .push(ArithmeticTerm::Number(Number::Integer(n.clone()))),
@@ -316,18 +324,25 @@ impl<'a> ArithmeticEvaluator<'a> {
 }
 
 // integer division rounding function -- 9.1.3.1.
-pub fn rnd_i<'a>(n: &'a Number) -> RefOrOwned<'a, Integer> {
+pub fn rnd_i<'a>(n: &'a Number) -> RefOrOwned<'a, Number> {
     match n {
-        &Number::Integer(ref n) => RefOrOwned::Borrowed(n),
+        &Number::Integer(_) => {
+            RefOrOwned::Borrowed(n)
+        }
         &Number::Float(OrderedFloat(f)) => {
-            RefOrOwned::Owned(Integer::from_f64(f.floor()).unwrap_or_else(|| Integer::from(0)))
+            RefOrOwned::Owned(Number::from(
+                Integer::from_f64(f.floor()).unwrap_or_else(|| Integer::from(0))
+            ))
+        }
+        &Number::Fixnum(n) => {
+            RefOrOwned::Owned(Number::from(n))
         }
         &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);
-            RefOrOwned::Owned(floor)
+
+            RefOrOwned::Owned(Number::from(floor))
         }
     }
 }
@@ -335,6 +350,7 @@ pub fn rnd_i<'a>(n: &'a Number) -> RefOrOwned<'a, Integer> {
 // floating point rounding function -- 9.1.4.1.
 pub fn rnd_f(n: &Number) -> f64 {
     match n {
+        &Number::Fixnum(n) => n as f64,
         &Number::Integer(ref n) => n.to_f64(),
         &Number::Float(OrderedFloat(f)) => f,
         &Number::Rational(ref r) => r.to_f64(),
@@ -370,22 +386,32 @@ where
     }
 }
 
+#[inline]
+fn float_fn_to_f(n: isize) -> Result<f64, EvalError> {
+    classify_float(n as f64, rnd_f)
+}
+
+#[inline]
 fn float_i_to_f(n: &Integer) -> Result<f64, EvalError> {
     classify_float(n.to_f64(), rnd_f)
 }
 
+#[inline]
 fn float_r_to_f(r: &Rational) -> Result<f64, EvalError> {
     classify_float(r.to_f64(), rnd_f)
 }
 
+#[inline]
 fn add_f(f1: f64, f2: f64) -> Result<OrderedFloat<f64>, EvalError> {
     Ok(OrderedFloat(classify_float(f1 + f2, rnd_f)?))
 }
 
+#[inline]
 fn mul_f(f1: f64, f2: f64) -> Result<OrderedFloat<f64>, EvalError> {
     Ok(OrderedFloat(classify_float(f1 * f2, rnd_f)?))
 }
 
+#[inline]
 fn div_f(f1: f64, f2: f64) -> Result<OrderedFloat<f64>, EvalError> {
     if FpCategory::Zero == f2.classify() {
         Err(EvalError::ZeroDivisor)
@@ -399,23 +425,46 @@ impl Add<Number> for Number {
 
     fn add(self, rhs: Number) -> Self::Output {
         match (self, rhs) {
-            (Number::Integer(n1), Number::Integer(n2)) => Ok(Number::Integer(n1 + n2)), // add_i
+            (Number::Fixnum(n1), Number::Fixnum(n2)) => {
+                Ok(if let Some(result) = n1.checked_add(n2) {
+                    Number::Fixnum(result)
+                } else {
+                    Number::from(Integer::from(n1) + Integer::from(n2))
+                })
+            }
+            (Number::Fixnum(n1), Number::Integer(n2)) |
+            (Number::Integer(n2), Number::Fixnum(n1)) => {
+                Ok(Number::from(Integer::from(n1) + &*n2))
+            }
+            (Number::Fixnum(n1), Number::Rational(n2)) |
+            (Number::Rational(n2), Number::Fixnum(n1)) => {
+                Ok(Number::from(Rational::from(n1) + &*n2))
+            }
+            (Number::Fixnum(n1), Number::Float(OrderedFloat(n2))) |
+            (Number::Float(OrderedFloat(n2)), Number::Fixnum(n1)) => {
+                Ok(Number::Float(add_f(float_fn_to_f(n1)?, n2)?))
+            }
+            (Number::Integer(n1), Number::Integer(n2)) => {
+                Ok(Number::from(Integer::from(&*n1) + &*n2)) // add_i
+            }
             (Number::Integer(n1), Number::Float(OrderedFloat(n2)))
-            | (Number::Float(OrderedFloat(n2)), Number::Integer(n1)) => {
+          | (Number::Float(OrderedFloat(n2)), Number::Integer(n1)) => {
                 Ok(Number::Float(add_f(float_i_to_f(&n1)?, n2)?))
             }
             (Number::Integer(n1), Number::Rational(n2))
-            | (Number::Rational(n2), Number::Integer(n1)) => {
-                Ok(Number::Rational(Rational::from(n1) + n2))
+          | (Number::Rational(n2), Number::Integer(n1)) => {
+                Ok(Number::from(Rational::from(&*n1) + &*n2))
             }
             (Number::Rational(n1), Number::Float(OrderedFloat(n2)))
-            | (Number::Float(OrderedFloat(n2)), Number::Rational(n1)) => {
+          | (Number::Float(OrderedFloat(n2)), Number::Rational(n1)) => {
                 Ok(Number::Float(add_f(float_r_to_f(&n1)?, n2)?))
             }
             (Number::Float(OrderedFloat(f1)), Number::Float(OrderedFloat(f2))) => {
                 Ok(Number::Float(add_f(f1, f2)?))
             }
-            (Number::Rational(r1), Number::Rational(r2)) => Ok(Number::Rational(r1 + r2)),
+            (Number::Rational(r1), Number::Rational(r2)) => {
+                Ok(Number::from(Rational::from(&*r1) + &*r2))
+            }
         }
     }
 }
@@ -425,9 +474,15 @@ impl Neg for Number {
 
     fn neg(self) -> Self::Output {
         match self {
-            Number::Integer(n) => Number::Integer(-n),
+            Number::Fixnum(n) =>
+                if let Some(n) = n.checked_neg() {
+                    Number::Fixnum(n)
+                } else {
+                    Number::from(-Integer::from(n))
+                }
+            Number::Integer(n) => Number::Integer(Rc::new(-Integer::from(&*n))),
             Number::Float(OrderedFloat(f)) => Number::Float(OrderedFloat(-f)),
-            Number::Rational(r) => Number::Rational(-r),
+            Number::Rational(r) => Number::Rational(Rc::new(-Rational::from(&*r))),
         }
     }
 }
@@ -445,14 +500,35 @@ impl Mul<Number> for Number {
 
     fn mul(self, rhs: Number) -> Self::Output {
         match (self, rhs) {
-            (Number::Integer(n1), Number::Integer(n2)) => Ok(Number::Integer(n1 * n2)), // mul_i
+            (Number::Fixnum(n1), Number::Fixnum(n2)) => {
+                Ok(if let Some(result) = n1.checked_mul(n2) {
+                    Number::Fixnum(result)
+                } else {
+                    Number::from(Integer::from(n1) * Integer::from(n2))
+                })
+            }
+            (Number::Fixnum(n1), Number::Integer(n2)) |
+            (Number::Integer(n2), Number::Fixnum(n1)) => {
+                Ok(Number::from(Integer::from(n1) * &*n2))
+            }
+            (Number::Fixnum(n1), Number::Rational(n2)) |
+            (Number::Rational(n2), Number::Fixnum(n1)) => {
+                Ok(Number::from(Rational::from(n1) * &*n2))
+            }
+            (Number::Fixnum(n1), Number::Float(OrderedFloat(n2))) |
+            (Number::Float(OrderedFloat(n2)), Number::Fixnum(n1)) => {
+                Ok(Number::Float(mul_f(float_fn_to_f(n1)?, n2)?))
+            }
+            (Number::Integer(n1), Number::Integer(n2)) => {
+                Ok(Number::Integer(Rc::new(Integer::from(&*n1) * &*n2))) // mul_i
+            }
             (Number::Integer(n1), Number::Float(OrderedFloat(n2)))
             | (Number::Float(OrderedFloat(n2)), Number::Integer(n1)) => {
                 Ok(Number::Float(mul_f(float_i_to_f(&n1)?, n2)?))
             }
             (Number::Integer(n1), Number::Rational(n2))
             | (Number::Rational(n2), Number::Integer(n1)) => {
-                Ok(Number::Rational(Rational::from(n1) * n2))
+                Ok(Number::Rational(Rc::new(Rational::from(&*n1) * &*n2)))
             }
             (Number::Rational(n1), Number::Float(OrderedFloat(n2)))
             | (Number::Float(OrderedFloat(n2)), Number::Rational(n1)) => {
@@ -461,7 +537,9 @@ impl Mul<Number> for Number {
             (Number::Float(OrderedFloat(f1)), Number::Float(OrderedFloat(f2))) => {
                 Ok(Number::Float(mul_f(f1, f2)?))
             }
-            (Number::Rational(r1), Number::Rational(r2)) => Ok(Number::Rational(r1 * r2)),
+            (Number::Rational(r1), Number::Rational(r2)) => {
+                Ok(Number::Rational(Rc::new(Rational::from(&*r1) * &*r2)))
+            }
         }
     }
 }
@@ -471,24 +549,72 @@ impl Div<Number> for Number {
 
     fn div(self, rhs: Number) -> Self::Output {
         match (self, rhs) {
-            (Number::Integer(n1), Number::Integer(n2)) => Ok(Number::Float(div_f(
-                float_i_to_f(&n1)?,
-                float_i_to_f(&n2)?,
-            )?)),
+            (Number::Fixnum(n1), Number::Fixnum(n2)) => {
+                Ok(Number::Float(div_f(
+                    float_fn_to_f(n1)?,
+                    float_fn_to_f(n2)?,
+                )?))
+            }
+            (Number::Fixnum(n1), Number::Integer(n2)) => {
+                Ok(Number::Float(div_f(
+                    float_fn_to_f(n1)?,
+                    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)?,
+                )?))
+            }
+            (Number::Fixnum(n1), Number::Rational(n2)) => {
+                Ok(Number::Float(div_f(
+                    float_fn_to_f(n1)?,
+                    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)?,
+                )?))
+            }
+            (Number::Fixnum(n1), Number::Float(OrderedFloat(n2))) => {
+                Ok(Number::Float(div_f(
+                    float_fn_to_f(n1)?,
+                    n2,
+                )?))
+            }
+            (Number::Float(OrderedFloat(n1)), Number::Fixnum(n2)) => {
+                Ok(Number::Float(div_f(
+                    n1,
+                    float_fn_to_f(n2)?,
+                )?))
+            }
+            (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::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)?))
             }
@@ -506,41 +632,172 @@ impl Div<Number> for Number {
     }
 }
 
+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.eq(&**n2),
+            (&Number::Integer(ref n1), &Number::Fixnum(n2)) => (&**n1).eq(&n2),
+            (&Number::Fixnum(n1), &Number::Rational(ref n2)) => n1.eq(&**n2),
+            (&Number::Rational(ref n1), &Number::Fixnum(n2)) => (&**n1).eq(&n2),
+            (&Number::Fixnum(n1), &Number::Float(n2)) => OrderedFloat(n1 as f64).eq(&n2),
+            (&Number::Float(n1), &Number::Fixnum(n2)) => n1.eq(&OrderedFloat(n2 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 for Number {
     fn partial_cmp(&self, rhs: &Number) -> Option<Ordering> {
-        match (self, rhs) {
-            (&Number::Integer(ref n1), &Number::Integer(ref n2)) => Some(n1.cmp(n2)),
-            (&Number::Integer(_), Number::Float(_)) => Some(Ordering::Greater),
-            (&Number::Float(_), &Number::Integer(_)) => Some(Ordering::Less),
-            (&Number::Integer(_), &Number::Rational(_)) => Some(Ordering::Greater),
-            (&Number::Rational(_), &Number::Integer(_)) => Some(Ordering::Less),
-            (&Number::Rational(_), Number::Float(_)) => Some(Ordering::Greater),
-            (&Number::Float(_), &Number::Rational(_)) => Some(Ordering::Less),
-            (&Number::Float(f1), &Number::Float(f2)) => Some(f1.cmp(&f2)),
-            (&Number::Rational(ref r1), &Number::Rational(ref r2)) => Some(r1.cmp(&r2)),
-        }
+        Some(self.cmp(rhs))
     }
 }
 
 impl Ord for Number {
     fn cmp(&self, rhs: &Number) -> Ordering {
         match (self, rhs) {
+            (&Number::Fixnum(n1), &Number::Fixnum(n2)) => n1.cmp(&n2),
+            (&Number::Fixnum(n1), Number::Integer(n2)) => Integer::from(n1).cmp(&*n2),
+            (Number::Integer(n1), &Number::Fixnum(n2)) => (&**n1).cmp(&Integer::from(n2)),
+            (&Number::Fixnum(n1), Number::Rational(n2)) => Rational::from(n1).cmp(&*n2),
+            (Number::Rational(n1), &Number::Fixnum(n2)) => (&**n1).cmp(&Rational::from(n2)),
+            (&Number::Fixnum(n1), &Number::Float(n2)) => OrderedFloat(n1 as f64).cmp(&n2),
+            (&Number::Float(n1), &Number::Fixnum(n2)) => n1.cmp(&OrderedFloat(n2 as f64)),
             (&Number::Integer(ref n1), &Number::Integer(ref n2)) => n1.cmp(n2),
-            (&Number::Integer(_), Number::Float(_)) => Ordering::Greater,
-            (&Number::Float(_), &Number::Integer(_)) => Ordering::Less,
-            (&Number::Integer(_), &Number::Rational(_)) => Ordering::Greater,
-            (&Number::Rational(_), &Number::Integer(_)) => Ordering::Less,
-            (&Number::Rational(_), Number::Float(_)) => Ordering::Greater,
-            (&Number::Float(_), &Number::Rational(_)) => Ordering::Less,
+            (&Number::Integer(ref 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(ref n1), &Number::Rational(ref n2)) => {
+                #[cfg(feature = "num")]
+                {
+                    Rational::from(&**n1).cmp(n2)
+                }
+                #[cfg(not(feature = "num"))]
+                {
+                    (&**n1).partial_cmp(&**n2).unwrap_or(Ordering::Less)
+                }
+            }
+            (&Number::Rational(ref n1), &Number::Integer(ref n2)) => {
+                #[cfg(feature = "num")]
+                {
+                    (&**n1).cmp(&Rational::from(&**n2))
+                }
+                #[cfg(not(feature = "num"))]
+                {
+                    (&**n1).partial_cmp(&**n2).unwrap_or(Ordering::Less)
+                }
+            }
+            (&Number::Rational(ref n1), &Number::Float(n2)) => OrderedFloat(n1.to_f64()).cmp(&n2),
+            (&Number::Float(n1), &Number::Rational(ref n2)) => n1.cmp(&OrderedFloat(n2.to_f64())),
             (&Number::Float(f1), &Number::Float(f2)) => f1.cmp(&f2),
             (&Number::Rational(ref r1), &Number::Rational(ref r2)) => r1.cmp(&r2),
         }
     }
 }
 
+impl<'a> TryFrom<(Addr, &'a Heap)> for Number {
+    type Error = ();
+
+    fn try_from((addr, heap): (Addr, &'a Heap)) -> Result<Number, Self::Error> {
+        match addr {
+            Addr::Fixnum(n) => {
+                Ok(Number::from(n))
+            }
+            Addr::Float(n) => {
+                Ok(Number::Float(n))
+            }
+            Addr::Usize(n) => {
+                if let Ok(n) = isize::try_from(n) {
+                    Ok(Number::from(n))
+                } else {
+                    Ok(Number::from(Integer::from(n)))
+                }
+            }
+            Addr::Con(h) => {
+                Number::try_from(&heap[h])
+            }
+            _ => {
+                Err(())
+            }
+        }
+    }
+}
+
+impl<'a> TryFrom<&'a HeapCellValue> for Number {
+    type Error = ();
+
+    fn try_from(value: &'a HeapCellValue) -> Result<Number, Self::Error> {
+        match value {
+            HeapCellValue::Addr(addr) => {
+                match addr {
+                    &Addr::Fixnum(n) => {
+                        Ok(Number::from(n))
+                    }
+                    &Addr::Float(n) => {
+                        Ok(Number::Float(n))
+                    }
+                    &Addr::Usize(n) => {
+                        if let Ok(n) = isize::try_from(n) {
+                            Ok(Number::from(n))
+                        } else {
+                            Ok(Number::from(Integer::from(n)))
+                        }
+                    }
+                    _ => {
+                        Err(())
+                    }
+                }
+            }
+            HeapCellValue::Integer(n) => {
+                Ok(Number::Integer(n.clone()))
+            }
+            HeapCellValue::Rational(n) => {
+                Ok(Number::Rational(n.clone()))
+            }
+            _ => {
+                Err(())
+            }
+        }
+    }
+}
+
+impl<'a> From<&'a Integer> for Number {
+    #[inline]
+    fn from(src: &'a Integer) -> Self {
+        Number::Integer(Rc::new(Integer::from(src)))
+    }
+}
+
 // Computes n ^ power. Ignores the sign of power.
-pub fn binary_pow(mut n: Integer, power: Integer) -> Integer {
-    let mut power = power.abs();
+pub fn binary_pow(mut n: Integer, power: &Integer) -> Integer {
+    let mut power = Integer::from(power.abs_ref());
 
     if power == 0 {
         return Integer::from(1);

src/clause_types.rs

@@ -1,14 +1,14 @@
-use prolog_parser::ast::*;
+use crate::prolog_parser::ast::*;
 
-use crate::prolog::forms::Number;
-use crate::prolog::machine::machine_indices::*;
-use crate::prolog::rug::rand::RandState;
+use crate::forms::Number;
+use crate::machine::machine_indices::*;
+use crate::rug::rand::RandState;
 
-use ref_thread_local::RefThreadLocal;
+use crate::ref_thread_local::RefThreadLocal;
 
 use std::collections::BTreeMap;
 
-#[derive(Clone, Copy, Eq, PartialEq)]
+#[derive(Debug, Clone, Copy, Eq, PartialEq)]
 pub enum CompareNumberQT {
     GreaterThan,
     LessThan,
@@ -31,7 +31,7 @@ impl CompareNumberQT {
     }
 }
 
-#[derive(Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum CompareTermQT {
     LessThan,
     LessThanOrEqual,
@@ -50,7 +50,7 @@ impl CompareTermQT {
     }
 }
 
-#[derive(Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub enum ArithmeticTerm {
     Reg(RegType),
     Interm(usize),
@@ -67,7 +67,7 @@ impl ArithmeticTerm {
     }
 }
 
-#[derive(Clone, Eq, PartialEq)]
+#[derive(Debug, Clone, Eq, PartialEq)]
 pub enum InlinedClauseType {
     CompareNumber(CompareNumberQT, ArithmeticTerm, ArithmeticTerm),
     IsAtom(RegType),
@@ -75,7 +75,6 @@ pub enum InlinedClauseType {
     IsCompound(RegType),
     IsInteger(RegType),
     IsRational(RegType),
-    IsString(RegType),
     IsFloat(RegType),
     IsNonVar(RegType),
     IsVar(RegType),
@@ -105,7 +104,6 @@ ref_thread_local! {
         m.insert(("compound", 1), ClauseType::Inlined(InlinedClauseType::IsCompound(r1)));
         m.insert(("integer", 1), ClauseType::Inlined(InlinedClauseType::IsInteger(r1)));
         m.insert(("rational", 1), ClauseType::Inlined(InlinedClauseType::IsRational(r1)));
-        m.insert(("string", 1), ClauseType::Inlined(InlinedClauseType::IsString(r1)));
         m.insert(("float", 1), ClauseType::Inlined(InlinedClauseType::IsFloat(r1)));
         m.insert(("nonvar", 1), ClauseType::Inlined(InlinedClauseType::IsNonVar(r1)));
         m.insert(("var", 1), ClauseType::Inlined(InlinedClauseType::IsVar(r1)));
@@ -117,7 +115,6 @@ ref_thread_local! {
         m.insert(("@>=", 2), ClauseType::BuiltIn(BuiltInClauseType::CompareTerm(CompareTermQT::GreaterThanOrEqual)));
         m.insert(("@=<", 2), ClauseType::BuiltIn(BuiltInClauseType::CompareTerm(CompareTermQT::LessThanOrEqual)));
         m.insert(("copy_term", 2), ClauseType::BuiltIn(BuiltInClauseType::CopyTerm));
-        m.insert(("cyclic_term", 1), ClauseType::BuiltIn(BuiltInClauseType::CyclicTerm));
         m.insert(("==", 2), ClauseType::BuiltIn(BuiltInClauseType::Eq));
         m.insert(("functor", 3), ClauseType::BuiltIn(BuiltInClauseType::Functor));
         m.insert(("ground", 1), ClauseType::BuiltIn(BuiltInClauseType::Ground));
@@ -141,7 +138,6 @@ impl InlinedClauseType {
             &InlinedClauseType::IsCompound(..) => "compound",
             &InlinedClauseType::IsInteger(..) => "integer",
             &InlinedClauseType::IsRational(..) => "rational",
-            &InlinedClauseType::IsString(..) => "string",
             &InlinedClauseType::IsFloat(..) => "float",
             &InlinedClauseType::IsNonVar(..) => "nonvar",
             &InlinedClauseType::IsVar(..) => "var",
@@ -149,7 +145,7 @@ impl InlinedClauseType {
     }
 }
 
-#[derive(Copy, Clone, Eq, PartialEq)]
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
 pub enum SystemClauseType {
     AbolishClause,
     AbolishModuleClause,
@@ -160,18 +156,31 @@ pub enum SystemClauseType {
     AtomCodes,
     AtomLength,
     BindFromRegister,
-    CallAttributeGoals,
     CallContinuation,
     CharCode,
+    CharType,
     CharsToNumber,
-    ClearAttrVarBindings,
     ClearAttributeGoals,
     CloneAttributeGoals,
     CodesToNumber,
     CopyTermWithoutAttrVars,
     CheckCutPoint,
+    Close,
     CopyToLiftedHeap,
     CreatePartialString,
+    CurrentHostname,
+    CurrentInput,
+    CurrentOutput,
+    DirectoryFiles,
+    FileSize,
+    FileExists,
+    DirectoryExists,
+    DirectorySeparator,
+    MakeDirectory,
+    DeleteFile,
+    WorkingDirectory,
+    PathCanonical,
+    FileTime,
     DeleteAttribute,
     DeleteHeadAttribute,
     DynamicModuleResolution(usize),
@@ -179,10 +188,15 @@ pub enum SystemClauseType {
     EnqueueAttributedVar,
     ExpandGoal,
     ExpandTerm,
-    FetchAttributeGoals,
     FetchGlobalVar,
     FetchGlobalVarWithOffset,
+    FirstStream,
+    FlushOutput,
+    GetByte,
     GetChar,
+    GetNChars,
+    GetCode,
+    GetSingleChar,
     ResetAttrVarState,
     TruncateIfNoLiftedHeapGrowthDiff,
     TruncateIfNoLiftedHeapGrowth,
@@ -217,8 +231,17 @@ pub enum SystemClauseType {
     NumberToChars,
     NumberToCodes,
     OpDeclaration,
+    Open,
+    NextStream,
     PartialStringTail,
+    PeekByte,
+    PeekChar,
+    PeekCode,
     PointsToContinuationResetMarker,
+    PutByte,
+    PutChar,
+    PutChars,
+    PutCode,
     REPL(REPLCodePtr),
     ReadQueryTerm,
     ReadTerm,
@@ -231,8 +254,12 @@ pub enum SystemClauseType {
     RetractClause,
     RestoreCutPolicy,
     SetCutPoint(RegType),
+    SetInput,
+    SetOutput,
     StoreGlobalVar,
     StoreGlobalVarWithOffset,
+    StreamProperty,
+    SetStreamPosition,
     InferenceLevel,
     CleanUpBlock,
     EraseBall,
@@ -243,7 +270,10 @@ pub enum SystemClauseType {
     GetDoubleQuotes,
     InstallNewBlock,
     Maybe,
-    RawInputReadChar,
+    CpuNow,
+    CurrentTime,
+    QuotedToken,
+    ReadTermFromChars,
     ResetBlock,
     ReturnFromVerifyAttr,
     SetBall,
@@ -251,7 +281,13 @@ pub enum SystemClauseType {
     SetDoubleQuotes,
     SetSeed,
     SkipMaxList,
+    Sleep,
+    SocketClientOpen,
+    SocketServerOpen,
+    SocketServerAccept,
+    SocketServerClose,
     Succeed,
+    TermAttributedVariables,
     TermVariables,
     TruncateLiftedHeapTo,
     UnifyWithOccursCheck,
@@ -260,6 +296,26 @@ pub enum SystemClauseType {
     Variant,
     WAMInstructions,
     WriteTerm,
+    WriteTermToChars,
+    ScryerPrologVersion,
+    CryptoRandomByte,
+    CryptoDataHash,
+    CryptoDataHKDF,
+    CryptoPasswordHash,
+    CryptoDataEncrypt,
+    CryptoDataDecrypt,
+    CryptoCurveScalarMult,
+    Ed25519Sign,
+    Ed25519Verify,
+    Ed25519NewKeyPair,
+    Ed25519KeyPairPublicKey,
+    Curve25519ScalarMult,
+    LoadHTML,
+    LoadXML,
+    GetEnv,
+    SetEnv,
+    UnsetEnv,
+    CharsBase64,
 }
 
 impl SystemClauseType {
@@ -274,9 +330,9 @@ impl SystemClauseType {
             &SystemClauseType::AtomCodes => clause_name!("$atom_codes"),
             &SystemClauseType::AtomLength => clause_name!("$atom_length"),
             &SystemClauseType::BindFromRegister => clause_name!("$bind_from_register"),
-            &SystemClauseType::CallAttributeGoals => clause_name!("$call_attribute_goals"),
             &SystemClauseType::CallContinuation => clause_name!("$call_continuation"),
             &SystemClauseType::CharCode => clause_name!("$char_code"),
+            &SystemClauseType::CharType => clause_name!("$char_type"),
             &SystemClauseType::CharsToNumber => clause_name!("$chars_to_number"),
             &SystemClauseType::CheckCutPoint => clause_name!("$check_cp"),
             &SystemClauseType::ClearAttributeGoals => clause_name!("$clear_attribute_goals"),
@@ -284,18 +340,31 @@ impl SystemClauseType {
             &SystemClauseType::CodesToNumber => clause_name!("$codes_to_number"),
             &SystemClauseType::CopyTermWithoutAttrVars => clause_name!("$copy_term_without_attr_vars"),
             &SystemClauseType::CreatePartialString => clause_name!("$create_partial_string"),
+            &SystemClauseType::CurrentInput => clause_name!("$current_input"),
+            &SystemClauseType::CurrentHostname => clause_name!("$current_hostname"),
+            &SystemClauseType::CurrentOutput => clause_name!("$current_output"),
+            &SystemClauseType::DirectoryFiles => clause_name!("$directory_files"),
+            &SystemClauseType::FileSize => clause_name!("$file_size"),
+            &SystemClauseType::FileExists => clause_name!("$file_exists"),
+            &SystemClauseType::DirectoryExists => clause_name!("$directory_exists"),
+            &SystemClauseType::DirectorySeparator => clause_name!("$directory_separator"),
+            &SystemClauseType::MakeDirectory => clause_name!("$make_directory"),
+            &SystemClauseType::DeleteFile => clause_name!("$delete_file"),
+            &SystemClauseType::WorkingDirectory => clause_name!("$working_directory"),
+            &SystemClauseType::PathCanonical => clause_name!("$path_canonical"),
+            &SystemClauseType::FileTime => clause_name!("$file_time"),
             &SystemClauseType::REPL(REPLCodePtr::CompileBatch) => clause_name!("$compile_batch"),
-	    &SystemClauseType::REPL(REPLCodePtr::UseModule) => clause_name!("$use_module"),
-	    &SystemClauseType::REPL(REPLCodePtr::UseQualifiedModule) => {
-		clause_name!("$use_qualified_module")
-	    }
-	    &SystemClauseType::REPL(REPLCodePtr::UseModuleFromFile) => {
-		clause_name!("$use_module_from_file")
-	    }
-	    &SystemClauseType::REPL(REPLCodePtr::UseQualifiedModuleFromFile) => {
-		clause_name!("$use_qualified_module_from_file")
-	    }
-            &SystemClauseType::ClearAttrVarBindings => clause_name!("$clear_attr_var_bindings"),
+            &SystemClauseType::REPL(REPLCodePtr::UseModule) => clause_name!("$use_module"),
+            &SystemClauseType::REPL(REPLCodePtr::UseQualifiedModule) => {
+                    clause_name!("$use_qualified_module")
+            }
+            &SystemClauseType::REPL(REPLCodePtr::UseModuleFromFile) => {
+                    clause_name!("$use_module_from_file")
+            }
+            &SystemClauseType::REPL(REPLCodePtr::UseQualifiedModuleFromFile) => {
+                    clause_name!("$use_qualified_module_from_file")
+            }
+            &SystemClauseType::Close => clause_name!("$close"),
             &SystemClauseType::CopyToLiftedHeap => clause_name!("$copy_to_lh"),
             &SystemClauseType::DeleteAttribute => clause_name!("$del_attr_non_head"),
             &SystemClauseType::DeleteHeadAttribute => clause_name!("$del_attr_head"),
@@ -304,12 +373,17 @@ impl SystemClauseType {
             &SystemClauseType::EnqueueAttributedVar => clause_name!("$enqueue_attr_var"),
             &SystemClauseType::ExpandTerm => clause_name!("$expand_term"),
             &SystemClauseType::ExpandGoal => clause_name!("$expand_goal"),
-            &SystemClauseType::FetchAttributeGoals => clause_name!("$fetch_attribute_goals"),
             &SystemClauseType::FetchGlobalVar => clause_name!("$fetch_global_var"),
             &SystemClauseType::FetchGlobalVarWithOffset => {
                 clause_name!("$fetch_global_var_with_offset")
             }
+            &SystemClauseType::FirstStream => clause_name!("$first_stream"),
+            &SystemClauseType::FlushOutput => clause_name!("$flush_output"),
+            &SystemClauseType::GetByte => clause_name!("$get_byte"),
             &SystemClauseType::GetChar => clause_name!("$get_char"),
+            &SystemClauseType::GetNChars => clause_name!("$get_n_chars"),
+            &SystemClauseType::GetCode => clause_name!("$get_code"),
+            &SystemClauseType::GetSingleChar => clause_name!("$get_single_char"),
             &SystemClauseType::ResetAttrVarState => clause_name!("$reset_attr_var_state"),
             &SystemClauseType::TruncateIfNoLiftedHeapGrowth => {
                 clause_name!("$truncate_if_no_lh_growth")
@@ -338,15 +412,21 @@ impl SystemClauseType {
             &SystemClauseType::GetSCCCleaner => clause_name!("$get_scc_cleaner"),
             &SystemClauseType::Halt => clause_name!("$halt"),
             &SystemClauseType::HeadIsDynamic => clause_name!("$head_is_dynamic"),
-            &SystemClauseType::OpDeclaration => clause_name!("$op$"),
+            &SystemClauseType::Open => clause_name!("$open"),
+            &SystemClauseType::OpDeclaration => clause_name!("$op"),
             &SystemClauseType::InstallSCCCleaner => clause_name!("$install_scc_cleaner"),
             &SystemClauseType::InstallInferenceCounter => {
                 clause_name!("$install_inference_counter")
             }
             &SystemClauseType::IsPartialString => clause_name!("$is_partial_string"),
             &SystemClauseType::PartialStringTail => clause_name!("$partial_string_tail"),
+            &SystemClauseType::PeekByte => clause_name!("$peek_byte"),
+            &SystemClauseType::PeekChar => clause_name!("$peek_char"),
+            &SystemClauseType::PeekCode => clause_name!("$peek_code"),
             &SystemClauseType::LiftedHeapLength => clause_name!("$lh_length"),
             &SystemClauseType::Maybe => clause_name!("maybe"),
+            &SystemClauseType::CpuNow => clause_name!("$cpu_now"),
+            &SystemClauseType::CurrentTime => clause_name!("$current_time"),
             &SystemClauseType::ModuleAssertDynamicPredicateToFront => {
                 clause_name!("$module_asserta")
             }
@@ -356,19 +436,38 @@ impl SystemClauseType {
             &SystemClauseType::ModuleHeadIsDynamic => clause_name!("$module_head_is_dynamic"),
             &SystemClauseType::ModuleExists => clause_name!("$module_exists"),
             &SystemClauseType::ModuleOf => clause_name!("$module_of"),
+            &SystemClauseType::NextStream => clause_name!("$next_stream"),
             &SystemClauseType::NoSuchPredicate => clause_name!("$no_such_predicate"),
             &SystemClauseType::NumberToChars => clause_name!("$number_to_chars"),
             &SystemClauseType::NumberToCodes => clause_name!("$number_to_codes"),
             &SystemClauseType::PointsToContinuationResetMarker => {
                 clause_name!("$points_to_cont_reset_marker")
             }
-            &SystemClauseType::RawInputReadChar => clause_name!("$raw_input_read_char"),
+            &SystemClauseType::PutByte => {
+                clause_name!("$put_byte")
+            }
+            &SystemClauseType::PutChar => {
+                clause_name!("$put_char")
+            }
+            &SystemClauseType::PutChars => {
+                clause_name!("$put_chars")
+            }
+            &SystemClauseType::PutCode => {
+                clause_name!("$put_code")
+            }
+            &SystemClauseType::QuotedToken => {
+                clause_name!("$quoted_token")
+            }
             &SystemClauseType::RedoAttrVarBinding => clause_name!("$redo_attr_var_binding"),
             &SystemClauseType::RemoveCallPolicyCheck => clause_name!("$remove_call_policy_check"),
             &SystemClauseType::RemoveInferenceCounter => clause_name!("$remove_inference_counter"),
             &SystemClauseType::RestoreCutPolicy => clause_name!("$restore_cut_policy"),
             &SystemClauseType::SetCutPoint(_) => clause_name!("$set_cp"),
+            &SystemClauseType::SetInput => clause_name!("$set_input"),
+            &SystemClauseType::SetOutput => clause_name!("$set_output"),
             &SystemClauseType::SetSeed => clause_name!("$set_seed"),
+            &SystemClauseType::StreamProperty => clause_name!("$stream_property"),
+            &SystemClauseType::SetStreamPosition => clause_name!("$set_stream_position"),
             &SystemClauseType::StoreGlobalVar => clause_name!("$store_global_var"),
             &SystemClauseType::StoreGlobalVarWithOffset => {
                 clause_name!("$store_global_var_with_offset")
@@ -385,6 +484,7 @@ impl SystemClauseType {
             &SystemClauseType::NextEP => clause_name!("$nextEP"),
             &SystemClauseType::ReadQueryTerm => clause_name!("$read_query_term"),
             &SystemClauseType::ReadTerm => clause_name!("$read_term"),
+            &SystemClauseType::ReadTermFromChars => clause_name!("$read_term_from_chars"),
             &SystemClauseType::ResetGlobalVarAtKey => clause_name!("$reset_global_var_at_key"),
             &SystemClauseType::ResetGlobalVarAtOffset => clause_name!("$reset_global_var_at_offset"),
             &SystemClauseType::RetractClause => clause_name!("$retract_clause"),
@@ -395,7 +495,13 @@ impl SystemClauseType {
             &SystemClauseType::SetCutPointByDefault(_) => clause_name!("$set_cp_by_default"),
             &SystemClauseType::SetDoubleQuotes => clause_name!("$set_double_quotes"),
             &SystemClauseType::SkipMaxList => clause_name!("$skip_max_list"),
+            &SystemClauseType::Sleep => clause_name!("$sleep"),
+            &SystemClauseType::SocketClientOpen => clause_name!("$socket_client_open"),
+            &SystemClauseType::SocketServerOpen => clause_name!("$socket_server_open"),
+            &SystemClauseType::SocketServerAccept => clause_name!("$socket_server_accept"),
+            &SystemClauseType::SocketServerClose => clause_name!("$socket_server_close"),
             &SystemClauseType::Succeed => clause_name!("$succeed"),
+            &SystemClauseType::TermAttributedVariables => clause_name!("$term_attributed_variables"),
             &SystemClauseType::TermVariables => clause_name!("$term_variables"),
             &SystemClauseType::TruncateLiftedHeapTo => clause_name!("$truncate_lh_to"),
             &SystemClauseType::UnifyWithOccursCheck => clause_name!("$unify_with_occurs_check"),
@@ -404,6 +510,26 @@ impl SystemClauseType {
             &SystemClauseType::Variant => clause_name!("$variant"),
             &SystemClauseType::WAMInstructions => clause_name!("$wam_instructions"),
             &SystemClauseType::WriteTerm => clause_name!("$write_term"),
+            &SystemClauseType::WriteTermToChars => clause_name!("$write_term_to_chars"),
+            &SystemClauseType::ScryerPrologVersion => clause_name!("$scryer_prolog_version"),
+            &SystemClauseType::CryptoRandomByte => clause_name!("$crypto_random_byte"),
+            &SystemClauseType::CryptoDataHash => clause_name!("$crypto_data_hash"),
+            &SystemClauseType::CryptoDataHKDF => clause_name!("$crypto_data_hkdf"),
+            &SystemClauseType::CryptoPasswordHash => clause_name!("$crypto_password_hash"),
+            &SystemClauseType::CryptoDataEncrypt => clause_name!("$crypto_data_encrypt"),
+            &SystemClauseType::CryptoDataDecrypt => clause_name!("$crypto_data_decrypt"),
+            &SystemClauseType::CryptoCurveScalarMult => clause_name!("$crypto_curve_scalar_mult"),
+            &SystemClauseType::Ed25519Sign => clause_name!("$ed25519_sign"),
+            &SystemClauseType::Ed25519Verify => clause_name!("$ed25519_verify"),
+            &SystemClauseType::Ed25519NewKeyPair => clause_name!("$ed25519_new_keypair"),
+            &SystemClauseType::Ed25519KeyPairPublicKey => clause_name!("$ed25519_keypair_public_key"),
+            &SystemClauseType::Curve25519ScalarMult => clause_name!("$curve25519_scalar_mult"),
+            &SystemClauseType::LoadHTML => clause_name!("$load_html"),
+            &SystemClauseType::LoadXML => clause_name!("$load_xml"),
+            &SystemClauseType::GetEnv => clause_name!("$getenv"),
+            &SystemClauseType::SetEnv => clause_name!("$setenv"),
+            &SystemClauseType::UnsetEnv => clause_name!("$unsetenv"),
+            &SystemClauseType::CharsBase64 => clause_name!("$chars_base64"),
         }
     }
 
@@ -420,11 +546,10 @@ impl SystemClauseType {
             ("$module_assertz", 5) => Some(SystemClauseType::ModuleAssertDynamicPredicateToBack),
             ("$asserta", 4) => Some(SystemClauseType::AssertDynamicPredicateToFront),
             ("$assertz", 4) => Some(SystemClauseType::AssertDynamicPredicateToBack),
-            ("$call_attribute_goals", 2) => Some(SystemClauseType::CallAttributeGoals),
             ("$call_continuation", 1) => Some(SystemClauseType::CallContinuation),
             ("$char_code", 2) => Some(SystemClauseType::CharCode),
+            ("$char_type", 2) => Some(SystemClauseType::CharType),
             ("$chars_to_number", 2) => Some(SystemClauseType::CharsToNumber),
-            ("$clear_attr_var_bindings", 0) => Some(SystemClauseType::ClearAttrVarBindings),
             ("$clear_attribute_goals", 0) => Some(SystemClauseType::ClearAttributeGoals),
             ("$clone_attribute_goals", 1) => Some(SystemClauseType::CloneAttributeGoals),
             ("$codes_to_number", 2) => Some(SystemClauseType::CodesToNumber),
@@ -433,6 +558,13 @@ impl SystemClauseType {
             ("$check_cp", 1) => Some(SystemClauseType::CheckCutPoint),
             ("$compile_batch", 0) => Some(SystemClauseType::REPL(REPLCodePtr::CompileBatch)),
             ("$copy_to_lh", 2) => Some(SystemClauseType::CopyToLiftedHeap),
+            ("$close", 2) => Some(SystemClauseType::Close),
+            ("$current_hostname", 1) => Some(SystemClauseType::CurrentHostname),
+            ("$current_input", 1) => Some(SystemClauseType::CurrentInput),
+            ("$current_output", 1) => Some(SystemClauseType::CurrentOutput),
+            ("$first_stream", 1) => Some(SystemClauseType::FirstStream),
+            ("$next_stream", 2) => Some(SystemClauseType::NextStream),
+            ("$flush_output", 1) => Some(SystemClauseType::FlushOutput),
             ("$del_attr_non_head", 1) => Some(SystemClauseType::DeleteAttribute),
             ("$del_attr_head", 1) => Some(SystemClauseType::DeleteHeadAttribute),
             ("$get_next_db_ref", 2) => Some(SystemClauseType::GetNextDBRef),
@@ -443,16 +575,34 @@ impl SystemClauseType {
             ("$enqueue_attribute_goal", 1) => Some(SystemClauseType::EnqueueAttributeGoal),
             ("$enqueue_attr_var", 1) => Some(SystemClauseType::EnqueueAttributedVar),
             ("$partial_string_tail", 2) => Some(SystemClauseType::PartialStringTail),
+            ("$peek_byte", 2) => Some(SystemClauseType::PeekByte),
+            ("$peek_char", 2) => Some(SystemClauseType::PeekChar),
+            ("$peek_code", 2) => Some(SystemClauseType::PeekCode),
             ("$is_partial_string", 1) => Some(SystemClauseType::IsPartialString),
             ("$expand_term", 2) => Some(SystemClauseType::ExpandTerm),
             ("$expand_goal", 2) => Some(SystemClauseType::ExpandGoal),
-            ("$fetch_attribute_goals", 1) => Some(SystemClauseType::FetchAttributeGoals),
             ("$fetch_global_var", 2) => Some(SystemClauseType::FetchGlobalVar),
             ("$fetch_global_var_with_offset", 3) => Some(SystemClauseType::FetchGlobalVarWithOffset),
-            ("$get_char", 1) => Some(SystemClauseType::GetChar),
+            ("$get_byte", 2) => Some(SystemClauseType::GetByte),
+            ("$get_char", 2) => Some(SystemClauseType::GetChar),
+            ("$get_n_chars", 3) => Some(SystemClauseType::GetNChars),
+            ("$get_code", 2) => Some(SystemClauseType::GetCode),
+            ("$get_single_char", 1) => Some(SystemClauseType::GetSingleChar),
             ("$points_to_cont_reset_marker", 1) => {
                 Some(SystemClauseType::PointsToContinuationResetMarker)
             }
+            ("$put_byte", 2) => {
+                Some(SystemClauseType::PutByte)
+            }
+            ("$put_char", 2) => {
+                Some(SystemClauseType::PutChar)
+            }
+            ("$put_chars", 2) => {
+                Some(SystemClauseType::PutChars)
+            }
+            ("$put_code", 2) => {
+                Some(SystemClauseType::PutCode)
+            }
             ("$reset_attr_var_state", 0) => Some(SystemClauseType::ResetAttrVarState),
             ("$truncate_if_no_lh_growth", 1) => {
                 Some(SystemClauseType::TruncateIfNoLiftedHeapGrowth)
@@ -468,12 +618,14 @@ impl SystemClauseType {
             ("$get_lh_from_offset_diff", 3) => Some(SystemClauseType::GetLiftedHeapFromOffsetDiff),
             ("$get_double_quotes", 1) => Some(SystemClauseType::GetDoubleQuotes),
             ("$get_scc_cleaner", 1) => Some(SystemClauseType::GetSCCCleaner),
-            ("$halt", 0) => Some(SystemClauseType::Halt),
+            ("$halt", 1) => Some(SystemClauseType::Halt),
             ("$head_is_dynamic", 1) => Some(SystemClauseType::HeadIsDynamic),
             ("$install_scc_cleaner", 2) => Some(SystemClauseType::InstallSCCCleaner),
             ("$install_inference_counter", 3) => Some(SystemClauseType::InstallInferenceCounter),
             ("$lh_length", 1) => Some(SystemClauseType::LiftedHeapLength),
             ("$maybe", 0) => Some(SystemClauseType::Maybe),
+            ("$cpu_now", 1) => Some(SystemClauseType::CpuNow),
+            ("$current_time", 1) => Some(SystemClauseType::CurrentTime),
             ("$module_exists", 1) => Some(SystemClauseType::ModuleExists),
             ("$module_of", 2) => Some(SystemClauseType::ModuleOf),
             ("$module_retract_clause", 5) => Some(SystemClauseType::ModuleRetractClause),
@@ -482,11 +634,16 @@ impl SystemClauseType {
             ("$number_to_chars", 2) => Some(SystemClauseType::NumberToChars),
             ("$number_to_codes", 2) => Some(SystemClauseType::NumberToCodes),
             ("$op", 3) => Some(SystemClauseType::OpDeclaration),
+            ("$open", 7) => Some(SystemClauseType::Open),
             ("$redo_attr_var_binding", 2) => Some(SystemClauseType::RedoAttrVarBinding),
             ("$remove_call_policy_check", 1) => Some(SystemClauseType::RemoveCallPolicyCheck),
             ("$remove_inference_counter", 2) => Some(SystemClauseType::RemoveInferenceCounter),
             ("$restore_cut_policy", 0) => Some(SystemClauseType::RestoreCutPolicy),
             ("$set_cp", 1) => Some(SystemClauseType::SetCutPoint(temp_v!(1))),
+            ("$set_input", 1) => Some(SystemClauseType::SetInput),
+            ("$set_output", 1) => Some(SystemClauseType::SetOutput),
+            ("$stream_property", 3) => Some(SystemClauseType::StreamProperty),
+            ("$set_stream_position", 2) => Some(SystemClauseType::SetStreamPosition),
             ("$inference_level", 2) => Some(SystemClauseType::InferenceLevel),
             ("$clean_up_block", 1) => Some(SystemClauseType::CleanUpBlock),
             ("$erase_ball", 0) => Some(SystemClauseType::EraseBall),
@@ -498,10 +655,11 @@ impl SystemClauseType {
             ("$get_current_block", 1) => Some(SystemClauseType::GetCurrentBlock),
             ("$get_cp", 1) => Some(SystemClauseType::GetCutPoint),
             ("$install_new_block", 1) => Some(SystemClauseType::InstallNewBlock),
-            ("$raw_input_read_char", 1) => Some(SystemClauseType::RawInputReadChar),
+            ("$quoted_token", 1) => Some(SystemClauseType::QuotedToken),
             ("$nextEP", 3) => Some(SystemClauseType::NextEP),
-            ("$read_query_term", 2) => Some(SystemClauseType::ReadQueryTerm),
-            ("$read_term", 2) => Some(SystemClauseType::ReadTerm),
+            ("$read_query_term", 5) => Some(SystemClauseType::ReadQueryTerm),
+            ("$read_term", 5) => Some(SystemClauseType::ReadTerm),
+            ("$read_term_from_chars", 2) => Some(SystemClauseType::ReadTermFromChars),
             ("$reset_block", 1) => Some(SystemClauseType::ResetBlock),
             ("$reset_cont_marker", 0) => Some(SystemClauseType::ResetContinuationMarker),
             ("$reset_global_var_at_key", 1) => Some(SystemClauseType::ResetGlobalVarAtKey),
@@ -513,35 +671,70 @@ impl SystemClauseType {
             ("$set_double_quotes", 1) => Some(SystemClauseType::SetDoubleQuotes),
             ("$set_seed", 1) => Some(SystemClauseType::SetSeed),
             ("$skip_max_list", 4) => Some(SystemClauseType::SkipMaxList),
+            ("$sleep", 1) => Some(SystemClauseType::Sleep),
+            ("$socket_client_open", 8) => Some(SystemClauseType::SocketClientOpen),
+            ("$socket_server_open", 3) => Some(SystemClauseType::SocketServerOpen),
+            ("$socket_server_accept", 7) => Some(SystemClauseType::SocketServerAccept),
+            ("$socket_server_close", 1) => Some(SystemClauseType::SocketServerClose),
             ("$store_global_var", 2) => Some(SystemClauseType::StoreGlobalVar),
             ("$store_global_var_with_offset", 2) => Some(SystemClauseType::StoreGlobalVarWithOffset),
+            ("$term_attributed_variables", 2) => Some(SystemClauseType::TermAttributedVariables),
             ("$term_variables", 2) => Some(SystemClauseType::TermVariables),
             ("$truncate_lh_to", 1) => Some(SystemClauseType::TruncateLiftedHeapTo),
             ("$unwind_environments", 0) => Some(SystemClauseType::UnwindEnvironments),
             ("$unwind_stack", 0) => Some(SystemClauseType::UnwindStack),
             ("$unify_with_occurs_check", 2) => Some(SystemClauseType::UnifyWithOccursCheck),
-	    ("$use_module", 1) => Some(SystemClauseType::REPL(REPLCodePtr::UseModule)),
-	    ("$use_module_from_file", 1) =>
-		Some(SystemClauseType::REPL(REPLCodePtr::UseModuleFromFile)),	    
-	    ("$use_qualified_module", 2) =>
-		Some(SystemClauseType::REPL(REPLCodePtr::UseQualifiedModule)),
-	    ("$use_qualified_module_from_file", 2) =>
-		Some(SystemClauseType::REPL(REPLCodePtr::UseQualifiedModuleFromFile)),
+            ("$directory_files", 2) => Some(SystemClauseType::DirectoryFiles),
+            ("$file_size", 2) => Some(SystemClauseType::FileSize),
+            ("$file_exists", 1) => Some(SystemClauseType::FileExists),
+            ("$directory_exists", 1) => Some(SystemClauseType::DirectoryExists),
+            ("$directory_separator", 1) => Some(SystemClauseType::DirectorySeparator),
+            ("$make_directory", 1) => Some(SystemClauseType::MakeDirectory),
+            ("$delete_file", 1) => Some(SystemClauseType::DeleteFile),
+            ("$working_directory", 2) => Some(SystemClauseType::WorkingDirectory),
+            ("$path_canonical", 2) => Some(SystemClauseType::PathCanonical),
+            ("$file_time", 3) => Some(SystemClauseType::FileTime),
+            ("$use_module", 1) => Some(SystemClauseType::REPL(REPLCodePtr::UseModule)),
+            ("$use_module_from_file", 1) =>
+                    Some(SystemClauseType::REPL(REPLCodePtr::UseModuleFromFile)),
+            ("$use_qualified_module", 2) =>
+                    Some(SystemClauseType::REPL(REPLCodePtr::UseQualifiedModule)),
+            ("$use_qualified_module_from_file", 2) =>
+                    Some(SystemClauseType::REPL(REPLCodePtr::UseQualifiedModuleFromFile)),
             ("$variant", 2) => Some(SystemClauseType::Variant),
-            ("$write_term", 5) => Some(SystemClauseType::WriteTerm),
             ("$wam_instructions", 3) => Some(SystemClauseType::WAMInstructions),
+            ("$write_term", 7) => Some(SystemClauseType::WriteTerm),
+            ("$write_term_to_chars", 7) => Some(SystemClauseType::WriteTermToChars),
+            ("$scryer_prolog_version", 1) => Some(SystemClauseType::ScryerPrologVersion),
+            ("$crypto_random_byte", 1) => Some(SystemClauseType::CryptoRandomByte),
+            ("$crypto_data_hash", 4) => Some(SystemClauseType::CryptoDataHash),
+            ("$crypto_data_hkdf", 7) => Some(SystemClauseType::CryptoDataHKDF),
+            ("$crypto_password_hash", 4) => Some(SystemClauseType::CryptoPasswordHash),
+            ("$crypto_data_encrypt", 6) => Some(SystemClauseType::CryptoDataEncrypt),
+            ("$crypto_data_decrypt", 6) => Some(SystemClauseType::CryptoDataDecrypt),
+            ("$crypto_curve_scalar_mult", 5) => Some(SystemClauseType::CryptoCurveScalarMult),
+            ("$ed25519_sign", 5) => Some(SystemClauseType::Ed25519Sign),
+            ("$ed25519_verify", 5) => Some(SystemClauseType::Ed25519Verify),
+            ("$ed25519_new_keypair", 1) => Some(SystemClauseType::Ed25519NewKeyPair),
+            ("$ed25519_keypair_public_key", 3) => Some(SystemClauseType::Ed25519KeyPairPublicKey),
+            ("$curve25519_scalar_mult", 3) => Some(SystemClauseType::Curve25519ScalarMult),
+            ("$load_html", 3) => Some(SystemClauseType::LoadHTML),
+            ("$load_xml", 3) => Some(SystemClauseType::LoadXML),
+            ("$getenv", 2) => Some(SystemClauseType::GetEnv),
+            ("$setenv", 2) => Some(SystemClauseType::SetEnv),
+            ("$unsetenv", 1) => Some(SystemClauseType::UnsetEnv),
+            ("$chars_base64", 4) => Some(SystemClauseType::CharsBase64),
             _ => None,
         }
     }
 }
 
-#[derive(Clone, Eq, PartialEq)]
+#[derive(Debug, Clone, Eq, PartialEq)]
 pub enum BuiltInClauseType {
     AcyclicTerm,
     Arg,
     Compare,
     CompareTerm(CompareTermQT),
-    CyclicTerm,
     CopyTerm,
     Eq,
     Functor,
@@ -554,7 +747,7 @@ pub enum BuiltInClauseType {
     Sort,
 }
 
-#[derive(Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub enum ClauseType {
     BuiltIn(BuiltInClauseType),
     CallN,
@@ -572,7 +765,6 @@ impl BuiltInClauseType {
             &BuiltInClauseType::Arg => clause_name!("arg"),
             &BuiltInClauseType::Compare => clause_name!("compare"),
             &BuiltInClauseType::CompareTerm(qt) => clause_name!(qt.name()),
-            &BuiltInClauseType::CyclicTerm => clause_name!("cyclic_term"),
             &BuiltInClauseType::CopyTerm => clause_name!("copy_term"),
             &BuiltInClauseType::Eq => clause_name!("=="),
             &BuiltInClauseType::Functor => clause_name!("functor"),
@@ -592,7 +784,6 @@ impl BuiltInClauseType {
             &BuiltInClauseType::Arg => 3,
             &BuiltInClauseType::Compare => 2,
             &BuiltInClauseType::CompareTerm(_) => 2,
-            &BuiltInClauseType::CyclicTerm => 1,
             &BuiltInClauseType::CopyTerm => 2,
             &BuiltInClauseType::Eq => 2,
             &BuiltInClauseType::Functor => 3,

src/codegen.rs

@@ -1,28 +1,30 @@
-use prolog_parser::ast::*;
+use crate::prolog_parser::ast::*;
 
-use crate::prolog::allocator::*;
-use crate::prolog::arithmetic::*;
-use crate::prolog::clause_types::*;
-use crate::prolog::fixtures::*;
-use crate::prolog::forms::*;
-use crate::prolog::indexing::*;
-use crate::prolog::instructions::*;
-use crate::prolog::iterators::*;
-use crate::prolog::machine::machine_indices::*;
-use crate::prolog::targets::*;
+use crate::allocator::*;
+use crate::arithmetic::*;
+use crate::clause_types::*;
+use crate::fixtures::*;
+use crate::forms::*;
+use crate::indexing::*;
+use crate::instructions::*;
+use crate::iterators::*;
+use crate::machine::machine_indices::*;
+use crate::targets::*;
 
-use indexmap::IndexMap;
+use crate::indexmap::{IndexMap, IndexSet};
 
 use std::cell::Cell;
 use std::rc::Rc;
 use std::vec::Vec;
 
+#[derive(Debug)]
 pub struct CodeGenerator<TermMarker> {
     marker: TermMarker,
     pub var_count: IndexMap<Rc<Var>, usize>,
     non_counted_bt: bool,
 }
 
+#[derive(Debug)]
 pub struct ConjunctInfo<'a> {
     pub perm_vs: VariableFixtures<'a>,
     pub num_of_chunks: usize,
@@ -50,56 +52,45 @@ impl<'a> ConjunctInfo<'a> {
         self.has_deep_cut as usize
     }
 
-    fn mark_unsafe_vars<Alloc: Allocator<'a>>(
+    fn mark_unsafe_vars(
         &self,
         mut unsafe_var_marker: UnsafeVarMarker,
-        marker: &Alloc,
-        code: &mut Code
+        code: &mut Code,
     ) {
-        // target the last goal of the rule for handling unsafe variables.
-        // we use this weird logic to find the last goal.
-        let right_index = if let Some(Line::Control(_)) = code.last() {
-            if code.len() >= 2 {
-                code.len() - 2
-            } else {
-                return;
-            }
-        } else {
-            if code.len() >= 1 {
-                code.len() - 1
-            } else {
-                return;
-            }
-        };
+        if code.is_empty() {
+            return;
+        }
 
-        let mut index = right_index;
+        let mut code_index = 0;
 
-        if let Line::Query(_) = &code[right_index] {
-            while let Line::Query(_) = &code[index] {
-                if index == 0 {
-                    break;
-                } else {
-                    index -= 1;
+        for phase in 0 .. {
+            while let Line::Query(ref query_instr) = &code[code_index] {
+                if !unsafe_var_marker.mark_safe_vars(query_instr) {
+                    unsafe_var_marker.mark_phase(query_instr, phase);
                 }
+
+                code_index += 1;
             }
 
-            if let Line::Query(_) = &code[index] {
+            if code_index + 1 < code.len() {
+                code_index += 1;
             } else {
-                index += 1;
+                break;
+            }
+        }
+
+        code_index = 0;
+
+        for phase in 0 .. {
+            while let Line::Query(ref mut query_instr) = &mut code[code_index] {
+                unsafe_var_marker.mark_unsafe_vars(query_instr, phase);
+                code_index += 1;
             }
 
-            unsafe_var_marker.record_unsafe_vars(&self.perm_vs, marker);
-
-            for line in code.iter() {
-                if let Line::Query(ref query_instr) = line {
-                    unsafe_var_marker.mark_safe_vars(query_instr);
-                }
-            }
-
-            for index in index..right_index + 1 {
-                if let &mut Line::Query(ref mut query_instr) = &mut code[index] {
-                    unsafe_var_marker.mark_unsafe_vars(query_instr);
-                }
+            if code_index + 1 < code.len() {
+                code_index += 1;
+            } else {
+                break;
             }
         }
     }
@@ -131,31 +122,45 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
         *self.var_count.get(var).unwrap()
     }
 
+    fn mark_var_in_non_callable(
+        &mut self,
+        name: Rc<Var>,
+        term_loc: GenContext,
+        vr: &'a Cell<VarReg>,
+        code: &mut Code,
+    ) -> RegType {
+        let mut target = Vec::new();
+        self.marker.mark_var(name, Level::Shallow, vr, term_loc, &mut target);
+
+        if !target.is_empty() {
+            code.extend(target.into_iter().map(Line::Query));
+        }
+
+        vr.get().norm()
+    }
+
     fn mark_non_callable(
         &mut self,
         name: Rc<Var>,
-        arity: usize,
+        arg: usize,
         term_loc: GenContext,
         vr: &'a Cell<VarReg>,
         code: &mut Code,
     ) -> RegType {
         match self.marker.bindings().get(&name) {
-            Some(&VarData::Temp(_, t, _)) if t != 0 => RegType::Temp(t),
-            Some(&VarData::Perm(p)) if p != 0 => RegType::Perm(p),
-            _ => {
-                let mut target = Vec::new();
-
-                self.marker.reset_arg(arity);
-                self.marker
-                    .mark_var(name, Level::Shallow, vr, term_loc, &mut target);
-
-                if !target.is_empty() {
-                    for query_instr in target {
-                        code.push(Line::Query(query_instr));
-                    }
+            Some(&VarData::Temp(_, t, _)) if t != 0 => {
+                RegType::Temp(t)
+            }
+            Some(&VarData::Perm(p)) if p != 0 => {
+                if let GenContext::Last(_) = term_loc {
+                    self.mark_var_in_non_callable(name.clone(), term_loc, vr, code);
+                    temp_v!(arg)
+                } else {
+                    RegType::Perm(p)
                 }
-
-                vr.get().norm()
+            }
+            _ => {
+                self.mark_var_in_non_callable(name, term_loc, vr, code)
             }
         }
     }
@@ -174,40 +179,49 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
         target.push(Target::to_void(1));
     }
 
-    fn subterm_to_instr<Target>(
+    fn deep_var_instr<Target: CompilationTarget<'a>>(
+        &mut self,
+        cell: &'a Cell<VarReg>,
+        var: &'a Rc<Var>,
+        term_loc: GenContext,
+        is_exposed: bool,
+        target: &mut Vec<Target>,
+    ) {
+        if is_exposed || self.get_var_count(var.as_ref()) > 1 {
+            self.marker.mark_var(var.clone(), Level::Deep, cell, term_loc, target);
+        } else {
+            Self::add_or_increment_void_instr(target);
+        }
+    }
+
+    fn subterm_to_instr<Target: CompilationTarget<'a>>(
         &mut self,
         subterm: &'a Term,
         term_loc: GenContext,
         is_exposed: bool,
         target: &mut Vec<Target>,
-    ) where
-        Target: CompilationTarget<'a>,
-    {
+    ) {
         match subterm {
             &Term::AnonVar if is_exposed => {
-                self.marker.mark_anon_var(Level::Deep, term_loc, target)
+                self.marker.mark_anon_var(Level::Deep, term_loc, target);
+            }
+            &Term::AnonVar => {
+                Self::add_or_increment_void_instr(target);
             }
-            &Term::AnonVar => Self::add_or_increment_void_instr(target),
             &Term::Cons(ref cell, _, _) | &Term::Clause(ref cell, _, _, _) => {
-                self.marker
-                    .mark_non_var(Level::Deep, term_loc, cell, target);
+                self.marker.mark_non_var(Level::Deep, term_loc, cell, target);
                 target.push(Target::clause_arg_to_instr(cell.get()));
             }
             &Term::Constant(_, ref constant) => {
-                target.push(Target::constant_subterm(constant.clone()))
+                target.push(Target::constant_subterm(constant.clone()));
             }
             &Term::Var(ref cell, ref var) => {
-                if is_exposed || self.get_var_count(var) > 1 {
-                    self.marker
-                        .mark_var(var.clone(), Level::Deep, cell, term_loc, target);
-                } else {
-                    Self::add_or_increment_void_instr(target);
-                }
+                self.deep_var_instr(cell, var, term_loc, is_exposed, target);
             }
         };
     }
 
-    fn compile_target<Target, Iter>(
+     fn compile_target<Target, Iter>(
         &mut self,
         iter: Iter,
         term_loc: GenContext,
@@ -221,6 +235,13 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
 
         for term in iter {
             match term {
+                TermRef::AnonVar(lvl @ Level::Shallow) => {
+                    if let GenContext::Head = term_loc {
+                        self.marker.advance_arg();
+                    } else {
+                        self.marker.mark_anon_var(lvl, term_loc, &mut target);
+                    }
+                }
                 TermRef::Clause(lvl, cell, ct, terms) => {
                     self.marker.mark_non_var(lvl, term_loc, cell, &mut target);
                     target.push(Target::to_structure(ct, terms.len(), cell.get()));
@@ -236,15 +257,22 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
                     self.subterm_to_instr(head, term_loc, is_exposed, &mut target);
                     self.subterm_to_instr(tail, term_loc, is_exposed, &mut target);
                 }
+                TermRef::Constant(lvl @ Level::Shallow, cell, Constant::String(ref string)) => {
+                    self.marker.mark_non_var(lvl, term_loc, cell, &mut target);
+                    target.push(Target::to_pstr(lvl, string.to_string(), cell.get(), false));
+                }
                 TermRef::Constant(lvl @ Level::Shallow, cell, constant) => {
                     self.marker.mark_non_var(lvl, term_loc, cell, &mut target);
                     target.push(Target::to_constant(lvl, constant.clone(), cell.get()));
                 }
-                TermRef::AnonVar(lvl @ Level::Shallow) => {
-                    if let GenContext::Head = term_loc {
-                        self.marker.advance_arg();
+                TermRef::PartialString(lvl, cell, string, tail) => {
+                    self.marker.mark_non_var(lvl, term_loc, cell, &mut target);
+
+                    if let Some(tail) = tail {
+                        target.push(Target::to_pstr(lvl, string, cell.get(), true));
+                        self.subterm_to_instr(tail, term_loc, is_exposed, &mut target);
                     } else {
-                        self.marker.mark_anon_var(lvl, term_loc, &mut target);
+                        target.push(Target::to_pstr(lvl, string, cell.get(), false));
                     }
                 }
                 TermRef::Var(lvl @ Level::Shallow, cell, ref var) if var.as_str() == "!" => {
@@ -263,14 +291,13 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
                         }
                     }
 
-                    self.marker
-                        .mark_var(var.clone(), lvl, cell, term_loc, &mut target);
+                    self.marker.mark_var(var.clone(), lvl, cell, term_loc, &mut target);
                 }
                 TermRef::Var(lvl @ Level::Shallow, cell, var) => {
-                    self.marker
-                        .mark_var(var.clone(), lvl, cell, term_loc, &mut target)
+                    self.marker.mark_var(var.clone(), lvl, cell, term_loc, &mut target);
+                }
+                _ => {
                 }
-                _ => {}
             };
         }
 
@@ -330,7 +357,9 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
                 &mut ControlInstruction::CallClause(_, _, _, ref mut last_call, _) => {
                     *last_call = true
                 }
-                &mut ControlInstruction::JmpBy(_, _, _, ref mut last_call) => *last_call = true,
+                &mut ControlInstruction::JmpBy(_, _, _, ref mut last_call) => {
+                    *last_call = true
+                }
                 &mut ControlInstruction::Proceed => {}
                 _ => dealloc_index += 1,
             },
@@ -350,33 +379,42 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
     ) -> Result<(), ParserError> {
         match ct {
             &InlinedClauseType::CompareNumber(cmp, ..) => {
-                if let &Term::Var(ref vr, ref name) = terms[0].as_ref() {
-                    self.mark_non_callable(name.clone(), 2, term_loc, vr, code);
-                }
-
-                if let &Term::Var(ref vr, ref name) = terms[1].as_ref() {
-                    self.mark_non_callable(name.clone(), 2, term_loc, vr, code);
-                }
+                self.marker.reset_arg(2);
 
                 let (mut lcode, at_1) = self.call_arith_eval(terms[0].as_ref(), 1)?;
                 let (mut rcode, at_2) = self.call_arith_eval(terms[1].as_ref(), 2)?;
 
+                let at_1 =
+                    if let &Term::Var(ref vr, ref name) = terms[0].as_ref() {
+                        ArithmeticTerm::Reg(
+                            self.mark_non_callable(name.clone(), 1, term_loc, vr, code)
+                        )
+                    } else {
+                        at_1.unwrap_or(interm!(1))
+                    };
+
+                let at_2 =
+                    if let &Term::Var(ref vr, ref name) = terms[1].as_ref() {
+                        ArithmeticTerm::Reg(
+                            self.mark_non_callable(name.clone(), 2, term_loc, vr, code)
+                        )
+                    } else {
+                        at_2.unwrap_or(interm!(2))
+                    };
+
                 code.append(&mut lcode);
                 code.append(&mut rcode);
 
-                code.push(compare_number_instr!(
-                    cmp,
-                    at_1.unwrap_or(interm!(1)),
-                    at_2.unwrap_or(interm!(2))
-                ));
+                code.push(compare_number_instr!(cmp, at_1, at_2));
             }
             &InlinedClauseType::IsAtom(..) => match terms[0].as_ref() {
-                &Term::Constant(_, Constant::Char(_))
-                | &Term::Constant(_, Constant::EmptyList)
-                | &Term::Constant(_, Constant::Atom(..)) => {
+                &Term::Constant(_, Constant::Char(_)) |
+                &Term::Constant(_, Constant::EmptyList) |
+                &Term::Constant(_, Constant::Atom(..)) => {
                     code.push(succeed!());
                 }
                 &Term::Var(ref vr, ref name) => {
+                    self.marker.reset_arg(1);
                     let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                     code.push(is_atom!(r));
                 }
@@ -392,6 +430,7 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
                     code.push(succeed!());
                 }
                 &Term::Var(ref vr, ref name) => {
+                    self.marker.reset_arg(1);
                     let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                     code.push(is_atomic!(r));
                 }
@@ -401,6 +440,7 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
                     code.push(succeed!());
                 }
                 &Term::Var(ref vr, ref name) => {
+                    self.marker.reset_arg(1);
                     let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                     code.push(is_compound!(r));
                 }
@@ -413,6 +453,7 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
                     code.push(succeed!());
                 }
                 &Term::Var(ref vr, ref name) => {
+                    self.marker.reset_arg(1);
                     let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                     code.push(is_rational!(r));
                 }
@@ -425,6 +466,7 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
                     code.push(succeed!());
                 }
                 &Term::Var(ref vr, ref name) => {
+                    self.marker.reset_arg(1);
                     let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                     code.push(is_float!(r));
                 }
@@ -432,23 +474,12 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
                     code.push(fail!());
                 }
             },
-            &InlinedClauseType::IsString(..) => match terms[0].as_ref() {
-                &Term::Constant(_, Constant::String(..)) => {
-                    code.push(succeed!());
-                }
-                &Term::Var(ref vr, ref name) => {
-                    let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
-                    code.push(is_string!(r));
-                }
-                _ => {
-                    code.push(fail!());
-                }
-            },
             &InlinedClauseType::IsNonVar(..) => match terms[0].as_ref() {
                 &Term::AnonVar => {
                     code.push(fail!());
                 }
                 &Term::Var(ref vr, ref name) => {
+                    self.marker.reset_arg(1);
                     let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                     code.push(is_nonvar!(r));
                 }
@@ -457,10 +488,12 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
                 }
             },
             &InlinedClauseType::IsInteger(..) => match terms[0].as_ref() {
-                &Term::Constant(_, Constant::Integer(_)) => {
+                &Term::Constant(_, Constant::Integer(_)) |
+                &Term::Constant(_, Constant::Fixnum(_)) => {
                     code.push(succeed!());
                 }
                 &Term::Var(ref vr, ref name) => {
+                    self.marker.reset_arg(1);
                     let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                     code.push(is_integer!(r));
                 }
@@ -476,6 +509,7 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
                     code.push(succeed!());
                 }
                 &Term::Var(ref vr, ref name) => {
+                    self.marker.reset_arg(1);
                     let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                     code.push(is_var!(r));
                 }
@@ -490,7 +524,7 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
         term: &'a Term,
         target_int: usize,
     ) -> Result<ArithCont, ArithmeticError> {
-        let mut evaluator = ArithmeticEvaluator::new(self.marker.bindings(), target_int);
+        let mut evaluator = ArithmeticEvaluator::new(&self.marker.bindings(), target_int);
         evaluator.eval(term)
     }
 
@@ -504,36 +538,27 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
         let (mut acode, at) = self.call_arith_eval(terms[1].as_ref(), 1)?;
         code.append(&mut acode);
 
-        Ok(match terms[0].as_ref() {
+        self.marker.reset_arg(2);
+
+        match terms[0].as_ref() {
             &Term::Var(ref vr, ref name) => {
                 let mut target = vec![];
 
-                self.marker.reset_arg(2);
-                self.marker
-                    .mark_var(name.clone(), Level::Shallow, vr, term_loc, &mut target);
+                self.marker.mark_var(name.clone(), Level::Shallow, vr, term_loc, &mut target);
 
                 if !target.is_empty() {
                     code.extend(target.into_iter().map(Line::Query));
                 }
-
-                if use_default_call_policy {
-                    code.push(is_call_by_default!(temp_v!(1), at.unwrap_or(interm!(1))))
-                } else {
-                    code.push(is_call!(temp_v!(1), at.unwrap_or(interm!(1))))
-                }
             }
-            &Term::Constant(_, ref c @ Constant::Integer(_)) => {
+            &Term::Constant(_, ref c @ Constant::Integer(_)) |
+            &Term::Constant(_, ref c @ Constant::Fixnum(_)) => {
                 code.push(Line::Query(put_constant!(
                     Level::Shallow,
                     c.clone(),
                     temp_v!(1)
                 )));
 
-                if use_default_call_policy {
-                    code.push(is_call_by_default!(temp_v!(1), at.unwrap_or(interm!(1))))
-                } else {
-                    code.push(is_call!(temp_v!(1), at.unwrap_or(interm!(1))))
-                }
+                self.marker.advance_arg();
             }
             &Term::Constant(_, ref c @ Constant::Float(_)) => {
                 code.push(Line::Query(put_constant!(
@@ -542,11 +567,7 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
                     temp_v!(1)
                 )));
 
-                if use_default_call_policy {
-                    code.push(is_call_by_default!(temp_v!(1), at.unwrap_or(interm!(1))))
-                } else {
-                    code.push(is_call!(temp_v!(1), at.unwrap_or(interm!(1))))
-                }
+                self.marker.advance_arg();
             }
             &Term::Constant(_, ref c @ Constant::Rational(_)) => {
                 code.push(Line::Query(put_constant!(
@@ -555,13 +576,27 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
                     temp_v!(1)
                 )));
 
-                if use_default_call_policy {
-                    code.push(is_call_by_default!(temp_v!(1), at.unwrap_or(interm!(1))))
-                } else {
-                    code.push(is_call!(temp_v!(1), at.unwrap_or(interm!(1))))
-                }
+                self.marker.advance_arg();
             }
-            _ => code.push(fail!()),
+            _ => {
+                code.push(fail!());
+                return Ok(());
+            }
+        }
+
+        let at =
+            if let &Term::Var(ref vr, ref name) = terms[1].as_ref() {
+                ArithmeticTerm::Reg(
+                    self.mark_non_callable(name.clone(), 2, term_loc, vr, code)
+                )
+            } else {
+                at.unwrap_or(interm!(1))
+            };
+
+        Ok(if use_default_call_policy {
+            code.push(is_call_by_default!(temp_v!(1), at));
+        } else {
+            code.push(is_call!(temp_v!(1), at));
         })
     }
 
@@ -684,6 +719,7 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
             head: (_, ref args, ref p1),
             ref clauses,
         } = rule;
+
         let mut code = Vec::new();
 
         self.marker.reset_at_head(args);
@@ -705,39 +741,31 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
         let iter = ChunkedIterator::from_rule_body(p1, clauses);
         self.compile_seq(iter, &conjunct_info, &mut code, false)?;
 
-        conjunct_info.mark_unsafe_vars(unsafe_var_marker, &self.marker, &mut code);
+        conjunct_info.mark_unsafe_vars(unsafe_var_marker, &mut code);
 
         Self::compile_cleanup(&mut code, &conjunct_info, clauses.last().unwrap_or(p1));
         Ok(code)
     }
 
     fn mark_unsafe_fact_vars(&self, fact: &mut CompiledFact) -> UnsafeVarMarker {
-        let mut unsafe_vars = IndexMap::new();
-
-        for var_status in self.marker.bindings().values() {
-            unsafe_vars.insert(var_status.as_reg_type(), false);
-        }
+        let mut safe_vars = IndexSet::new();
 
         for fact_instr in fact.iter_mut() {
             match fact_instr {
-                &mut FactInstruction::UnifyValue(reg) => {
-                    if let Some(found) = unsafe_vars.get_mut(&reg) {
-                        if !*found {
-                            *found = true;
-                            *fact_instr = FactInstruction::UnifyLocalValue(reg);
-                        }
+                &mut FactInstruction::UnifyValue(r) => {
+                    if !safe_vars.contains(&r) {
+                        *fact_instr = FactInstruction::UnifyLocalValue(r);
+                        safe_vars.insert(r);
                     }
                 }
-                &mut FactInstruction::UnifyVariable(reg) => {
-                    if let Some(found) = unsafe_vars.get_mut(&reg) {
-                        *found = true;
-                    }
+                &mut FactInstruction::UnifyVariable(r) => {
+                    safe_vars.insert(r);
                 }
                 _ => {}
-            };
+            }
         }
 
-        UnsafeVarMarker { unsafe_vars }
+        UnsafeVarMarker::from_safe_vars(safe_vars)
     }
 
     pub fn compile_fact<'b: 'a>(&mut self, term: &'b Term) -> Code {
@@ -802,7 +830,7 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
         let iter = ChunkedIterator::from_term_sequence(query);
         self.compile_seq(iter, &conjunct_info, &mut code, true)?;
 
-        conjunct_info.mark_unsafe_vars(UnsafeVarMarker::new(), &self.marker, &mut code);
+        conjunct_info.mark_unsafe_vars(UnsafeVarMarker::new(), &mut code);
 
         if let Some(query_term) = query.last() {
             Self::compile_cleanup(&mut code, &conjunct_info, query_term);

src/debray_allocator.rs

@@ -1,17 +1,18 @@
-use indexmap::IndexMap;
+use crate::indexmap::IndexMap;
 
-use prolog_parser::ast::*;
+use crate::prolog_parser::ast::*;
 
-use crate::prolog::allocator::*;
-use crate::prolog::fixtures::*;
-use crate::prolog::forms::*;
-use crate::prolog::machine::machine_indices::*;
-use crate::prolog::targets::*;
+use crate::allocator::*;
+use crate::fixtures::*;
+use crate::forms::*;
+use crate::machine::machine_indices::*;
+use crate::targets::*;
 
 use std::cell::Cell;
 use std::collections::BTreeSet;
 use std::rc::Rc;
 
+#[derive(Debug)]
 pub struct DebrayAllocator {
     bindings: IndexMap<Rc<Var>, VarData>,
     arg_c: usize,
@@ -292,7 +293,9 @@ impl<'a> Allocator<'a> for DebrayAllocator {
 
                 (pr, true)
             }
-            r => (r, false),
+            r => {
+                (r, false)
+            }
         };
 
         self.mark_reserved_var(var, lvl, cell, term_loc, target, r, is_new_var);

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 +1,57 @@
+/*  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)).
+
+
+permutation([], []).
+permutation([X|Xs], Ys) :-
+    permutation(Xs, Yss),
+    select(X, Ys, Yss).
+
+
+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

@@ -1,11 +1,10 @@
-use prolog_parser::ast::*;
+use crate::prolog_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};
+use crate::indexmap::{IndexMap, IndexSet};
 
 use std::cell::Cell;
 use std::collections::BTreeSet;
@@ -14,6 +13,7 @@ use std::rc::Rc;
 use std::vec::Vec;
 
 // labeled with chunk numbers.
+#[derive(Debug)]
 pub enum VarStatus {
     Perm(usize),
     Temp(usize, TempVarData), // Perm(chunk_num) | Temp(chunk_num, _)
@@ -23,6 +23,7 @@ pub type OccurrenceSet = BTreeSet<(GenContext, usize)>;
 
 // Perm: 0 initially, a stack register once processed.
 // Temp: labeled with chunk_num and temp offset (unassigned if 0).
+#[derive(Debug)]
 pub enum VarData {
     Perm(usize),
     Temp(usize, usize, TempVarData),
@@ -37,6 +38,7 @@ impl VarData {
     }
 }
 
+#[derive(Debug)]
 pub struct TempVarData {
     pub last_term_arity: usize,
     pub use_set: OccurrenceSet,
@@ -80,6 +82,7 @@ impl TempVarData {
 
 type VariableFixture<'a> = (VarStatus, Vec<&'a Cell<VarReg>>);
 
+#[derive(Debug)]
 pub struct VariableFixtures<'a>{
     perm_vars: IndexMap<Rc<Var>, VariableFixture<'a>>,
     last_chunk_temp_vars: IndexSet<Rc<Var>>
@@ -91,7 +94,7 @@ impl<'a> VariableFixtures<'a> {
             perm_vars: IndexMap::new(),
             last_chunk_temp_vars: IndexSet::new()
         }
-                          
+
     }
 
     pub fn insert(&mut self, var: Rc<Var>, vs: VariableFixture<'a>) {
@@ -249,68 +252,69 @@ impl<'a> VariableFixtures<'a> {
     }
 }
 
+#[derive(Debug)]
 pub struct UnsafeVarMarker {
-    pub unsafe_vars: IndexMap<RegType, bool>,
+    pub unsafe_vars: IndexMap<RegType, usize>,
+    pub safe_vars: IndexSet<RegType>,
 }
 
 impl UnsafeVarMarker {
     pub 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 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 fn mark_safe_vars(&mut self, query_instr: &QueryInstruction) -> bool {
         match query_instr {
-            QueryInstruction::PutVariable(RegType::Temp(r), _) => {
-                if let Some(found) = self.unsafe_vars.get_mut(&RegType::Temp(*r)) {
-                    *found = true;
-                }
+            &QueryInstruction::PutVariable(r @ RegType::Temp(_), _)
+          | &QueryInstruction::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 fn mark_phase(&mut self, query_instr: &QueryInstruction, phase: usize) {
+        match query_instr {
+            &QueryInstruction::PutValue(r @ RegType::Perm(_), _)
+          | &QueryInstruction::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 fn mark_unsafe_vars(&mut self, query_instr: &mut QueryInstruction, 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;
+                if let Some(p) = self.unsafe_vars.swap_remove(&RegType::Perm(i)) {
+                    if p == phase {
                         *query_instr = QueryInstruction::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 QueryInstruction::SetValue(r) => {
+                if !self.safe_vars.contains(&r) {
+                    *query_instr = QueryInstruction::SetLocalValue(r);
+
+                    self.safe_vars.insert(r);
+                    self.unsafe_vars.remove(&r);
                 }
             }
             _ => {}

src/forms.rs

@@ -1,14 +1,14 @@
-use prolog_parser::ast::*;
-use prolog_parser::parser::OpDesc;
-use prolog_parser::tabled_rc::*;
+use crate::prolog_parser::ast::*;
+use crate::prolog_parser::parser::OpDesc;
+use crate::prolog_parser::tabled_rc::*;
 
-use crate::prolog::clause_types::*;
-use crate::prolog::machine::machine_errors::*;
-use crate::prolog::machine::machine_indices::*;
-use crate::prolog::ordered_float::OrderedFloat;
-use crate::prolog::rug::{Integer, Rational};
+use crate::clause_types::*;
+use crate::machine::machine_errors::*;
+use crate::machine::machine_indices::*;
+use crate::ordered_float::OrderedFloat;
+use crate::rug::{Integer, Rational};
 
-use indexmap::IndexMap;
+use crate::indexmap::IndexMap;
 
 use std::cell::Cell;
 use std::collections::VecDeque;
@@ -21,7 +21,7 @@ pub type PredicateKey = (ClauseName, usize); // name, arity.
 // of vars (we get their adjoining cells this way).
 pub type JumpStub = Vec<Term>;
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub enum TopLevel {
     Declaration(Declaration),
     Fact(Term, usize, usize), // Term, line_num, col_num
@@ -41,7 +41,7 @@ impl TopLevel {
     }
 }
 
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub enum Level {
     Deep,
     Root,
@@ -57,7 +57,7 @@ impl Level {
     }
 }
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub enum QueryTerm {
     // register, clause type, subterms, use default call policy.
     Clause(Cell<RegType>, ClauseType, Vec<Box<Term>>, bool),
@@ -85,13 +85,13 @@ impl QueryTerm {
     }
 }
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub struct Rule {
     pub head: (ClauseName, Vec<Box<Term>>, QueryTerm),
     pub clauses: Vec<QueryTerm>,
 }
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub struct Predicate(pub Vec<PredicateClause>);
 
 impl Predicate {
@@ -113,7 +113,7 @@ impl Predicate {
     }
 }
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub enum ListingSource {
     File(ClauseName, PathBuf), // filename, path
     User,
@@ -282,9 +282,9 @@ impl ClauseConsistency for Rule {
     fn name_and_module(&self) -> Option<(ClauseName, ClauseName)> {
         Some((self.head.0.owning_module(), self.head.0.clone()))
     }
-    
+
     fn arity(&self) -> usize {
-        self.head.1.len()    
+        self.head.1.len()
     }
 }
 
@@ -325,7 +325,7 @@ impl ClauseConsistency for Predicate {
 
 pub type CompiledResult = (Predicate, VecDeque<TopLevel>);
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub enum PredicateClause {
     Fact(Term, usize, usize), // Term, line number, column number.
     Rule(Rule, usize, usize), // Term, line number, column number.
@@ -370,21 +370,34 @@ impl PredicateClause {
     }
 }
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub enum ModuleSource {
     Library(ClauseName),
     File(ClauseName),
 }
 
+impl ModuleSource {
+    pub fn as_functor_stub(&self) -> MachineStub {
+        match self {
+            ModuleSource::Library(ref name) => {
+                functor!("library", [clause_name(name.clone())])
+            }
+            ModuleSource::File(ref name) => {
+                functor!(clause_name(name.clone()))
+            }
+        }
+    }
+}
+
 pub type ScopedPredicateKey = (ClauseName, PredicateKey); // module name, predicate indicator.
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub enum MultiFileIndicator {
     LocalScoped(ClauseName, usize), // name, arity
     ModuleScoped(ScopedPredicateKey),
 }
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub enum Declaration {
     Dynamic(ClauseName, usize), // name, arity
     EndOfFile,
@@ -394,6 +407,7 @@ pub enum Declaration {
     MultiFile(MultiFileIndicator),
     NonCountedBacktracking(ClauseName, usize), // name, arity
     Op(OpDecl),
+    SetPrologFlag(DoubleQuotes),
     UseModule(ModuleSource),
     UseQualifiedModule(ModuleSource, Vec<ModuleExport>),
 }
@@ -418,7 +432,7 @@ impl Declaration {
     }
 }
 
-#[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
 pub struct OpDecl(pub usize, pub Specifier, pub ClauseName);
 
 impl OpDecl {
@@ -491,11 +505,11 @@ pub fn fetch_atom_op_spec(
     spec: Option<SharedOpDesc>,
     op_dir: &OpDir,
 ) -> Option<SharedOpDesc> {
-    fetch_op_spec(name.clone(), 1, spec.clone(), op_dir)
-        .or_else(|| fetch_op_spec(name, 2, spec, op_dir))
+    fetch_op_spec_from_existing(name.clone(), 1, spec.clone(), op_dir)
+        .or_else(|| fetch_op_spec_from_existing(name, 2, spec, op_dir))
 }
 
-pub fn fetch_op_spec(
+pub fn fetch_op_spec_from_existing(
     name: ClauseName,
     arity: usize,
     spec: Option<SharedOpDesc>,
@@ -510,7 +524,15 @@ pub fn fetch_op_spec(
         }
     }
 
-    spec.or_else(|| match arity {
+    spec.or_else(|| fetch_op_spec(name, arity, op_dir))
+}
+
+pub fn fetch_op_spec(
+    name: ClauseName,
+    arity: usize,
+    op_dir: &OpDir,
+) -> Option<SharedOpDesc> {
+    match arity {
         2 => op_dir
             .get(&(name, Fixity::In))
             .and_then(|OpDirValue(spec, _)| {
@@ -528,7 +550,7 @@ pub fn fetch_op_spec(
             }
 
             op_dir
-                .get(&(name.clone(), Fixity::Post))
+                .get(&(name, Fixity::Post))
                 .and_then(|OpDirValue(spec, _)| {
                     if spec.prec() > 0 {
                         Some(spec.clone())
@@ -537,24 +559,27 @@ pub fn fetch_op_spec(
                     }
                 })
         }
-        _ => None,
-    })
+        _ => {
+            None
+        }
+    }
 }
 
 pub type ModuleDir = IndexMap<ClauseName, Module>;
 
-#[derive(Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq)]
 pub enum ModuleExport {
     OpDecl(OpDecl),
     PredicateKey(PredicateKey),
 }
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub struct ModuleDecl {
     pub name: ClauseName,
     pub exports: Vec<ModuleExport>,
 }
 
+#[derive(Debug)]
 pub struct Module {
     pub atom_tbl: TabledData<Atom>,
     pub module_decl: ModuleDecl,
@@ -572,11 +597,33 @@ pub struct Module {
     pub listing_src: ListingSource,
  }
 
-#[derive(Clone, PartialEq, Eq)]
+#[derive(Debug, Clone)]
 pub enum Number {
     Float(OrderedFloat<f64>),
-    Integer(Integer),
-    Rational(Rational),
+    Integer(Rc<Integer>),
+    Rational(Rc<Rational>),
+    Fixnum(isize),
+}
+
+impl From<Integer> for Number {
+    #[inline]
+    fn from(n: Integer) -> Self {
+        Number::Integer(Rc::new(n))
+    }
+}
+
+impl From<Rational> for Number {
+    #[inline]
+    fn from(n: Rational) -> Self {
+        Number::Rational(Rc::new(n))
+    }
+}
+
+impl From<isize> for Number {
+    #[inline]
+    fn from(n: isize) -> Self {
+        Number::Fixnum(n)
+    }
 }
 
 impl Default for Number {
@@ -585,48 +632,74 @@ impl Default for Number {
     }
 }
 
-impl Number {
-    pub fn to_constant(self) -> Constant {
+impl Into<Constant> for Number {
+    #[inline]
+    fn into(self) -> Constant {
         match self {
+            Number::Fixnum(n) => Constant::Fixnum(n),
             Number::Integer(n) => Constant::Integer(n),
             Number::Float(f) => Constant::Float(f),
             Number::Rational(r) => Constant::Rational(r),
         }
     }
+}
 
+impl Into<HeapCellValue> for Number {
+    #[inline]
+    fn into(self) -> HeapCellValue {
+        match self {
+            Number::Fixnum(n) => HeapCellValue::Addr(Addr::Fixnum(n)),
+            Number::Integer(n) => HeapCellValue::Integer(n),
+            Number::Float(f) => HeapCellValue::Addr(Addr::Float(f)),
+            Number::Rational(r) => HeapCellValue::Rational(r),
+        }
+    }
+}
+
+
+impl Number {
     #[inline]
     pub fn is_positive(&self) -> bool {
         match self {
-            &Number::Integer(ref n) => n > &0,
+            &Number::Fixnum(n) => n > 0,
+            &Number::Integer(ref n) => &**n > &0,
             &Number::Float(OrderedFloat(f)) => f.is_sign_positive(),
-            &Number::Rational(ref r) => r > &0,
+            &Number::Rational(ref r) => &**r > &0,
         }
     }
 
     #[inline]
     pub fn is_negative(&self) -> bool {
         match self {
-            &Number::Integer(ref n) => n < &0,
+            &Number::Fixnum(n) => n < 0,
+            &Number::Integer(ref n) => &**n < &0,
             &Number::Float(OrderedFloat(f)) => f.is_sign_negative(),
-            &Number::Rational(ref r) => r < &0,
+            &Number::Rational(ref r) => &**r < &0,
         }
     }
 
     #[inline]
     pub fn is_zero(&self) -> bool {
         match self {
-            &Number::Integer(ref n) => n == &0,
+            &Number::Fixnum(n) => n == 0,
+            &Number::Integer(ref n) => &**n == &0,
             &Number::Float(f) => f == OrderedFloat(0f64),
-            &Number::Rational(ref r) => r == &0,
+            &Number::Rational(ref r) => &**r == &0,
         }
     }
 
     #[inline]
     pub fn abs(self) -> Self {
         match self {
-            Number::Integer(n) => Number::Integer(n.abs()),
+            Number::Fixnum(n) =>
+                if let Some(n) = n.checked_abs() {
+                    Number::from(n)
+                } else {
+                    Number::from(Integer::from(n).abs())
+                }
+            Number::Integer(n) => Number::from(Integer::from(n.abs_ref())),
             Number::Float(f) => Number::Float(OrderedFloat(f.abs())),
-            Number::Rational(r) => Number::Rational(r.abs()),
+            Number::Rational(r) => Number::from(Rational::from(r.abs_ref())),
         }
     }
 }

src/heap_iter.rs

@@ -0,0 +1,342 @@
+use crate::machine::machine_indices::*;
+use crate::machine::machine_state::*;
+
+use crate::indexmap::IndexSet;
+
+use std::cmp::Ordering;
+use std::ops::Deref;
+use std::vec::Vec;
+
+#[derive(Debug)]
+pub struct HCPreOrderIterator<'a> {
+    pub machine_st: &'a MachineState,
+    pub state_stack: Vec<Addr>,
+}
+
+impl<'a> HCPreOrderIterator<'a> {
+    pub fn new(machine_st: &'a MachineState, a: Addr) -> Self {
+        HCPreOrderIterator {
+            machine_st,
+            state_stack: vec![a],
+        }
+    }
+
+    #[inline]
+    pub fn machine_st(&self) -> &MachineState {
+        &self.machine_st
+    }
+
+    fn follow_heap(&mut self, h: usize) -> Addr {
+        match &self.machine_st.heap[h] {
+            &HeapCellValue::NamedStr(arity, _, _) => {
+                for idx in (1 .. arity + 1).rev() {
+                    self.state_stack.push(Addr::HeapCell(h + idx));
+                }
+
+                Addr::Str(h)
+            }
+            &HeapCellValue::Addr(a) => {
+                self.follow(a)
+            }
+            HeapCellValue::PartialString(..) => {
+                self.follow(Addr::PStrLocation(h, 0))
+            }
+            HeapCellValue::Atom(..) | HeapCellValue::DBRef(_)
+          | HeapCellValue::Integer(_) | HeapCellValue::Rational(_) => {
+                Addr::Con(h)
+            }
+            HeapCellValue::Stream(_) => {
+                Addr::Stream(h)
+            }
+            &HeapCellValue::TcpListener(_) => {
+                Addr::TcpListener(h)
+            }
+        }
+    }
+
+    // called under the assumption that the location at r is about to
+    // be visited, and so any follow up states need to be added to
+    // state_stack. returns the dereferenced Addr from Ref.
+    fn follow(&mut self, addr: Addr) -> Addr {
+        let da = self.machine_st.store(self.machine_st.deref(addr));
+
+        match da {
+            Addr::Lis(a) => {
+                self.state_stack.push(Addr::HeapCell(a + 1));
+                self.state_stack.push(Addr::HeapCell(a));
+
+                da
+            }
+            Addr::PStrLocation(h, n) => {
+                if let &HeapCellValue::PartialString(ref pstr, has_tail) = &self.machine_st.heap[h] {
+                    if let Some(c) = pstr.range_from(n ..).next() {
+                        if !pstr.at_end(n + c.len_utf8()) {
+                            self.state_stack.push(Addr::PStrLocation(h, n + c.len_utf8()));
+                        } else if has_tail {
+                            self.state_stack.push(Addr::HeapCell(h + 1));
+                        } else {
+                            self.state_stack.push(Addr::EmptyList);
+                        }
+
+                        self.state_stack.push(Addr::Char(c));
+                    } else if has_tail {
+                        return self.follow(Addr::HeapCell(h + 1));
+                    }
+                } else {
+                    unreachable!()
+                }
+
+                Addr::PStrLocation(h, n)
+            }
+            Addr::Str(s) => {
+                self.follow_heap(s) // record terms of structure.
+            }
+            Addr::Con(h) => {
+                if let &HeapCellValue::PartialString(ref pstr, has_tail) = &self.machine_st.heap[h] {
+                    if let Some(c) = pstr.range_from(0 ..).next() {
+                        self.state_stack.push(Addr::PStrLocation(h, c.len_utf8()));
+                        self.state_stack.push(Addr::Char(c));
+
+                        Addr::PStrLocation(h, 0)
+                    } else if has_tail {
+                        self.follow(Addr::HeapCell(h + 1))
+                    } else {
+                        Addr::EmptyList
+                    }
+                } else {
+                    Addr::Con(h)
+                }
+            }
+            da => {
+                da
+            }
+        }
+    }
+}
+
+impl<'a> Iterator for HCPreOrderIterator<'a> {
+    type Item = Addr;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.state_stack.pop().map(|a| self.follow(a))
+    }
+}
+
+pub trait MutStackHCIterator<'b> where Self: Iterator
+{
+    type MutStack;
+
+    fn stack(&'b mut self) -> Self::MutStack;
+}
+
+#[derive(Debug)]
+pub struct HCPostOrderIterator<'a> {
+    base_iter: HCPreOrderIterator<'a>,
+    parent_stack: Vec<(usize, Addr)>, // number of children, parent node.
+}
+
+impl<'a> Deref for HCPostOrderIterator<'a> {
+    type Target = HCPreOrderIterator<'a>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.base_iter
+    }
+}
+
+impl<'a> HCPostOrderIterator<'a> {
+    pub fn new(base_iter: HCPreOrderIterator<'a>) -> Self {
+        HCPostOrderIterator {
+            base_iter,
+            parent_stack: vec![],
+        }
+    }
+}
+
+impl<'a> Iterator for HCPostOrderIterator<'a> {
+    type Item = Addr;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            if let Some((child_count, node)) = self.parent_stack.pop() {
+                if child_count == 0 {
+                    return Some(node);
+                }
+
+                self.parent_stack.push((child_count - 1, node));
+            }
+
+            if let Some(item) = self.base_iter.next() {
+                match self.base_iter.machine_st.heap.index_addr(&item).as_ref() {
+                    &HeapCellValue::NamedStr(arity, ..) => {
+                        self.parent_stack.push((arity, item));
+                    }
+                    &HeapCellValue::Addr(Addr::Lis(a)) => {
+                        self.parent_stack.push((2, Addr::Lis(a)));
+                    }
+                    &HeapCellValue::Addr(Addr::PStrLocation(h, n)) => {
+                        match &self.machine_st.heap[h] {
+                            &HeapCellValue::PartialString(ref pstr, _) => {
+                                let c = pstr.range_from(n ..).next().unwrap();
+                                let next_n = n + c.len_utf8();
+
+                                if !pstr.at_end(next_n) {
+                                    self.parent_stack.push((2, Addr::PStrLocation(h, next_n)));
+                                }
+                            }
+                            _ => {
+                                unreachable!()
+                            }
+                        }
+                    }
+                    _ => {
+                        return Some(item);
+                    }
+                }
+            } else {
+                return None;
+            }
+        }
+    }
+}
+
+impl MachineState {
+    pub fn pre_order_iter<'a>(&'a self, a: Addr) -> HCPreOrderIterator<'a> {
+        HCPreOrderIterator::new(self, a)
+    }
+
+    pub fn post_order_iter<'a>(&'a self, a: Addr) -> HCPostOrderIterator<'a> {
+        HCPostOrderIterator::new(HCPreOrderIterator::new(self, a))
+    }
+
+    pub fn acyclic_pre_order_iter<'a>(&'a self, a: Addr,) -> HCAcyclicIterator<'a> {
+        HCAcyclicIterator::new(HCPreOrderIterator::new(self, a))
+    }
+
+    pub fn zipped_acyclic_pre_order_iter<'a>(
+        &'a self,
+        a1: Addr,
+        a2: Addr,
+    ) -> HCZippedAcyclicIterator<'a> {
+        HCZippedAcyclicIterator::new(
+            HCPreOrderIterator::new(self, a1),
+            HCPreOrderIterator::new(self, a2),
+        )
+    }
+}
+
+impl<'b, 'a: 'b> MutStackHCIterator<'b> for HCPreOrderIterator<'a> {
+    type MutStack = &'b mut Vec<Addr>;
+
+    fn stack(&'b mut self) -> Self::MutStack {
+        &mut self.state_stack
+    }
+}
+
+#[derive(Debug)]
+pub struct HCAcyclicIterator<'a> {
+    iter: HCPreOrderIterator<'a>,
+    seen: IndexSet<Addr>,
+}
+
+impl<'a> HCAcyclicIterator<'a> {
+    pub fn new(iter: HCPreOrderIterator<'a>) -> Self {
+        HCAcyclicIterator {
+            iter,
+            seen: IndexSet::new(),
+        }
+    }
+}
+
+impl<'a> Deref for HCAcyclicIterator<'a> {
+    type Target = HCPreOrderIterator<'a>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.iter
+    }
+}
+
+impl<'b, 'a: 'b> MutStackHCIterator<'b> for HCAcyclicIterator<'a> {
+    type MutStack = &'b mut Vec<Addr>;
+
+    fn stack(&'b mut self) -> Self::MutStack {
+        self.iter.stack()
+    }
+}
+
+impl<'a> Iterator for HCAcyclicIterator<'a>
+{
+    type Item = Addr;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while let Some(addr) = self.iter.stack().pop() {
+            if !self.seen.contains(&addr) {
+                self.iter.stack().push(addr.clone());
+                self.seen.insert(addr);
+
+                break;
+            }
+        }
+
+        self.iter.next()
+    }
+}
+
+#[derive(Debug)]
+pub struct HCZippedAcyclicIterator<'a> {
+    i1: HCPreOrderIterator<'a>,
+    i2: HCPreOrderIterator<'a>,
+    seen: IndexSet<(Addr, Addr)>,
+    pub first_to_expire: Ordering,
+}
+
+impl<'b, 'a: 'b> MutStackHCIterator<'b> for HCZippedAcyclicIterator<'a> {
+    type MutStack = (&'b mut Vec<Addr>, &'b mut Vec<Addr>);
+
+    fn stack(&'b mut self) -> Self::MutStack {
+        (self.i1.stack(), self.i2.stack())
+    }
+}
+
+impl<'a> HCZippedAcyclicIterator<'a> {
+    pub fn new(i1: HCPreOrderIterator<'a>, i2: HCPreOrderIterator<'a>) -> Self {
+        HCZippedAcyclicIterator {
+            i1,
+            i2,
+            seen: IndexSet::new(),
+            first_to_expire: Ordering::Equal,
+        }
+    }
+}
+
+impl<'a> Iterator for HCZippedAcyclicIterator<'a>
+{
+    type Item = (Addr, Addr);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while let (Some(a1), Some(a2)) = (self.i1.stack().pop(), self.i2.stack().pop()) {
+            if !self.seen.contains(&(a1.clone(), a2.clone())) {
+                self.i1.stack().push(a1.clone());
+                self.i2.stack().push(a2.clone());
+
+                self.seen.insert((a1, a2));
+
+                break;
+            }
+        }
+
+        match (self.i1.next(), self.i2.next()) {
+            (Some(v1), Some(v2)) => Some((v1, v2)),
+            (Some(_), None) => {
+                self.first_to_expire = Ordering::Greater;
+                None
+            }
+            (None, Some(_)) => {
+                self.first_to_expire = Ordering::Less;
+                None
+            }
+            _ => {
+                None
+            }
+        }
+    }
+}

src/indexing.rs

@@ -1,20 +1,26 @@
-use prolog_parser::ast::*;
+use crate::prolog_parser::ast::*;
+use crate::prolog_parser::tabled_rc::*;
 
-use crate::prolog::instructions::*;
+use crate::instructions::*;
+use crate::rug::Integer;
 
-use indexmap::IndexMap;
+use crate::indexmap::IndexMap;
 
 use std::collections::VecDeque;
+use std::convert::TryFrom;
 use std::hash::Hash;
+use std::rc::Rc;
 
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 enum IntIndex {
     External(usize),
     Fail,
     Internal(usize),
 }
 
+#[derive(Debug)]
 pub struct CodeOffsets {
+    atom_tbl: TabledData<Atom>,
     pub constants: IndexMap<Constant, ThirdLevelIndex>,
     pub lists: ThirdLevelIndex,
     pub structures: IndexMap<(ClauseName, usize), ThirdLevelIndex>,
@@ -23,6 +29,7 @@ pub struct CodeOffsets {
 impl CodeOffsets {
     pub fn new() -> Self {
         CodeOffsets {
+            atom_tbl: TabledData::new(Rc::new("_index".to_string())),
             constants: IndexMap::new(),
             lists: Vec::new(),
             structures: IndexMap::new(),
@@ -48,6 +55,94 @@ impl CodeOffsets {
         }
     }
 
+    fn intercept_overlapping_constant(&mut self, constant: &Constant, index: usize) {
+        match constant {
+            &Constant::Atom(ref name, ref op) if name.is_char() => {
+                let c = name.as_str().chars().next().unwrap();
+                let code = self.constants
+                    .entry(Constant::Char(c))
+                    .or_insert(vec![]);
+
+                code.push(Self::add_index(code.is_empty(), index));
+
+                if op.is_some() {
+                    let code = self.constants
+                        .entry(Constant::Atom(name.clone(), None))
+                        .or_insert(vec![]);
+
+                    code.push(Self::add_index(false, index));
+                }
+            }
+            &Constant::Atom(ref name, Some(_)) => {
+                let code = self.constants
+                    .entry(Constant::Atom(name.clone(), None))
+                    .or_insert(vec![]);
+
+                code.push(Self::add_index(code.is_empty(), index));
+            }
+            &Constant::Char(c) => {
+                let atom = clause_name!(c.to_string(), self.atom_tbl.clone());
+
+                let code = self.constants
+                    .entry(Constant::Atom(atom, None))
+                    .or_insert(vec![]);
+
+                code.push(Self::add_index(code.is_empty(), index));
+            }
+            &Constant::Fixnum(n) => {
+                let code = self.constants
+                    .entry(Constant::Integer(Rc::new(Integer::from(n))))
+                    .or_insert(vec![]);
+
+                code.push(Self::add_index(code.is_empty(), index));
+
+                if n >= 0 {
+                    if let Ok(n) = usize::try_from(n) {
+                        let code = self.constants
+                            .entry(Constant::Usize(n))
+                            .or_insert(vec![]);
+
+                        code.push(Self::add_index(code.is_empty(), index));
+                    }
+                }
+            }
+            &Constant::Integer(ref n) => {
+                if let Some(n) = n.to_isize() {
+                    let code = self.constants
+                        .entry(Constant::Fixnum(n))
+                        .or_insert(vec![]);
+
+                    code.push(Self::add_index(code.is_empty(), index));
+                }
+
+                if let Some(n) = n.to_usize() {
+                    let code = self.constants
+                        .entry(Constant::Usize(n))
+                        .or_insert(vec![]);
+
+                    code.push(Self::add_index(code.is_empty(), index));
+                }
+            }
+            &Constant::Usize(n) => {
+                let code = self.constants
+                    .entry(Constant::Integer(Rc::new(Integer::from(n))))
+                    .or_insert(vec![]);
+
+                code.push(Self::add_index(code.is_empty(), index));
+
+                if let Ok(n) = isize::try_from(n) {
+                    let code = self.constants
+                        .entry(Constant::Fixnum(n))
+                        .or_insert(vec![]);
+
+                    code.push(Self::add_index(code.is_empty(), index));
+                }
+            }
+            _ => {
+            }
+        }
+    }
+
     pub fn index_term(&mut self, first_arg: &Term, index: usize) {
         match first_arg {
             &Term::Clause(_, ref name, ref terms, _) => {
@@ -59,27 +154,22 @@ impl CodeOffsets {
                 let is_initial_index = code.is_empty();
                 code.push(Self::add_index(is_initial_index, index));
             }
-            &Term::Cons(..) => {
+            &Term::Cons(..) | &Term::Constant(_, Constant::String(_)) => {
                 let is_initial_index = self.lists.is_empty();
                 self.lists.push(Self::add_index(is_initial_index, index));
             }
-            &Term::Constant(_, Constant::String(n, ref s)) => {
-                let is_initial_index = self.lists.is_empty();
-                self.lists.push(Self::add_index(is_initial_index, index));
-
-                let constant = Constant::String(n, s.clone());
-                let code = self.constants.entry(constant).or_insert(Vec::new());
-
-                let is_initial_index = code.is_empty();
-                code.push(Self::add_index(is_initial_index, index));
-            }
             &Term::Constant(_, ref constant) => {
-                let code = self.constants.entry(constant.clone()).or_insert(Vec::new());
+                self.intercept_overlapping_constant(constant, index);
+
+                let code = self.constants
+                    .entry(constant.clone())
+                    .or_insert(vec![]);
 
                 let is_initial_index = code.is_empty();
                 code.push(Self::add_index(is_initial_index, index));
             }
-            _ => {}
+            _ => {
+            }
         };
     }
 
@@ -227,12 +317,11 @@ impl CodeOffsets {
     fn switch_on_lst_offset_from(
         lst_loc: IntIndex,
         prelude_len: usize,
-        lst_offset: usize,
     ) -> usize {
         match lst_loc {
             IntIndex::External(o) => o + prelude_len + 1,
             IntIndex::Fail => 0,
-            IntIndex::Internal(_) => prelude_len - lst_offset + 1,
+            IntIndex::Internal(_) => 1, // this internal is always 0.
         }
     }
 
@@ -245,8 +334,6 @@ impl CodeOffsets {
         let mut prelude = VecDeque::new();
 
         let lst_loc = Self::switch_on_list(self.lists, &mut prelude);
-        let lst_offset = prelude.len();
-
         let str_loc = Self::switch_on_structure(self.structures, &mut prelude);
         let con_loc = Self::switch_on_constant(self.constants, &mut prelude);
 
@@ -254,18 +341,19 @@ impl CodeOffsets {
 
         for (index, line) in prelude.iter_mut().enumerate() {
             match line {
-                &mut Line::IndexedChoice(IndexedChoiceInstruction::Try(ref mut i))
-              | &mut Line::IndexedChoice(IndexedChoiceInstruction::Retry(ref mut i))
-              | &mut Line::IndexedChoice(IndexedChoiceInstruction::Trust(ref mut i)) => {
-                    *i += prelude_length - index
+                &mut Line::IndexedChoice(IndexedChoiceInstruction::Try(ref mut i)) |
+                &mut Line::IndexedChoice(IndexedChoiceInstruction::Retry(ref mut i)) |
+                &mut Line::IndexedChoice(IndexedChoiceInstruction::Trust(ref mut i)) => {
+                    *i += prelude_length - index;
+                }
+                _ => {
                 }
-                _ => {}
             }
         }
 
         let str_loc = Self::switch_on_str_offset_from(str_loc, prelude.len(), con_loc);
         let con_loc = Self::switch_on_con_offset_from(con_loc, prelude.len());
-        let lst_loc = Self::switch_on_lst_offset_from(lst_loc, prelude.len(), lst_offset);
+        let lst_loc = Self::switch_on_lst_offset_from(lst_loc, prelude.len());
 
         let switch_instr =
             IndexingInstruction::SwitchOnTerm(prelude.len() + 1, con_loc, lst_loc, str_loc);

src/instructions.rs

@@ -1,29 +1,30 @@
-use prolog_parser::ast::*;
+use crate::prolog_parser::ast::*;
 
-use crate::prolog::clause_types::*;
-use crate::prolog::forms::*;
-use crate::prolog::machine::machine_errors::MachineStub;
-use crate::prolog::machine::machine_indices::*;
+use crate::clause_types::*;
+use crate::forms::*;
+use crate::machine::heap::*;
+use crate::machine::machine_errors::MachineStub;
+use crate::machine::machine_indices::*;
+use crate::rug::Integer;
 
-use crate::prolog::rug::Integer;
-
-use indexmap::IndexMap;
+use crate::indexmap::IndexMap;
 
 use std::collections::VecDeque;
+use std::rc::Rc;
 
 fn reg_type_into_functor(r: RegType) -> MachineStub {
     match r {
-        RegType::Temp(r) => functor!("x", 1, [heap_integer!(Integer::from(r))]),
-        RegType::Perm(r) => functor!("y", 1, [heap_integer!(Integer::from(r))]),
+        RegType::Temp(r) => functor!("x", [integer(r)]),
+        RegType::Perm(r) => functor!("y", [integer(r)]),
     }
 }
 
 impl Level {
     fn into_functor(self) -> MachineStub {
         match self {
-            Level::Root => functor!("level", 1, [heap_atom!("root")]),
-            Level::Shallow => functor!("level", 1, [heap_atom!("shallow")]),
-            Level::Deep => functor!("level", 1, [heap_atom!("deep")]),
+            Level::Root => functor!("level", [atom("root")]),
+            Level::Shallow => functor!("level", [atom("shallow")]),
+            Level::Deep => functor!("level", [atom("deep")]),
         }
     }
 }
@@ -31,15 +32,20 @@ impl Level {
 impl ArithmeticTerm {
     fn into_functor(&self) -> MachineStub {
         match self {
-            &ArithmeticTerm::Reg(r) => reg_type_into_functor(r),
-            &ArithmeticTerm::Interm(i) => {
-                functor!("intermediate", 1, [heap_integer!(Integer::from(i))])
+            &ArithmeticTerm::Reg(r) => {
+                reg_type_into_functor(r)
+            }
+            &ArithmeticTerm::Interm(i) => {
+                functor!("intermediate", [integer(i)])
+            }
+            &ArithmeticTerm::Number(ref n) => {
+                vec![n.clone().into()]
             }
-            &ArithmeticTerm::Number(ref n) => vec![heap_con!(n.clone().to_constant())],
         }
     }
 }
 
+#[derive(Debug)]
 pub enum ChoiceInstruction {
     DefaultRetryMeElse(usize),
     DefaultTrustMe,
@@ -52,22 +58,25 @@ impl ChoiceInstruction {
     pub fn to_functor(&self) -> MachineStub {
         match self {
             &ChoiceInstruction::TryMeElse(offset) => {
-                functor!("try_me_else", 1, [heap_integer!(Integer::from(offset))])
+                functor!("try_me_else", [integer(offset)])
             }
             &ChoiceInstruction::RetryMeElse(offset) => {
-                functor!("retry_me_else", 1, [heap_integer!(Integer::from(offset))])
+                functor!("retry_me_else", [integer(offset)])
+            }
+            &ChoiceInstruction::TrustMe => {
+                functor!("trust_me")
+            }
+            &ChoiceInstruction::DefaultRetryMeElse(offset) => {
+                functor!("default_retry_me_else", [integer(offset)])
+            }
+            &ChoiceInstruction::DefaultTrustMe => {
+                functor!("default_trust_me")
             }
-            &ChoiceInstruction::TrustMe => vec![heap_atom!("trust_me")],
-            &ChoiceInstruction::DefaultRetryMeElse(offset) => functor!(
-                "default_retry_me_else",
-                1,
-                [heap_integer!(Integer::from(offset))]
-            ),
-            &ChoiceInstruction::DefaultTrustMe => vec![heap_atom!("default_trust_me")],
         }
     }
 }
 
+#[derive(Debug)]
 pub enum CutInstruction {
     Cut(RegType),
     GetLevel(RegType),
@@ -79,25 +88,25 @@ impl CutInstruction {
     pub fn to_functor(&self, h: usize) -> MachineStub {
         match self {
             &CutInstruction::Cut(r) => {
-                let mut stub = functor!("cut", 1, [heap_str!(h + 2)]);
-                stub.append(&mut reg_type_into_functor(r));
-                stub
+                let rt_stub = reg_type_into_functor(r);
+                functor!("cut", [aux(h, 0)], [rt_stub])
             }
             &CutInstruction::GetLevel(r) => {
-                let mut stub = functor!("get_level", 1, [heap_str!(h + 2)]);
-                stub.append(&mut reg_type_into_functor(r));
-                stub
+                let rt_stub = reg_type_into_functor(r);
+                functor!("get_level", [aux(h, 0)], [rt_stub])
             }
             &CutInstruction::GetLevelAndUnify(r) => {
-                let mut stub = functor!("get_level_and_unify", 1, [heap_str!(h + 2)]);
-                stub.append(&mut reg_type_into_functor(r));
-                stub
+                let rt_stub = reg_type_into_functor(r);
+                functor!("get_level_and_unify", [aux(h, 0)], [rt_stub])
+            }
+            &CutInstruction::NeckCut => {
+                functor!("neck_cut")
             }
-            &CutInstruction::NeckCut => vec![heap_atom!("neck_cut")],
         }
     }
 }
 
+#[derive(Debug)]
 pub enum IndexedChoiceInstruction {
     Retry(usize),
     Trust(usize),
@@ -122,18 +131,19 @@ impl IndexedChoiceInstruction {
     pub fn to_functor(&self) -> MachineStub {
         match self {
             &IndexedChoiceInstruction::Try(offset) => {
-                functor!("try", 1, [heap_integer!(Integer::from(offset))])
+                functor!("try", [integer(offset)])
             }
             &IndexedChoiceInstruction::Trust(offset) => {
-                functor!("trust", 1, [heap_integer!(Integer::from(offset))])
+                functor!("trust", [integer(offset)])
             }
             &IndexedChoiceInstruction::Retry(offset) => {
-                functor!("retry", 1, [heap_integer!(Integer::from(offset))])
+                functor!("retry", [integer(offset)])
             }
         }
     }
 }
 
+#[derive(Debug)]
 pub enum Line {
     Arithmetic(ArithmeticInstruction),
     Choice(ChoiceInstruction),
@@ -169,7 +179,7 @@ impl Line {
     }
 }
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub enum ArithmeticInstruction {
     Add(ArithmeticTerm, ArithmeticTerm, usize),
     Sub(ArithmeticTerm, ArithmeticTerm, usize),
@@ -220,14 +230,11 @@ fn arith_instr_unary_functor(
 ) -> MachineStub {
     let at_stub = at.into_functor();
 
-    let mut stub = functor!(
+    functor!(
         name,
-        2,
-        [heap_cell!(h + 4), heap_integer!(Integer::from(t))]
-    );
-
-    stub.extend(at_stub.into_iter());
-    stub
+        [aux(h, 0), integer(t)],
+        [at_stub]
+    )
 }
 
 fn arith_instr_bin_functor(
@@ -240,20 +247,11 @@ fn arith_instr_bin_functor(
     let at_1_stub = at_1.into_functor();
     let at_2_stub = at_2.into_functor();
 
-    let mut stub = functor!(
+    functor!(
         name,
-        3,
-        [
-            heap_cell!(h + 4),
-            heap_cell!(h + 4 + at_1_stub.len()),
-            heap_integer!(Integer::from(t))
-        ]
-    );
-
-    stub.extend(at_1_stub.into_iter());
-    stub.extend(at_2_stub.into_iter());
-
-    stub
+        [aux(h, 0), aux(h, 1), integer(t)],
+        [at_1_stub, at_2_stub]
+    )
 }
 
 impl ArithmeticInstruction {
@@ -319,17 +317,39 @@ impl ArithmeticInstruction {
             &ArithmeticInstruction::Gcd(ref at_1, ref at_2, t) => {
                 arith_instr_bin_functor(h, "gcd", at_1, at_2, t)
             }
-            &ArithmeticInstruction::Sign(ref at, t) => arith_instr_unary_functor(h, "sign", at, t),
-            &ArithmeticInstruction::Cos(ref at, t) => arith_instr_unary_functor(h, "cos", at, t),
-            &ArithmeticInstruction::Sin(ref at, t) => arith_instr_unary_functor(h, "sin", at, t),
-            &ArithmeticInstruction::Tan(ref at, t) => arith_instr_unary_functor(h, "tan", at, t),
-            &ArithmeticInstruction::Log(ref at, t) => arith_instr_unary_functor(h, "log", at, t),
-            &ArithmeticInstruction::Exp(ref at, t) => arith_instr_unary_functor(h, "exp", at, t),
-            &ArithmeticInstruction::ACos(ref at, t) => arith_instr_unary_functor(h, "acos", at, t),
-            &ArithmeticInstruction::ASin(ref at, t) => arith_instr_unary_functor(h, "asin", at, t),
-            &ArithmeticInstruction::ATan(ref at, t) => arith_instr_unary_functor(h, "atan", at, t),
-            &ArithmeticInstruction::Sqrt(ref at, t) => arith_instr_unary_functor(h, "sqrt", at, t),
-            &ArithmeticInstruction::Abs(ref at, t) => arith_instr_unary_functor(h, "abs", at, t),
+            &ArithmeticInstruction::Sign(ref at, t) => {
+                arith_instr_unary_functor(h, "sign", at, t)
+            }
+            &ArithmeticInstruction::Cos(ref at, t)  => {
+                arith_instr_unary_functor(h, "cos", at, t)
+            }
+            &ArithmeticInstruction::Sin(ref at, t)  => {
+                arith_instr_unary_functor(h, "sin", at, t)
+            }
+            &ArithmeticInstruction::Tan(ref at, t)  => {
+                arith_instr_unary_functor(h, "tan", at, t)
+            }
+            &ArithmeticInstruction::Log(ref at, t)  => {
+                arith_instr_unary_functor(h, "log", at, t)
+            }
+            &ArithmeticInstruction::Exp(ref at, t)  => {
+                arith_instr_unary_functor(h, "exp", at, t)
+            }
+            &ArithmeticInstruction::ACos(ref at, t) => {
+                arith_instr_unary_functor(h, "acos", at, t)
+            }
+            &ArithmeticInstruction::ASin(ref at, t) => {
+                arith_instr_unary_functor(h, "asin", at, t)
+            }
+            &ArithmeticInstruction::ATan(ref at, t) => {
+                arith_instr_unary_functor(h, "atan", at, t)
+            }
+            &ArithmeticInstruction::Sqrt(ref at, t) => {
+                arith_instr_unary_functor(h, "sqrt", at, t)
+            }
+            &ArithmeticInstruction::Abs(ref at, t) => {
+                arith_instr_unary_functor(h, "abs", at, t)
+            }
             &ArithmeticInstruction::Float(ref at, t) => {
                 arith_instr_unary_functor(h, "float", at, t)
             }
@@ -345,8 +365,12 @@ impl ArithmeticInstruction {
             &ArithmeticInstruction::Floor(ref at, t) => {
                 arith_instr_unary_functor(h, "floor", at, t)
             }
-            &ArithmeticInstruction::Neg(ref at, t) => arith_instr_unary_functor(h, "-", at, t),
-            &ArithmeticInstruction::Plus(ref at, t) => arith_instr_unary_functor(h, "+", at, t),
+            &ArithmeticInstruction::Neg(ref at, t) => {
+                arith_instr_unary_functor(h, "-", at, t)
+            }
+            &ArithmeticInstruction::Plus(ref at, t) => {
+                arith_instr_unary_functor(h, "+", at, t)
+            }
             &ArithmeticInstruction::BitwiseComplement(ref at, t) => {
                 arith_instr_unary_functor(h, "\\", at, t)
             }
@@ -354,6 +378,7 @@ impl ArithmeticInstruction {
     }
 }
 
+#[derive(Debug)]
 pub enum ControlInstruction {
     Allocate(usize), // num_frames.
     // name, arity, perm_vars after threshold, last call, use default call policy.
@@ -378,33 +403,28 @@ impl ControlInstruction {
     pub fn to_functor(&self) -> MachineStub {
         match self {
             &ControlInstruction::Allocate(num_frames) => {
-                functor!("allocate", 1, [heap_integer!(Integer::from(num_frames))])
+                functor!("allocate", [integer(num_frames)])
+            }
+            &ControlInstruction::CallClause(ref ct, arity, _, false, _) => {
+                functor!("call", [clause_name(ct.name()), integer(arity)])
+            }
+            &ControlInstruction::CallClause(ref ct, arity, _, true, _) => {
+                functor!("execute", [clause_name(ct.name()), integer(arity)])
+            }
+            &ControlInstruction::Deallocate => {
+                functor!("deallocate")
             }
-            &ControlInstruction::CallClause(ref ct, arity, _, false, _) => functor!(
-                "call",
-                2,
-                [
-                    heap_con!(Constant::Atom(ct.name(), None)),
-                    heap_integer!(Integer::from(arity))
-                ]
-            ),
-            &ControlInstruction::CallClause(ref ct, arity, _, true, _) => functor!(
-                "execute",
-                2,
-                [
-                    heap_con!(Constant::Atom(ct.name(), None)),
-                    heap_integer!(Integer::from(arity))
-                ]
-            ),
-            &ControlInstruction::Deallocate => vec![heap_atom!("deallocate")],
             &ControlInstruction::JmpBy(_, offset, ..) => {
-                functor!("jmp_by", 1, [heap_integer!(Integer::from(offset))])
+                functor!("jmp_by", [integer(offset)])
+            }
+            &ControlInstruction::Proceed => {
+                functor!("proceed")
             }
-            &ControlInstruction::Proceed => vec![heap_atom!("proceed")],
         }
     }
 }
 
+#[derive(Debug)]
 pub enum IndexingInstruction {
     SwitchOnTerm(usize, usize, usize, usize),
     SwitchOnConstant(usize, IndexMap<Constant, usize>),
@@ -420,34 +440,36 @@ impl From<IndexingInstruction> for Line {
 impl IndexingInstruction {
     pub fn to_functor(&self) -> MachineStub {
         match self {
-            &IndexingInstruction::SwitchOnTerm(vars, constants, lists, structures) => functor!(
-                "switch_on_term",
-                4,
-                [
-                    heap_integer!(Integer::from(vars)),
-                    heap_integer!(Integer::from(constants)),
-                    heap_integer!(Integer::from(lists)),
-                    heap_integer!(Integer::from(structures))
-                ]
-            ),
-            &IndexingInstruction::SwitchOnConstant(constants, _) => functor!(
-                "switch_on_constant",
-                1,
-                [heap_integer!(Integer::from(constants))]
-            ),
-            &IndexingInstruction::SwitchOnStructure(structures, _) => functor!(
-                "switch_on_structure",
-                1,
-                [heap_integer!(Integer::from(structures))]
-            ),
+            &IndexingInstruction::SwitchOnTerm(vars, constants, lists, structures) => {
+                functor!(
+                    "switch_on_term",
+                    [integer(vars),
+                     integer(constants),
+                     integer(lists),
+                     integer(structures)]
+                )
+            }
+            &IndexingInstruction::SwitchOnConstant(constants, _) => {
+                functor!(
+                    "switch_on_constant",
+                    [integer(constants)]
+                )
+            }
+            &IndexingInstruction::SwitchOnStructure(structures, _) => {
+                functor!(
+                    "switch_on_structure",
+                    [integer(structures)]
+                )
+            }
         }
     }
 }
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub enum FactInstruction {
     GetConstant(Level, Constant, RegType),
     GetList(Level, RegType),
+    GetPartialString(Level, String, RegType, bool),
     GetStructure(ClauseType, usize, RegType),
     GetValue(RegType, usize),
     GetVariable(RegType, usize),
@@ -461,96 +483,106 @@ pub enum FactInstruction {
 impl FactInstruction {
     pub fn to_functor(&self, h: usize) -> MachineStub {
         match self {
-            &FactInstruction::GetConstant(lvl, ref constant, r) => {
-                let mut stub = functor!(
+            &FactInstruction::GetConstant(lvl, ref c, r) => {
+                let lvl_stub = lvl.into_functor();
+                let rt_stub  = reg_type_into_functor(r);
+
+                functor!(
                     "get_constant",
-                    3,
-                    [
-                        heap_str!(h + 4),
-                        heap_con!(constant.clone()),
-                        heap_str!(h + 6)
-                    ]
-                );
-
-                stub.append(&mut lvl.into_functor());
-                stub.append(&mut reg_type_into_functor(r));
-
-                stub
+                    [aux(h, 0), constant(h, c), aux(h, 1)],
+                    [lvl_stub, rt_stub]
+                )
             }
             &FactInstruction::GetList(lvl, r) => {
-                let mut stub = functor!("get_list", 2, [heap_str!(h + 3), heap_str!(h + 5)]);
-                stub.append(&mut lvl.into_functor());
-                stub.append(&mut reg_type_into_functor(r));
+                let lvl_stub = lvl.into_functor();
+                let rt_stub  = reg_type_into_functor(r);
 
-                stub
+                functor!(
+                    "get_list",
+                    [aux(h, 0), aux(h, 1)],
+                    [lvl_stub, rt_stub]
+                )
+            }
+            &FactInstruction::GetPartialString(lvl, ref s, r, has_tail) => {
+                let lvl_stub = lvl.into_functor();
+                let rt_stub  = reg_type_into_functor(r);
+
+                functor!(
+                    "get_partial_string",
+                    [aux(h, 0), string(h, s), aux(h, 1), boolean(has_tail)],
+                    [lvl_stub, rt_stub]
+                )
             }
             &FactInstruction::GetStructure(ref ct, arity, r) => {
-                let mut stub = functor!(
-                    "get_structure",
-                    3,
-                    [
-                        heap_con!(Constant::Atom(ct.name(), None)),
-                        heap_integer!(Integer::from(arity)),
-                        heap_str!(h + 4)
-                    ]
-                );
-                stub.append(&mut reg_type_into_functor(r));
+                let rt_stub = reg_type_into_functor(r);
 
-                stub
+                functor!(
+                    "get_structure",
+                    [clause_name(ct.name()), integer(arity), aux(h, 0)],
+                    [rt_stub]
+                )
             }
             &FactInstruction::GetValue(r, arg) => {
-                let mut stub = functor!(
-                    "get_value",
-                    2,
-                    [heap_str!(h + 3), heap_integer!(Integer::from(arg))]
-                );
-                stub.append(&mut reg_type_into_functor(r));
+                let rt_stub = reg_type_into_functor(r);
 
-                stub
+                functor!(
+                    "get_value",
+                    [aux(h, 0), integer(arg)],
+                    [rt_stub]
+                )
             }
             &FactInstruction::GetVariable(r, arg) => {
-                let mut stub = functor!(
-                    "get_variable",
-                    2,
-                    [heap_str!(h + 3), heap_integer!(Integer::from(arg))]
-                );
-                stub.append(&mut reg_type_into_functor(r));
+                let rt_stub = reg_type_into_functor(r);
 
-                stub
+                functor!(
+                    "get_variable",
+                    [aux(h, 0), integer(arg)],
+                    [rt_stub]
+                )
             }
-            &FactInstruction::UnifyConstant(ref constant) => {
-                functor!("unify_constant", 1, [heap_con!(constant.clone())])
+            &FactInstruction::UnifyConstant(ref c) => {
+                functor!("unify_constant", [constant(h, c)], [])
             }
             &FactInstruction::UnifyLocalValue(r) => {
-                let mut stub = functor!("unify_local_value", 1, [heap_str!(h + 2)]);
-                stub.append(&mut reg_type_into_functor(r));
+                let rt_stub = reg_type_into_functor(r);
 
-                stub
+                functor!(
+                    "unify_local_value",
+                    [aux(h, 0)],
+                    [rt_stub]
+                )
             }
             &FactInstruction::UnifyVariable(r) => {
-                let mut stub = functor!("unify_variable", 1, [heap_str!(h + 2)]);
-                stub.append(&mut reg_type_into_functor(r));
+                let rt_stub = reg_type_into_functor(r);
 
-                stub
+                functor!(
+                    "unify_variable",
+                    [aux(h, 0)],
+                    [rt_stub]
+                )
             }
             &FactInstruction::UnifyValue(r) => {
-                let mut stub = functor!("unify_value", 1, [heap_str!(h + 2)]);
-                stub.append(&mut reg_type_into_functor(r));
+                let rt_stub = reg_type_into_functor(r);
 
-                stub
+                functor!(
+                    "unify_value",
+                    [aux(h, 0)],
+                    [rt_stub]
+                )
             }
             &FactInstruction::UnifyVoid(vars) => {
-                functor!("unify_void", 1, [heap_integer!(Integer::from(vars))])
+                functor!("unify_void", [integer(vars)])
             }
         }
     }
 }
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub enum QueryInstruction {
     GetVariable(RegType, usize),
     PutConstant(Level, Constant, RegType),
     PutList(Level, RegType),
+    PutPartialString(Level, String, RegType, bool),
     PutStructure(ClauseType, usize, RegType),
     PutUnsafeValue(usize, usize),
     PutValue(RegType, usize),
@@ -567,103 +599,106 @@ impl QueryInstruction {
         match self {
             &QueryInstruction::PutUnsafeValue(norm, arg) => functor!(
                 "put_unsafe_value",
-                2,
-                [
-                    heap_integer!(Integer::from(norm)),
-                    heap_integer!(Integer::from(arg))
-                ]
+                [integer(norm), integer(arg)]
             ),
-            &QueryInstruction::PutConstant(lvl, ref constant, r) => {
-                let mut stub = functor!(
+            &QueryInstruction::PutConstant(lvl, ref c, r) => {
+                let lvl_stub = lvl.into_functor();
+                let rt_stub  = reg_type_into_functor(r);
+
+                functor!(
                     "put_constant",
-                    3,
-                    [
-                        heap_str!(h + 4),
-                        heap_con!(constant.clone()),
-                        heap_str!(h + 6)
-                    ]
-                );
-
-                stub.append(&mut lvl.into_functor());
-                stub.append(&mut reg_type_into_functor(r));
-
-                stub
+                    [aux(h, 0), constant(h, c), aux(h, 1)],
+                    [lvl_stub, rt_stub]
+                )
             }
             &QueryInstruction::PutList(lvl, r) => {
-                let mut stub = functor!("put_list", 2, [heap_str!(h + 3), heap_str!(h + 5)]);
+                let lvl_stub = lvl.into_functor();
+                let rt_stub  = reg_type_into_functor(r);
 
-                stub.append(&mut lvl.into_functor());
-                stub.append(&mut reg_type_into_functor(r));
+                functor!(
+                    "put_list",
+                    [aux(h, 0), aux(h, 1)],
+                    [lvl_stub, rt_stub]
+                )
+            }
+            &QueryInstruction::PutPartialString(lvl, ref s, r, has_tail) => {
+                let lvl_stub = lvl.into_functor();
+                let rt_stub  = reg_type_into_functor(r);
 
-                stub
+                functor!(
+                    "put_partial_string",
+                    [aux(h, 0), string(h, s), aux(h, 1), boolean(has_tail)],
+                    [lvl_stub, rt_stub]
+                )
             }
             &QueryInstruction::PutStructure(ref ct, arity, r) => {
-                let mut stub = functor!(
-                    "put_structure",
-                    3,
-                    [
-                        heap_con!(Constant::Atom(ct.name(), None)),
-                        heap_integer!(Integer::from(arity)),
-                        heap_str!(h + 4)
-                    ]
-                );
+                let rt_stub = reg_type_into_functor(r);
 
-                stub.append(&mut reg_type_into_functor(r));
-                stub
+                functor!(
+                    "put_structure",
+                    [clause_name(ct.name()), integer(arity), aux(h, 0)],
+                    [rt_stub]
+                )
             }
             &QueryInstruction::PutValue(r, arg) => {
-                let mut stub = functor!(
-                    "put_value",
-                    2,
-                    [heap_str!(h + 3), heap_integer!(Integer::from(arg))]
-                );
+                let rt_stub = reg_type_into_functor(r);
 
-                stub.append(&mut reg_type_into_functor(r));
-                stub
+                functor!(
+                    "put_value",
+                    [aux(h, 0), integer(arg)],
+                    [rt_stub]
+                )
             }
             &QueryInstruction::GetVariable(r, arg) => {
-                let mut stub = functor!(
-                    "get_variable",
-                    2,
-                    [heap_str!(h + 3), heap_integer!(Integer::from(arg))]
-                );
+                let rt_stub = reg_type_into_functor(r);
 
-                stub.append(&mut reg_type_into_functor(r));
-                stub
+                functor!(
+                    "get_variable",
+                    [aux(h, 0), integer(arg)],
+                    [rt_stub]
+                )
             }
             &QueryInstruction::PutVariable(r, arg) => {
-                let mut stub = functor!(
-                    "put_variable",
-                    2,
-                    [heap_str!(h + 3), heap_integer!(Integer::from(arg))]
-                );
+                let rt_stub = reg_type_into_functor(r);
 
-                stub.append(&mut reg_type_into_functor(r));
-                stub
+                functor!(
+                    "put_variable",
+                    [aux(h, 0), integer(arg)],
+                    [rt_stub]
+                )
             }
-            &QueryInstruction::SetConstant(ref constant) => {
-                functor!("set_constant", 1, [heap_con!(constant.clone())])
+            &QueryInstruction::SetConstant(ref c) => {
+                functor!("set_constant", [constant(h, c)], [])
             }
             &QueryInstruction::SetLocalValue(r) => {
-                let mut stub = functor!("set_local_value", 1, [heap_str!(h + 2)]);
+                let rt_stub = reg_type_into_functor(r);
 
-                stub.append(&mut reg_type_into_functor(r));
-                stub
+                functor!(
+                    "set_local_value",
+                    [aux(h, 0)],
+                    [rt_stub]
+                )
             }
             &QueryInstruction::SetVariable(r) => {
-                let mut stub = functor!("set_variable", 1, [heap_str!(h + 2)]);
+                let rt_stub = reg_type_into_functor(r);
 
-                stub.append(&mut reg_type_into_functor(r));
-                stub
+                functor!(
+                    "set_variable",
+                    [aux(h, 0)],
+                    [rt_stub]
+                )
             }
             &QueryInstruction::SetValue(r) => {
-                let mut stub = functor!("set_value", 1, [heap_str!(h + 2)]);
+                let rt_stub = reg_type_into_functor(r);
 
-                stub.append(&mut reg_type_into_functor(r));
-                stub
+                functor!(
+                    "set_value",
+                    [aux(h, 0)],
+                    [rt_stub]
+                )
             }
             &QueryInstruction::SetVoid(vars) => {
-                functor!("set_void", 1, [heap_integer!(Integer::from(vars))])
+                functor!("set_void", [integer(vars)])
             }
         }
     }

src/iterators.rs

@@ -1,21 +1,23 @@
-use prolog_parser::ast::*;
+use crate::prolog_parser::ast::*;
 
-use crate::prolog::clause_types::*;
-use crate::prolog::forms::*;
-use crate::prolog::machine::machine_indices::*;
+use crate::clause_types::*;
+use crate::forms::*;
+use crate::machine::machine_indices::*;
 
 use std::cell::Cell;
 use std::collections::VecDeque;
+use std::fmt;
 use std::iter::*;
 use std::rc::Rc;
 use std::vec::Vec;
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub 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>>),
+    PartialString(Level, &'a Cell<RegType>, String, Option<&'a Term>),
     Var(Level, &'a Cell<VarReg>, Rc<Var>),
 }
 
@@ -27,10 +29,12 @@ impl<'a> TermRef<'a> {
           | TermRef::Constant(lvl, ..)
           | TermRef::Var(lvl, ..)
           | TermRef::Clause(lvl, ..) => lvl,
+          | TermRef::PartialString(lvl, ..) => lvl,
         }
     }
 }
 
+#[derive(Debug)]
 pub enum TermIterState<'a> {
     AnonVar(Level),
     Constant(Level, &'a Cell<RegType>, &'a Constant),
@@ -43,13 +47,67 @@ pub enum TermIterState<'a> {
     ),
     InitialCons(Level, &'a Cell<RegType>, &'a Term, &'a Term),
     FinalCons(Level, &'a Cell<RegType>, &'a Term, &'a Term),
+    PartialString(Level, &'a Cell<RegType>, String, Option<&'a Term>),
     Var(Level, &'a Cell<VarReg>, Rc<Var>),
 }
 
+fn is_partial_string<'a>(
+    head: &'a Term,
+    mut tail: &'a Term,
+) -> Option<(String, Option<&'a Term>)>
+{
+    let mut string =
+        match head {
+            &Term::Constant(_, Constant::Atom(ref atom, _)) if atom.is_char() => {
+                atom.as_str().chars().next().unwrap().to_string()
+            }
+            &Term::Constant(_, Constant::Char(c)) => {
+                c.to_string()
+            }
+            _ => {
+                return None;
+            }
+        };
+
+    while let Term::Cons(_, ref head, ref succ) = tail {
+        match head.as_ref() {
+            &Term::Constant(_, Constant::Atom(ref atom, _)) if atom.is_char() => {
+                string.push(atom.as_str().chars().next().unwrap());
+            }
+            &Term::Constant(_, Constant::Char(c)) => {
+                string.push(c);
+            }
+            _ => {
+                return None;
+            }
+        };
+
+        tail = succ.as_ref();
+    }
+
+    match tail {
+        Term::AnonVar | Term::Var(..) => {
+            return Some((string, Some(tail)));
+        }
+        Term::Constant(_, Constant::EmptyList) => {
+            return Some((string, None));
+        }
+        Term::Constant(_, Constant::String(tail)) => {
+            string += &tail;
+            return Some((string, None));
+        }
+        _ => {
+            return None;
+        }
+    }
+}
+
 impl<'a> TermIterState<'a> {
     pub fn subterm_to_state(lvl: Level, term: &'a Term) -> TermIterState<'a> {
         match term {
-            &Term::AnonVar => TermIterState::AnonVar(lvl),
+            &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())
@@ -62,12 +120,17 @@ impl<'a> TermIterState<'a> {
             &Term::Cons(ref cell, ref head, ref 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::Constant(ref cell, ref constant) => {
+                TermIterState::Constant(lvl, cell, constant)
+            }
+            &Term::Var(ref cell, ref var) => {
+                TermIterState::Var(lvl, cell, var.clone())
+            }
         }
     }
 }
 
+#[derive(Debug)]
 pub struct QueryIterator<'a> {
     state_stack: Vec<TermIterState<'a>>,
 }
@@ -128,7 +191,7 @@ impl<'a> QueryIterator<'a> {
                 QueryIterator {
                     state_stack: vec![state],
                 }
-            }            
+            }
             &QueryTerm::Clause(ref cell, ref ct, ref terms, _) => {
                 let state = TermIterState::Clause(Level::Root, 0, cell, ct.clone(), terms);
                 QueryIterator {
@@ -169,7 +232,9 @@ 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::AnonVar(lvl) => {
+                    return Some(TermRef::AnonVar(lvl));
+                }
                 TermIterState::Clause(lvl, child_num, cell, ct, child_terms) => {
                     if child_num == child_terms.len() {
                         match ct {
@@ -182,7 +247,9 @@ impl<'a> Iterator for QueryIterator<'a> {
                                     lvl => Some(TermRef::Clause(lvl, cell, ct, child_terms)),
                                 }
                             }
-                            _ => return None,
+                            _ => {
+                                return None;
+                            }
                         };
                     } else {
                         self.state_stack.push(TermIterState::Clause(
@@ -192,23 +259,41 @@ impl<'a> Iterator for QueryIterator<'a> {
                             ct,
                             child_terms,
                         ));
+
                         self.push_subterm(lvl.child_level(), child_terms[child_num].as_ref());
                     }
                 }
                 TermIterState::InitialCons(lvl, cell, head, tail) => {
-                    self.state_stack
-                        .push(TermIterState::FinalCons(lvl, cell, head, tail));
+                    if let Some((string, tail)) = is_partial_string(head, tail) {
+                        self.state_stack.push(TermIterState::PartialString(
+                            lvl,
+                            cell,
+                            string,
+                            tail,
+                        ));
 
-                    self.push_subterm(lvl.child_level(), tail);
-                    self.push_subterm(lvl.child_level(), head);
+                        if let Some(tail) = tail {
+                            self.push_subterm(lvl.child_level(), tail);
+                        }
+                    } else {
+                        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::PartialString(lvl, cell, string, tail) => {
+                    return Some(TermRef::PartialString(lvl, cell, string, tail));
                 }
                 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))
+                    return Some(TermRef::Constant(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)),
             };
         }
 
@@ -216,6 +301,7 @@ impl<'a> Iterator for QueryIterator<'a> {
     }
 }
 
+#[derive(Debug)]
 pub struct FactIterator<'a> {
     state_queue: VecDeque<TermIterState<'a>>,
     iterable_root: bool,
@@ -223,8 +309,7 @@ pub struct FactIterator<'a> {
 
 impl<'a> FactIterator<'a> {
     fn push_subterm(&mut self, lvl: Level, term: &'a Term) {
-        self.state_queue
-            .push_back(TermIterState::subterm_to_state(lvl, term));
+        self.state_queue.push_back(TermIterState::subterm_to_state(lvl, term));
     }
 
     pub fn from_rule_head_clause(terms: &'a Vec<Box<Term>>) -> Self {
@@ -241,7 +326,9 @@ 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::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)]
@@ -273,7 +360,9 @@ 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::AnonVar(lvl) => {
+                    return Some(TermRef::AnonVar(lvl));
+                }
                 TermIterState::Clause(lvl, _, cell, ct, child_terms) => {
                     for child_term in child_terms {
                         self.push_subterm(lvl.child_level(), child_term);
@@ -285,16 +374,27 @@ impl<'a> Iterator for FactIterator<'a> {
                     };
                 }
                 TermIterState::InitialCons(lvl, cell, head, tail) => {
-                    self.push_subterm(Level::Deep, head);
-                    self.push_subterm(Level::Deep, tail);
+                    if let Some((string, tail)) = is_partial_string(head, tail) {
+                        if let Some(tail) = tail {
+                            self.push_subterm(Level::Deep, tail);
+                        }
 
-                    return Some(TermRef::Cons(lvl, cell, head, tail));
+                        return Some(TermRef::PartialString(lvl, cell, string, tail));
+                    } else {
+                        self.push_subterm(Level::Deep, head);
+                        self.push_subterm(Level::Deep, tail);
+
+                        return Some(TermRef::Cons(lvl, cell, head, tail));
+                    }
                 }
                 TermIterState::Constant(lvl, cell, constant) => {
                     return Some(TermRef::Constant(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));
+                }
+                _ => {
+                }
             }
         }
 
@@ -310,6 +410,7 @@ pub fn breadth_first_iter(term: &Term, iterable_root: bool) -> FactIterator {
     FactIterator::new(term, iterable_root)
 }
 
+#[derive(Debug)]
 pub enum ChunkedTerm<'a> {
     HeadClause(ClauseName, &'a Vec<Box<Term>>),
     BodyTerm(&'a QueryTerm),
@@ -347,6 +448,18 @@ pub struct ChunkedIterator<'a> {
     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>);
 

src/lib/arithmetic.pl

@@ -0,0 +1,123 @@
+:- module(arithmetic, [expmod/4, lsb/2, msb/2, number_to_rational/2,
+                       number_to_rational/3,
+                       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
+    ),
+    !.
+
+number(X) :-
+    (   integer(X)
+    ;   float(X)
+    ;   rational(X)
+    ).
+
+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).

src/lib/assoc.pl

@@ -63,12 +63,12 @@ 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, ?, ?).
 */
-					  
+
 %!  empty_assoc(?Assoc) is semidet.
 %
 %   Is true if Assoc is the empty association list.

src/lib/atts.pl

@@ -1,9 +1,10 @@
 :- module(atts, [op(1199, fx, attribute), call_residue_vars/2,
-		 '$absent_attr'/2, '$copy_attr_list'/2, '$get_attr'/2,
-		 '$put_attr'/2, '$absent_from_list'/2,
-		 '$get_from_list'/3, '$add_to_list'/3, '$del_attr'/3,
-		 '$del_attr_step'/3, '$del_attr_buried'/4,
-		 '$default_attr_list'/4]).
+                 term_attributed_variables/2,
+		         '$absent_attr'/2, '$copy_attr_list'/2, '$get_attr'/2,
+		         '$put_attr'/2, '$absent_from_list'/2,
+		         '$get_from_list'/3, '$add_to_list'/3, '$del_attr'/3,
+		         '$del_attr_step'/3, '$del_attr_buried'/4,
+		         '$default_attr_list'/4]).
 
 :- use_module(library(dcgs)).
 :- use_module(library(terms)).
@@ -56,7 +57,8 @@
 '$del_attr'(Ls0, V, Attr) :-
     Ls0 = [Att | Ls1],
     nonvar(Att),
-    (  Att \= Attr -> '$del_attr_buried'(Ls0, Ls1, V, Attr)
+    (  Att \= Attr ->
+       '$del_attr_buried'(Ls0, Ls1, V, Attr)
     ;  '$enqueue_attr_var'(V),
        '$del_attr_head'(V),
        '$del_attr'(Ls1, V, Attr)
@@ -132,11 +134,11 @@ put_attr(Name, Arity) -->
 			    '$put_attr'(V, Attr)),
      (put_atts(V,  Attr) :- !, functor(Attr, Head, Arity),
 			    functor(AttrForm, Head, Arity),
-			    '$get_attr_list'(V, Ls), 
-			    '$del_attr'(Ls, V, AttrForm), 
+			    '$get_attr_list'(V, Ls),
+			    '$del_attr'(Ls, V, AttrForm),
 			    '$put_attr'(V, Attr)),
      (put_atts(V, -Attr) :- !, functor(Attr, _, _),
-			    '$get_attr_list'(V, Ls), 
+			    '$get_attr_list'(V, Ls),
 			    '$del_attr'(Ls, V, Attr))].
 
 get_attr(Name, Arity) -->
@@ -158,4 +160,6 @@ 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

@@ -6,14 +6,13 @@
 :- use_module(library(error)).
 
 between(Lower, Upper, X) :-
-    (  Upper == inf ->
-       must_be(integer, Lower),
-       can_be(integer, X),
-       enumerate_nats(Lower, X)
-    ;  must_be(integer, Lower),
-       must_be(integer, Upper),
-       can_be(integer, X),
-       between_(Lower, Upper, X)
+    must_be(integer, Lower),
+    must_be(integer, Upper),
+    can_be(integer, X),
+    (   nonvar(X) ->
+        Lower =< X,
+        X =< Upper
+    ;   between_(Lower, Upper, X)
     ).
 
 between_(Lower, Upper, Lower) :-

src/lib/builtins.pl

@@ -24,6 +24,8 @@ user:term_expansion((:- op(Pred, Spec, [Op | OtherOps])), OpResults) :-
 :- op(400, yfx, [div, //, rdiv, <<, >>, mod, rem]).
 :- op(200, fy, [+, -, \]).
 
+:- op(1200, xfx, -->).
+
 % arithmetic comparison operators.
 :- op(700, xfx, [>, <, =\=, =:=, >=, =<]).
 
@@ -41,24 +43,35 @@ user:term_expansion((:- op(Pred, Spec, [Op | OtherOps])), OpResults) :-
 :- module(builtins, [(=)/2, (\=)/2, (\+)/1, (',')/2, (->)/2, (;)/2,
                      (=..)/2, (:)/2, (:)/3, (:)/4, (:)/5, (:)/6,
                      (:)/7, (:)/8, (:)/9, (:)/10, (:)/11, (:)/12,
-                     abolish/1, asserta/1, assertz/1, atom_chars/2,
-                     atom_codes/2, atom_concat/3, atom_length/2,
-                     bagof/3, catch/3, char_code/2, clause/2,
-                     current_op/3, current_predicate/1,
-                     current_prolog_flag/2, expand_goal/2,
-                     expand_term/2, fail/0, false/0, findall/3,
-                     findall/4, get_char/1, halt/0, max_arity/1,
-                     number_chars/2, number_codes/2, once/1, op/3,
-                     read_term/2, repeat/0, retract/1,
-                     set_prolog_flag/2, setof/3, sub_atom/5,
+                     abolish/1, asserta/1, assertz/1,
+                     at_end_of_stream/0, at_end_of_stream/1,
+                     atom_chars/2, atom_codes/2, atom_concat/3,
+                     atom_length/2, bagof/3, catch/3, char_code/2,
+                     clause/2, close/1, close/2, current_input/1,
+                     current_output/1, current_op/3,
+                     current_predicate/1, current_prolog_flag/2,
+                     expand_goal/2, expand_term/2, fail/0, false/0,
+                     findall/3, findall/4, flush_output/0,
+                     flush_output/1, get_byte/1, get_byte/2,
+                     get_char/1, get_char/2, get_code/1, get_code/2,
+                     halt/0, halt/1, max_arity/1, number_chars/2,
+                     number_codes/2, once/1, op/3, open/3, open/4,
+                     peek_byte/1, peek_byte/2, peek_char/1,
+                     peek_char/2, peek_code/1, peek_code/2,
+                     put_byte/1, put_byte/2, put_code/1, put_code/2,
+                     put_char/1, put_char/2, read_term/2, read_term/3,
+                     repeat/0, retract/1, set_prolog_flag/2,
+                     set_input/1, set_stream_position/2, set_output/1,
+                     setof/3, stream_property/2, sub_atom/5,
                      subsumes_term/2, term_variables/2, throw/1,
                      true/0, unify_with_occurs_check/2, write/1,
-                     write_canonical/1, write_term/2, writeq/1]).
+                     write_canonical/1, write_term/2, write_term/3,
+                     writeq/1]).
 
 
 % the maximum arity flag. needs to be replaced with
 % current_prolog_flag(max_arity, MAX_ARITY).
-max_arity(255).
+max_arity(1023).
 
 % unify.
 X = X.
@@ -212,18 +225,41 @@ comma_errors(G1, G2, B) :- '$call_with_default_policy'(','(G1, G2, B)).
 
 ;(G1, G2) :- '$get_b_value'(B), ;(G1, G2, B).
 
+:- non_counted_backtracking semicolon_compound_selector/3.
+semicolon_compound_selector(->(G2, G3), G4, B) :-
+    (  call(G2) ->
+       call(G3)
+    ;  '$set_cp'(B),
+       call(G4)
+    ).
+semicolon_compound_selector(','(G2, G3), G4, B) :-
+    (  ','(G2, G3, B)
+    ;  '$set_cp'(B),
+       call(G4)
+    ).
+semicolon_compound_selector(';'(G2, G3), G4, B) :-
+    (  ';'(G2, G3, B)
+    ;  '$set_cp'(B),
+       call(G4)
+    ).
+
 :- non_counted_backtracking (;)/3.
-;(G1, G4, B) :- compound(G1),
-		'$call_with_default_policy'(G1 = ->(G2, G3)),
-		!,
-		(  call(G2) -> call(G3)
-		;  '$set_cp'(B),
-		   call(G4)
-		).
-;(G1, G2, B) :- G1 == !, '$set_cp'(B), call(G2).
-;(G1, G2, B) :- G2 == !, call(G1), '$set_cp'(B).
-;(G, _, _) :- call(G).
-;(_, G, _) :- call(G).
+;(G1, G4, B) :-
+    ( (  G1 = (_ -> _)
+      ;  G1 = (_ , _)
+      ;  G1 = (_ ; _)
+      ) ->
+      !,
+      semicolon_compound_selector(G1, G4, B)
+    ).
+;(G1, G2, B) :-
+    G1 == !, !, '$set_cp'(B), call(G2).
+;(G1, G2, B) :-
+    G2 == !, !, call(G1), '$set_cp'(B).
+;(G, _, _) :-
+    call(G).
+;(_, G, _) :-
+    call(G).
 
 G1 -> G2 :- '$get_b_value'(B), '$call_with_default_policy'(->(G1, G2, B)).
 
@@ -261,8 +297,11 @@ univ_errors(Term, List, N) :-
 Term =.. List :- '$call_with_default_policy'(univ_errors(Term, List, N)),
 		 '$call_with_default_policy'(univ_worker(Term, List, N)).
 
+
 :- non_counted_backtracking univ_worker/3.
-univ_worker(Term, List, _) :- atomic(Term), !, '$call_with_default_policy'(List = [Term]).
+
+univ_worker(Term, List, _) :-
+    atomic(Term), !, '$call_with_default_policy'(List = [Term]).
 univ_worker(Term, [Name|Args], N) :-
     var(Term), !,
     '$call_with_default_policy'(Arity is N-1),
@@ -273,7 +312,9 @@ univ_worker(Term, List, _) :-
     '$call_with_default_policy'(get_args(Args, Term, 1, Arity)),
     '$call_with_default_policy'(List = [Name|Args]).
 
+
 :- non_counted_backtracking get_args/4.
+
 get_args(Args, _, _, 0) :-
     !, '$call_with_default_policy'(Args = []).
 get_args([Arg], Func, N, N) :-
@@ -283,34 +324,39 @@ get_args([Arg|Args], Func, I0, N) :-
     '$call_with_default_policy'(I1 is I0 + 1),
     '$call_with_default_policy'(get_args(Args, Func, I1, N)).
 
-% write, write_canonical, writeq, write_term.
-is_write_option(Functor) :-
-    Functor =.. [Name, Arg],
-    ( Arg == true -> true
-    ; Arg == false -> true
-    ; Name == variable_names -> must_be_var_names_list(Arg)
-    ; var(Arg) -> throw(error(instantiation_error, write_term/2))
-    ; throw(error(domain_error(write_option, Functor), write_term/2))
-    ), % 8.14.2.3 e)
-    ( Name == ignore_ops -> true
-    ; Name == quoted -> true
-    ; Name == numbervars -> true
-    ; Name == variable_names -> true
-    ; throw(error(domain_error(write_option, Functor), write_term/2))
-    ). % 8.14.2.3 e)
+parse_write_options(Options, OptionValues, Stub) :-
+    DefaultOptions = [ignore_ops-false, max_depth-0, numbervars-false,
+                      quoted-false, variable_names-[]],
+    parse_options_list(Options, parse_write_options_, DefaultOptions, OptionValues, Stub).
 
-inst_member_or([X|Xs], Y, Z) :-
-    (  var(X) -> throw(error(instantiation_error, write_term/2))
-    ;  is_write_option(X) -> ( Y = X, ! ; inst_member_or(Xs, Y, Z) )
-    ;  throw(error(domain_error(write_option, X), write_term/2))
+parse_write_options_(ignore_ops(IgnoreOps), ignore_ops-IgnoreOps) :-
+    (  nonvar(IgnoreOps), lists:member(IgnoreOps, [true, false])
+    ;
+       throw(error(domain_error(write_option, ignore_ops(IgnoreOps)), _))
+    ).
+parse_write_options_(quoted(Quoted), quoted-Quoted) :-
+    (  nonvar(Quoted), lists:member(Quoted, [true, false])
+    ;
+       throw(error(domain_error(write_option, quoted(Quoted)), _))
+    ).
+parse_write_options_(numbervars(NumberVars), numbervars-NumberVars) :-
+    (  nonvar(NumberVars), lists:member(NumberVars, [true, false])
+    ;
+       throw(error(domain_error(write_option, numbervars(NumberVars)), _))
+    ).
+parse_write_options_(variable_names(VNNames), variable_names-VNNames) :-
+    must_be_var_names_list(VNNames).
+parse_write_options_(max_depth(MaxDepth), max_depth-MaxDepth) :-
+    (  integer(MaxDepth), MaxDepth >= 0
+    ;
+       throw(error(domain_error(write_option, max_depth(MaxDepth)), _))
     ).
-inst_member_or([], Y, Y).
 
 must_be_var_names_list(VarNames) :-
     '$skip_max_list'(_, -1, VarNames, Tail),
     (  Tail == [] -> must_be_var_names_list_(VarNames, VarNames)
     ;  var(Tail)  -> throw(error(instantiation_error, write_term/2))
-    ;  throw(error(domain_error(write_options, variable_names(VarNames)), write_term/2))
+    ;  throw(error(domain_error(write_option, variable_names(VarNames)), write_term/2))
     ).
 
 must_be_var_names_list_([], List).
@@ -319,44 +365,90 @@ must_be_var_names_list_([VarName | VarNames], List) :-
        (  VarName = (Atom = _) ->
 	      (  atom(Atom) -> must_be_var_names_list_(VarNames, List)
 	      ;  var(Atom)  -> throw(error(instantiation_error, write_term/2))
-	      ;  throw(error(domain_error(write_options, variable_names(List)), write_term/2))
+	      ;  throw(error(domain_error(write_option, variable_names(List)), write_term/2))
 	      )
-       ;  throw(error(domain_error(write_options, variable_names(List)), write_term/2))
+       ;  throw(error(domain_error(write_option, variable_names(List)), write_term/2))
        )
-    ;  throw(error(instantiation_error, write_term/2)) % throw(error(domain_error(write_options, variable_names(List)), write_term/2))
+    ;  throw(error(instantiation_error, write_term/2))
     ).
 
-write_term(_, Options) :-
-    var(Options), throw(error(instantiation_error, write_term/2)).
+
 write_term(Term, Options) :-
-    '$skip_max_list'(_, -1, Options, Options0),
-    (  var(Options0)  -> throw(error(instantiation_error, write_term/2))
-    ;  Options0 == [] -> true
-    ;  throw(error(type_error(list, Options), write_term/2))
-    ), % 8.14.2.3 c)
-    inst_member_or(Options, ignore_ops(IgnoreOps), ignore_ops(false)),
-    inst_member_or(Options, numbervars(NumberVars), numbervars(false)),
-    inst_member_or(Options, quoted(Quoted), quoted(false)),
-    inst_member_or(Options, variable_names(VarNames), variable_names([])),
-    '$write_term'(Term, IgnoreOps, NumberVars, Quoted, VarNames).
+    current_output(Stream),
+    write_term(Stream, Term, Options).
 
-write(Term) :- write_term(Term, [numbervars(true)]).
+write_term(Stream, Term, Options) :-
+    parse_write_options(Options, [IgnoreOps, MaxDepth, NumberVars, Quoted, VNNames], write_term/3),
+    '$write_term'(Stream, Term, IgnoreOps, NumberVars, Quoted, VNNames, MaxDepth).
 
-write_canonical(Term) :- write_term(Term, [ignore_ops(true), quoted(true)]).
 
-writeq(Term) :- write_term(Term, [quoted(true), numbervars(true)]).
+write(Term) :-
+    current_output(Stream),
+    '$write_term'(Stream, Term, false, true, false, [], 0).
 
-%% TODO: complete the predicate! Most read options are missing.
-read_term(Term, Options) :-
-    '$skip_max_list'(_, -1, Options, Options0),
-    (  Options0 == [] -> true
-    ;  var(Options0)  -> throw(error(instantiation_error, read_term/2)) % 8.14.1.3 b)
-    ;  throw(error(type_error(list, Options), read_term/2)) % 8.14.1.3 d)
-    ),
-    (  Options = [variable_names(VarList)] -> '$read_term'(Term, VarList)
-    ;  Options = [] -> read(Term)
-    ;  false
+write_canonical(Term) :-
+    current_output(Stream),
+    '$write_term'(Stream, Term, true, false, true, [], 0).
+
+writeq(Term) :-
+    current_output(Stream),
+    '$write_term'(Stream, Term, false, true, true, [], 0).
+
+
+
+select_rightmost_options([Option-Value | OptionPairs], OptionValues) :-
+    (  pairs:same_key(Option, OptionPairs, OtherValues, _),
+       OtherValues == []  ->
+       OptionValues = [Value | OptionValues0],
+       select_rightmost_options(OptionPairs, OptionValues0)
+    ;
+       select_rightmost_options(OptionPairs, OptionValues)
     ).
+select_rightmost_options([], []).
+
+
+parse_options_list(Options, Selector, DefaultPairs, OptionValues, Stub) :-
+    '$skip_max_list'(_, -1, Options, Tail),
+    (  Tail == [] ->
+       true
+    ;  var(Tail) ->
+       throw(error(instantiation_error, Stub))       % 8.11.5.3c)
+    ;  Tail \== [] ->
+       throw(error(type_error(list, Options), Stub)) % 8.11.5.3e)
+    ),
+    (  lists:maplist(nonvar, Options),
+       catch(lists:maplist(Selector, Options, OptionPairs0),
+             error(E, _),
+             throw(error(E, Stub))) ->
+       lists:append(DefaultPairs, OptionPairs0, OptionPairs1),
+       keysort(OptionPairs1, OptionPairs),
+       select_rightmost_options(OptionPairs, OptionValues)
+    ;
+       throw(error(instantiation_error, Stub))       % 8.11.5.3c)
+    ).
+
+
+parse_read_term_options(Options, OptionValues, Stub) :-
+    DefaultOptions = [singletons-_, variables-_, variable_names-_],
+    parse_options_list(Options, parse_read_term_options_, DefaultOptions, OptionValues, Stub).
+
+
+parse_read_term_options_(singletons(Vars), singletons-Vars).
+parse_read_term_options_(variables(Vars), variables-Vars).
+parse_read_term_options_(variable_names(Vars), variable_names-Vars).
+parse_read_term_options_(E,_) :-
+    throw(error(domain_error(read_option, E), _)).
+
+
+
+read_term(Stream, Term, Options) :-
+    parse_read_term_options(Options, [Singletons, VariableNames, Variables], read_term/3),
+    '$read_term'(Stream, Term, Singletons, Variables, VariableNames).
+
+read_term(Term, Options) :-
+    current_input(Stream),
+    read_term(Stream, Term, Options).
+
 
 % expand_goal.
 
@@ -448,7 +540,7 @@ set_difference([], _, []) :- !.
 set_difference(Xs, [], Xs).
 
 group_by_variant([V2-S2 | Pairs], V1-S1, [S2 | Solutions], Pairs0) :-
-    non_iso:variant(V1, V2), !, V1 = V2, group_by_variant(Pairs, V2-S2, Solutions, Pairs0).
+    iso_ext:variant(V1, V2), !, V1 = V2, group_by_variant(Pairs, V2-S2, Solutions, Pairs0).
 group_by_variant(Pairs, _, [], Pairs).
 
 group_by_variants([V-S|Pairs], [V-Solution|Solutions]) :-
@@ -456,7 +548,10 @@ group_by_variants([V-S|Pairs], [V-Solution|Solutions]) :-
     group_by_variants(Pairs0, Solutions).
 group_by_variants([], []).
 
-iterate_variants([V-Solution|GroupSolutions], V, Solution).
+iterate_variants([V-Solution|GroupSolutions], V, Solution) :-
+    (  GroupSolutions == [] -> !
+    ;  true
+    ).
 iterate_variants([_|GroupSolutions], Ws, Solution) :-
     iterate_variants(GroupSolutions, Ws, Solution).
 
@@ -472,7 +567,9 @@ findall_with_existential(Template, Goal, PairedSolutions, Witnesses0, Witnesses)
     (  nonvar(Goal), Goal = _ ^ _ ->
        rightmost_power(Goal, Goal1, ExistentialVars0),
        term_variables(ExistentialVars0, ExistentialVars),
-       set_difference(Witnesses0, ExistentialVars, Witnesses),
+       sort(Witnesses0, Witnesses1),
+       sort(ExistentialVars, ExistentialVars1),
+       set_difference(Witnesses1, ExistentialVars1, Witnesses),
        findall(Witnesses-Template, Goal1, PairedSolutions)
     ;  Witnesses = Witnesses0,
        findall(Witnesses-Template, Goal, PairedSolutions)
@@ -491,7 +588,10 @@ bagof(Template, Goal, Solution) :-
     iterate_variants(GroupedSolutions, Witnesses, Solution).
 
 iterate_variants_and_sort([V-Solution0|GroupSolutions], V, Solution) :-
-    sort(Solution0, Solution).
+    sort(Solution0, Solution),
+    (  GroupSolutions == [] -> !
+    ;  true
+    ).
 iterate_variants_and_sort([_|GroupSolutions], Ws, Solution) :-
     iterate_variants_and_sort(GroupSolutions, Ws, Solution).
 
@@ -531,18 +631,19 @@ setof(Template, Goal, Solution) :-
 
 clause(H, B) :-
     (  var(H) -> throw(error(instantiation_error, clause/2))
-    ;  functor(H, Name, Arity) -> (  Name == '.' -> throw(error(type_error(callable, H), clause/2))
-				  ;  Name == (:), Arity =:= 2 ->
-				     arg(1, H, Module),
-				     arg(2, H, F),
-				     '$module_clause'(F, B, Module)
-				  %% '$no_such_predicate' fails if H is not callable.
-				  ;  '$no_such_predicate'(H) -> '$fail'
-				  ;  '$head_is_dynamic'(H) -> '$clause_body_is_valid'(B),
-							      '$get_clause'(H, B)
-				  ;  throw(error(permission_error(access, private_procedure, Name/Arity),
-						 clause/2))
-				  )
+    ;  functor(H, Name, Arity) ->
+       (  Name == '.' -> throw(error(type_error(callable, H), clause/2))
+	   ;  Name == (:), Arity =:= 2 ->
+		  arg(1, H, Module),
+		  arg(2, H, F),
+		  '$module_clause'(F, B, Module)
+	   %% '$no_such_predicate' fails if H is not callable.
+	   ;  '$no_such_predicate'(H) -> '$fail'
+	   ;  '$head_is_dynamic'(H) -> '$clause_body_is_valid'(B),
+							       '$get_clause'(H, B)
+	   ;  throw(error(permission_error(access, private_procedure, Name/Arity),
+					  clause/2))
+	   )
     ;  throw(error(type_error(callable, H), clause/2))
     ).
 
@@ -813,7 +914,14 @@ op(Priority, OpSpec, Op) :-
     ;  throw(error(type_error(list, Op), op/3)) % 8.14.3.3 f)
     ).
 
-halt :- '$halt'.
+
+halt :- halt(0).
+
+halt(N) :-
+        (   -2^31 =< N, N =< 2^31 - 1 ->
+            '$halt'(N)
+        ;   throw(error(domain_error(exit_code, N), halt/1))
+        ).
 
 atom_length(Atom, Length) :-
     (  var(Atom)  -> throw(error(instantiation_error, atom_length/2)) % 8.16.1.3 a)
@@ -833,10 +941,10 @@ atom_chars(Atom, List) :-
     ),
     (  var(Atom) ->
        (  var(Tail) -> throw(error(instantiation_error, atom_chars/2))
-       ;  ground(List), Tail == [] -> '$atom_chars'(Atom, List)
+       ;  ground(List) -> '$atom_chars'(Atom, List)
        ;  throw(error(instantiation_error, atom_chars/2))
        )
-    ;  atom(Atom) -> can_be_chars_or_vars(List, atom_chars/2), '$atom_chars'(Atom, List)
+    ;  atom(Atom) -> '$atom_chars'(Atom, List)
     ;  throw(error(type_error(atom, Atom), atom_chars/2))
     ).
 
@@ -850,7 +958,7 @@ atom_codes(Atom, List) :-
        ;  ground(List), Tail == [] -> '$atom_codes'(Atom, List)
        ;  throw(error(instantiation_error, atom_codes/2))
        )
-    ;  atom(Atom) -> can_be_codes_or_vars(List, atom_codes/2), '$atom_codes'(Atom, List)
+    ;  atom(Atom) -> '$atom_codes'(Atom, List)
     ;  throw(error(type_error(atom, Atom), atom_codes/2))
     ).
 
@@ -907,11 +1015,11 @@ char_code(Char, Code) :-
     ).
 
 get_char(C) :-
-    (  var(C) -> '$get_char'(C)
-    ;  C == end_of_file  -> '$get_char'(C)
-    ;  atom_length(C, 1) -> '$get_char'(C)
-    ;  throw(error(type_error(in_character, C), get_char/1))
-    ).
+    current_input(S),
+    '$get_char'(S, C).
+
+get_char(S, C) :-
+    '$get_char'(S, C).
 
 can_be_number(N, PI) :-
     (  var(N) -> true
@@ -928,45 +1036,6 @@ must_be_number(N, PI) :-
     ;  throw(error(instantiation_error, PI))
     ).
 
-can_be_chars_or_vars(Cs, _)  :- var(Cs), !.
-can_be_chars_or_vars(Cs, PI) :-
-    (  string(Cs) ->
-       current_prolog_flag(double_quotes, chars)
-    ;  chars_or_vars(Cs, PI)
-    ).
-
-chars_or_vars([], _).
-chars_or_vars([C|Cs], PI) :-
-    (  nonvar(C) ->
-       (  catch(atom_length(C, 1), _, false) ->
-	  (  nonvar(Cs) -> chars_or_vars(Cs, PI)
-	  ;  false
-	  )
-       ;  throw(error(type_error(character, C), PI))
-       )
-    ;  chars_or_vars(Cs, PI)
-    ).
-
-can_be_codes_or_vars(Cs, _)  :- var(Cs), !.
-can_be_codes_or_vars(Cs, PI) :- 
-    (  string(Cs) ->
-       current_prolog_flag(double_quotes, codes)
-    ;  codes_or_vars(Cs, PI)
-    ).
-
-codes_or_vars([], _).
-codes_or_vars([C|Cs], PI) :-
-    (  nonvar(C) ->
-       (  catch(char_code(_, C), _, false) ->
-	  (  nonvar(Cs) -> codes_or_vars(Cs, PI)
-	  ;  false
-	  )
-       ;  integer(C) -> throw(error(representation_error(character_code), PI))
-       ;  throw(error(type_error(integer, C), PI))
-       )
-    ;  codes_or_vars(Cs, PI)
-    ).
-
 number_chars(N, Chs) :-
    (  ground(Chs)
    -> can_be_number(N, number_chars/2),
@@ -1006,3 +1075,226 @@ subsumes_term(General, Specific) :-
    ).
 
 unify_with_occurs_check(X, Y) :- '$unify_with_occurs_check'(X, Y).
+
+current_input(S) :- '$current_input'(S).
+
+current_output(S) :- '$current_output'(S).
+
+set_input(S) :-
+    (  var(S) ->
+       throw(error(instantiation_error, set_input/1))
+    ;  '$set_input'(S)
+    ).
+
+set_output(S) :-
+    (  var(S) ->
+       throw(error(instantiation_error, set_output/1))
+    ;  '$set_output'(S)
+    ).
+
+
+parse_stream_options(Options, OptionValues, Stub) :-
+    DefaultOptions = [alias-[], eof_action-eof_code, reposition-false, type-text],
+    parse_options_list(Options, parse_stream_options_, DefaultOptions, OptionValues, Stub).
+
+
+parse_stream_options_(type(Type), type-Type) :-
+    (  nonvar(Type), lists:member(Type, [text, binary]), !, true
+    ;
+       throw(error(domain_error(stream_option, type(Type)), _))
+    ).
+parse_stream_options_(reposition(Bool), reposition-Bool) :-
+    (  nonvar(Bool), lists:member(Bool, [true, false]), !, true
+    ;
+       throw(error(domain_error(stream_option, reposition(Bool)), _))
+    ).
+parse_stream_options_(alias(A), alias-A) :-
+    (  atom(A), A \== [], !, true
+    ;
+       throw(error(domain_error(stream_option, alias(A)), _))
+    ).
+parse_stream_options_(eof_action(Action), eof_action-Action) :-
+    (  nonvar(Action), lists:member(Action, [eof_code, error, reset]), !, true
+    ;
+       throw(error(domain_error(stream_option, eof_action(Action)), _))
+    ).
+parse_stream_options_(E, _) :-
+    throw(error(domain_error(stream_option, E), _)). % 8.11.5.3i)
+
+
+open(SourceSink, Mode, Stream) :-
+    open(SourceSink, Mode, Stream, []).
+
+open(SourceSink, Mode, Stream, StreamOptions) :-
+    (  var(SourceSink) ->
+       throw(error(instantiation_error, open/4)) % 8.11.5.3a)
+    ;  var(Mode) ->
+       throw(error(instantiation_error, open/4)) % 8.11.5.3b)
+    ;  \+ atom(Mode) ->
+       throw(error(type_error(atom, Mode), open/4)) % 8.11.5.3d)
+    ;  nonvar(Stream) ->
+       throw(error(type_error(variable, Stream), open/4)) % 8.11.5.3f)
+    ;
+       parse_stream_options(StreamOptions, [Alias, EOFAction, Reposition, Type], open/4),
+       '$open'(SourceSink, Mode, Stream, Alias, EOFAction, Reposition, Type)
+    ).
+
+
+parse_close_options(Options, OptionValues, Stub) :-
+    DefaultOptions = [force-false],
+    parse_options_list(Options, parse_close_options_, DefaultOptions, OptionValues, Stub).
+
+parse_close_options_(force(Force), force-Force) :-
+    (  nonvar(Force), lists:member(Force, [true, false]), !
+    ;
+       throw(error(domain_error(close_option, force(Force)), _))
+    ).
+parse_close_options_(E, _) :-
+    throw(error(domain_error(close_option, E), _)).
+
+
+close(Stream, CloseOptions) :-
+    parse_close_options(CloseOptions, [Force], close/2),
+    '$close'(Stream, CloseOptions).
+
+close(Stream) :-
+    '$close'(Stream, []).
+
+
+flush_output(S) :-
+    '$flush_output'(S).
+
+flush_output :-
+    current_output(S),
+    '$flush_output'(S).
+
+
+get_byte(S, B) :-
+    '$get_byte'(S, B).
+
+get_byte(B) :-
+    current_input(S),
+    '$get_byte'(S, B).
+
+
+put_char(C) :-
+    current_output(S),
+    '$put_char'(S, C).
+
+put_char(S, C) :-
+    '$put_char'(S, C).
+
+
+put_byte(C) :-
+    current_output(S),
+    '$put_byte'(S, C).
+
+put_byte(S, C) :-
+    '$put_byte'(S, C).
+
+
+put_code(C) :-
+    current_output(S),
+    '$put_code'(S, C).
+
+put_code(S, C) :-
+    '$put_code'(S, C).
+
+
+get_code(C) :-
+    current_input(S),
+    '$get_code'(S, C).
+
+get_code(S, C) :-
+    '$get_code'(S, C).
+
+
+peek_byte(S, B) :-
+    '$peek_byte'(S, B).
+
+peek_byte(B) :-
+    current_input(S),
+    '$peek_byte'(S, B).
+
+
+peek_code(C) :-
+    current_input(S),
+    '$peek_code'(S, C).
+
+peek_code(S, C) :-
+    '$peek_code'(S, C).
+
+
+peek_char(C) :-
+    current_input(S),
+    '$peek_char'(S, C).
+
+peek_char(S, C) :-
+    '$peek_char'(S, C).
+
+
+check_stream_property(file_name(F), file_name, F) :-
+    ( var(F) -> true ; atom(F) ).
+check_stream_property(mode(M), mode, M) :-
+    ( var(M) -> true ; lists:member(M, [read, write, append]) ).
+check_stream_property(D, direction, D) :-
+    ( var(D) -> true ; lists:member(D, [input, output, input_output]), ! ).
+check_stream_property(alias(A), alias, A) :-
+    ( var(A) -> true ; atom(A) ).
+check_stream_property(position(P), position, P) :-
+    ( var(P) -> true ; integer(P), P >= 0 ).
+check_stream_property(end_of_stream(E), end_of_stream, E) :-
+    ( var(E) -> true ; lists:member(E, [not, at, past]) ).
+check_stream_property(eof_action(A), eof_action, A) :-
+    ( var(A) -> true ; lists:member(A, [error, eof_code, reset]) ).
+check_stream_property(reposition(B), reposition, B) :-
+    ( var(B) -> true ; lists:member(B, [true, false]) ).
+check_stream_property(type(T), type, T) :-
+    ( var(T) -> true ; lists:member(T, [text, binary]) ).
+
+
+stream_iter_(S, S).
+stream_iter_(S, S1) :-
+    '$next_stream'(S, S0),
+    stream_iter_(S0, S1).
+
+stream_iter(S) :-
+    (  nonvar(S) ->
+       true
+    ;  '$first_stream'(S0),
+       stream_iter_(S0, S)
+    ).
+
+
+stream_property(S, P) :-
+    (  nonvar(P), \+ check_stream_property(P, _, _) ->
+       throw(error(domain_error(stream_property, P), stream_property/2))
+    ;  stream_iter(S),
+       check_stream_property(P, PropertyName, PropertyValue),
+       '$stream_property'(S, PropertyName, PropertyValue)
+    ).
+
+
+at_end_of_stream(S_or_a) :-
+    (  atom(S_or_a) ->
+       stream_property(S, alias(S_or_a))
+    ;  S = S_or_a
+    ),
+    stream_property(S, end_of_stream(E)),
+    ( E = at -> true ; E = past ).
+
+at_end_of_stream :-
+    current_input(S),
+    stream_property(S, end_of_stream(E)),
+    !,
+    ( E = at ; E = past ).
+
+
+set_stream_position(S_or_a, Position) :-
+    (  var(Position) ->
+       throw(error(instantiation_error, set_stream_position/2))
+    ;  integer(Position), Position >= 0 ->
+       true
+    ;  throw(error(domain_error(stream_position, Position)))
+    ),
+    '$set_stream_position'(S_or_a, Position).

src/lib/charsio.pl

@@ -0,0 +1,242 @@
+:- module(charsio, [char_type/2,
+                    chars_utf8bytes/2,
+                    get_single_char/1,
+                    read_line_to_chars/3,
+                    read_term_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)).
+
+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_([], _, VarList, [], _).
+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) :-
+    (   var(Char) -> instantiation_error(char_type/2)
+    ;   atom_length(Char, 1) ->
+        (   ground(Type) ->
+            (   ctype(Type) ->
+                '$char_type'(Char, Type)
+            ;   domain_error(char_type, Type, char_type/2)
+            )
+        ;   ctype(Type),
+            '$char_type'(Char, Type)
+        )
+    ;   type_error(in_character, Char, char_type/2)
+    ).
+
+
+ctype(alnum).
+ctype(alpha).
+ctype(alphabetic).
+ctype(ascii).
+ctype(ascii_graphic).
+ctype(ascii_punctuation).
+ctype(binary_digit).
+ctype(control).
+ctype(decimal_digit).
+ctype(exponent).
+ctype(graphic).
+ctype(hexadecimal_digit).
+ctype(layout).
+ctype(lower).
+ctype(meta).
+ctype(numeric).
+ctype(octal_digit).
+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_term_from_chars(Chars, Term) :-
+    (  var(Chars) ->
+       instantiation_error(read_term_from_chars/2)
+    ;  nonvar(Term) ->
+       throw(error(uninstantiation_error(Term), read_term_from_chars/2))
+    ;  '$skip_max_list'(_, -1, Chars, Chars0),
+       Chars0 == [],
+       partial_string(Chars) ->
+       true
+    ;
+       type_error(complete_string, Chars, read_term_from_chars/2)
+    ),
+    '$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)
+            )
+        ).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   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="
+      ;  false.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+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(list, Bs),
+            maplist(must_be(character), Bs),
+            '$chars_base64'(Cs, Bs, Padding, Charset)
+        ;   must_be(list, Cs),
+            maplist(must_be(character), Cs),
+            '$chars_base64'(Cs, Bs, Padding, Charset)
+        ).

src/lib/clpb.pl

@@ -30,9 +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,
@@ -96,75 +98,14 @@ 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].
 
@@ -728,10 +669,6 @@ 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),
@@ -1157,7 +1094,7 @@ labeling_var(V) :- V == 1, !.
 labeling_var(V) :- domain_error(clpb_variable, V).
 
 variables_in_index_order(Vs0, Vs) :-
-        maplist(var_with_index, Vs0, IVs0),	
+        maplist(var_with_index, Vs0, IVs0),
         keysort(IVs0, IVs),
         pairs_values(IVs, Vs).
 
@@ -1184,7 +1121,7 @@ indomain(1).
 % Examples:
 %
 % ==
-% ?- sat(A =< B), Vs = [A,B], sat_count(+[1|Vs], Count). 
+% ?- sat(A =< B), Vs = [A,B], sat_count(+[1|Vs], Count).
 % Vs = [A, B],
 % Count = 3,
 % sat(A=:=A*B).
@@ -1506,7 +1443,7 @@ max_variable_node(Node, V0-N0, V-N) :-
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
 ands_fusion(Ands0, Ands) :-
-        maplist(with_variables, Ands0, Pairs0),	
+        maplist(with_variables, Ands0, Pairs0),
         keysort(Pairs0, Pairs),
         group_pairs_by_key(Pairs, Groups),
         pairs_values(Groups, Andss),

src/lib/cont.pl

@@ -1,4 +1,3 @@
-
 :- module(cont, [reset/3, shift/1]).
 
 reset(Goal, Ball, Cont) :-
@@ -7,14 +6,14 @@ reset(Goal, Ball, Cont) :-
     '$bind_from_register'(Cont, 3),
     '$bind_from_register'(Ball, 4).
 
-shift(Term) :-
+shift(Ball) :-
     '$nextEP'(first, E, P),
     get_chunks(E, P, L),
     (  L == [] ->
-       Cont = none
+       Cont = cont(true)
     ;  Cont = cont(call_continuation(L))
     ),
-    '$write_cont_and_term'(_, _, Cont, Term),
+    '$write_cont_and_term'(_, _, Cont, Ball),
     '$unwind_environments'.
 
 get_chunks(E, P, L) :-

src/lib/crypto.pl

@@ -0,0 +1,826 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written May 2020 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 as 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)).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   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]
+   ;  false.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+
+hex_bytes(Hs, Bytes) :-
+        (   ground(Hs) ->
+            must_be(list, Hs),
+            maplist(must_be(atom), 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_byte_chars(Chars, Context) :-
+        must_be(list, Chars),
+        (   member(Char, Chars),
+            char_code(Char, Code),
+            \+ between(0, 255, Code) ->
+            domain_error(byte_char, Char, 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) :- '$crypto_random_byte'(B).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Hashing
+   =======
+
+   crypto_data_hash(+Data, -Hash, +Options)
+
+   Where Data is a list of characters, and Hash is the computed hash
+   as a list of hexadecimal characters.
+
+   Options is a list of:
+
+     - algorithm(+A)
+       where A is one of ripemd160, sha256, sha384, sha512, sha512_256,
+       sha3_224, sha3_256, sha3_384, sha3_512, blake2s256, blake2b512,
+       or a variable. If A is a variable, then it is unified with the
+       default algorithm, which is an algorithm that is considered
+       cryptographically secure at the time of this writing.
+     - encoding(+Encoding)
+       The default encoding is utf8. The alternative is octet,
+       to treat the input as a list of raw bytes.
+
+   Example:
+
+   ?- crypto_data_hash("abc", Hs, [algorithm(sha256)]).
+      Hs = "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
+   ;  false.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   SHA256 is the current default for several hash-related predicates.
+   It is deemed sufficiently secure for the foreseeable future.  Yet,
+   application programmers must be aware that the default may change in
+   future versions. The hash predicates all yield the algorithm they
+   used if a Prolog variable is used for the pertaining option.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+crypto_data_hash(Data0, Hash, Options0) :-
+        must_be(list, Options0),
+        options_data_chars(Options0, Data0, Data, Encoding),
+        functor_hash_options(algorithm, A, Options0, _),
+        (   hash_algorithm(A) -> true
+        ;   domain_error(hash_algorithm, A, crypto_data_hash/3)
+        ),
+        '$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 is 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.
+
+   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
+        ),
+        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)
+        ),
+        '$crypto_data_encrypt'(PlainText, Encoding, Key, IV, Tag, CipherText).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+  crypto_data_decrypt(+CipherText,
+                      +Algorithm,
+                      +Key,
+                      +IV,
+                      -PlainText,
+                      +Options).
+
+   Decrypt the given CipherText, using the symmetric algorithm
+   Algorithm, key Key, and initialization vector IV, to give
+   PlainText. CipherText must be a list of characters, and Key and IV
+   must be lists of bytes. PlainText is created as a list of
+   characters.
+
+   Currently, the only supported algorithm is 'chacha20-poly1305',
+   a very secure, fast and versatile authenticated encryption method.
+
+   Options is a list of:
+
+    - encoding(+Encoding)
+    Encoding to use for PlainText. The default is utf8. The
+    alternative is octet, which is used if the data are raw bytes.
+
+    - tag(+Tag)
+    For authenticated encryption schemes, the tag must be specified as
+    a list of bytes exactly as they were generated upon encryption.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+crypto_data_decrypt(CipherText0, Algorithm, Key, IV, PlainText, Options) :-
+        option(tag(Tag), Options, []),
+        must_be_bytes(Tag, crypto_data_decrypt/6),
+        must_be_bytes(Key, crypto_data_decrypt/6),
+        must_be_bytes(IV, crypto_data_decrypt/6),
+        must_be(atom, Algorithm),
+        option(encoding(Encoding), Options, utf8),
+        must_be(atom, Encoding),
+        member(Encoding, [utf8,octet]),
+        must_be(list, CipherText0),
+        encoding_chars(octet, CipherText0, CipherText1),
+        maplist(char_code, TagChars, Tag),
+        append(CipherText1, TagChars, CipherText),
+        (   Algorithm = 'chacha20-poly1305' -> true
+        ;   domain_error('chacha20-poly1305', Algorithm, crypto_data_decrypt/6)
+        ),
+        '$crypto_data_decrypt'(CipherText, octet, 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_byte_chars(Cs, crypto_encoding).
+encoding_chars(utf8, Cs, Cs) :-
+        must_be(list, Cs),
+        maplist(must_be(character), 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) :-
+        '$ed25519_new_keypair'(Pair).
+
+ed25519_keypair_public_key(Pair, PublicKey) :-
+        must_be_byte_chars(Pair, ed25519_keypair_public_key),
+        '$ed25519_keypair_public_key'(Pair, octet, PublicKey).
+
+ed25519_sign(Key, Data0, Signature, Options) :-
+        must_be_byte_chars(Key, ed25519_sign),
+        options_data_chars(Options, Data0, Data, Encoding),
+        '$ed25519_sign'(Key, octet, Data, Encoding, Signature0),
+        hex_bytes(Signature, Signature0).
+
+ed25519_verify(Key, Data0, Signature0, Options) :-
+        must_be_byte_chars(Key, ed25519_verify),
+        options_data_chars(Options, Data0, Data, Encoding),
+        hex_bytes(Signature0, Signature),
+        '$ed25519_verify'(Key, octet, 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) ->
+            Scalar #>= 0,
+            Scalar #< 2^256,
+            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, 0-0, N-_).
+
+pow(B, N0-I0, N-I) :-
+        B in 0..255,
+        N #= N0 + B*256^I0,
+        I #= I0 + 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]), Hex),
+        hex_bytes(Hex, Bytes),
+        '$crypto_curve_scalar_mult'(Name, Scalar, Bytes, SX, SY),
+        number_chars(RX, SX),
+        number_chars(RY, SY).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+?- 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(secp112r1,
+                  curve(secp112r1,
+                        0x00db7c2abf62e35e668076bead208b,
+                        0x00db7c2abf62e35e668076bead2088,
+                        0x659ef8ba043916eede8911702b22,
+                        point(0x09487239995a5ee76b55f9c2f098,
+                              0xa89ce5af8724c0a23e0e0ff77500),
+                        0x00db7c2abf62e35e7628dfac6561c5,
+                        14,
+                        1)).
+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

@@ -1,14 +1,11 @@
-% :- op(1105, xfy, ('|')).
-
-:- module(dcgs, [op(1200, xfx, -->), phrase/2, phrase/3]).
+:- module(dcgs,
+          [op(1105, xfy, '|'),
+		   phrase/2,
+		   phrase/3]).
 
+:- use_module(library(error)).
 :- use_module(library(lists), [append/3]).
 
-user:term_expansion(Term0, Term) :-
-    nonvar(Term0),
-    dcg_rule(Term0, (Head :- Body)),
-    Term = (Head :- Body).
-
 phrase(GRBody, S0) :-
     phrase(GRBody, S0, []).
 
@@ -31,8 +28,8 @@ phrase_((A -> B ; C), S0, S) :-
     ).
 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_((A | B), S0, S) :-
+    (  phrase(A, S0, S) ; phrase(B, S0, S)  ).
 phrase_({G}, S0, S) :-
     (  call(G), S0 = S  ).
 phrase_(call(G), S0, S) :-
@@ -95,7 +92,7 @@ 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
@@ -107,6 +104,7 @@ 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),
@@ -119,9 +117,9 @@ 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)).
@@ -130,3 +128,8 @@ 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, (Head :- Body)),
+    Term = (Head :- Body).

src/lib/debug.pl

@@ -0,0 +1,22 @@
+% Source: https://stackoverflow.com/a/30791637
+
+:- module(debug, [
+    op(900, fx, $),
+    op(900, fx, $-),
+    op(950, fy, *),
+    (*)/1,
+    ($)/1,
+    ($-)/1
+]).
+
+:- use_module(library(format), [portray_clause/1]).
+
+$-(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/error.pl

@@ -1,5 +1,9 @@
 :- module(error, [must_be/2,
-                  can_be/2]).
+                  can_be/2,
+                  instantiation_error/1,
+                  domain_error/3,
+                  type_error/3
+                  ]).
 
 /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Written September 2018 by Markus Triska (triska@metalevel.at)
@@ -23,7 +27,8 @@
 
        - integer
        - atom
-       - list.
+       - list
+       - boolean
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
 must_be(Type, Term) :-
@@ -32,31 +37,41 @@ must_be(Type, Term) :-
 
 must_be_(Type, _) :-
         var(Type),
-        instantiation_error(Type).
+        instantiation_error(must_be/2).
 must_be_(var, Term) :-
         (   var(Term) -> true
-        ;   throw(error(uninstantiation_error, _))
+        ;   throw(error(uninstantiation_error, must_be/2))
         ).
 must_be_(integer, Term) :- check_(integer, integer, Term).
 must_be_(atom, Term)    :- check_(atom, atom, Term).
+must_be_(character, T)  :- check_(character, character, T).
 must_be_(list, Term)    :- check_(ilist, list, Term).
 must_be_(type, Term)    :- check_(type, type, Term).
+must_be_(boolean, Term) :- check_(boolean, boolean, Term).
 
 check_(Pred, Type, Term) :-
-        (   var(Term) -> instantiation_error(Term)
+        (   var(Term) -> instantiation_error(must_be/2)
         ;   call(Pred, Term) -> true
-        ;   type_error(Type, Term)
+        ;   type_error(Type, Term, must_be/2)
         ).
 
-ilist(V) :- var(V), instantiation_error(V).
+boolean(B) :- ( B == true ; B == false ).
+
+character(C) :-
+        atom(C),
+        atom_length(C, 1).
+
+ilist(V) :- var(V), instantiation_error(must_be/2).
 ilist([]).
 ilist([_|Ls]) :- ilist(Ls).
 
 type(type).
 type(integer).
 type(atom).
+type(character).
 type(list).
 type(var).
+type(boolean).
 
 /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    can_be(Type, Term)
@@ -76,12 +91,14 @@ can_be(Type, Term) :-
         must_be(type, Type),
         (   var(Term) -> true
         ;   can_(Type, Term) -> true
-        ;   type_error(Type, Term)
+        ;   type_error(Type, Term, can_be/2)
         ).
 
 can_(integer, Term) :- integer(Term).
 can_(atom, Term)    :- atom(Term).
+can_(character, T)  :- character(T).
 can_(list, Term)    :- list_or_partial_list(Term).
+can_(boolean, Term) :- boolean(Term).
 
 list_or_partial_list(Var) :- var(Var).
 list_or_partial_list([]).
@@ -92,11 +109,11 @@ list_or_partial_list([_|Ls]) :-
    Shorthands for throwing ISO errors.
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
-instantiation_error(_Term) :-
-    throw(error(instantiation_error, _)).
+instantiation_error(Context) :-
+    throw(error(instantiation_error, Context)).
 
-domain_error(Type, Term) :-
-    throw(error(domain_error(Type, Term), _)).
+domain_error(Type, Term, Context) :-
+    throw(error(domain_error(Type, Term), Context)).
 
-type_error(Type, Term) :-
-    throw(error(type_error(Type, Term), _)).
+type_error(Type, Term, Context) :-
+    throw(error(type_error(Type, Term), Context)).

src/lib/files.pl

@@ -0,0 +1,200 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written June 2020 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,
+                  make_directory/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)).
+
+list_of_chars(Cs) :-
+        must_be(list, Cs),
+        maplist(must_be(character), Cs).
+
+directory_files(Directory, Files) :-
+        list_of_chars(Directory),
+        can_be(list, Files),
+        '$directory_files'(Directory, Files).
+
+file_size(File, Size) :-
+        list_of_chars(File),
+        can_be(integer, Size),
+        '$file_size'(File, Size).
+
+file_exists(File) :-
+        list_of_chars(File),
+        '$file_exists'(File).
+
+directory_exists(Directory) :-
+        list_of_chars(Directory),
+        '$directory_exists'(Directory).
+
+make_directory(Directory) :-
+        list_of_chars(Directory),
+        '$make_directory'(Directory).
+
+delete_file(File) :-
+        list_of_chars(File),
+        '$delete_file'(File).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   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),
+        '$working_directory'(Dir0, Dir).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   True iff Cs is the canonical, absolute path of Ps.
+
+   All intermediate components are normalized, and all symbolic links
+   are resolved.
+
+   The predicate fails in the following situations, though not
+   necessarily *only* in these cases:
+
+      1. Ps is a path that does not exist.
+      2. A non-final component in Ps is not a directory.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+path_canonical(Ps, Cs) :-
+        must_be(list, Ps),
+        maplist(must_be(character), Ps),
+        can_be(list, Cs),
+        '$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) :-
+        '$file_time'(File, Which, T0),
+        read_term_from_chars(T0, T).
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   path_segments(Ps, Segments): True iff Segments are the segments of Ps.
+
+   Segments is the list of components of the path Ps that are
+   separated by the platform-specific directory separator. Each
+   segment is a list of characters.
+
+   At least one of the arguments must be instantiated.
+
+   Examples:
+
+      ?- path_segments("/hello/there", Segments).
+         Segments = [[],"hello","there"]
+      ;  false.
+
+      ?- path_segments(Path, ["hello","there"]).
+         Path = "hello/there"
+      ;  false.
+
+
+   To obtain the platform-specific directory separator, you can use:
+
+      ?- path_segments(Separator, ["",""]).
+         Separator = "/"
+      ;  false.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+path_segments(Path, Segments) :-
+        '$directory_separator'(Sep),
+        (   var(Path) ->
+            must_be(list, Segments),
+            maplist(list_of_chars, Segments),
+            append_with_separator(Segments, Sep, Path)
+        ;   list_of_chars(Path),
+            path_to_segments(Path, Sep, Segments)
+        ).
+
+append_with_separator([], _, []).
+append_with_separator([Segment|Segments], Sep, Path) :-
+        append_with_separator_(Segments, Segment, Sep, Path).
+
+append_with_separator_([], Segment, _, Segment).
+append_with_separator_([Segment|Segments], Prev, Sep, Path) :-
+        append(Prev, [Sep|Rest], Path),
+        append_with_separator_(Segments, Segment, Sep, Rest).
+
+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 +1,580 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written March 2020 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)
+     ~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.
+     ~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(write, Ls).
+
+   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!"
+   %@ ;  false.
+
+   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/2,
+                   listing/1
+                  ]).
+
+:- use_module(library(dcgs)).
+:- use_module(library(lists)).
+:- use_module(library(error)).
+:- use_module(library(charsio)).
+:- use_module(library(between)).
+
+format_(Fs, Args) -->
+        { must_be(list, Fs),
+          must_be(list, Args),
+          phrase(cells(Fs,Args,0,[]), 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)) --> list(Cs).
+format_element(glue(Fill,Num)) -->
+        { length(Ls, Num),
+          maplist(=(Fill), Ls) },
+        list(Ls).
+
+list([]) --> [].
+list([L|Ls]) --> [L], list(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 from_to(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 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) --> !,
+        cells(Fs, Args, Tab, [chars("~")|Es]).
+cells([~,w|Fs], [Arg|Args], Tab, Es) --> !,
+        { write_term_to_chars(Arg, [], Chars) },
+        cells(Fs, Args, Tab, [chars(Chars)|Es]).
+cells([~,q|Fs], [Arg|Args], Tab, Es) --> !,
+        { write_term_to_chars(Arg, [quoted(true)], Chars) },
+        cells(Fs, Args, Tab, [chars(Chars)|Es]).
+cells([~,a|Fs], [Arg|Args], Tab, Es) --> !,
+        { atom_chars(Arg, Chars) },
+        cells(Fs, Args, Tab, [chars(Chars)|Es]).
+cells([~|Fs0], Args0, Tab, Es) -->
+        { 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.",list(Zs),list(Cs0)), Cs)
+              ;   BeforeComma is L - Num,
+                  length(Bs, BeforeComma),
+                  append(Bs, Ds, Cs0),
+                  phrase((list(Bs),".",list(Ds)), Cs)
+              ) }
+        ),
+        cells(Fs, Args, Tab, [chars(Cs)|Es]).
+cells([~|Fs0], Args0, Tab, Es) -->
+        { numeric_argument(Fs0, Num, ['D'|Fs], Args0, [Arg|Args]) },
+        !,
+        { number_chars(Num, NCs),
+          phrase(("~",list(NCs),"d"), FStr),
+          phrase(format_(FStr, [Arg]), Cs0),
+          phrase(upto_what(Bs0, .), Cs0, Ds),
+          reverse(Bs0, Bs1),
+          phrase(groups_of_three(Bs1), Bs2),
+          reverse(Bs2, Bs),
+          append(Bs, Ds, Cs) },
+        cells(Fs, Args, Tab, [chars(Cs)|Es]).
+cells([~,i|Fs], [_|Args], Tab, Es) --> !,
+        cells(Fs, Args, Tab, Es).
+cells([~,n|Fs], Args, Tab, Es) --> !,
+        cell(Tab, Tab, Es),
+        n_newlines(1),
+        cells(Fs, Args, 0, []).
+cells([~|Fs0], Args0, Tab, Es) -->
+        { numeric_argument(Fs0, Num, [n|Fs], Args0, Args) },
+        !,
+        cell(Tab, Tab, Es),
+        n_newlines(Num),
+        cells(Fs, Args, 0, []).
+cells([~,s|Fs], [Arg|Args], Tab, Es) --> !,
+        cells(Fs, Args, Tab, [chars(Arg)|Es]).
+cells([~,f|Fs], [Arg|Args], Tab, Es) --> !,
+        { format_number_chars(Arg, Chars) },
+        cells(Fs, Args, Tab, [chars(Chars)|Es]).
+cells([~|Fs0], Args0, Tab, Es) -->
+        { 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]).
+cells([~|Fs0], Args0, Tab, Es) -->
+        { numeric_argument(Fs0, Num, [r|Fs], Args0, [Arg|Args]) },
+        !,
+        { integer_to_radix(Arg, Num, lowercase, Cs) },
+        cells(Fs, Args, Tab, [chars(Cs)|Es]).
+cells([~|Fs0], Args0, Tab, Es) -->
+        { numeric_argument(Fs0, Num, ['R'|Fs], Args0, [Arg|Args]) },
+        !,
+        { integer_to_radix(Arg, Num, uppercase, Cs) },
+        cells(Fs, Args, Tab, [chars(Cs)|Es]).
+cells([~,'`',Char,t|Fs], Args, Tab, Es) --> !,
+        cells(Fs, Args, Tab, [glue(Char,_)|Es]).
+cells([~,t|Fs], Args, Tab, Es) --> !,
+        cells(Fs, Args, Tab, [glue(' ',_)|Es]).
+cells([~|Fs0], Args0, Tab, Es) -->
+        { numeric_argument(Fs0, Num, ['|'|Fs], Args0, Args) },
+        !,
+        cell(Tab, Num, Es),
+        cells(Fs, Args, Num, []).
+cells([~|Fs0], Args0, Tab0, Es) -->
+        { numeric_argument(Fs0, Num, [+|Fs], Args0, Args) },
+        !,
+        { Tab is Tab0 + Num },
+        cell(Tab0, Tab, Es),
+        cells(Fs, Args, Tab, []).
+cells([~,C|_], _, _, _) -->
+        { atom_chars(A, [~,C]),
+          domain_error(format_string, A, format_//2) }.
+cells(Fs0, Args, Tab, Es) -->
+        { phrase(upto_what(Fs1, ~), Fs0, Fs),
+          Fs1 = [_|_] },
+        cells(Fs, Args, Tab, [chars(Fs1)|Es]).
+
+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 = [].
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+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]) --> !, [A,B,C], ",", groups_of_three([D|Rs]).
+groups_of_three(Ls) --> list(Ls).
+
+cell(From, To, Es0) -->
+        (   { Es0 == [] } -> []
+        ;   { reverse(Es0, Es) },
+            [cell(From,To,Es)]
+        ).
+
+%?- numeric_argument("2f", Num, ['f'|Fs], Args0, Args).
+
+%?- numeric_argument("100b", Num, Rs, Args0, Args).
+
+numeric_argument(Ds, Num, Rest, Args0, Args) :-
+        (   Ds = [*|Rest] ->
+            Args0 = [Num|Args]
+        ;   numeric_argument_(Ds, [], Ns, Rest),
+            foldl(pow10, Ns, 0-0, Num-_),
+            Args0 = Args
+        ).
+
+numeric_argument_([D|Ds], Ns0, Ns, Rest) :-
+        (   member(D, "0123456789") ->
+            number_chars(N, [D]),
+            numeric_argument_(Ds, [N|Ns0], Ns, Rest)
+        ;   Ns = Ns0,
+            Rest = [D|Ds]
+        ).
+
+
+pow10(D, N0-Pow0, N-Pow) :-
+        N is N0 + D*10^Pow0,
+        Pow is Pow0 + 1.
+
+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) ->
+            domain_error(radix, R, 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(format_(Fs, Args), Cs),
+        % we use a specialised internal predicate that uses only a
+        % single "write" operation for efficiency. It is equivalent to
+        % maplist(put_char(Stream), Cs). It also works for binary streams.
+        '$put_chars'(Stream, Cs),
+        flush_output(Stream).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+?- phrase(cells("hello", [], 0, []), Cs).
+
+?- phrase(cells("hello~10|", [], 0, []), Cs).
+?- phrase(cells("~ta~t~10|", [], 0, []), Cs).
+
+?- phrase(format_("~`at~50|", []), Ls).
+
+?- phrase(cells("~`at~50|", [], 0, []), Cs),
+   phrase(format_cells(Cs), Ls).
+?- phrase(cells("~ta~t~tb~tc~21|", [], 0, []), Cs).
+Cs = [cell(0,21,[glue(' ',_38),chars([a]),glue(' ',_62),glue(' ',_67),chars([b]),glue(' ',_91),chars([c])])].
+?- phrase(cells("~ta~t~4|", [], 0, []), Cs).
+Cs = [cell(0,4,[glue(' ',_38),chars([a]),glue(' ',_62)])].
+
+?- phrase(format_cell(cell(0,1,[glue(a,_94)])), Ls).
+
+?- phrase(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
+;  false.
+
+?- format("~ta~tb~tc~10|", []).
+  a  b   c   true
+;  false.
+
+?- format("~tabc~3|", []).
+
+?- format("~ta~t~4|", []).
+
+?- format("~ta~t~tb~tc~20|", []).
+    a        b     c   true
+;  false.
+
+?- format("~2f~n", [3]).
+3.00
+   true
+
+?- format("~20f", [0.1]).
+0.10000000000000000000   true % this should use higher accuracy!
+;  false.
+
+?- 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(portray_clause_(Term), Ls),
+        format(Stream, "~s", [Ls]).
+
+portray_clause_(Term) -->
+        { term_variables(Term, Vs),
+          foldl(var_name, Vs, VNs, 0, _) },
+        portray_(Term, VNs), ".\n".
+
+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) },
+        list(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_((A ; Else), C, I, VNs) --> % ( If -> Then ; Else )
+        { nonvar(A), A = (If -> Then) },
+        !,
+        indent_to(C, I),
+        "(  ",
+        { C1 is I + 3 },
+        body_(If, C1, C1, VNs), " ->\n",
+        body_(Then, 0, C1, VNs), "\n",
+        else_branch(Else, C1, 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, C1, I, VNs).
+body_(Goal, C, I, VNs) -->
+        indent_to(C, I), literal(Goal, VNs).
+
+
+else_branch(Else, C, I, VNs) -->
+        indent_to(0, I),
+        ";  ",
+        body_(Else, C, C, VNs), "\n",
+        indent_to(0, I),
+        ")".
+
+indent_to(CurrentColumn, Indent) -->
+        { Delta is Indent - CurrentColumn },
+        format_("~t~*|", [Delta]).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+?- 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/gensym.pl

@@ -3,7 +3,7 @@
 
 :- use_module(library(error)).
 :- use_module(library(lists)).
-:- use_module(library(non_iso)).
+:- use_module(library(iso_ext)).
 :- use_module(library(si)).
 
 gensym_key(Base, BaseKey) :-

src/lib/http/http_open.pl

@@ -0,0 +1,84 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written June 2020 by Markus Triska (triska@metalevel.at)
+   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. Redirects are followed.
+
+   Currently, Options must be the empty list. Options may be
+   added in the future to give more control over the connection.
+
+   We use HTTP/1.0 until we can read chunked transfer-encoding.
+
+   Example:
+
+       ?- http_open("https://github.com/mthom/scryer-prolog", S, []).
+       %@    S = '$stream'(0x7f86f94a6cd0)
+       %@ ;  false.
+
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(http_open, [http_open/3]).
+
+:- use_module(library(sockets)).
+:- use_module(library(error)).
+:- use_module(library(format)).
+:- use_module(library(charsio)).
+:- use_module(library(dcgs)).
+:- use_module(library(lists), [member/2]).
+
+http_open(Address, Stream, Options) :-
+        must_be(list, Options),
+        must_be(list, Address),
+        once(phrase((list(SchemeCs), "://", list(Rest)), Address)),
+        atom_chars(Scheme, SchemeCs),
+        chars_host_url(Rest, Host, URL),
+        connect(Scheme, Host, Stream0),
+        format(Stream0, "\
+GET ~s HTTP/1.0\r\n\
+Host: ~w\r\n\
+User-Agent: Scryer Prolog\r\n\
+Connection: close\r\n\r\n\
+", [URL,Host]),
+        read_line_to_chars(Stream0, StatusLine, []),
+        once(phrase(("HTTP/1.",(['0']|['1'])," ",[D1]), StatusLine, _)),
+        read_header_lines(Stream0, HeaderLines),
+        handle_response(D1, HeaderLines, Stream0, Stream).
+
+list([]) --> [].
+list([L|Ls]) --> [L], list(Ls).
+
+handle_response('2', _, Stream, Stream).              % ok
+handle_response('3', HeaderLines, Stream0, Stream) :- % redirect
+        close(Stream0),
+        once((member(Line, HeaderLines),
+              phrase(("Location: ",list(Location),"\r\n"), Line))),
+        http_open(Location, Stream, []).
+
+% Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
+
+read_header_lines(Stream, Hs) :-
+        read_line_to_chars(Stream, Cs, []),
+        (   Cs == "" -> Hs = []
+        ;   Cs == "\r\n" -> Hs = []
+        ;   Hs = [Cs|Rest],
+            read_header_lines(Stream, Rest)
+        ).
+
+chars_host_url(Cs, Host, [/|Us]) :-
+        (   phrase((list(Hs),"/",list(Us)), Cs) ->
+            true
+        ;   Hs = Cs,
+            Us = []
+        ),
+        atom_chars(Host, Hs).
+
+connect(https, Host, Stream) :-
+        socket_client_open(Host:443, Stream, [tls(true)]).
+connect(http, Host, Stream) :-
+        socket_client_open(Host:80, Stream, []).
+

src/lib/iso_ext.pl

@@ -1,13 +1,13 @@
 %% for builtins that are not part of the ISO standard.
 %% must be loaded at the REPL with
 
-%% ?- use_module(library(non_iso)).
+%% ?- use_module(library(iso_ext)).
 
-:- module(non_iso, [bb_b_put/2, bb_get/2, bb_put/2, call_cleanup/2,
-		    call_with_inference_limit/3, forall/2, maybe/0,
-		    partial_string/1, partial_string/3,
-		    partial_string_tail/2, set_random/1,
-		    setup_call_cleanup/3, variant/2]).
+:- 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,
+                    variant/2]).
 
 forall(Generate, Test) :-
     \+ (Generate, \+ Test).
@@ -22,9 +22,9 @@ bb_put(Key, _) :- throw(error(type_error(atom, Key), bb_put/2)).
 bb_b_put(Key, NewValue) :-
     (  '$bb_get_with_offset'(Key, OldValue, OldOffset) ->
        call_cleanup((store_global_var_with_offset(Key, NewValue) ; false),
-		    reset_global_var_at_offset(Key, OldValue, OldOffset))
+                    reset_global_var_at_offset(Key, OldValue, OldOffset))
     ;  call_cleanup((store_global_var_with_offset(Key, NewValue) ; false),
-		    reset_global_var_at_key(Key))
+                    reset_global_var_at_key(Key))
     ).
 
 store_global_var_with_offset(Key, Value) :- '$store_global_var_with_offset'(Key, Value).
@@ -68,7 +68,8 @@ scc_helper(C, G, Bb) :-
     ; '$reset_block'(NBb),
       '$fail').
 scc_helper(_, _, Bb) :-
-    '$reset_block'(Bb), '$get_ball'(Ball),
+    '$reset_block'(Bb),
+    '$get_ball'(Ball),
     '$call_with_default_policy'(run_cleaners_with_handling),
     '$erase_ball',
     '$call_with_default_policy'(throw(Ball)).
@@ -143,27 +144,14 @@ call_with_inference_limit(_, _, R, Bb, B) :-
 
 variant(X, Y) :- '$variant'(X, Y).
 
-% succeeds with probability 0.5.
-maybe :- '$maybe'.
-
-set_random(Seed) :-
-    (  nonvar(Seed) ->
-       (  Seed = seed(S) ->
-	  (  var(S) -> throw(error(instantiation_error, set_random/1))
-	  ;  integer(S) -> '$set_seed'(S)
-	  ;  throw(error(type_error(integer(S), set_random/1)))
-	  )
-       )
-    ;  throw(error(instantiation_error, set_random/1))
-    ).
-
 partial_string(String, L, L0) :-
-    (  String == [] -> throw(error(type_error(list, []), partial_string/3))
+    (  String == [] ->
+       L = L0
     ;  catch(atom_chars(Atom, String),
-	     error(E, _),
-	     throw(error(E, partial_string/3)))
-    ),
-    '$create_partial_string'(Atom, L, L0).
+         error(E, _),
+         throw(error(E, partial_string/3))),
+       '$create_partial_string'(Atom, L, L0)
+    ).
 
 partial_string(String) :-
     '$is_partial_string'(String).

src/lib/lists.pl

@@ -1,8 +1,8 @@
-:- module(lists, [member/2, select/3, append/3, foldl/4, foldl/5,
+:- module(lists, [member/2, select/3, append/2, append/3, foldl/4, foldl/5,
 		  memberchk/2, reverse/2, length/2, maplist/2,
 		  maplist/3, maplist/4, maplist/5, maplist/6,
-		  maplist/7, maplist/8, maplist/9, same_length/2,
-		  sumlist/2]).
+		  maplist/7, maplist/8, maplist/9, same_length/2, nth0/3,
+		  sum_list/2, transpose/2, list_to_set/2]).
 
 
 :- use_module(library(error)).
@@ -21,9 +21,9 @@ length(Xs, N) :-
     ;  var(Xs0)  -> R is N-M, length_rundown(Xs0, R)).
 length(_, N) :-
     integer(N), !,
-    throw(error(domain_error(not_less_than_zero, N), length/2)).
+    domain_error(not_less_than_zero, N, length/2).
 length(_, N) :-
-    throw(error(type_error(integer, N), length/2)).
+    type_error(integer, N, length/2).
 
 length_addendum([], N, N).
 length_addendum([_|Xs], N, M) :-
@@ -44,6 +44,12 @@ select(X, [X|Xs], Xs).
 select(X, [Y|Xs], [Y|Ys]) :- select(X, Xs, Ys).
 
 
+append([], []).
+append([L0|Ls0], Ls) :-
+    append(L0, Rest, Ls),
+    append(Ls0, Rest).
+
+
 append([], R, R).
 append([X|L], R, [X|S]) :- append(L, R, S).
 
@@ -57,7 +63,7 @@ reverse(Xs, Ys) :-
     ).
 
 reverse([], [], YsRev, YsRev).
-reverse([X1|Xs], [Y1|Ys], YsPreludeRev, Xss) :-
+reverse([_|Xs], [Y1|Ys], YsPreludeRev, Xss) :-
     reverse(Xs, Ys, [Y1|YsPreludeRev], Xss).
 
 
@@ -98,18 +104,14 @@ maplist(Cont, [E1|E1s], [E2|E2s], [E3|E3s], [E4|E4s], [E5|E5s], [E6|E6s], [E7|E7
 
 maplist(_, [], [], [], [], [], [], [], []).
 maplist(Cont, [E1|E1s], [E2|E2s], [E3|E3s], [E4|E4s], [E5|E5s], [E6|E6s], [E7|E7s], [E8|E8s]) :-
-    call(Cont, E1, E2, E3, E4, E5, E6, E7),
+    call(Cont, E1, E2, E3, E4, E5, E6, E7, E8),
     maplist(Cont, E1s, E2s, E3s, E4s, E5s, E6s, E7s, E8s).
 
 
-sumlist_([], S, S).
-sumlist_([N|Ns], S, S0) :-
-    S1 is S0 + N,
-    sumlist_(Ns, S, S1).
+sum_list(Ls, S) :-
+        foldl(sum_, Ls, 0, S).
 
-sumlist(Ns, S) :-
-    must_be(list, Ns),
-    sumlist_(Ns, S, 0).
+sum_(L, S0, S) :- S is S0 + L.
 
 
 
@@ -134,3 +136,67 @@ 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).
+
+transpose(Ls, Ts) :-
+        lists_transpose(Ls, Ts).
+
+lists_transpose([], []).
+lists_transpose([L|Ls], Ts) :-
+        maplist(same_length(L), Ls),
+        foldl(transpose_, L, Ts, [L|Ls], _).
+
+transpose_(_, Fs, Lists0, Lists) :-
+        maplist(list_first_rest, Lists0, Fs, Lists).
+
+list_first_rest([L|Ls], L, Ls).
+
+
+list_to_set(Ls0, Ls) :-
+        maplist(with_var, Ls0, LVs0),
+        keysort(LVs0, LVs),
+        same_elements(LVs),
+        pick_firsts(LVs0, Ls).
+
+pick_firsts([], []).
+pick_firsts([E-V|EVs], Fs0) :-
+        (   V == visited ->
+            Fs0 = Fs
+        ;   V = visited,
+            Fs0 = [E|Fs]
+        ),
+        pick_firsts(EVs, Fs).
+
+with_var(E, E-_).
+
+same_elements([]).
+same_elements([EV|EVs]) :-
+        foldl(unify_same, EVs, EV, _).
+
+unify_same(E-V, Prev-Var, E-V) :-
+        (   Prev == E ->
+            Var = V
+        ;   true
+        ).
+
+
+nth0(N, Es, E) :-
+        can_be(integer, N),
+        can_be(list, Es),
+        (   integer(N) ->
+            nth0_index(N, Es, E)
+        ;   nth0_search(N, Es, E)
+        ).
+
+nth0_index(0, [E|_], E) :- !.
+nth0_index(N, [_|Es], E) :-
+        N > 0,
+        N1 is N - 1,
+        nth0_index(N1, Es, E).
+
+nth0_search(N, Es, E) :-
+        nth0_search(0, N, Es, E).
+
+nth0_search(N, N, [E|_], E).
+nth0_search(N0, N, [_|Es], E) :-
+        N1 is N0 + 1,
+        nth0_search(N1, N, Es, E).

src/lib/os.pl

@@ -0,0 +1,58 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Predicates for reasoning about the operating system (OS) environment.
+   Written July 2020 by Markus Triska (triska@metalevel.at).
+
+   Lists of characters are used throughout to represent keys and values.
+
+   Example:
+
+       ?- getenv("LANG", Ls).
+          Ls = "en_US.UTF-8"
+       ;  false.
+
+   Public domain code.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(os, [getenv/2,
+               setenv/2,
+               unsetenv/1]).
+
+:- use_module(library(error)).
+:- use_module(library(charsio)).
+:- use_module(library(lists)).
+
+getenv(Key, Value) :-
+        must_be_env_var(Key),
+        '$getenv'(Key, Value).
+
+setenv(Key, Value) :-
+        must_be_env_var(Key),
+        must_be_chars(Value),
+        '$setenv'(Key, Value).
+
+unsetenv(Key) :-
+        must_be_env_var(Key),
+        '$unsetenv'(Key).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   For now, we only support a restricted subset of variable names.
+
+   The reason is that Rust may panic if a key is empty, contains an
+   ASCII equals sign '=' or the NUL character '\0', or when the value
+   contains the NUL character.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+must_be_env_var(Cs) :-
+        must_be_chars(Cs),
+        Cs = [_|_],
+        (   maplist(permitted, Cs) -> true
+        ;   domain_error(env_var, Cs, os)
+        ).
+
+permitted(C) :- char_type(C, alnum).
+permitted(C) :- char_type(C, ascii_punctuation).
+permitted('_').
+
+must_be_chars(Cs) :-
+        must_be(list, Cs),
+        maplist(must_be(character), Cs).

src/lib/pairs.pl

@@ -0,0 +1,33 @@
+:- module(pairs, [pairs_keys_values/3,
+		  pairs_keys/2,
+		  pairs_values/2,
+		  group_pairs_by_key/2,
+		  map_list_to_pairs/3]).
+
+
+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).
+
+
+group_pairs_by_key([], []).
+group_pairs_by_key([K-V|KVs0], [K-[V|Vs]|KVs]) :-
+        same_key(K, KVs0, Vs, KVs1),
+        group_pairs_by_key(KVs1, KVs).
+
+same_key(K0, [K1-V|KVs0], [V|Vs], KVs) :-
+        K0 == K1, !,
+        same_key(K0, KVs0, Vs, KVs).
+same_key(_, KVs, [], KVs).

src/lib/pio.pl

@@ -0,0 +1,42 @@
+:- module(pio, [phrase_from_file/2,
+                phrase_from_file/3]).
+
+:- use_module(library(dcgs)).
+:- use_module(library(error)).
+:- use_module(library(freeze)).
+:- use_module(library(iso_ext), [setup_call_cleanup/3, partial_string/3]).
+:- use_module(library(lists), [member/2]).
+
+phrase_from_file(NT, File) :-
+    phrase_from_file(NT, File, []).
+
+phrase_from_file(NT, File, Options) :-
+    (   var(File) -> instantiation_error(phrase_from_file/3)
+    ;   (\+ atom(File) ; File = []) ->
+            domain_error(source_sink, File, phrase_from_file/3)
+    ;   must_be(list, Options),
+        (   member(Var, Options), var(Var) -> instantiation_error(phrase_from_file/3)
+        ;   member(type(Type), Options) ->
+            must_be(atom, Type),
+            member(Type, [text,binary])
+        ;   Type = text
+        ),
+        setup_call_cleanup(open(File, read, Stream, [reposition(true)|Options]),
+                           (   stream_to_lazy_list(Stream, Xs),
+                               phrase(NT, Xs) ),
+                           close(Stream))
+   ).
+
+
+stream_to_lazy_list(Stream, Xs) :-
+        stream_property(Stream, position(Pos)),
+        freeze(Xs, reader_step(Stream, Pos, Xs)).
+
+reader_step(Stream, Pos, Xs0) :-
+        set_stream_position(Stream, Pos),
+        (   at_end_of_stream(Stream)
+        ->  Xs0 = []
+        ;   '$get_n_chars'(Stream, 4096, Cs),
+            partial_string(Cs, Xs0, Xs),
+            stream_to_lazy_list(Stream, Xs)
+        ).

src/lib/random.pl

@@ -0,0 +1,59 @@
+:- module(random, [maybe/0, random/1, random_integer/3, set_random/1]).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   To retain desirable declarative properties, predicates that internally
+   use random numbers should be equipped with an argument that specifies
+   the random seed. This makes everything completely reproducible.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- use_module(library(error)).
+
+% succeeds with probability 0.5.
+maybe :- '$maybe'.
+
+% The higher the precision, the slower it gets.
+random_number_precision(64).
+
+random(R) :-
+    var(R),
+    random_number_precision(N),
+    rnd(N, R).
+
+random_integer(Lower, Upper, R) :-
+    var(R),
+    (   (var(Lower) ; var(Upper)) ->
+            instantiation_error(random_integer/3)
+    ;   \+ integer(Lower) ->
+            domain_error(integer, Lower, random_integer/3)
+    ;   \+ integer(Upper) ->
+            domain_error(integer, Upper, random_integer/3)
+    ;   Upper > Lower,
+        random(R0),
+        R is floor((Upper - Lower) * R0 + Lower)
+    ).
+
+rnd(N, R) :-
+    rnd_(N, 0, R).
+
+rnd_(0, R, R) :- !.
+rnd_(N, R0, R) :-
+    maybe,
+    !,
+    N1 is N - 1,
+    rnd_(N1, R0, R).
+rnd_(N, R0, R) :-
+    N1 is N - 1,
+    R1 is R0 + 1.0 / 2.0 ^ N,
+    rnd_(N1, R1, R).
+
+set_random(Seed) :-
+    (   nonvar(Seed) ->
+        (  Seed = seed(S) ->
+        (  var(S) -> instantiation_error(set_random/1)
+        ;  integer(S) -> '$set_seed'(S)
+        ;  type_error(integer, S, set_random/1)
+        )
+        )
+    ;   instantiation_error(set_random/1)
+    ).
+

src/lib/sgml.pl

@@ -0,0 +1,92 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Predicates for parsing HTML and XML documents.
+   Written June 2020 by Markus Triska (triska@metalevel.at)
+   Part of Scryer Prolog.
+
+   Currently, two predicates are provided:
+
+   -  load_html(+Source, -Es, +Options)
+   -  load_xml(+Source, -Es, +Options)
+
+   These predicates parse HTML and XML documents, respectively.
+
+   Source must be a stream, specified as stream(S), or a file,
+   specified as file(Name), where Name is a list of characters, or a
+   list of characters with the document contents.
+
+   Es is unified with the abstract syntax tree of the parsed document,
+   represented as a list of elements where each is of the form:
+
+   * a list of characters, representing text
+   * element(Name, Attrs, Children)
+     - Name is the name of the tag
+     - Attrs is a list of Key=Value pairs:
+       Key is an atom, and Value is a list of characters
+     - Children is a list of elements as specified here.
+
+   Currently, Options are ignored. In the future, more options may be
+   provided to control parsing.
+
+   Example:
+
+      ?- load_html("<html><head><title>Hello!</title></head></html>", Es, []).
+
+   Yielding:
+
+         Es = [element(html,[],
+                [element(head,[],
+                  [element(title,[],
+                    ["Hello!"])]),
+                 element(body,[],[])])].
+
+   library(xpath) provides convenient reasoning about parsed documents.
+   For example, to fetch the title of the document above, we can use:
+
+      ?- load_html("<html><head><title>Hello!</title></head></html>", Es, []),
+         xpath(Es, //title(text), T).
+
+   Yielding T = "Hello!".
+
+   Use http_open/3 from library(http/http_open) to read answers from
+   web servers via streams.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(sgml, [load_html/3,
+                 load_xml/3]).
+
+:- use_module(library(iso_ext)).
+:- use_module(library(error)).
+:- use_module(library(dcgs)).
+:- use_module(library(pio)).
+
+load_html(Source, Es, Options) :-
+        load_structure_(Source, Es, Options, html).
+load_xml(Source, Es, Options) :-
+        load_structure_(Source, Es, Options, xml).
+
+list([]) --> [].
+list([L|Ls]) --> [L], list(Ls).
+
+load_structure_([], [], _, _).
+load_structure_([C|Cs], [E], Options, What) :-
+        load_(What, [C|Cs], E, Options).
+load_structure_(file(Fs), [E], Options, What) :-
+        must_be(list, Options),
+        must_be(list, Fs),
+        atom_chars(File, Fs),
+        once(phrase_from_file(list(Cs), File)),
+        load_(What, Cs, E, Options).
+load_structure_(stream(Stream), [E], Options, What) :-
+        must_be(list, Options),
+        read_to_end(Stream, Cs),
+        load_(What, Cs, E, Options).
+
+load_(html, Cs, E, Options) :- '$load_html'(Cs, E, Options).
+load_(xml, Cs, E, Options) :- '$load_xml'(Cs, E, Options).
+
+read_to_end(Stream, Cs) :-
+        '$get_n_chars'(Stream, 4096, Cs0),
+        (   Cs0 = [] -> Cs = []
+        ;   partial_string(Cs0, Cs, Rest),
+            read_to_end(Stream, Rest)
+        ).

src/lib/sockets.pl

@@ -0,0 +1,67 @@
+
+:- module(sockets, [socket_client_open/3,
+                    socket_server_open/2,
+                    socket_server_accept/4,
+                    socket_server_close/1,
+                    current_hostname/1]).
+
+:- use_module(library(error)).
+:- use_module(library(lists)).
+
+parse_socket_options_(tls(TLS), tls-TLS) :-
+    must_be(boolean, TLS), !.
+parse_socket_options_(Option, OptionPair) :-
+    builtins:parse_stream_options_(Option, OptionPair).
+
+parse_socket_options(Options, OptionValues, Stub) :-
+    DefaultOptions = [alias-[], eof_action-eof_code, reposition-false, tls-false, type-text],
+    builtins:parse_options_list(Options, parse_socket_options_, DefaultOptions, OptionValues, Stub).
+
+socket_client_open(Addr, Stream, Options) :-
+    (  var(Addr) ->
+       throw(error(instantiation_error, socket_client_open/3))
+    ;
+       true
+    ),
+    must_be(var, Stream),
+    must_be(list, Options),
+    (  Addr = Address:Port,
+       atom(Address),
+       ( atom(Port) ; integer(Port) ) ->
+       true
+    ;
+       throw(error(type_error(socket_address, Addr), socket_client_open/3))
+    ),
+    parse_socket_options(Options,
+                         [Alias, EOFAction, Reposition, TLS, Type],
+                         socket_client_open/3),
+    '$socket_client_open'(Address, Port, Stream, Alias, EOFAction, Reposition, Type, TLS).
+
+
+socket_server_open(Addr, ServerSocket) :-
+    must_be(var, ServerSocket),
+    (  ( integer(Addr) ; var(Addr) ) ->
+       '$socket_server_open'([], Addr, ServerSocket)
+    ;
+       Addr = Address:Port,
+       must_be(atom, Address),
+       can_be(integer, Port),
+       '$socket_server_open'(Address, Port, ServerSocket)
+    ).
+
+
+socket_server_accept(ServerSocket, Client, Stream, Options) :-
+    must_be(var, Client),
+    must_be(var, Stream),
+    builtins:parse_stream_options(Options,
+                                  [Alias, EOFAction, Reposition, Type],
+                                  socket_server_accept/4),
+    '$socket_server_accept'(ServerSocket, Client, Stream, Alias, EOFAction, Reposition, Type).
+
+
+socket_server_close(ServerSocket) :-
+    '$socket_server_close'(ServerSocket).
+
+
+current_hostname(HostName) :-
+    '$current_hostname'(HostName).

src/lib/tabling.pl

@@ -8,17 +8,17 @@
 	    op(1150, fx, table)
 	  ]).
 
-:- use_module('tabling/double_linked_list').
-:- use_module('tabling/table_data_structure').
-:- use_module('tabling/batched_worklist').
-:- use_module('tabling/wrapper').
-:- use_module('tabling/global_worklist').
-:- use_module('tabling/table_link_manager').
+:- use_module(library(tabling/double_linked_list)).
+:- use_module(library(tabling/table_data_structure)).
+:- use_module(library(tabling/batched_worklist)).
+:- use_module(library(tabling/wrapper)).
+:- use_module(library(tabling/global_worklist)).
+:- use_module(library(tabling/table_link_manager)).
 
 :- use_module(library(cont)).
 :- use_module(library(lists)).
 %:- use_module(library(debug)).
-:- use_module(library(non_iso)).
+:- use_module(library(iso_ext)).
 
 %% :- meta_predicate
 %% 	start_tabling(+, 0).
@@ -135,19 +135,15 @@ activate(Wrapper,Worker,T) :-
 
 delim(Wrapper,Worker,Table) :-
 %   debug(tabling, 'ACT: ~p on ~p', [Wrapper, Table]),
-   reset(Worker,SourceCall,Continuation),
-   ( Continuation == none, var(SourceCall) ->
+    reset(Worker,SourceCall,Continuation),
+   ( Continuation = none ->
      (	 add_answer(Table,Wrapper)
      ->	 true %debug(tabling, 'ADD: ~p', [Wrapper])
      ;	 %debug(tabling, 'DUP: ~p', [Wrapper]),
 	 fail
      )
    ;
-     (   Continuation = cont(Cont) ->
-	 true
-     ;   Continuation = none ->
-	 Cont = true
-     ),
+     Continuation = cont(Cont),
      SourceCall = call_info(_,SourceTable),
      TargetCall = call_info(Wrapper,Table),
      Dependency = dependency(SourceCall,Cont,TargetCall),
@@ -178,7 +174,7 @@ completion_step(SourceTableID) :-
     fail
   ;
     true
-  ).  
+  ).
 
 table_get_work(NBWorklistID,Answer,Dependency) :-
   % get_worklist(Table, Worklist),
@@ -192,7 +188,7 @@ table_get_work(NBWorklistID,Answer,Dependency) :-
 table_get_work_(NBWorklistID,Answer,Dependency) :-
   worklist_do_all_work(NBWorklistID,Answer,Dependency0), % This will eventually fail
   copy_term(Dependency0,Dependency).
-  
+
 table_get_work_(NBWorklistID,_Answer,_Dependency) :-
   bb_get(NBWorklistID, table_nb_worklist(Worklist)),
   unset_flag_executing_all_work(Worklist),

src/lib/tabling/batched_worklist.pl

@@ -45,8 +45,8 @@
 	    wkl_worklist_work_done/1			% +WorkList
 	  ]).
 
-:- use_module(global_worklist).
-:- use_module(double_linked_list).
+:- use_module(library(tabling/global_worklist)).
+:- use_module(library(tabling/double_linked_list)).
 
 :- use_module(library(atts)).
 :- use_module(library(lists)).
@@ -291,7 +291,7 @@ wkl_add_to_existing_answer_cluster(Worklist, Answer) :-
 wkl_add_to_new_answer_cluster(
     wkl_worklist(Dll,_Ria,_FlagExecutingWork,_AlreadyInMetaworklist,_TableIdentifier),
     Answer,AnswerClusterPointer
-) :-  
+) :-
     dll_append_left(Dll,wkl_answer_cluster(AnswerFlag),AnswerClusterPointer),
     put_atts(AnswerFlag, wkl_answer_cluster([Answer])).
 

src/lib/tabling/double_linked_list.pl

@@ -208,4 +208,3 @@ dll_get_reverse_contents_(List, Contents) :-
        dll_get_pointer_to_previous(List, Prev),
        dll_get_reverse_contents_(Prev, Rest)
     ).
-

src/lib/tabling/global_worklist.pl

@@ -1,4 +1,4 @@
-/*    Ported to Scryer Prolog by Mark Thom (2019/2020). 
+/*    Ported to Scryer Prolog by Mark Thom (2019/2020).
  */
 
 :- module(global_worklist,
@@ -9,7 +9,7 @@
 	  ]).
 
 :- use_module(library(atts)).
-:- use_module(library(non_iso)).
+:- use_module(library(iso_ext)).
 
 :- attribute table_global_worklist/1.
 
@@ -21,7 +21,7 @@ put_new_global_worklist :-
      bb_b_put(table_global_worklist_initialized, [])
   ).
 
-add_to_global_worklist(TableIdentifier) :-  
+add_to_global_worklist(TableIdentifier) :-
   bb_get(table_global_worklist, TableGlobalWorklistFlag),
   get_atts(TableGlobalWorklistFlag, table_global_worklist(L1)),
   put_atts(TableGlobalWorklistFlag, table_global_worklist([TableIdentifier|L1])),
@@ -34,7 +34,7 @@ worklist_empty :-
 
 pop_worklist(TableIdentifier) :-
   bb_get(table_global_worklist,TableGlobalWorklistFlag),
-  get_atts(TableGlobalWorklistFlag, table_global_worklist(L1)),  
+  get_atts(TableGlobalWorklistFlag, table_global_worklist(L1)),
   L1 = [TableIdentifier|L2],
   put_atts(TableGlobalWorklistFlag, table_global_worklist(L2)),
   bb_put(table_global_worklist, TableGlobalWorklistFlag).

src/lib/tabling/table_data_structure.pl

@@ -15,8 +15,8 @@
 	    get_nb_identifiers/3                % +Table, -NbWorklistID, -NbAnswerTreeID
 	  ]).
 
-:- use_module(table_link_manager).
-:- use_module(trie).
+:- use_module(library(tabling/table_link_manager)).
+:- use_module(library(tabling/trie)).
 
 /*  Part of SWI-Prolog
 
@@ -53,11 +53,11 @@
     POSSIBILITY OF SUCH DAMAGE.
 */
 
-:- use_module(batched_worklist).
+:- use_module(library(tabling/batched_worklist)).
 
 :- use_module(library(atts)).
 :- use_module(library(gensym)).
-:- use_module(library(non_iso)).
+:- use_module(library(iso_ext)).
 
 :- attribute table_status/1, newly_created_table_identifiers/1.
 

src/lib/tabling/table_link_manager.pl

@@ -44,10 +44,10 @@
 
 :- use_module(library(atts)).
 :- use_module(library(lists)).
-:- use_module(library(non_iso)).
+:- use_module(library(iso_ext)).
 :- use_module(library(terms)).
 
-:- use_module(trie).
+:- use_module(library(tabling/trie)).
 
 :- attribute trie_table_link/1.
 

src/lib/tabling/trie.pl

@@ -66,7 +66,7 @@
 % p_trie_arity_univ(+Term,-FunctorData,-ArgumentsList).
 p_trie_arity_univ(Term,functor_data(Name,Arity),Arguments) :-
   (  var(Term) ->
-     Name = var,
+     Name = Term,
      Arity = 0,
      Arguments = []
   ;  Term =.. [Name|Arguments],
@@ -187,7 +187,7 @@ trie_insert_1_1_1(>,_V,_L,R,Assoc,FunctorData,Trie,First,Rest,Value) :-
   % Look in the right part of the assoc tree.
   trie_insert_1_1(R,Assoc,FunctorData,Trie,First,Rest,Value).
 
-trie_insert_2(RegularTerm,Rest,Trie,Value) :-  
+trie_insert_2(RegularTerm,Rest,Trie,Value) :-
   p_trie_arity_univ(RegularTerm,FunctorData,KList),
   append(KList,Rest,KList2),
   trie_insert_1(KList2,FunctorData,Trie,Value).

src/lib/time.pl

@@ -0,0 +1,129 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written 2020 by Markus Triska (triska@metalevel.at)
+   Part of Scryer Prolog.
+
+   This library provides predicates for reasoning about time.
+
+   current_time(T) yields the current system time in an opaque form,
+   called a time stamp. Use format_time//2 to describe strings that
+   contain attributes of the time stamp.
+
+   The nonterminal format_time//2 describes a list of characters that
+   are formatted according to a format string. Usage:
+
+     phrase(format_time(FormatString, TimeStamp), Cs)
+
+   TimeStamp represents a moment in time in an opaque form, as for
+   example obtained by current_time/1.
+
+   FormatString is a list of characters that are interpreted literally,
+   except for the following specifiers (and possibly more in the future):
+
+     %Y    year of the time stamp. Example: 2020.
+     %m    month number (01-12), zero-padded to 2 digits
+     %d    day number (01-31), zero-padded to 2 digits
+     %H    hour number (00-24), zero-padded to 2 digits
+     %M    minute number (00-59), zero-padded to 2 digits
+     %S    second number (00-60), zero-padded to 2 digits
+     %b    abbreviated month name, always 3 letters
+     %a    abbreviated weekday name, always 3 letters
+     %A    full weekday name
+     %j    day of the year (001-366), zero-padded to 3 digits
+     %%    the literal %
+
+   Example:
+
+     ?- current_time(T), phrase(format_time("%d.%m.%Y (%H:%M:%S)", T), Cs).
+        T = [...], Cs = "11.06.2020 (00:24:32)"
+     ;  false.
+
+   sleep(S) sleeps for S seconds (a floating point number).
+
+   time(Goal) reports the execution time of Goal.
+
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(time, [max_sleep_time/1, sleep/1, time/1, current_time/1, format_time//2]).
+
+:- use_module(library(format)).
+:- use_module(library(iso_ext)).
+:- use_module(library(error)).
+:- use_module(library(dcgs)).
+:- use_module(library(lists)).
+:- use_module(library(charsio), [read_term_from_chars/2]).
+
+current_time(T) :-
+        '$current_time'(T0),
+        read_term_from_chars(T0, T).
+
+format_time([], _) --> [].
+format_time(['%','%'|Fs], T) --> !, "%", format_time(Fs, T).
+format_time(['%',Spec|Fs], T) --> !,
+        (   { member(Spec=Value, T) } ->
+            list(Value)
+        ;   { domain_error(time_specifier, Spec, format_time//2) }
+        ),
+        format_time(Fs, T).
+format_time([F|Fs], T) --> [F], format_time(Fs, T).
+
+list([]) --> [].
+list([L|Ls]) --> [L], list(Ls).
+
+max_sleep_time(0xfffffffffffffbff).
+
+sleep(T) :-
+    builtins:must_be_number(T, sleep),
+    (   T < 0 ->
+        domain_error(not_less_than_zero, T, sleep/1)
+    ;   max_sleep_time(N), T > N ->
+        throw(error(representation_error(max_sleep_time), sleep/1))
+    ;   '$sleep'(T)
+    ).
+
+
+% '$cpu_now' can be replaced by statistics/2 once that is implemented.
+
+time(Goal) :-
+        '$cpu_now'(T0),
+        setup_call_cleanup(true,
+                           (   Goal,
+                               report_time(T0)
+                           ),
+                           report_time(T0)).
+
+report_time(T0) :-
+        '$cpu_now'(T),
+        Time is T - T0,
+        (   bb_get('$first_answer', true) ->
+            format("   % CPU time: ~3f seconds~n", [Time])
+        ;   format("% CPU time: ~3f seconds~n   ", [Time])
+        ).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+?- time((true;false)).
+   % CPU time: 0.000 seconds
+   true
+;  % CPU time: 0.001 seconds
+   false.
+
+:- time(use_module(library(clpz))).
+   % CPU time: 2.762 seconds
+   true
+;  false.
+
+:- time(use_module(library(lists))).
+   % CPU time: 0.000 seconds
+   true
+;  % CPU time: 0.001 seconds
+   false.
+
+?- time(member(X, [a,b,c])).
+   % CPU time: 0.000 seconds
+   X = a
+;  % CPU time: 0.002 seconds
+   X = b
+;  % CPU time: 0.004 seconds
+   X = c
+;  % CPU time: 0.007 seconds
+   false.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

src/lib/xpath.pl

@@ -0,0 +1,642 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   The original copyright and licence information is shown below.
+
+   Adapted in June 2020 by Markus Triska (triska@metalevel.at)
+   Part of Scryer Prolog.
+
+   In order to improve portability and reliability of this library, I
+   have changed various parts of the original code to make it
+   conforming to the Prolog ISO standard. I have removed all
+   occurrences of proprietary non-standard ad hoc data types.
+
+   In Scryer Prolog, we represent strings as lists of characters.
+   This makes them amenable to processing with DCGs and other
+   built-in mechanisms such as existing predicates on lists.
+   Scryer Prolog represents lists of characters very compactly,
+   making it an ideal representation for large amounts of text. It
+   fully conforms to the ISO standard and is very portable.
+
+   This library is intended to be used in tandem with load_html/3
+   from library(sgml), which creates DOM trees from markup documents.
+   It can be combined with http_open/3 from library(http/http_open)
+   to read such documents directly from network connections.
+
+   For instance, to inspect all links to Prolog files (*.pl) on
+   Scryer Prolog's project page, we can use:
+
+      :- use_module(library(http/http_open)).
+      :- use_module(library(sgml)).
+      :- use_module(library(lists)).
+      :- use_module(library(xpath)).
+
+      link_to_pl_file(File) :-
+          http_open("https://github.com/mthom/scryer-prolog", S, []),
+          load_html(stream(S), DOM, []),
+          xpath(DOM, //a(@href), File),
+          append(_, ".pl", File).
+
+   Yielding:
+
+      ?- link_to_pl_file(File).
+      %@    File = "/mthom/scryer-prolog/blob/master/src/lib/tabling.pl"
+      %@ ;  File = "/mthom/scryer-prolog/blob/master/src/lib/dif.pl"
+      %@ ;  File = "/mthom/scryer-prolog/blob/master/src/lib/freeze.pl"
+      %@ ;  ...
+
+   Parts of the original functionality may not yet work. Please
+   consider such parts opportunities for improvements, and file
+   issues in case you need additional features.
+
+   The original copyright information follows.
+
+   ======================================================================
+
+
+    Author:        Jan Wielemaker
+    E-mail:        J.Wielemaker@vu.nl
+    WWW:           http://www.swi-prolog.org
+    Copyright (c)  2009-2019, University of Amsterdam
+                              VU University Amsterdam
+                              CWI, Amsterdam
+    All rights reserved.
+
+    Redistribution and use in source and binary forms, with or without
+    modification, are permitted provided that the following conditions
+    are met:
+
+    1. Redistributions of source code must retain the above copyright
+       notice, this list of conditions and the following disclaimer.
+
+    2. Redistributions in binary form must reproduce the above copyright
+       notice, this list of conditions and the following disclaimer in
+       the documentation and/or other materials provided with the
+       distribution.
+
+    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+    POSSIBILITY OF SUCH DAMAGE.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(xpath,
+          [ xpath/3,                    % +DOM, +Spec, -Value
+            xpath_chk/3,                % +DOM, +Spec, -Value
+
+            op(400, fx, //),
+            op(400, fx, /),
+            op(200, fy, @)
+          ]).
+
+:- use_module(library(lists),[member/2,memberchk/2]).
+:- use_module(library(error)).
+:- use_module(library(dcgs)).
+:- use_module(library(si)).
+
+/** <module> Select nodes in an XML DOM
+
+The library xpath.pl provides predicates to select nodes from an XML DOM
+tree as produced by library(sgml) based  on descriptions inspired by the
+XPath language.
+
+The   predicate   xpath/3   selects   a   sub-structure   of   the   DOM
+non-deterministically based on an  XPath-like   specification.  Not  all
+selectors of XPath are implemented, but the ability to mix xpath/3 calls
+with arbitrary Prolog code  provides  a   powerful  tool  for extracting
+information from XML parse-trees.
+
+@see http://www.w3.org/TR/xpath
+*/
+
+element_name(element(Name,_,_), Name).
+element_attributes(element(_,Attributes,_), Attributes).
+element_content(element(_,_,Content), Content).
+
+%!  xpath_chk(+DOM, +Spec, ?Content) is semidet.
+%
+%   Semi-deterministic version of xpath/3.
+
+xpath_chk(DOM, Spec, Content) :-
+    xpath(DOM, Spec, Content),
+    !.
+
+%!  xpath(+DOM, +Spec, ?Content) is nondet.
+%
+%   Match an element in a DOM structure.   The syntax is inspired by
+%   XPath, using () rather than  []   to  select  inside an element.
+%   First we can construct paths using / and //:
+%
+%       $ =|//|=Term :
+%       Select any node in the DOM matching term.
+%       $ =|/|=Term :
+%       Match the root against Term.
+%       $ Term :
+%       Select the immediate children of the root matching Term.
+%
+%   The Terms above are of type   _callable_.  The functor specifies
+%   the element name. The element name   '*'  refers to any element.
+%   The name =self= refers to the   top-element  itself and is often
+%   used for processing matches of an  earlier xpath/3 query. A term
+%   NS:Term refers to an XML  name   in  the  namespace NS. Optional
+%   arguments specify additional  constraints   and  functions.  The
+%   arguments are processed from left  to right. Defined conditional
+%   argument values are:
+%
+%       $ index(?Index) :
+%       True if the element is the Index-th child of its parent,
+%       where 1 denotes the first child. Index can be one of:
+%         $ `Var` :
+%         `Var` is unified with the index of the matched element.
+%         $ =last= :
+%         True for the last element.
+%         $ =last= - `IntExpr` :
+%         True for the last-minus-nth element. For example,
+%         `last-1` is the element directly preceding the last one.
+%         $ `IntExpr` :
+%         True for the element whose index equals `IntExpr`.
+%       $ Integer :
+%       The N-th element with the given name, with 1 denoting the
+%       first element. Same as index(Integer).
+%       $ =last= :
+%       The last element with the given name. Same as
+%       index(last).
+%       $ =last= - IntExpr :
+%       The IntExpr-th element before the last.
+%       Same as index(last-IntExpr).
+%
+%   Defined function argument values are:
+%
+%       $ =self= :
+%       Evaluate to the entire element
+%       $ =content= :
+%       Evaluate to the content of the element (a list)
+%       $ =text= :
+%       Evaluates to all text from the sub-tree, represented
+%       as a list of characters.
+%       $ `text(atom)` :
+%       Evaluates to all text from the sub-tree as an atom.
+%       $ =normalize_space= :
+%       As =text=, but uses normalize_space/2 to normalise
+%       white-space in the output
+%       $ =number= :
+%       Extract an integer or float from the value.  Ignores
+%       leading and trailing white-space
+%       $ =|@|=Attribute :
+%       Evaluates to the value of the given attribute.  Attribute
+%       can be a compound term. In this case the functor name
+%       denotes the element and arguments perform transformations
+%       on the attribute value.  Defined transformations are:
+%
+%         - number
+%         Translate the value into a number using
+%         xsd_number_chars/2.
+%         - integer
+%         As `number`, but subsequently transform the value
+%         into an integer using the round/1 function.
+%         - float
+%         As `number`, but subsequently transform the value
+%         into a float using the float/1 function.
+%         - lower
+%         Translate the value to lower case, preserving
+%         the type.
+%         - upper
+%         Translate the value to upper case, preserving
+%         the type.
+%
+%   In addition, the argument-list can be _conditions_:
+%
+%       $ Left = Right :
+%       Succeeds if the left-hand unifies with the right-hand.
+%       If the left-hand side is a function, this is evaluated.
+%       The right-hand side is _never_ evaluated, and thus the
+%       condition `content = content` defines that the content
+%       of the element is the atom `content`.
+%       The functions `lower_case` and `upper_case` can be applied
+%       to Right (see example below).
+%       $ contains(Haystack, Needle) :
+%       Succeeds if Needle is a sub-list of Haystack.
+%       $ XPath :
+%       Succeeds if XPath matches in the currently selected
+%       sub-DOM.  For example, the following expression finds
+%       an =h3= element inside a =div= element, where the =div=
+%       element itself contains an =h2= child with a =strong=
+%       child.
+%
+%         ==
+%         //div(h2/strong)/h3
+%         ==
+%
+%       This is equivalent to the conjunction of XPath goals below.
+%
+%         ==
+%            ...,
+%            xpath(DOM, //(div), Div),
+%            xpath(Div, h2/strong, _),
+%            xpath(Div, h3, Result)
+%         ==
+%
+%   **Examples**:
+%
+%   Match each table-row in DOM:
+%
+%       ==
+%       xpath(DOM, //tr, TR)
+%       ==
+%
+%   Match the last cell  of  each   tablerow  in  DOM.  This example
+%   illustrates that a result can be the input of subsequent xpath/3
+%   queries. Using multiple queries  on   the  intermediate  TR term
+%   guarantee that all results come from the same table-row:
+%
+%       ==
+%       xpath(DOM, //tr, TR),
+%       xpath(TR,  /td(last), TD)
+%       ==
+%
+%   Match each =href= attribute in an <a> element
+%
+%       ==
+%       xpath(DOM, //a(@href), HREF)
+%       ==
+%
+%   Suppose we have a table containing  rows where each first column
+%   is the name of a product with a   link to details and the second
+%   is the price (a number).  The   following  predicate matches the
+%   name, URL and price:
+%
+%       ==
+%       product(DOM, Name, URL, Price) :-
+%           xpath(DOM, //tr, TR),
+%           xpath(TR, td(1), C1),
+%           xpath(C1, /self(normalize_space), Name),
+%           xpath(C1, a(@href), URL),
+%           xpath(TR, td(2, number), Price).
+%       ==
+%
+%   Suppose we want to select  books   with  genre="thriller" from a
+%   tree containing elements =|<book genre=...>|=
+%
+%       ==
+%       thriller(DOM, Book) :-
+%           xpath(DOM, //book(@genre=thiller), Book).
+%       ==
+%
+%   Match the elements =|<table align="center">|= _and_ =|<table
+%   align="CENTER">|=:
+%
+%       ```prolog
+%           //table(@align(lower) = center)
+%       ```
+%
+%   Get the `width` and `height` of a `div` element as a number,
+%   and the `div` node itself:
+%
+%       ==
+%           xpath(DOM, //div(@width(number)=W, @height(number)=H), Div)
+%       ==
+%
+%   Note that `div` is an infix operator, so parentheses must be
+%   used in cases like the following:
+%
+%       ==
+%           xpath(DOM, //(div), Div)
+%       ==
+
+xpath(DOM, Spec, Content) :-
+    in_dom(Spec, DOM, Content).
+
+in_dom(//Spec, DOM, Value) :-
+    !,
+    element_spec(Spec, Name, Modifiers),
+    sub_dom(I, Len, Name, E, DOM),
+    modifiers(Modifiers, I, Len, E, Value).
+in_dom(/Spec, E, Value) :-
+    !,
+    element_spec(Spec, Name, Modifiers),
+    (   Name == self
+    ->  true
+    ;   element_name(E, Name)
+    ),
+    modifiers(Modifiers, 1, 1, E, Value).
+in_dom(A/B, DOM, Value) :-
+    !,
+    in_dom(A, DOM, Value0),
+    in_dom(B, Value0, Value).
+in_dom(A//B, DOM, Value) :-
+    !,
+    in_dom(A, DOM, Value0),
+    in_dom(//B, Value0, Value).
+in_dom(Spec, element(_, _, Content), Value) :-
+    element_spec(Spec, Name, Modifiers),
+    count_named_elements(Content, Name, CLen),
+    CLen > 0,
+    nth_element(N, Name, E, Content),
+    modifiers(Modifiers, N, CLen, E, Value).
+
+element_spec(Var, _, _) :-
+    var(Var),
+    !,
+    instantiation_error(Var).
+element_spec(NS:Term, NS:Name, Modifiers) :-
+    !,
+    callable_name_arguments(Term, Name0, Modifiers),
+    star(Name0, Name).
+element_spec(Term, Name, Modifiers) :-
+    !,
+    callable_name_arguments(Term, Name0, Modifiers),
+    star(Name0, Name).
+
+callable_name_arguments(Atom, Name, Arguments) :-
+    atom(Atom),
+    !,
+    Name = Atom, Arguments = [].
+callable_name_arguments(Compound, Name, Arguments) :-
+    Compound =.. [Name|Arguments].
+
+
+star(*, _) :- !.
+star(Name, Name).
+
+
+%!  sub_dom(-Index, -Count, +Name, -Sub, +DOM) is nondet.
+%
+%   Sub is a node in DOM with Name.
+%
+%   @param Count    is the total number of nodes in the content
+%                   list Sub appears that have the same name.
+%   @param Index    is the 1-based index of Sub of nodes with
+%                   Name.
+
+sub_dom(1, 1, Name, DOM, DOM) :-
+    element_name(DOM, Name0),
+    \+ Name \= Name0.
+sub_dom(N, Len, Name, E, element(_,_,Content)) :-
+    !,
+    sub_dom_2(N, Len, Name, E, Content).
+sub_dom(N, Len, Name, E, Content) :-
+    list_si(Content),
+    sub_dom_2(N, Len, Name, E, Content).
+
+sub_dom_2(N, Len, Name, Element, Content) :-
+    (   count_named_elements(Content, Name, Len),
+        nth_element(N, Name, Element, Content)
+    ;   member(element(_,_,C2), Content),
+        sub_dom_2(N, Len, Name, Element, C2)
+    ).
+
+
+%!  count_named_elements(+Content, +Name, -Count) is det.
+%
+%   Count is the number of nodes with Name in Content.
+
+count_named_elements(Content, Name, Count) :-
+    count_named_elements(Content, Name, 0, Count).
+
+count_named_elements([], _, Count, Count).
+count_named_elements([element(Name,_,_)|T], Name0, C0, C) :-
+    \+ Name \= Name0,
+    !,
+    C1 is C0+1,
+    count_named_elements(T, Name0, C1, C).
+count_named_elements([_|T], Name, C0, C) :-
+    count_named_elements(T, Name, C0, C).
+
+
+%!  nth_element(?N, +Name, -Element, +Content:list) is nondet.
+%
+%   True if Element is the N-th element with name in Content.
+
+nth_element(N, Name, Element, Content) :-
+    nth_element_(1, N, Name, Element, Content).
+
+nth_element_(I, N, Name, E, [H|T]) :-
+    element_name(H, Name0),
+    \+ Name \= Name0,
+    !,
+    (   N = I,
+        E = H
+    ;   I2 is I + 1,
+        (   nonvar(N), I2 > N
+        ->  !, fail
+        ;   true
+        ),
+        nth_element_(I2, N, Name, E, T)
+    ).
+nth_element_(I, N, Name, E, [_|T]) :-
+    nth_element_(I, N, Name, E, T).
+
+
+%!  modifiers(+Modifiers, +I, +Clen, +DOM, -Value)
+%
+%
+
+modifiers([], _, _, Value, Value).
+modifiers([H|T], I, L, Value0, Value) :-
+    modifier(H, I, L, Value0, Value1),
+    modifiers(T, I, L, Value1, Value).
+
+modifier(M, _, _, _, _) :-
+    var(M),
+    !,
+    instantiation_error(M).
+modifier(Index, I, L, Value0, Value) :-
+    implicit_index_modifier(Index),
+    !,
+    Value = Value0,
+    index_modifier(Index, I, L).
+modifier(index(Index), I, L, Value, Value) :-
+    !,
+    index_modifier(Index, I, L).
+modifier(Function, _, _, In, Out) :-
+    xpath_function(Function),
+    !,
+    xpath_function(Function, In, Out).
+modifier(Function, _, _, In, Out) :-
+    xpath_condition(Function, In),
+    Out = In.
+
+implicit_index_modifier(I) :-
+    integer(I),
+    !.
+implicit_index_modifier(last).
+implicit_index_modifier(last-_Expr).
+
+index_modifier(Var, I, _L) :-
+    var(Var),
+    !,
+    Var = I.
+index_modifier(last, I, L) :-
+    !,
+    I =:= L.
+index_modifier(last-Expr, I, L) :-
+    !,
+    I =:= L-Expr.
+index_modifier(N, I, _) :-
+    N =:= I.
+
+xpath_function(self, DOM, DOM).                                % self
+xpath_function(content, Element, Value) :-                     % content
+    element_content(Element, Value).
+xpath_function(text, DOM, Text) :-                             % text
+    text_of_dom(DOM, chars, Text).
+xpath_function(text(As), DOM, Text) :-                         % text(atom)
+    text_of_dom(DOM, As, Text).
+xpath_function(normalize_space, DOM, Text) :-                  % normalize_space
+    text_of_dom(DOM, chars, Text0),
+    normalize_space(Text0, Text).
+xpath_function(number, DOM, Number) :-                         % number
+    text_of_dom(DOM, chars, Text0),
+    normalize_space(Text0, Text),
+    catch(xsd_number_chars(Number, Text), _, fail).
+xpath_function(@Name, element(_, Attrs, _), Value) :-          % @Name
+    (   atom(Name)
+    ->  memberchk(Name=Value, Attrs)
+    ;   compound(Name)
+    ->  Name =.. [AName|AOps],
+        memberchk(AName=Value0, Attrs),
+        translate_attribute(AOps, Value0, Value)
+    ;   member(Name=Value, Attrs)
+    ).
+xpath_function(quote(Value), _, Value).                         % quote(Value)
+
+xpath_function(self).
+xpath_function(content).
+xpath_function(text).
+xpath_function(text(_)).
+xpath_function(normalize_space).
+xpath_function(number).
+xpath_function(@_).
+xpath_function(quote(_)).
+
+translate_attribute([], Value, Value).
+translate_attribute([H|T], Value0, Value) :-
+    translate_attr(H, Value0, Value1),
+    translate_attribute(T, Value1, Value).
+
+translate_attr(number, Value0, Value) :-
+    xsd_number_chars(Value, Value0).
+translate_attr(integer, Value0, Value) :-
+    xsd_number_chars(Value1, Value0),
+    Value is round(Value1).
+translate_attr(float, Value0, Value) :-
+    xsd_number_chars(Value1, Value0),
+    Value is float(Value1).
+% The implementation of these translations is left for later.
+% translate_attr(lower, Value0, Value) :- ...
+% translate_attr(upper, Value0, Value) :- ...
+
+xpath_condition(Left = Right, Value) :-                        % =
+    !,
+    var_or_function(Left, Value, LeftValue),
+    process_equality(LeftValue, Right).
+xpath_condition(contains(Haystack, Needle), Value) :-          % contains(Haystack, Needle)
+    !,
+    val_or_function(Haystack, Value, HaystackValue),
+    val_or_function(Needle, Value, NeedleValue),
+    (   phrase((list(_),list(NeedleValue),list(_)), HaystackValue)
+    ->  true
+    ).
+xpath_condition(Spec, Dom) :-
+    in_dom(Spec, Dom, _).
+
+
+%!  process_equality(+Left, +Right) is semidet.
+%
+%   Provides (very) partial support for XSLT   functions that can be
+%   applied according to the XPath 2 specification.
+%
+%   For example the XPath expression  in   [1],  and  the equivalent
+%   Prolog expression in [2], would both   match the HTML element in
+%   [3].
+%
+%     ==
+%     [1] //table[align=lower-case(center)]
+%     [2] //table(@align=lower_case(center))
+%     [3] <table align="CENTER">
+%     ==
+
+process_equality(Left, Right) :-
+    var(Right),
+    !,
+    Left = Right.
+process_equality(Left, lower_case(Right)) :-
+    !,
+    downcase_atom(Left, Right).
+process_equality(Left, upper_case(Right)) :-
+    !,
+    upcase_atom(Left, Right).
+process_equality(Left, Right) :-
+    Left = Right.
+
+
+var_or_function(Arg, _, Arg) :-
+    var(Arg),
+    !.
+var_or_function(Func, Value0, Value) :-
+    xpath_function(Func),
+    !,
+    xpath_function(Func, Value0, Value).
+var_or_function(Value, _, Value).
+
+val_or_function(Arg, _, Arg) :-
+    var(Arg),
+    !,
+    instantiation_error(Arg).
+val_or_function(Func, Value0, Value) :-                         % TBD
+    xpath_function(Func, Value0, Value),
+    !.
+val_or_function(Value, _, Value).
+
+
+%!  text_of_dom(+DOM, +As, -Text:(chars | atom)) is det.
+%
+%   Text is the joined textual content of DOM.
+
+text_of_dom(DOM, As, Text) :-
+    phrase(text_of(DOM), Text0),
+    (   As == chars ->
+        Text = Text0
+    ;   As == atom ->
+        atom_chars(Text, Text0)
+    ;   domain_error(As, atom_or_chars, xpath)
+    ).
+
+text_of(element(_,_,Content)) -->
+    text_of_list(Content).
+text_of([]) -->
+    [].
+text_of([H|T]) -->
+    text_of(H),
+    text_of(T).
+
+
+text_of_list([]) -->
+    [].
+text_of_list([H|T]) -->
+    text_of_1(H),
+    text_of_list(T).
+
+
+text_of_1(element(_,_,Content)) -->
+        text_of_list(Content).
+text_of_1([C|Cs]) --> list([C|Cs]).
+
+list([]) --> [].
+list([L|Ls]) --> [L], list(Ls).
+
+% For now, we use number_chars/2 to parse XML numbers.
+% If the need arises, we can extend this to additional
+% float constants and syntax that may occur in XML files.
+
+xsd_number_chars(Number, Chars) :-
+        number_chars(Number, Chars).
+
+normalize_space(Text0, Text) :-
+        Text0 = Text.           % no conversion for the moment.

src/machine/attributed_variables.pl

@@ -1,6 +1,7 @@
+:- module('$atts', []).
+
 driver(Vars, Values) :-
     iterate(Vars, Values, ListOfListsOfGoalLists),
-    '$clear_attr_var_bindings',
     !,
     call_goals(ListOfListsOfGoalLists),
     '$return_from_verify_attr'.
@@ -17,6 +18,14 @@ gather_modules([Attr|Attrs], [Module|Modules]) :-
     '$module_of'(Module, Attr),  % write the owning module of Attr to Module.
     gather_modules(Attrs, Modules).
 
+call_verify_attributes(Attrs, _, _, []) :-
+    var(Attrs), !.
+call_verify_attributes([], _, _, []).
+call_verify_attributes([Attr|Attrs], Var, Value, ListOfGoalLists) :-
+    gather_modules([Attr|Attrs], Modules0),
+    sort(Modules0, Modules),
+    verify_attrs(Modules, Var, Value, ListOfGoalLists).
+
 verify_attrs([Module|Modules], Var, Value, [Goals|ListOfGoalLists]) :-
     catch(Module:verify_attributes(Var, Value, Goals),
           error(evaluation_error((Module:verify_attributes)/3), verify_attributes/3),
@@ -24,14 +33,6 @@ verify_attrs([Module|Modules], Var, Value, [Goals|ListOfGoalLists]) :-
     verify_attrs(Modules, Var, Value, ListOfGoalLists).
 verify_attrs([], _, _, []).
 
-call_verify_attributes(Attrs, _, _, []) :-
-    var(Attrs), !.
-call_verify_attributes([], _, _, []).
-call_verify_attributes([Attr|Attrs], Var, Value, ListOfGoalLists) :-
-    gather_modules([Attr|Attrs], Modules0),
-    sort(Modules0, Modules),    
-    verify_attrs(Modules, Var, Value, ListOfGoalLists).
-
 call_goals([ListOfGoalLists | ListsCubed]) :-
     call_goals_0(ListOfGoalLists),
     call_goals(ListsCubed).

src/machine/attributed_variables.rs

@@ -1,5 +1,9 @@
-use crate::prolog::machine::*;
+use crate::heap_iter::*;
+use crate::machine::*;
 
+use crate::indexmap::IndexSet;
+
+use std::cmp::Ordering;
 use std::vec::IntoIter;
 
 pub static VERIFY_ATTRS: &str = include_str!("attributed_variables.pl");
@@ -7,6 +11,7 @@ pub static PROJECT_ATTRS: &str = include_str!("project_attributes.pl");
 
 pub(super) type Bindings = Vec<(usize, Addr)>;
 
+#[derive(Debug)]
 pub(super) struct AttrVarInitializer {
     pub(super) attribute_goals: Vec<Addr>,
     pub(super) attr_var_queue: Vec<usize>,
@@ -18,7 +23,8 @@ pub(super) struct AttrVarInitializer {
 }
 
 impl AttrVarInitializer {
-    pub(super) fn new(verify_attrs_loc: usize, project_attrs_loc: usize) -> Self {
+    pub(super)
+    fn new(verify_attrs_loc: usize, project_attrs_loc: usize) -> Self {
         AttrVarInitializer {
             attribute_goals: vec![],
             attr_var_queue: vec![],
@@ -31,21 +37,24 @@ impl AttrVarInitializer {
     }
 
     #[inline]
-    pub(super) fn reset(&mut self) {
-	self.attribute_goals.clear();
+    pub(super)
+    fn reset(&mut self) {
+	    self.attribute_goals.clear();
         self.attr_var_queue.clear();
         self.bindings.clear();
     }
 
     #[inline]
-    pub(super) fn backtrack(&mut self, queue_b: usize, bindings_b: usize) {
+    pub(super)
+    fn backtrack(&mut self, queue_b: usize, bindings_b: usize) {
         self.attr_var_queue.truncate(queue_b);
         self.bindings.truncate(bindings_b);
     }
 }
 
 impl MachineState {
-    pub(super) fn push_attr_var_binding(&mut self, h: usize, addr: Addr) {
+    pub(super)
+    fn push_attr_var_binding(&mut self, h: usize, addr: Addr) {
         if self.attr_var_init.bindings.is_empty() {
             self.attr_var_init.instigating_p = self.p.local();
 
@@ -66,18 +75,17 @@ impl MachineState {
             .attr_var_init
             .bindings
             .iter()
-            .map(|(ref h, _)| Addr::AttrVar(*h));
+            .map(|(ref h, _)| HeapCellValue::Addr(Addr::AttrVar(*h)));
 
         let var_list_addr = Addr::HeapCell(self.heap.to_list(iter));
 
         let iter = self
             .attr_var_init
             .bindings
-            .iter()
-            .map(|(_, ref addr)| addr.clone());
+            .drain(0 ..)
+            .map(|(_, addr)| HeapCellValue::Addr(addr));
 
         let value_list_addr = Addr::HeapCell(self.heap.to_list(iter));
-
         (var_list_addr, value_list_addr)
     }
 
@@ -92,7 +100,8 @@ impl MachineState {
         self[temp_v!(2)] = value_list_addr;
     }
 
-    pub(super) fn gather_attr_vars_created_since(&self, b: usize) -> IntoIter<Addr> {
+    pub(super)
+    fn gather_attr_vars_created_since(&self, b: usize) -> IntoIter<Addr> {
         let mut attr_vars: Vec<_> = self.attr_var_init.attr_var_queue[b..]
             .iter()
             .filter_map(|h| match self.store(self.deref(Addr::HeapCell(*h))) {
@@ -101,13 +110,16 @@ impl MachineState {
             })
             .collect();
 
-        attr_vars.sort_unstable_by(|a1, a2| self.compare_term_test(a1, a2));
+        attr_vars.sort_unstable_by(|a1, a2| {
+            self.compare_term_test(a1, a2).unwrap_or(Ordering::Less)
+        });
 
         self.term_dedup(&mut attr_vars);
         attr_vars.into_iter()
     }
 
-    pub(super) fn verify_attr_interrupt(&mut self, p: usize) {
+    pub(super)
+    fn verify_attr_interrupt(&mut self, p: usize) {
         self.allocate(self.num_of_args + 2);
 
         let e = self.e;
@@ -118,9 +130,9 @@ impl MachineState {
         }
 
         self.stack.index_and_frame_mut(e)[self.num_of_args + 1] =
-            Addr::Con(Constant::CutPoint(self.b0));
+            Addr::CutPoint(self.b0);
         self.stack.index_and_frame_mut(e)[self.num_of_args + 2] =
-            Addr::Con(Constant::Usize(self.num_of_args));
+            Addr::Usize(self.num_of_args);
 
         self.verify_attributes();
 
@@ -128,4 +140,37 @@ impl MachineState {
         self.b0 = self.b;
         self.p = CodePtr::Local(LocalCodePtr::DirEntry(p));
     }
+
+    pub(super)
+    fn attr_vars_of_term(&self, addr: Addr) -> Vec<Addr> {
+        let mut seen_set  = IndexSet::new();
+        let mut seen_vars = vec![];
+
+        let mut iter = self.acyclic_pre_order_iter(addr);
+
+        while let Some(addr) = iter.next() {
+            if let HeapCellValue::Addr(Addr::AttrVar(h)) = self.heap.index_addr(&addr).as_ref() {
+                if seen_set.contains(h) {
+                    continue;
+                }
+
+                seen_vars.push(addr);
+                seen_set.insert(*h);
+
+                let mut l = h + 1;
+                let mut list_elements = vec![];
+
+                while let Addr::Lis(elem) = self.store(self.deref(Addr::HeapCell(l))) {
+                    list_elements.push(self.heap[elem].as_addr(elem));
+                    l = elem + 1;
+                }
+
+                for element in list_elements.into_iter().rev() {
+                    iter.stack().push(element);
+                }
+            }
+        }
+
+        seen_vars
+    }
 }

src/machine/code_repo.rs

@@ -1,17 +1,18 @@
-use crate::prolog::clause_types::*;
-use crate::prolog::codegen::*;
-use crate::prolog::debray_allocator::*;
-use crate::prolog::forms::*;
-use crate::prolog::instructions::*;
-use crate::prolog::machine::compile::*;
-use crate::prolog::machine::machine_errors::*;
-use crate::prolog::machine::machine_indices::*;
+use crate::clause_types::*;
+use crate::codegen::*;
+use crate::debray_allocator::*;
+use crate::forms::*;
+use crate::instructions::*;
+use crate::machine::compile::*;
+use crate::machine::machine_errors::*;
+use crate::machine::machine_indices::*;
 
-use indexmap::IndexSet;
+use crate::indexmap::IndexSet;
 
 use std::collections::VecDeque;
 use std::mem;
 
+#[derive(Debug)]
 pub struct CodeRepo {
     pub(super) cached_query: Code,
     pub(super) goal_expanders: Code,
@@ -52,15 +53,27 @@ impl CodeRepo {
         self.term_dir
             .get_mut(&key)
             .map(|entry| {
-                (
-                    Predicate((entry.0).0.drain(len..).collect()),
-                    entry.1.drain(queue_len..).collect(),
-                )
+                let terms =
+                    if len < (entry.0).0.len() {
+                        (entry.0).0.drain(len ..).collect()
+                    } else {
+                        vec![]
+                    };
+
+                let queue =
+                    if queue_len < entry.1.len() {
+                        entry.1.drain(queue_len ..).collect()
+                    } else {
+                        VecDeque::new()
+                    };
+
+                (Predicate(terms), queue)
             })
-            .unwrap_or((Predicate::new(), VecDeque::from(vec![])))
+            .unwrap_or((Predicate::new(), VecDeque::new()))
     }
 
-    pub(crate) fn add_in_situ_result(
+    pub(crate)
+    fn add_in_situ_result(
         &mut self,
         result: &CompiledResult,
         in_situ_code_dir: &mut InSituCodeDir,
@@ -89,7 +102,7 @@ impl CodeRepo {
             _ => {
                 in_situ_code_dir.insert((name, arity), p);
             }
-        }        
+        }
 
         let mut cg = CodeGenerator::<DebrayAllocator>::new(non_counted_bt);
         let mut decl_code = cg.compile_predicate(&decl.0)?;
@@ -100,16 +113,19 @@ impl CodeRepo {
     }
 
     #[inline]
-    pub(super) fn size_of_cached_query(&self) -> usize {
+    pub(super)
+    fn size_of_cached_query(&self) -> usize {
         self.cached_query.len()
     }
 
     #[inline]
-    pub(super) fn take_in_situ_code(&mut self) -> Code {
+    pub(super)
+    fn take_in_situ_code(&mut self) -> Code {
         mem::replace(&mut self.in_situ_code, Code::new())
     }
 
-    pub(super) fn lookup_instr<'a>(
+    pub(super)
+    fn lookup_instr<'a>(
         &'a self,
         last_call: bool,
         p: &CodePtr,

src/machine/code_walker.rs

@@ -1,4 +1,4 @@
-use crate::prolog::instructions::*;
+use crate::instructions::*;
 
 use std::collections::VecDeque;
 

src/machine/compile.rs

@@ -1,27 +1,26 @@
-use prolog_parser::ast::*;
-use prolog_parser::parser::get_desc;
-use prolog_parser::tabled_rc::TabledData;
+use crate::prolog_parser::ast::*;
+use crate::prolog_parser::parser::get_desc;
+use crate::prolog_parser::tabled_rc::TabledData;
 
-use crate::prolog::codegen::*;
-use crate::prolog::debray_allocator::*;
-use crate::prolog::forms::*;
-use crate::prolog::instructions::*;
-use crate::prolog::iterators::*;
-use crate::prolog::machine::code_walker::*;
-use crate::prolog::machine::machine_errors::*;
-use crate::prolog::machine::machine_indices::*;
-use crate::prolog::machine::term_expansion::ExpansionAdditionResult;
-use crate::prolog::machine::toplevel::*;
-use crate::prolog::machine::*;
+use crate::codegen::*;
+use crate::debray_allocator::*;
+use crate::forms::*;
+use crate::instructions::*;
+use crate::iterators::*;
+use crate::machine::code_walker::*;
+use crate::machine::machine_errors::*;
+use crate::machine::machine_indices::*;
+use crate::machine::term_expansion::ExpansionAdditionResult;
+use crate::machine::toplevel::*;
+use crate::machine::*;
 
-use indexmap::{IndexMap, IndexSet};
+use crate::indexmap::{IndexMap, IndexSet};
 
-use ref_thread_local::RefThreadLocal;
+use crate::ref_thread_local::RefThreadLocal;
 
 use std::cell::Cell;
 use std::collections::VecDeque;
 use std::fs::File;
-use std::io::Read;
 use std::mem;
 use std::path::PathBuf;
 
@@ -60,9 +59,9 @@ fn fix_filename(
     Ok(path)
 }
 
-fn load_module<R: Read>(
+fn load_module(
     wam: &mut Machine,
-    stream: ParsingStream<R>,
+    stream: Stream,
     suppress_warnings: bool,
     listing_src: &ListingSource,
 ) -> Result<ClauseName, SessionError> {
@@ -78,7 +77,13 @@ fn load_module<R: Read>(
         listing_src.clone(),
     );
 
-    let results = compiler.gather_items(wam, stream, &mut indices);
+    let mut stream = parsing_stream(stream)?;
+
+    let results = compiler.gather_items(
+        wam,
+        &mut stream,
+        &mut indices,
+    );
 
     let module_name = if let Some(ref module) = &compiler.module {
         module.module_decl.name.clone()
@@ -114,14 +119,14 @@ fn load_module_from_file(
     let mut path_buf = fix_filename(wam.indices.atom_tbl.clone(), path_buf)?;
     let filename = clause_name!(path_buf.to_string_lossy().to_string(), wam.indices.atom_tbl);
 
-    let file_handle = File::open(&path_buf).or_else(|_| {
+    let file_handle = Stream::from_file_as_input(filename.clone(), File::open(&path_buf).or_else(|_| {
         Err(SessionError::InvalidFileName(filename.clone()))
-    })?;
+    })?);
 
     path_buf.pop();
 
     let listing_src = ListingSource::from_file_and_path(filename, path_buf);
-    load_module(wam, parsing_stream(file_handle), suppress_warnings, &listing_src)
+    load_module(wam, file_handle, suppress_warnings, &listing_src)
 }
 
 pub type PredicateCompileQueue = (Predicate, VecDeque<TopLevel>);
@@ -185,6 +190,8 @@ fn set_first_index(code: &mut Code) {
                 if *offset == 0 =>
             {
                 *offset = code_len - idx;
+                debug_assert!(*offset > 0);
+
                 break;
             }
             _ => {}
@@ -320,10 +327,11 @@ fn setup_module_expansions(wam: &mut Machine, module: &Module) {
     );
 }
 
-pub(super) fn compile_into_module<R: Read>(
+pub(super)
+fn compile_into_module(
     wam: &mut Machine,
     module_name: ClauseName,
-    src: ParsingStream<R>,
+    src: Stream,
     name: ClauseName,
 ) -> EvalSession {
     let mut indices = default_index_store!(wam.atom_tbl_of(&name));
@@ -333,37 +341,45 @@ pub(super) fn compile_into_module<R: Read>(
     indices.op_dir   = module.op_dir.clone();
     indices.atom_tbl = module.atom_tbl.clone();
 
-    let mut compiler = ListingCompiler::new(&wam.code_repo, true, module.listing_src.clone());
+    let mut compiler = ListingCompiler::new(
+        &wam.code_repo,
+        true,
+        module.listing_src.clone(),
+    );
 
     match compile_into_module_impl(wam, &mut compiler, module, src, indices) {
-        Ok(()) => EvalSession::EntrySuccess,
+        Ok(()) => {
+            EvalSession::EntrySuccess
+        }
         Err(e) => {
-            if let Some(module) = compiler.module.take() {
-                wam.indices.insert_module(module);
-            }
-
             compiler.drop_expansions(&mut wam.code_repo);
             EvalSession::from(e)
         }
     }
 }
 
-fn compile_into_module_impl<R: Read>(
+fn compile_into_module_impl(
     wam: &mut Machine,
     compiler: &mut ListingCompiler,
     module: Module,
-    src: ParsingStream<R>,
+    src: Stream,
     mut indices: IndexStore,
 ) -> Result<(), SessionError> {
     setup_module_expansions(wam, &module);
 
     let module_name = module.module_decl.name.clone();
-    compiler.module = Some(module);
+    // compiler.module = Some(module); This trips the goal expansion up. Should be possible to 'merge' modules.
+    // A much better strategy!
+    wam.indices.insert_module(module);
 
     wam.code_repo.compile_hook(CompileTimeHook::TermExpansion)?;
     wam.code_repo.compile_hook(CompileTimeHook::GoalExpansion)?;
 
-    let mut results = compiler.gather_items(wam, src, &mut indices)?;
+    let mut results = compiler.gather_items(
+        wam,
+        &mut parsing_stream(src)?,
+        &mut indices,
+    )?;
 
     compiler.adapt_in_situ_code(
         results.worker_results,
@@ -383,21 +399,22 @@ fn compile_into_module_impl<R: Read>(
     clause_code_generator.generate_clause_code(&results.dynamic_clause_map, wam)?;
 
     let top_level_term_dir = results.top_level_term_dirs.consolidate();
+    let module = wam.indices.take_module(module_name).unwrap();
 
     add_module(
         wam,
-        compiler.module.take().unwrap(),
+        module,
         indices,
         top_level_term_dir,
     );
 
     wam.code_repo.code.extend(results.in_situ_code.into_iter());
-
     clause_code_generator.add_clause_code(wam, results.dynamic_clause_map);
 
     Ok(compiler.drop_expansions(&mut wam.code_repo))
 }
 
+#[derive(Debug)]
 pub struct GatherResult {
     dynamic_clause_map: DynamicClauseMap,
     pub(crate) worker_results: Vec<PredicateCompileQueue>,
@@ -412,6 +429,7 @@ pub struct GatherResult {
     in_situ_module_dir: ModuleStubDir,
 }
 
+#[derive(Debug)]
 pub struct ClauseCodeGenerator {
     len_offset: usize,
     code: Code,
@@ -451,6 +469,7 @@ impl ClauseCodeGenerator {
                             vec![Box::new(head.clone()), Box::new(tail.clone())],
                             None,
                         );
+
                         PredicateClause::Fact(clause, 0, 0)
                     })
                     .collect(),
@@ -518,6 +537,7 @@ fn insert_or_refresh_term_dir_quantum(
     }
 }
 
+#[derive(Debug)]
 pub struct ListingCompiler {
     module: Option<Module>,
     user_term_dir: TermDir,
@@ -548,8 +568,8 @@ fn add_module(
     term_dir: TermDir,
 ) {
     module.code_dir.extend(indices.code_dir);
-    module.op_dir.extend(indices.op_dir.into_iter());
-    module.term_dir.extend(term_dir.into_iter());
+    module.op_dir.extend(indices.op_dir);
+    module.term_dir.extend(term_dir);
 
     wam.add_in_situ_module_dir(indices.module_dir);
     wam.add_module(module);
@@ -568,7 +588,7 @@ fn add_non_module_code(
     clause_code_generator.generate_clause_code(&dynamic_clause_map, wam)?;
 
     add_toplevel(wam, indices, term_dir);
-    wam.code_repo.code.extend(code.into_iter());
+    wam.code_repo.code.extend(code);
     clause_code_generator.add_clause_code(wam, dynamic_clause_map);
 
     Ok(())
@@ -582,21 +602,22 @@ fn load_library(
 ) -> Result<ClauseName, SessionError> {
     match LIBRARIES.borrow().get(name.as_str()) {
         Some(code) => {
-            let mut lib_path = current_dir();
-
-            lib_path.pop();
-            lib_path.push("lib");
-
-            let listing_src = ListingSource::from_file_and_path(name, lib_path);
+            let listing_src = ListingSource::User;
 
             load_module(
                 wam,
-                parsing_stream(code.as_bytes()),
+                Stream::from(*code),
                 suppress_warnings,
                 &listing_src,
             )
         }
-        None => Err(SessionError::ModuleNotFound)
+        None => {
+            let err = ExistenceError::ModuleSource(ModuleSource::Library(
+                name.clone()
+            ));
+
+            Err(SessionError::ExistenceError(err))
+        }
     }
 }
 
@@ -614,7 +635,7 @@ impl ListingCompiler {
                 .term_dir_entry_len((clause_name!("term_expansion"), 2)),
             orig_goal_expansion_lens: code_repo
                 .term_dir_entry_len((clause_name!("goal_expansion"), 2)),
-	    initialization_goals: (vec![], VecDeque::from(vec![])),
+	        initialization_goals: (vec![], VecDeque::from(vec![])),
             suppress_warnings,
             listing_src
         }
@@ -682,7 +703,11 @@ impl ListingCompiler {
 
             Ok(wam_indices.insert_module(submodule))
         } else {
-            Err(SessionError::ModuleNotFound)
+            let err = ExistenceError::ModuleSource(ModuleSource::File(
+                module_name,
+            ));
+
+            Err(SessionError::ExistenceError(err))
         }
     }
 
@@ -716,7 +741,11 @@ impl ListingCompiler {
 
             Ok(wam_indices.insert_module(submodule))
         } else {
-            Err(SessionError::ModuleNotFound)
+            let err = ExistenceError::ModuleSource(ModuleSource::File(
+                module_name
+            ));
+
+            Err(SessionError::ExistenceError(err))
         }
     }
 
@@ -729,14 +758,14 @@ impl ListingCompiler {
     }
 
     fn generate_init_goal_code(
-	&mut self,
+	    &mut self,
     ) -> Result<Code, SessionError> {
-	let query_terms = mem::replace(&mut self.initialization_goals.0, vec![]);
-	let queue = mem::replace(&mut self.initialization_goals.1, VecDeque::new());
+	    let query_terms = mem::replace(&mut self.initialization_goals.0, vec![]);
+	    let queue = mem::replace(&mut self.initialization_goals.1, VecDeque::new());
 
-	compile_query(query_terms, queue)
-	    .map(|(code, _)| code)
-	    .map_err(SessionError::from)
+	    compile_query(query_terms, queue)
+	        .map(|(code, _)| code)
+	        .map_err(SessionError::from)
     }
 
     fn set_code_index(
@@ -875,7 +904,7 @@ impl ListingCompiler {
                 .or_insert((Predicate::new(), VecDeque::from(vec![])));
 
             len += 1;
-            queue_len += queue_len;
+            queue_len += queue.len();
 
             (preds.0).0.push(clause);
             preds.1.extend(queue.into_iter());
@@ -952,12 +981,12 @@ impl ListingCompiler {
                     Err(SessionError::from(ParserError::InvalidModuleDecl))
                 }
             }
-	    Declaration::ModuleInitialization(query_terms, queue) => {
-		self.initialization_goals.0.extend(query_terms.into_iter());
-		self.initialization_goals.1.extend(queue.into_iter());
+	        Declaration::ModuleInitialization(query_terms, queue) => {
+		        self.initialization_goals.0.extend(query_terms.into_iter());
+		        self.initialization_goals.1.extend(queue.into_iter());
 
-		Ok(())
-	    }
+		        Ok(())
+	        }
             Declaration::MultiFile(..) => {
                 Ok(())
             }
@@ -968,6 +997,10 @@ impl ListingCompiler {
             Declaration::Op(op_decl) => {
                 self.submit_op(wam, indices, &op_decl)
             }
+            Declaration::SetPrologFlag(dbl_quotes) => {
+                wam.machine_st.flags.double_quotes = dbl_quotes;
+                Ok(())
+            }
             Declaration::UseModule(ModuleSource::Library(name)) => {
                 let name = if !wam.indices.modules.contains_key(&name) {
                     load_library(wam, name, true)?
@@ -1018,10 +1051,10 @@ impl ListingCompiler {
         }
     }
 
-    fn setup_multifile_decl<R: Read>(
+    fn setup_multifile_decl(
         &self,
         indicator: MultiFileIndicator,
-        worker: &mut TopLevelBatchWorker<R>,
+        worker: &mut TopLevelBatchWorker,
     ) -> Result<(), SessionError> {
         match indicator {
             MultiFileIndicator::LocalScoped(name, arity) => {
@@ -1042,7 +1075,11 @@ impl ListingCompiler {
                         insert_or_refresh_term_dir_quantum(term_dir, key, term_dirs);
                     }
                     None => {
-                        return Err(SessionError::ModuleNotFound);
+                        let err = ExistenceError::ModuleSource(ModuleSource::File(
+                            module_name,
+                        ));
+
+                        return Err(SessionError::ExistenceError(err));
                     }
                 }
             }
@@ -1051,10 +1088,10 @@ impl ListingCompiler {
         Ok(())
     }
 
-    fn process_and_commit_decl<R: Read>(
+    fn process_and_commit_decl(
         &mut self,
         decl: Declaration,
-        worker: &mut TopLevelBatchWorker<R>,
+        worker: &mut TopLevelBatchWorker,
         indices: &mut IndexStore,
         flags: MachineFlags,
     ) -> Result<(), SessionError> {
@@ -1067,9 +1104,9 @@ impl ListingCompiler {
                     .entry((name.clone(), arity))
                     .or_insert(vec![]);
 
-		indices.code_dir
-		       .entry((name.clone(), arity))
-		       .or_insert(CodeIndex::dynamic_undefined(self.get_module_name()));
+		        indices.code_dir
+		            .entry((name.clone(), arity))
+		            .or_insert(CodeIndex::dynamic_undefined(self.get_module_name()));
             }
             &Declaration::Hook(hook, _, ref queue) if self.module.is_none() => worker
                 .term_stream
@@ -1101,15 +1138,16 @@ impl ListingCompiler {
         result
     }
 
-    pub(crate) fn gather_items<R: Read>(
+    pub(crate)
+    fn gather_items(
         &mut self,
         wam: &mut Machine,
-        mut src: ParsingStream<R>,
+        src: &mut ParsingStream<Stream>,
         indices: &mut IndexStore,
     ) -> Result<GatherResult, SessionError> {
         let flags = wam.machine_flags();
         let atom_tbl = indices.atom_tbl.clone();
-        let mut worker = TopLevelBatchWorker::new(&mut src, atom_tbl.clone(), flags, wam);
+        let mut worker = TopLevelBatchWorker::new(src, atom_tbl.clone(), flags, wam);
 
         let mut toplevel_results = vec![];
         let mut toplevel_indices = default_index_store!(atom_tbl.clone());
@@ -1246,6 +1284,17 @@ fn compile_work_impl(
                 .filter(|(name, _)| name.owning_module().as_str() != "builtins")
                 .map(ModuleExport::PredicateKey)
                 .collect();
+
+            module.module_decl.exports.extend(
+                indices.op_dir.iter()
+                    .map(|((name, _), OpDirValue (shared_op_desc, _))|
+                        ModuleExport::OpDecl(OpDecl(
+                            shared_op_desc.prec(),
+                            shared_op_desc.assoc(),
+                            name.clone(),
+                        ))
+                    )
+            );
         }
 
         let mut clause_code_generator =
@@ -1286,7 +1335,7 @@ fn compile_work_impl(
     let init_goal_code = compiler.generate_init_goal_code()?;
 
     if init_goal_code.len() > 0 {
-	if !wam.run_init_code(init_goal_code) {
+	    if !wam.run_init_code(init_goal_code) {
             println!("Warning: initialization goal for {} failed",
                      compiler.listing_src.name());
         }
@@ -1302,30 +1351,35 @@ fn compile_work_impl(
     Ok(())
 }
 
-fn compile_work<R: Read>(
+fn compile_work(
     compiler: &mut ListingCompiler,
     wam: &mut Machine,
-    src: ParsingStream<R>,
+    src: Stream,
     mut indices: IndexStore,
 ) -> EvalSession {
+    let mut stream = try_eval_session!(parsing_stream(src));
+    let src = &mut stream;
     let results = try_eval_session!(compiler.gather_items(wam, src, &mut indices));
+
     try_eval_session!(compile_work_impl(compiler, wam, indices, results));
+
     EvalSession::EntrySuccess
 }
 
 /* This is a truncated version of compile_user_module, used for
 compiling code composing special forms, ie. the code that calls
 M:verify_attributes on attributed variables. */
-pub fn compile_special_form<R: Read>(
+pub fn compile_special_form(
     wam: &mut Machine,
-    src: ParsingStream<R>,
+    src: Stream,
     listing_src: ListingSource,
 ) -> Result<usize, SessionError> {
     let mut indices = default_index_store!(wam.indices.atom_tbl.clone());
     setup_indices(wam, clause_name!("builtins"), &mut indices)?;
 
+    let mut src = parsing_stream(src)?;
     let mut compiler = ListingCompiler::new(&wam.code_repo, true, listing_src);
-    let mut results = compiler.gather_items(wam, src, &mut indices)?;
+    let mut results = compiler.gather_items(wam, &mut src, &mut indices)?;
 
     compiler.adapt_in_situ_code(
         results.worker_results,
@@ -1348,9 +1402,9 @@ pub fn compile_special_form<R: Read>(
 }
 
 #[inline]
-pub fn compile_listing<R: Read>(
+pub fn compile_listing(
     wam: &mut Machine,
-    src: ParsingStream<R>,
+    src: Stream,
     indices: IndexStore,
     suppress_warnings: bool,
     listing_src: ListingSource,
@@ -1373,20 +1427,24 @@ pub(super) fn setup_indices(
     module: ClauseName,
     indices: &mut IndexStore,
 ) -> Result<(), SessionError> {
-    if let Some(module) = wam.indices.take_module(module) {
+    if let Some(module) = wam.indices.take_module(module.clone()) {
         let flags = wam.machine_flags();
         let result = indices.use_module(&mut wam.code_repo, flags, &module);
 
         wam.indices.insert_module(module);
         result
     } else {
-        Err(SessionError::ModuleNotFound)
+        let err = ExistenceError::ModuleSource(ModuleSource::Library(
+            module
+        ));
+
+        Err(SessionError::ExistenceError(err))
     }
 }
 
-pub fn compile_user_module<R: Read>(
+pub fn compile_user_module(
     wam: &mut Machine,
-    src: ParsingStream<R>,
+    src: Stream,
     suppress_warnings: bool,
     listing_src: ListingSource,
 ) -> EvalSession {

src/machine/copier.rs

@@ -0,0 +1,314 @@
+use crate::machine::machine_indices::*;
+use crate::machine::stack::*;
+
+use std::mem;
+use std::ops::IndexMut;
+
+type Trail = Vec<(Ref, HeapCellValue)>;
+
+#[derive(Debug, Clone, Copy)]
+pub enum AttrVarPolicy {
+    DeepCopy,
+    StripAttributes
+}
+
+pub(crate)
+trait CopierTarget: IndexMut<usize, Output = HeapCellValue> {
+    fn deref(&self, val: Addr) -> Addr;
+    fn push(&mut self, val: HeapCellValue);
+    fn stack(&mut self) -> &mut Stack;
+    fn store(&self, val: Addr) -> Addr;
+    fn threshold(&self) -> usize;
+}
+
+pub(crate)
+fn copy_term<T: CopierTarget>(target: T, addr: Addr, attr_var_policy: AttrVarPolicy) {
+    let mut copy_term_state = CopyTermState::new(target, attr_var_policy);
+    copy_term_state.copy_term_impl(addr);
+}
+
+#[derive(Debug)]
+struct CopyTermState<T: CopierTarget> {
+    trail: Trail,
+    scan: usize,
+    old_h: usize,
+    target: T,
+    attr_var_policy: AttrVarPolicy,
+}
+
+impl<T: CopierTarget> CopyTermState<T> {
+    fn new(target: T, attr_var_policy: AttrVarPolicy) -> Self {
+        CopyTermState {
+            trail: Trail::new(),
+            scan: 0,
+            old_h: target.threshold(),
+            target,
+            attr_var_policy
+        }
+    }
+
+    #[inline]
+    fn value_at_scan(&mut self) -> &mut HeapCellValue {
+        let scan = self.scan;
+        &mut self.target[scan]
+    }
+
+    fn trail_list_cell(&mut self, addr: usize, threshold: usize) {
+        let trail_item = mem::replace(
+            &mut self.target[addr],
+            HeapCellValue::Addr(Addr::Lis(threshold)),
+        );
+
+        self.trail.push((
+            Ref::HeapCell(addr),
+            trail_item,
+        ));
+    }
+
+    fn copy_list(&mut self, addr: usize) {
+        for offset in 0 .. 2 {
+            if let Addr::Lis(h) = self.target[addr + offset].as_addr(addr + offset) {
+                if h >= self.old_h {
+                    *self.value_at_scan() = HeapCellValue::Addr(Addr::Lis(h));
+                    self.scan += 1;
+
+                    return;
+                }
+            }
+        }
+
+        let threshold = self.target.threshold();
+
+        *self.value_at_scan() = HeapCellValue::Addr(Addr::Lis(threshold));
+
+        for i in 0 .. 2 {
+            let hcv = self.target[addr + i].context_free_clone();
+            self.target.push(hcv);
+        }
+
+        let cdr = self.target.store(self.target.deref(Addr::HeapCell(addr + 1)));
+
+        if !cdr.is_ref() {
+            self.trail_list_cell(addr + 1, threshold);
+        } else {
+            let car = self.target.store(self.target.deref(Addr::HeapCell(addr)));
+
+            if !car.is_ref() {
+                self.trail_list_cell(addr, threshold);
+            }
+        }
+
+        self.scan += 1;
+    }
+
+    fn copy_partial_string(&mut self, addr: usize, n: usize) {
+        if let &HeapCellValue::Addr(Addr::PStrLocation(h, _)) = &self.target[addr] {
+            if h >= self.old_h {
+                *self.value_at_scan() = HeapCellValue::Addr(Addr::PStrLocation(h, n));
+                self.scan += 1;
+
+                return;
+            }
+        }
+
+        let threshold = self.target.threshold();
+
+        *self.value_at_scan() =
+            HeapCellValue::Addr(Addr::PStrLocation(threshold, n));
+
+        self.scan += 1;
+
+        let (pstr, has_tail) =
+            match &self.target[addr] {
+                &HeapCellValue::PartialString(ref pstr, has_tail) => {
+                    (pstr.clone_from_offset(0), has_tail)
+                }
+                _ => {
+                    unreachable!()
+                }
+            };
+
+        self.target.push(HeapCellValue::PartialString(pstr, has_tail));
+
+        let replacement = HeapCellValue::Addr(Addr::PStrLocation(threshold, n));
+
+        let trail_item = mem::replace(
+            &mut self.target[addr],
+            replacement,
+        );
+
+        self.trail.push((
+            Ref::HeapCell(addr),
+            trail_item,
+        ));
+
+        if has_tail {
+            let tail_addr = self.target[addr + 1].as_addr(addr + 1);
+            self.target.push(HeapCellValue::Addr(tail_addr));
+        }
+    }
+
+    fn reinstantiate_var(&mut self, addr: Addr, frontier: usize) {
+        match addr {
+            Addr::HeapCell(h) => {
+                self.target[frontier] = HeapCellValue::Addr(Addr::HeapCell(frontier));
+                self.target[h] = HeapCellValue::Addr(Addr::HeapCell(frontier));
+
+                self.trail.push((
+                    Ref::HeapCell(h),
+                    HeapCellValue::Addr(Addr::HeapCell(h)),
+                ));
+            }
+            Addr::StackCell(fr, sc) => {
+                self.target[frontier] = HeapCellValue::Addr(Addr::HeapCell(frontier));
+                self.target.stack().index_and_frame_mut(fr)[sc] = Addr::HeapCell(frontier);
+
+                self.trail.push((
+                    Ref::StackCell(fr, sc),
+                    HeapCellValue::Addr(Addr::StackCell(fr, sc)),
+                ));
+            }
+            Addr::AttrVar(h) => {
+                let threshold = if let AttrVarPolicy::DeepCopy = self.attr_var_policy {
+                    self.target.threshold()
+                } else {
+                    frontier
+                };
+
+                self.target[frontier] = HeapCellValue::Addr(Addr::HeapCell(threshold));
+                self.target[h] = HeapCellValue::Addr(Addr::HeapCell(threshold));
+
+                self.trail.push((
+                    Ref::AttrVar(h),
+                    HeapCellValue::Addr(Addr::AttrVar(h)),
+                ));
+
+                if let AttrVarPolicy::DeepCopy = self.attr_var_policy {
+                    self.target.push(HeapCellValue::Addr(Addr::AttrVar(threshold)));
+
+                    let list_val = self.target[h + 1].context_free_clone();
+                    self.target.push(list_val);
+                }
+            }
+            _ => {
+                unreachable!()
+            }
+        }
+    }
+
+    fn copy_var(&mut self, addr: Addr) {
+        let rd = self.target.store(self.target.deref(addr));
+
+        match rd {
+            Addr::AttrVar(h) | Addr::HeapCell(h) if h >= self.old_h => {
+                *self.value_at_scan() = HeapCellValue::Addr(rd);
+                self.scan += 1;
+            }
+            _ if addr == rd => {
+                self.reinstantiate_var(addr, self.scan);
+                self.scan += 1;
+            }
+            _ => {
+                *self.value_at_scan() = HeapCellValue::Addr(rd);
+            }
+        }
+    }
+
+    fn copy_structure(&mut self, addr: usize) {
+        match self.target[addr].context_free_clone() {
+            HeapCellValue::NamedStr(arity, name, fixity) => {
+                let threshold = self.target.threshold();
+
+                *self.value_at_scan() = HeapCellValue::Addr(Addr::Str(threshold));
+
+                let trail_item = mem::replace(
+                    &mut self.target[addr],
+                    HeapCellValue::Addr(Addr::Str(threshold)),
+                );
+
+                self.trail.push((
+                    Ref::HeapCell(addr),
+                    trail_item,
+                ));
+
+                self.target.push(HeapCellValue::NamedStr(arity, name, fixity));
+
+                for i in 0..arity {
+                    let hcv = self.target[addr + 1 + i].context_free_clone();
+                    self.target.push(hcv);
+                }
+            }
+            HeapCellValue::Addr(Addr::Str(addr)) => {
+                *self.value_at_scan() = HeapCellValue::Addr(Addr::Str(addr))
+            }
+            _ => {
+                unreachable!()
+            }
+        }
+
+        self.scan += 1;
+    }
+
+    fn copy_term_impl(&mut self, addr: Addr) {
+        self.scan = self.target.threshold();
+        self.target.push(HeapCellValue::Addr(addr));
+
+        while self.scan < self.target.threshold() {
+            match self.value_at_scan() {
+                &mut HeapCellValue::Addr(addr) => {
+                    match addr {
+                        Addr::Con(h) => {
+                            let addr = self.target[h].as_addr(h);
+
+                            if addr == Addr::Con(h) {
+                                *self.value_at_scan() = self.target[h].context_free_clone();
+                            } else {
+                                *self.value_at_scan() = HeapCellValue::Addr(addr);
+                            }
+                        }
+                        Addr::Lis(h) => {
+                            if h >= self.old_h {
+                                self.scan += 1;
+                            } else {
+                                self.copy_list(h);
+                            }
+                        }
+                        addr @ Addr::AttrVar(_) |
+                        addr @ Addr::HeapCell(_) |
+                        addr @ Addr::StackCell(..) => {
+                            self.copy_var(addr);
+                        }
+                        Addr::Str(addr) => {
+                            self.copy_structure(addr);
+                        }
+                        Addr::PStrLocation(addr, n) => {
+                            self.copy_partial_string(addr, n);
+                        }
+                        Addr::Stream(h) => {
+                            *self.value_at_scan() = self.target[h].context_free_clone();
+                        }
+                        _ => {
+                            self.scan += 1;
+                        }
+                    }
+                }
+                _ => {
+                    self.scan += 1;
+                }
+            }
+        }
+
+        self.unwind_trail();
+    }
+
+    fn unwind_trail(&mut self) {
+        for (r, value) in self.trail.drain(0..) {
+            match r {
+                Ref::AttrVar(h) | Ref::HeapCell(h) =>
+                    self.target[h] = value,
+                Ref::StackCell(fr, sc) =>
+                    self.target.stack().index_and_frame_mut(fr)[sc] = value.as_addr(0),
+            }
+        }
+    }
+}

src/machine/dynamic_database.rs

@@ -1,11 +1,12 @@
-use prolog_parser::ast::*;
+use crate::prolog_parser::ast::*;
 
-use crate::prolog::heap_print::*;
-use crate::prolog::machine::compile::*;
-use crate::prolog::machine::machine_errors::*;
-use crate::prolog::machine::*;
+use crate::heap_print::*;
+use crate::machine::*;
+use crate::machine::compile::*;
+use crate::machine::machine_errors::*;
+use crate::machine::streams::*;
 
-use std::io::Read;
+use std::convert::TryFrom;
 
 impl Machine {
     pub(super) fn atom_tbl_of(&self, name: &ClauseName) -> TabledData<Atom> {
@@ -15,9 +16,9 @@ impl Machine {
         }
     }
 
-    fn compile_into_machine<R: Read>(
+    fn compile_into_machine(
         &mut self,
-        src: ParsingStream<R>,
+        src: Stream,
         name: ClauseName,
         arity: usize,
     ) -> EvalSession {
@@ -42,13 +43,38 @@ impl Machine {
         let arity = self.machine_st[arity].clone();
 
         let name = match self.machine_st.store(self.machine_st.deref(name)) {
-            Addr::Con(Constant::Atom(name, _)) => name,
+            Addr::Con(h) =>
+                if let HeapCellValue::Atom(ref name, _) = &self.machine_st.heap[h] {
+                    name.clone()
+                } else {
+                    unreachable!()
+                },
             _ => unreachable!(),
         };
 
         let arity = match self.machine_st.store(self.machine_st.deref(arity)) {
-            Addr::Con(Constant::Integer(arity)) => arity.to_usize().unwrap(),
-            _ => unreachable!(),
+            Addr::Con(h) => {
+                match &self.machine_st.heap[h] {
+                    HeapCellValue::Integer(ref arity) => {
+                        arity.to_usize().unwrap()
+                    }
+                    HeapCellValue::Addr(Addr::Fixnum(arity)) => {
+                        usize::try_from(*arity).unwrap()
+                    }
+                    _ => {
+                        unreachable!()
+                    }
+                }
+            }
+            Addr::Fixnum(arity) => {
+                usize::try_from(arity).unwrap()
+            }
+            Addr::Usize(n) => {
+                n
+            }
+            _ => {
+                unreachable!()
+            }
         };
 
         (name, arity)
@@ -75,6 +101,18 @@ impl Machine {
     }
 
     fn make_undefined(&mut self, name: ClauseName, arity: usize) {
+        let module_name = name.owning_module();
+
+        match self.indices.modules.get(&module_name) {
+            Some(ref module) => {
+                if let Some(idx) = module.code_dir.get(&(name.clone(), arity)) {
+                    set_code_index!(idx, IndexPtr::DynamicUndefined, module_name);
+                }
+            }
+            None => {
+            }
+        }
+
         if let Some(idx) = self.indices.code_dir.get(&(name, arity)) {
             set_code_index!(idx, IndexPtr::DynamicUndefined, clause_name!("user"));
         }
@@ -87,7 +125,7 @@ impl Machine {
             }
         }
     }
-    
+
     fn abolish_dynamic_clause(&mut self, name: RegType, arity: RegType) {
         let (name, arity) = self.get_predicate_key(name, arity);
 
@@ -102,16 +140,21 @@ impl Machine {
         let module_addr = self.machine_st[module].clone();
 
         let module_name = match self.machine_st.store(self.machine_st.deref(module_addr)) {
-            Addr::Con(Constant::Atom(module, _)) => match self.indices.modules.get_mut(&module) {
-                Some(ref mut module) => {
-                    module.code_dir.remove(&(name.clone(), arity));
-                    module.module_decl.name.clone()
-                }
-                _ => {
-                    self.machine_st.fail = true;
-                    return;
-                }
-            },
+            Addr::Con(h) =>
+                if let HeapCellValue::Atom(ref module, _) = &self.machine_st.heap[h] {
+                    match self.indices.modules.get_mut(module) {
+                        Some(ref mut module) => {
+                            module.code_dir.remove(&(name.clone(), arity));
+                            module.module_decl.name.clone()
+                        }
+                        _ => {
+                            self.machine_st.fail = true;
+                            return;
+                        }
+                    }
+                } else {
+                    unreachable!()
+                },
             _ => unreachable!(),
         };
 
@@ -130,7 +173,12 @@ impl Machine {
     ) {
         let machine_st = mem::replace(&mut self.machine_st, MachineState::new());
 
-        let result = self.compile_into_machine(parsing_stream(pred_str.as_bytes()), name, arity);
+        let result = self.compile_into_machine(
+            Stream::from(pred_str),
+            name,
+            arity,
+        );
+
         self.machine_st = machine_st;
 
         if let EvalSession::Error(err) = result {
@@ -158,21 +206,34 @@ impl Machine {
                 place.push_to_queue(&mut addrs, added_clause);
                 self.print_new_dynamic_clause(addrs, name.clone(), arity)
             }
-            Err(err) => return self.machine_st.throw_exception(err),
+            Err(err) => {
+                return self.machine_st.throw_exception(err);
+            }
         };
 
-        self.handle_eval_result_from_dynamic_compile(pred_str, name, arity, place.predicate_name());
+        self.handle_eval_result_from_dynamic_compile(
+            pred_str,
+            name,
+            arity,
+            place.predicate_name(),
+        );
     }
 
     fn set_module_atom_tbl(&mut self, module_addr: Addr, name: &mut ClauseName) -> bool {
         let atom_tbl = match self.machine_st.store(self.machine_st.deref(module_addr)) {
-            Addr::Con(Constant::Atom(module, _)) => match self.indices.modules.get(&module) {
-                Some(ref module) => module.atom_tbl.clone(),
-                None => {
+            Addr::Con(h) =>
+                if let HeapCellValue::Atom(ref module, _) = &self.machine_st.heap[h] {
+                    match self.indices.modules.get(module) {
+                        Some(ref module) => module.atom_tbl.clone(),
+                        None => {
+                            self.machine_st.fail = true;
+                            return false;
+                        }
+                    }
+                } else {
                     self.machine_st.fail = true;
                     return false;
-                }
-            },
+                },
             _ => unreachable!(),
         };
 
@@ -200,8 +261,24 @@ impl Machine {
     fn retract_from_dynamic_predicate_in_module(&mut self) {
         let index = self.machine_st[temp_v!(3)].clone();
         let index = match self.machine_st.store(self.machine_st.deref(index)) {
-            Addr::Con(Constant::Integer(n)) => n.to_usize().unwrap(),
-            _ => unreachable!(),
+            Addr::Con(h) =>
+                match &self.machine_st.heap[h] {
+                    HeapCellValue::Integer(ref arity) => {
+                        arity.to_usize().unwrap()
+                    }
+                    HeapCellValue::Addr(Addr::Fixnum(arity)) => {
+                        usize::try_from(*arity).unwrap()
+                    }
+                    _ => {
+                        unreachable!()
+                    }
+                }
+            Addr::Fixnum(arity) => {
+                usize::try_from(arity).unwrap()
+            }
+            _ => {
+                unreachable!()
+            }
         };
 
         let (mut name, arity) = self.get_predicate_key(temp_v!(1), temp_v!(2));
@@ -217,10 +294,12 @@ impl Machine {
                     if addrs.is_empty() {
                         self.make_undefined(name.clone(), arity);
                     }
-                    
+
                     self.print_new_dynamic_clause(addrs, name.clone(), arity)
                 }
-                Err(err) => return self.machine_st.throw_exception(err),
+                Err(err) => {
+                    return self.machine_st.throw_exception(err);
+                }
             };
 
             self.handle_eval_result_from_dynamic_compile(
@@ -235,8 +314,28 @@ impl Machine {
     fn retract_from_dynamic_predicate(&mut self) {
         let index = self.machine_st[temp_v!(3)].clone();
         let index = match self.machine_st.store(self.machine_st.deref(index)) {
-            Addr::Con(Constant::Integer(n)) => n.to_usize().unwrap(),
-            _ => unreachable!(),
+            Addr::Con(h) => {
+                match &self.machine_st.heap[h] {
+                    HeapCellValue::Integer(ref arity) => {
+                        arity.to_usize().unwrap()
+                    }
+                    HeapCellValue::Addr(Addr::Fixnum(arity)) => {
+                        usize::try_from(*arity).unwrap()
+                    }
+                    _ => {
+                        unreachable!()
+                    }
+                }
+            }
+            Addr::Usize(n) => {
+                n
+            }
+            Addr::Fixnum(n) => {
+                usize::try_from(n).unwrap()
+            }
+            _ => {
+                unreachable!()
+            }
         };
 
         let (name, arity) = self.get_predicate_key(temp_v!(1), temp_v!(2));
@@ -250,10 +349,12 @@ impl Machine {
                 if addrs.is_empty() {
                     self.make_undefined(name.clone(), arity);
                 }
-                 
+
                 self.print_new_dynamic_clause(addrs, name.clone(), arity)
             }
-            Err(err) => return self.machine_st.throw_exception(err),
+            Err(err) => {
+                return self.machine_st.throw_exception(err);
+            }
         };
 
         self.handle_eval_result_from_dynamic_compile(

src/machine/heap.rs

@@ -1,15 +1,17 @@
 use core::marker::PhantomData;
 
-use crate::prolog_parser::ast::*;
+use crate::prolog_parser::ast::Constant;
 
-use crate::prolog::machine::machine_indices::*;
-use crate::prolog::machine::partial_string::*;
-use crate::prolog::machine::raw_block::*;
+use crate::machine::machine_indices::*;
+use crate::machine::partial_string::*;
+use crate::machine::raw_block::*;
 
+use std::convert::TryFrom;
 use std::mem;
 use std::ops::{Index, IndexMut};
 use std::ptr;
 
+#[derive(Debug)]
 pub(crate) struct StandardHeapTraits {}
 
 impl RawBlockTraits for StandardHeapTraits {
@@ -24,6 +26,7 @@ impl RawBlockTraits for StandardHeapTraits {
     }
 }
 
+#[derive(Debug)]
 pub(crate) struct HeapTemplate<T: RawBlockTraits> {
     buf: RawBlock<T>,
     _marker: PhantomData<HeapCellValue>,
@@ -38,13 +41,14 @@ impl<T: RawBlockTraits> Drop for HeapTemplate<T> {
     }
 }
 
+#[derive(Debug)]
 pub(crate)
-struct HeapIntoIterator<T: RawBlockTraits> {
+struct HeapIntoIter<T: RawBlockTraits> {
     offset: usize,
     buf: RawBlock<T>,
 }
 
-impl<T: RawBlockTraits> Drop for HeapIntoIterator<T> {
+impl<T: RawBlockTraits> Drop for HeapIntoIter<T> {
     fn drop(&mut self) {
         let mut heap =
             HeapTemplate { buf: self.buf.take(), _marker: PhantomData };
@@ -54,7 +58,7 @@ impl<T: RawBlockTraits> Drop for HeapIntoIterator<T> {
     }
 }
 
-impl<T: RawBlockTraits> Iterator for HeapIntoIterator<T> {
+impl<T: RawBlockTraits> Iterator for HeapIntoIter<T> {
     type Item = HeapCellValue;
 
     fn next(&mut self) -> Option<Self::Item> {
@@ -71,20 +75,21 @@ impl<T: RawBlockTraits> Iterator for HeapIntoIterator<T> {
     }
 }
 
+#[derive(Debug)]
 pub(crate)
-struct HeapIterator<'a, T: RawBlockTraits> {
+struct HeapIter<'a, T: RawBlockTraits> {
     offset: usize,
     buf: &'a RawBlock<T>,
 }
 
-impl<'a, T: RawBlockTraits> HeapIterator<'a, T> {
+impl<'a, T: RawBlockTraits> HeapIter<'a, T> {
     pub(crate)
     fn new(buf: &'a RawBlock<T>, offset: usize) -> Self {
-        HeapIterator { buf, offset }
+        HeapIter { buf, offset }
     }
 }
 
-impl<'a, T: RawBlockTraits> Iterator for HeapIterator<'a, T> {
+impl<'a, T: RawBlockTraits> Iterator for HeapIter<'a, T> {
     type Item = &'a HeapCellValue;
 
     fn next(&mut self) -> Option<Self::Item> {
@@ -101,20 +106,29 @@ impl<'a, T: RawBlockTraits> Iterator for HeapIterator<'a, T> {
     }
 }
 
+#[allow(dead_code)]
 pub(crate)
-struct HeapIteratorMut<'a, T: RawBlockTraits> {
+fn print_heap_terms<'a, I: Iterator<Item = &'a HeapCellValue>>(heap: I, h: usize) {
+    for (index, term) in heap.enumerate() {
+        println!("{} : {}", h + index, term);
+    }
+}
+
+#[derive(Debug)]
+pub(crate)
+struct HeapIterMut<'a, T: RawBlockTraits> {
     offset: usize,
     buf: &'a mut RawBlock<T>,
 }
 
-impl<'a, T: RawBlockTraits> HeapIteratorMut<'a, T> {
+impl<'a, T: RawBlockTraits> HeapIterMut<'a, T> {
     pub(crate)
     fn new(buf: &'a mut RawBlock<T>, offset: usize) -> Self {
-        HeapIteratorMut { buf, offset }
+        HeapIterMut { buf, offset }
     }
 }
 
-impl<'a, T: RawBlockTraits> Iterator for HeapIteratorMut<'a, T> {
+impl<'a, T: RawBlockTraits> Iterator for HeapIterMut<'a, T> {
     type Item = &'a mut HeapCellValue;
 
     fn next(&mut self) -> Option<Self::Item> {
@@ -140,44 +154,195 @@ impl<T: RawBlockTraits> HeapTemplate<T> {
 
     #[inline]
     pub(crate)
-    fn push(&mut self, val: HeapCellValue) {
-        unsafe {
-            let new_top = self.buf.new_block(mem::size_of::<HeapCellValue>());
-            ptr::write(self.buf.top as *mut _, val);
-            self.buf.top = new_top;
+    fn clone(&self, h: usize) -> HeapCellValue {
+        match &self[h] {
+            &HeapCellValue::Addr(addr) => {
+                HeapCellValue::Addr(addr)
+            }
+            &HeapCellValue::Atom(ref name, ref op) => {
+                HeapCellValue::Atom(name.clone(), op.clone())
+            }
+            &HeapCellValue::DBRef(ref db_ref) => {
+                HeapCellValue::DBRef(db_ref.clone())
+            }
+            &HeapCellValue::Integer(ref n) => {
+                HeapCellValue::Integer(n.clone())
+            }
+            &HeapCellValue::NamedStr(arity, ref name, ref op) => {
+                HeapCellValue::NamedStr(arity, name.clone(), op.clone())
+            }
+            &HeapCellValue::PartialString(..) => {
+                HeapCellValue::Addr(Addr::PStrLocation(h, 0))
+            }
+            &HeapCellValue::Rational(ref r) => {
+                HeapCellValue::Rational(r.clone())
+            }
+            &HeapCellValue::Stream(_) => {
+                HeapCellValue::Addr(Addr::Stream(h))
+            }
+            &HeapCellValue::TcpListener(_) => {
+                HeapCellValue::Addr(Addr::TcpListener(h))
+            }
         }
     }
 
     #[inline]
     pub(crate)
-    fn allocate_pstr(&mut self, mut src: &str) -> Option<Addr> {
+    fn put_complete_string(&mut self, s: &str) -> Addr {
+        if s.is_empty() {
+            return Addr::EmptyList;
+        }
+
+        let addr = self.allocate_pstr(s);
+        self.pop();
+
+        let h = self.h();
+
+        match &mut self[h - 1] {
+            &mut HeapCellValue::PartialString(_, ref mut has_tail) => {
+                *has_tail = false;
+            }
+            _ => {
+                unreachable!()
+            }
+        }
+
+        addr
+    }
+
+    #[inline]
+    pub(crate)
+    fn put_constant(&mut self, c: Constant) -> Addr {
+        match c {
+            Constant::Atom(name, op) => {
+                Addr::Con(self.push(HeapCellValue::Atom(name, op)))
+            }
+            Constant::Char(c) => {
+                Addr::Char(c)
+            }
+            Constant::EmptyList => {
+                Addr::EmptyList
+            }
+            Constant::Fixnum(n) => {
+                Addr::Fixnum(n)
+            }
+            Constant::Integer(n) => {
+                Addr::Con(self.push(HeapCellValue::Integer(n)))
+            }
+            Constant::Rational(r) => {
+                Addr::Con(self.push(HeapCellValue::Rational(r)))
+            }
+            Constant::Float(f) => {
+                Addr::Float(f)
+            }
+            Constant::String(s) => {
+                if s.is_empty() {
+                    Addr::EmptyList
+                } else {
+                    self.put_complete_string(&s)
+                }
+            }
+            Constant::Usize(n) => {
+                Addr::Usize(n)
+            }
+        }
+    }
+
+    #[inline]
+    pub(crate)
+    fn pop(&mut self) {
+        let h = self.h();
+
+        if h > 0 {
+            self.truncate(h - 1);
+        }
+    }
+
+    #[inline]
+    pub(crate)
+    fn push(&mut self, val: HeapCellValue) -> usize {
+        let h = self.h();
+
+        unsafe {
+            let new_top = self.buf.new_block(mem::size_of::<HeapCellValue>());
+            ptr::write(self.buf.top as *mut _, val);
+            self.buf.top = new_top;
+        }
+
+        h
+    }
+
+    #[inline]
+    pub(crate)
+    fn atom_at(&self, h: usize) -> bool {
+        if let HeapCellValue::Atom(..) = &self[h] {
+            true
+        } else {
+            false
+        }
+    }
+
+    #[inline]
+    pub(crate)
+    fn to_unifiable(&mut self, non_heap_value: HeapCellValue) -> Addr {
+        match non_heap_value {
+            HeapCellValue::Addr(addr) => {
+                addr
+            }
+            val @ HeapCellValue::Atom(..) |
+            val @ HeapCellValue::Integer(_) |
+            val @ HeapCellValue::DBRef(_) |
+            val @ HeapCellValue::Rational(_) => {
+                Addr::Con(self.push(val))
+            }
+            val @ HeapCellValue::NamedStr(..) => {
+                Addr::Str(self.push(val))
+            }
+            HeapCellValue::PartialString(pstr, has_tail) => {
+                let h = self.push(HeapCellValue::PartialString(pstr, has_tail));
+
+                if has_tail {
+                    self.push(HeapCellValue::Addr(Addr::EmptyList));
+                }
+
+                Addr::Con(h)
+            }
+            val @ HeapCellValue::Stream(..) => {
+                Addr::Stream(self.push(val))
+            }
+            val @ HeapCellValue::TcpListener(..) => {
+                Addr::TcpListener(self.push(val))
+            }
+        }
+    }
+
+    #[inline]
+    pub(crate)
+    fn allocate_pstr(&mut self, src: &str) -> Addr {
+        self.write_pstr(src)
+            .unwrap_or_else(|| Addr::EmptyList)
+    }
+
+    #[inline]
+    fn write_pstr(&mut self, mut src: &str) -> Option<Addr> {
         let orig_h = self.h();
-        
+
         loop {
             if src == "" {
                 return if orig_h == self.h() {
                     None
                 } else {
-                    let prev_h = self.h() - 1;
-
-                    match &mut self[prev_h] {
-                        HeapCellValue::PartialString(ref mut pstr) => {
-                            let s = pstr.block_as_str();
-                            pstr.tail = Addr::PStrTail(prev_h, s.len());
-                        }
-                        _ => {
-                            unreachable!()
-                        }
-                    }
+                    let tail_h = self.h() - 1;
+                    self[tail_h] = HeapCellValue::Addr(Addr::HeapCell(tail_h));
 
                     Some(Addr::PStrLocation(orig_h, 0))
                 };
             }
-            
+
             let h = self.h();
 
-            let (mut pstr, rest_src) =
-                match PartialString::new(src, h) {
+            let (pstr, rest_src) =
+                match PartialString::new(src) {
                     Some(tuple) => {
                         tuple
                     }
@@ -188,46 +353,21 @@ impl<T: RawBlockTraits> HeapTemplate<T> {
                         } else if orig_h == h {
                             return None;
                         } else {
-                            let prev_h = h - 1;
-
-                            match &mut self[prev_h] {
-                                HeapCellValue::PartialString(ref mut pstr) => {
-                                    let s = pstr.block_as_str();
-                                    pstr.tail = Addr::PStrTail(prev_h, s.len());
-                                }
-                                _ => {
-                                    unreachable!()
-                                }
-                            }
-
+                            self[h - 1] = HeapCellValue::Addr(Addr::HeapCell(h - 1));
                             return Some(Addr::PStrLocation(orig_h, 0));
                         }
                     }
                 };
 
-            let new_top = unsafe {
-                self.buf.new_block(mem::size_of::<HeapCellValue>())
-            };
+            self.push(HeapCellValue::PartialString(pstr, true));
 
             if rest_src != "" {
-                pstr.tail = Addr::PStrLocation(h+1, 0);
+                self.push(HeapCellValue::Addr(Addr::PStrLocation(h + 2, 0)));
                 src = rest_src;
             } else {
-                pstr.tail = Addr::PStrTail(h, src.len());
-            }
-
-            unsafe{
-                ptr::write(
-                    self.buf.top as *mut _,
-                    HeapCellValue::PartialString(pstr),
-                );
-            }
-            
-            self.buf.top = new_top;
-            
-            if rest_src == "" {                
+                self.push(HeapCellValue::Addr(Addr::HeapCell(h + 1)));
                 return Some(Addr::PStrLocation(orig_h, 0));
-            }            
+            }
         }
     }
 
@@ -279,35 +419,39 @@ impl<T: RawBlockTraits> HeapTemplate<T> {
     }
 
     pub(crate)
-    fn to_list<Iter: Iterator<Item = Addr>>(&mut self, values: Iter) -> usize {
+    fn to_list<Iter, SrcT>(&mut self, values: Iter) -> usize
+        where Iter: Iterator<Item = SrcT>,
+              SrcT: Into<HeapCellValue>
+    {
         let head_addr = self.h();
+        let mut h = head_addr;
 
-        for value in values {
-            let h = self.h();
-
+        for value in values.map(|v| v.into()) {
             self.push(HeapCellValue::Addr(Addr::Lis(h + 1)));
-            self.push(HeapCellValue::Addr(value));
+            self.push(value);
+
+            h += 2;
         }
 
-        self.push(HeapCellValue::Addr(Addr::Con(Constant::EmptyList)));
+        self.push(HeapCellValue::Addr(Addr::EmptyList));
 
         head_addr
     }
 
     /* Create an iterator starting from the passed offset. */
     pub(crate)
-    fn iter_from<'a>(&'a self, offset: usize) -> HeapIterator<'a, T> {
-        HeapIterator::new(&self.buf, offset * mem::size_of::<HeapCellValue>())
+    fn iter_from<'a>(&'a self, offset: usize) -> HeapIter<'a, T> {
+        HeapIter::new(&self.buf, offset * mem::size_of::<HeapCellValue>())
     }
 
     pub(crate)
-    fn iter_mut_from<'a>(&'a mut self, offset: usize) -> HeapIteratorMut<'a, T> {
-        HeapIteratorMut::new(&mut self.buf, offset * mem::size_of::<HeapCellValue>())
+    fn iter_mut_from<'a>(&'a mut self, offset: usize) -> HeapIterMut<'a, T> {
+        HeapIterMut::new(&mut self.buf, offset * mem::size_of::<HeapCellValue>())
     }
 
     pub(crate)
-    fn into_iter(mut self) -> HeapIntoIterator<T> {
-        HeapIntoIterator { buf: self.buf.take(), offset: 0 }
+    fn into_iter(mut self) -> HeapIntoIter<T> {
+        HeapIntoIter { buf: self.buf.take(), offset: 0 }
     }
 
     pub(crate)
@@ -320,8 +464,9 @@ impl<T: RawBlockTraits> HeapTemplate<T> {
     pub(crate)
     fn to_local_code_ptr(&self, addr: &Addr) -> Option<LocalCodePtr> {
         let extract_integer = |s: usize| -> Option<usize> {
-            match self[s].as_addr(s) {
-                Addr::Con(Constant::Integer(n)) => n.to_usize(),
+            match &self[s] {
+                &HeapCellValue::Addr(Addr::Fixnum(n)) => usize::try_from(n).ok(),
+                &HeapCellValue::Integer(ref n) => n.to_usize(),
                 _ => None
             }
         };
@@ -361,6 +506,19 @@ impl<T: RawBlockTraits> HeapTemplate<T> {
             _ => None
         }
     }
+
+    #[inline]
+    pub
+    fn index_addr<'a>(&'a self, addr: &Addr) -> RefOrOwned<'a, HeapCellValue> {
+        match addr {
+            &Addr::Con(h) | &Addr::Str(h) | &Addr::Stream(h) | &Addr::TcpListener(h) => {
+                RefOrOwned::Borrowed(&self[h])
+            }
+            addr => {
+                RefOrOwned::Owned(HeapCellValue::Addr(*addr))
+            }
+        }
+    }
 }
 
 impl<T: RawBlockTraits> Index<usize> for HeapTemplate<T> {

src/machine/machine_errors.rs

@@ -0,0 +1,843 @@
+use crate::prolog_parser::ast::*;
+
+use crate::forms::{ModuleSource, Number, PredicateKey};
+use crate::machine::heap::*;
+use crate::machine::machine_indices::*;
+use crate::machine::machine_state::*;
+use crate::rug::Integer;
+
+use std::rc::Rc;
+
+pub(crate) type MachineStub = Vec<HeapCellValue>;
+
+#[derive(Debug, Clone, Copy)]
+enum ErrorProvenance {
+    Constructed, // if constructed, offset the addresses.
+    Received,    // otherwise, preserve the addresses.
+}
+
+#[derive(Debug)]
+pub(crate) struct MachineError {
+    stub: MachineStub,
+    location: Option<(usize, usize)>, // line_num, col_num
+    from: ErrorProvenance,
+}
+
+pub(crate)
+trait TypeError {
+    fn type_error(self, h: usize, valid_type: ValidType) -> MachineError;
+}
+
+impl TypeError for Addr {
+    fn type_error(self, _: usize, valid_type: ValidType) -> MachineError {
+        let stub = functor!(
+            "type_error",
+            [atom(valid_type.as_str()), addr(self)]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received
+        }
+    }
+}
+
+impl TypeError for HeapCellValue {
+    fn type_error(self, _: usize, valid_type: ValidType) -> MachineError {
+        let stub = functor!(
+            "type_error",
+            [atom(valid_type.as_str()), value(self)]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received
+        }
+    }
+}
+
+impl TypeError for MachineStub {
+    fn type_error(self, h: usize, valid_type: ValidType) -> MachineError {
+        let stub = functor!(
+            "type_error",
+            [atom(valid_type.as_str()), aux(h, 0)],
+            [self]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Constructed
+        }
+    }
+}
+
+impl TypeError for Number {
+    fn type_error(self, _h: usize, valid_type: ValidType) -> MachineError {
+        let stub = functor!(
+            "type_error",
+            [atom(valid_type.as_str()), number(self)]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received
+        }
+    }
+}
+
+pub(crate)
+trait PermissionError {
+    fn permission_error(self, h: usize, index_str: &'static str, perm: Permission) -> MachineError;
+}
+
+impl PermissionError for Addr {
+    fn permission_error(self, _: usize, index_str: &'static str, perm: Permission) -> MachineError {
+        let stub = functor!(
+            "permission_error",
+            [atom(perm.as_str()), atom(index_str), addr(self)]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received
+        }
+    }
+}
+
+impl PermissionError for MachineStub {
+    fn permission_error(self, h: usize, index_str: &'static str, perm: Permission) -> MachineError {
+        let stub = functor!(
+            "permission_error",
+            [atom(perm.as_str()), atom(index_str), aux(h, 0)],
+            [self]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Constructed
+        }
+    }
+}
+
+pub(super)
+trait DomainError {
+    fn domain_error(self, error: DomainErrorType) -> MachineError;
+}
+
+impl DomainError for Addr {
+    fn domain_error(self, error: DomainErrorType) -> MachineError {
+        let stub = functor!(
+            "domain_error",
+            [atom(error.as_str()), addr(self)]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received,
+        }
+    }
+}
+
+impl DomainError for Number {
+    fn domain_error(self, error: DomainErrorType) -> MachineError {
+        let stub = functor!(
+            "domain_error",
+            [atom(error.as_str()), number(self)]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received,
+        }
+    }
+}
+
+impl MachineError {
+    pub(super)
+    fn functor_stub(name: ClauseName, arity: usize) -> MachineStub {
+        functor!(
+            "/",
+            SharedOpDesc::new(400, YFX),
+            [clause_name(name), integer(arity)]
+        )
+    }
+
+    #[inline]
+    pub(super)
+    fn interrupt_error() -> Self {
+        let stub = functor!("$interrupt_thrown");
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received,
+        }
+    }
+
+    pub(super)
+    fn evaluation_error(eval_error: EvalError) -> Self {
+        let stub = functor!("evaluation_error", [atom(eval_error.as_str())]);
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received,
+        }
+    }
+
+    pub(super)
+    fn type_error<T: TypeError>(h: usize, valid_type: ValidType, culprit: T) -> Self {
+        culprit.type_error(h, valid_type)
+    }
+
+    pub(super)
+    fn module_resolution_error(
+        h: usize,
+        mod_name: ClauseName,
+        name: ClauseName,
+        arity: usize,
+    ) -> Self {
+        let res_stub = functor!(
+            ":",
+            SharedOpDesc::new(600, XFY),
+            [clause_name(mod_name), clause_name(name)]
+        );
+
+        let ind_stub = functor!(
+            "/",
+            SharedOpDesc::new(400, YFX),
+            [aux(h + 2, 0), integer(arity)],
+            [res_stub]
+        );
+
+        let stub = functor!(
+            "evaluation_error",
+            [aux(h, 0)],
+            [ind_stub]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Constructed,
+        }
+    }
+
+    pub(super)
+    fn existence_error(h: usize, err: ExistenceError) -> Self {
+        match err {
+            ExistenceError::Module(name) => {
+                let stub = functor!(
+                    "existence_error",
+                    [atom("source_sink"), clause_name(name)]
+                );
+
+                MachineError {
+                    stub,
+                    location: None,
+                    from: ErrorProvenance::Received,
+                }
+            }
+            ExistenceError::Procedure(name, arity) => {
+                let culprit = functor!(
+                    "/",
+                    SharedOpDesc::new(400, YFX),
+                    [clause_name(name), integer(arity)]
+                );
+
+                let stub = functor!(
+                    "existence_error",
+                    [atom("procedure"), aux(h, 0)],
+                    [culprit]
+                );
+
+                MachineError {
+                    stub,
+                    location: None,
+                    from: ErrorProvenance::Constructed,
+                }
+            }
+            ExistenceError::ModuleSource(source) => {
+                let source_stub = source.as_functor_stub();
+
+                let stub = functor!(
+                    "existence_error",
+                    [atom("source_sink"), aux(h, 0)],
+                    [source_stub]
+                );
+
+                MachineError {
+                    stub,
+                    location: None,
+                    from: ErrorProvenance::Constructed,
+                }
+            }
+            ExistenceError::SourceSink(culprit) => {
+                let stub = functor!(
+                    "existence_error",
+                    [atom("source_sink"), addr(culprit)]
+                );
+
+                MachineError {
+                    stub,
+                    location: None,
+                    from: ErrorProvenance::Received,
+                }
+            }
+            ExistenceError::Stream(culprit) => {
+                let stub = functor!(
+                    "existence_error",
+                    [atom("stream"), addr(culprit)]
+                );
+
+                MachineError {
+                    stub,
+                    location: None,
+                    from: ErrorProvenance::Received,
+                }
+            }
+        }
+    }
+
+    pub(super)
+    fn permission_error<T: PermissionError>(
+        h: usize,
+        err: Permission,
+        index_str: &'static str,
+        culprit: T,
+    ) -> Self {
+        culprit.permission_error(
+            h,
+            index_str,
+            err,
+        )
+    }
+
+    fn arithmetic_error(h: usize, err: ArithmeticError) -> Self {
+        match err {
+            ArithmeticError::UninstantiatedVar => {
+                Self::instantiation_error()
+            }
+            ArithmeticError::NonEvaluableFunctor(name, arity) => {
+                let culprit = functor!(
+                    "/",
+                    SharedOpDesc::new(400, YFX),
+                    [constant(h, &name), integer(arity)]
+                );
+
+                Self::type_error(h, ValidType::Evaluable, culprit)
+            }
+        }
+    }
+
+    #[inline]
+    pub(super)
+    fn domain_error<T: DomainError>(error: DomainErrorType, culprit: T) -> Self {
+        culprit.domain_error(error)
+    }
+
+    pub(super)
+    fn instantiation_error() -> Self {
+        let stub = functor!("instantiation_error");
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received,
+        }
+    }
+
+    pub(super)
+    fn uninstantiation_error(culprit: Addr) -> Self {
+        let stub = functor!(
+            "uninstantiation_error",
+            [addr(culprit)]
+        );
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received,
+        }
+    }
+
+    pub(super)
+    fn session_error(h: usize, err: SessionError) -> Self {
+        match err {
+            SessionError::CannotOverwriteBuiltIn(pred_str) |
+            SessionError::CannotOverwriteImport(pred_str) => {
+                Self::permission_error(
+                    h,
+                    Permission::Modify,
+                    "private_procedure",
+                    functor!(clause_name(pred_str)),
+                )
+            }
+            SessionError::ExistenceError(err) => {
+                Self::existence_error(h, err)
+            }
+            SessionError::InvalidFileName(filename) => {
+                Self::existence_error(h, ExistenceError::Module(filename))
+            }
+            SessionError::ModuleDoesNotContainExport(..) => {
+                Self::permission_error(
+                    h,
+                    Permission::Access,
+                    "private_procedure",
+                    functor!("module_does_not_contain_claimed_export"),
+                )
+            }
+            SessionError::NamelessEntry => {
+                Self::permission_error(
+                    h,
+                    Permission::Create,
+                    "static_procedure",
+                    functor!("nameless_procedure")
+                )
+            }
+            SessionError::OpIsInfixAndPostFix(op) => {
+                Self::permission_error(
+                    h,
+                    Permission::Create,
+                    "operator",
+                    functor!(clause_name(op)),
+                )
+            }
+            SessionError::ParserError(err) => {
+                Self::syntax_error(h, err)
+            }
+            SessionError::QueryCannotBeDefinedAsFact => {
+                Self::permission_error(
+                    h,
+                    Permission::Create,
+                    "static_procedure",
+                    functor!("query_cannot_be_defined_as_fact")
+                )
+            }
+        }
+    }
+
+    pub(super)
+    fn syntax_error(h: usize, err: ParserError) -> Self {
+        if let ParserError::Arithmetic(err) = err {
+            return Self::arithmetic_error(h, err);
+        }
+
+        let location = err.line_and_col_num();
+        let stub = functor!(err.as_str());
+
+        let stub = functor!(
+            "syntax_error",
+            [aux(h, 0)],
+            [stub]
+        );
+
+        MachineError {
+            stub,
+            location,
+            from: ErrorProvenance::Constructed,
+        }
+    }
+
+    pub(super)
+    fn representation_error(flag: RepFlag) -> Self {
+        let stub = functor!("representation_error", [atom(flag.as_str())]);
+
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received,
+        }
+    }
+
+    fn into_iter(self, offset: usize) -> Box<dyn Iterator<Item = HeapCellValue>> {
+        match self.from {
+            ErrorProvenance::Constructed => {
+                Box::new(self.stub.into_iter().map(move |hcv| match hcv {
+                    HeapCellValue::Addr(addr) => HeapCellValue::Addr(addr + offset),
+                    hcv => hcv,
+                }))
+            }
+            ErrorProvenance::Received => Box::new(self.stub.into_iter()),
+        }
+    }
+
+    fn len(&self) -> usize {
+        self.stub.len()
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum Permission {
+    Access,
+    Create,
+    InputStream,
+    Modify,
+    Open,
+    OutputStream,
+    Reposition,
+}
+
+impl Permission {
+    #[inline]
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Permission::Access => "access",
+            Permission::Create => "create",
+            Permission::InputStream => "input",
+            Permission::Modify => "modify",
+            Permission::Open => "open",
+            Permission::OutputStream => "output",
+            Permission::Reposition => "reposition",
+        }
+    }
+}
+
+// from 7.12.2 b) of 13211-1:1995
+#[derive(Debug, Clone, Copy)]
+pub enum ValidType {
+    Atom,
+    Atomic,
+    //    Boolean,
+    Byte,
+    Callable,
+    Character,
+    Compound,
+    Evaluable,
+    Float,
+    InByte,
+    InCharacter,
+    Integer,
+    List,
+    Number,
+    Pair,
+    //    PredicateIndicator,
+    //    Variable
+    TcpListener,
+}
+
+impl ValidType {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            ValidType::Atom => "atom",
+            ValidType::Atomic => "atomic",
+            //            ValidType::Boolean => "boolean",
+            ValidType::Byte => "byte",
+            ValidType::Callable => "callable",
+            ValidType::Character => "character",
+            ValidType::Compound => "compound",
+            ValidType::Evaluable => "evaluable",
+            ValidType::Float => "float",
+            ValidType::InByte => "in_byte",
+            ValidType::InCharacter => "in_character",
+            ValidType::Integer => "integer",
+            ValidType::List => "list",
+            ValidType::Number => "number",
+            ValidType::Pair => "pair",
+            //            ValidType::PredicateIndicator => "predicate_indicator",
+            //            ValidType::Variable => "variable"
+            ValidType::TcpListener => "tcp_listener",
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum DomainErrorType {
+    IOMode,
+    NotLessThanZero,
+    Order,
+    SourceSink,
+    Stream,
+    StreamOrAlias,
+}
+
+impl DomainErrorType {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            DomainErrorType::IOMode => "io_mode",
+            DomainErrorType::NotLessThanZero => "not_less_than_zero",
+            DomainErrorType::Order => "order",
+            DomainErrorType::SourceSink => "source_sink",
+            DomainErrorType::Stream => "stream",
+            DomainErrorType::StreamOrAlias => "stream_or_alias",
+        }
+    }
+}
+
+// from 7.12.2 f) of 13211-1:1995
+#[derive(Debug, Clone, Copy)]
+pub enum RepFlag {
+    Character,
+    CharacterCode,
+    InCharacterCode,
+    MaxArity,
+    //    MaxInteger,
+    //    MinInteger
+}
+
+impl RepFlag {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            RepFlag::Character => "character",
+            RepFlag::CharacterCode => "character_code",
+            RepFlag::InCharacterCode => "in_character_code",
+            RepFlag::MaxArity => "max_arity",
+            //            RepFlag::MaxInteger => "max_integer",
+            //            RepFlag::MinInteger => "min_integer"
+        }
+    }
+}
+
+// from 7.12.2 g) of 13211-1:1995
+#[derive(Debug, Clone, Copy)]
+pub enum EvalError {
+    FloatOverflow,
+    Undefined,
+    //    Underflow,
+    ZeroDivisor,
+}
+
+impl EvalError {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            EvalError::FloatOverflow => "float_overflow",
+            EvalError::Undefined => "undefined",
+            //            EvalError::FloatUnderflow => "underflow",
+            EvalError::ZeroDivisor => "zero_divisor",
+        }
+    }
+}
+
+// used by '$skip_max_list'.
+#[derive(Debug, Clone, Copy)]
+pub(super) enum CycleSearchResult {
+    EmptyList,
+    NotList,
+    PartialList(usize, Ref),           // the list length (up to max), and an offset into the heap.
+    ProperList(usize),                 // the list length.
+    PStrLocation(usize, usize, usize), // the list length (up to max), the heap offset, byte offset into the string.
+    UntouchedList(usize),              // the address of an uniterated Addr::Lis(address).
+}
+
+impl MachineState {
+    // see 8.4.3 of Draft Technical Corrigendum 2.
+    pub(super)
+    fn check_sort_errors(&self) -> CallResult {
+        let stub = MachineError::functor_stub(clause_name!("sort"), 2);
+        let list = self.store(self.deref(self[temp_v!(1)].clone()));
+        let sorted = self.store(self.deref(self[temp_v!(2)].clone()));
+
+        match self.detect_cycles(list.clone()) {
+            CycleSearchResult::PartialList(..) => {
+                return Err(self.error_form(MachineError::instantiation_error(), stub))
+            }
+            CycleSearchResult::NotList => {
+                return Err(self.error_form(MachineError::type_error(0, ValidType::List, list), stub))
+            }
+            _ => {}
+        };
+
+        match self.detect_cycles(sorted.clone()) {
+            CycleSearchResult::NotList if !sorted.is_ref() => {
+                Err(self.error_form(MachineError::type_error(0, ValidType::List, sorted), stub))
+            }
+            _ => Ok(()),
+        }
+    }
+
+    fn check_for_list_pairs(&self, list: Addr) -> CallResult {
+        let stub = MachineError::functor_stub(clause_name!("keysort"), 2);
+
+        match self.detect_cycles(list.clone()) {
+            CycleSearchResult::NotList if !list.is_ref() => {
+                Err(self.error_form(MachineError::type_error(0, ValidType::List, list), stub))
+            }
+            _ => {
+                let mut addr = list;
+
+                while let Addr::Lis(l) = self.store(self.deref(addr)) {
+                    let mut new_l = l;
+
+                    loop {
+                        match self.heap.clone(new_l) {
+                            HeapCellValue::Addr(Addr::Str(l)) => {
+                                new_l = l;
+                            }
+                            HeapCellValue::NamedStr(2, ref name, Some(_))
+                                if name.as_str() == "-" => {
+                                break;
+                            }
+                            HeapCellValue::Addr(Addr::HeapCell(_)) => {
+                                break;
+                            }
+                            HeapCellValue::Addr(Addr::StackCell(..)) => {
+                                break;
+                            }
+                            _ => {
+                                return Err(self.error_form(
+                                    MachineError::type_error(0, ValidType::Pair, Addr::HeapCell(l)),
+                                    stub,
+                                ))
+                            }
+                        };
+                    }
+
+                    addr = Addr::HeapCell(l + 1);
+                }
+
+                Ok(())
+            }
+        }
+    }
+
+    // see 8.4.4 of Draft Technical Corrigendum 2.
+    pub(super)
+    fn check_keysort_errors(&self) -> CallResult {
+        let stub = MachineError::functor_stub(clause_name!("keysort"), 2);
+
+        let pairs  = self.store(self.deref(self[temp_v!(1)].clone()));
+        let sorted = self.store(self.deref(self[temp_v!(2)].clone()));
+
+        match self.detect_cycles(pairs.clone()) {
+            CycleSearchResult::PartialList(..) => {
+                Err(self.error_form(MachineError::instantiation_error(), stub))
+            }
+            CycleSearchResult::NotList => {
+                Err(self.error_form(MachineError::type_error(0, ValidType::List, pairs), stub))
+            }
+            _ => Ok(()),
+        }?;
+
+        self.check_for_list_pairs(sorted)
+    }
+
+    #[inline]
+    pub(crate)
+    fn type_error<T: TypeError>(
+        &self,
+        valid_type: ValidType,
+        culprit: T,
+        caller: ClauseName,
+        arity: usize,
+    ) -> MachineStub {
+        let stub = MachineError::functor_stub(caller, arity);
+        let err = MachineError::type_error(
+            self.heap.h(),
+            valid_type,
+            culprit,
+        );
+
+        return self.error_form(err, stub);
+    }
+
+    #[inline]
+    pub(crate)
+    fn representation_error(
+        &self,
+        rep_flag: RepFlag,
+        caller: ClauseName,
+        arity: usize,
+    ) -> MachineStub {
+        let stub = MachineError::functor_stub(caller, arity);
+        let err = MachineError::representation_error(
+            rep_flag,
+        );
+
+        return self.error_form(err, stub);
+    }
+
+    pub(super)
+    fn error_form(&self, err: MachineError, src: MachineStub) -> MachineStub {
+        let location = err.location;
+        let err_len = err.len();
+
+        let h = self.heap.h();
+        let mut stub = vec![
+            HeapCellValue::NamedStr(2, clause_name!("error"), None),
+            HeapCellValue::Addr(Addr::HeapCell(h + 3)),
+            HeapCellValue::Addr(Addr::HeapCell(h + 3 + err_len)),
+        ];
+
+        stub.extend(err.into_iter(3));
+
+        if let Some((line_num, _)) = location {
+            let colon_op_desc = Some(SharedOpDesc::new(600, XFY));
+
+            stub.push(HeapCellValue::NamedStr(2, clause_name!(":"), colon_op_desc));
+            stub.push(HeapCellValue::Addr(Addr::HeapCell(h + 6 + err_len)));
+            stub.push(HeapCellValue::Integer(Rc::new(Integer::from(line_num))));
+        }
+
+        stub.extend(src.into_iter());
+        stub
+    }
+
+    pub(super)
+    fn throw_exception(&mut self, err: MachineStub) {
+        let h = self.heap.h();
+
+        self.ball.boundary = 0;
+        self.ball.stub.truncate(0);
+
+        self.heap.append(err);
+
+        self.registers[1] = Addr::HeapCell(h);
+
+        self.set_ball();
+        self.unwind_stack();
+    }
+}
+
+#[derive(Debug)]
+pub enum ExistenceError {
+    Module(ClauseName),
+    ModuleSource(ModuleSource),
+    Procedure(ClauseName, usize),
+    SourceSink(Addr),
+    Stream(Addr),
+}
+
+#[derive(Debug)]
+pub enum SessionError {
+    CannotOverwriteBuiltIn(ClauseName),
+    CannotOverwriteImport(ClauseName),
+    ExistenceError(ExistenceError),
+    InvalidFileName(ClauseName),
+    ModuleDoesNotContainExport(ClauseName, PredicateKey),
+    NamelessEntry,
+    OpIsInfixAndPostFix(ClauseName),
+    QueryCannotBeDefinedAsFact,
+    ParserError(ParserError),
+}
+
+#[derive(Debug)]
+pub enum EvalSession {
+    EntrySuccess,
+    Error(SessionError),
+}
+
+impl From<SessionError> for EvalSession {
+    fn from(err: SessionError) -> Self {
+        EvalSession::Error(err)
+    }
+}
+
+impl From<ParserError> for SessionError {
+    fn from(err: ParserError) -> Self {
+        SessionError::ParserError(err)
+    }
+}
+
+impl From<ParserError> for EvalSession {
+    fn from(err: ParserError) -> Self {
+        EvalSession::from(SessionError::ParserError(err))
+    }
+}

src/machine/machine_indices.rs

@@ -1,32 +1,38 @@
-use prolog_parser::ast::*;
-use prolog_parser::tabled_rc::*;
+use crate::prolog_parser::ast::*;
+use crate::prolog_parser::tabled_rc::*;
 
-use crate::prolog::clause_types::*;
-use crate::prolog::fixtures::*;
-use crate::prolog::forms::*;
-use crate::prolog::machine::code_repo::CodeRepo;
-use crate::prolog::machine::Ball;
-use crate::prolog::machine::heap::*;
-use crate::prolog::machine::partial_string::*;
-use crate::prolog::machine::raw_block::RawBlockTraits;
-use crate::prolog::instructions::*;
-use crate::prolog::rug::Integer;
+use crate::clause_types::*;
+use crate::fixtures::*;
+use crate::forms::*;
+use crate::machine::code_repo::CodeRepo;
+use crate::machine::Ball;
+use crate::machine::heap::*;
+use crate::machine::machine_state::*;
+use crate::machine::partial_string::*;
+use crate::machine::raw_block::RawBlockTraits;
+use crate::machine::streams::Stream;
+use crate::instructions::*;
+use crate::ordered_float::OrderedFloat;
+use crate::rug::{Integer, Rational};
 
-use indexmap::IndexMap;
+use crate::indexmap::IndexMap;
 
 use std::cell::RefCell;
 use std::cmp::Ordering;
-use std::collections::{BTreeMap, VecDeque};
+use std::collections::{BTreeMap, BTreeSet, VecDeque};
+use std::convert::TryFrom;
+use std::fmt;
 use std::mem;
+use std::net::TcpListener;
 use std::ops::{Add, AddAssign, Sub, SubAssign};
 use std::rc::Rc;
 
-#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct OrderedOpDirKey(pub ClauseName, pub Fixity);
 
 pub type OssifiedOpDir = BTreeMap<OrderedOpDirKey, (usize, Specifier)>;
 
-#[derive(Clone, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum DBRef {
     NamedPred(ClauseName, usize, Option<SharedOpDesc>),
     Op(
@@ -38,25 +44,40 @@ pub enum DBRef {
     ),
 }
 
-#[derive(Clone, PartialEq, Eq, Hash)]
-pub enum Addr {
-    AttrVar(usize),
-    Con(Constant),
-    DBRef(DBRef),
-    Lis(usize),
-    HeapCell(usize),
-    StackCell(usize, usize),
-    Str(usize),
-    PStrLocation(usize, usize), // location of pstr in heap, offset into string in bytes.
-    PStrTail(usize, usize), // location of pstr in heap, offset into string in bytes.
+// 7.2
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+pub enum TermOrderCategory {
+    Variable,
+    FloatingPoint,
+    Integer,
+    Atom,
+    Compound,
 }
 
-#[derive(Clone, Copy, Hash, Eq, PartialEq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum Addr {
+    AttrVar(usize),
+    Char(char),
+    Con(usize),
+    CutPoint(usize),
+    EmptyList,
+    Fixnum(isize),
+    Float(OrderedFloat<f64>),
+    Lis(usize),
+    HeapCell(usize),
+    PStrLocation(usize, usize), // location of pstr in heap, offset into string in bytes.
+    StackCell(usize, usize),
+    Str(usize),
+    Stream(usize),
+    TcpListener(usize),
+    Usize(usize),
+}
+
+#[derive(Debug, Clone, Copy, Hash, Eq, PartialEq, PartialOrd)]
 pub enum Ref {
     AttrVar(usize),
     HeapCell(usize),
     StackCell(usize, usize),
-    PStrTail(usize, usize),
 }
 
 impl Ref {
@@ -65,7 +86,28 @@ impl Ref {
             Ref::AttrVar(h) => Addr::AttrVar(h),
             Ref::HeapCell(h) => Addr::HeapCell(h),
             Ref::StackCell(fr, sc) => Addr::StackCell(fr, sc),
-            Ref::PStrTail(h, n) => Addr::PStrTail(h, n),
+        }
+    }
+}
+
+impl Ord for Ref {
+    fn cmp(&self, other: &Ref) -> Ordering {
+        match (self, other) {
+            (Ref::AttrVar(h1), Ref::AttrVar(h2))
+          | (Ref::HeapCell(h1), Ref::HeapCell(h2))
+          | (Ref::HeapCell(h1), Ref::AttrVar(h2))
+          | (Ref::AttrVar(h1), Ref::HeapCell(h2)) => {
+                h1.cmp(&h2)
+            }
+            (Ref::StackCell(fr1, sc1), Ref::StackCell(fr2, sc2)) => {
+                fr1.cmp(&fr2).then_with(|| sc1.cmp(&sc2))
+            }
+            (Ref::StackCell(..), _) => {
+                Ordering::Greater
+            }
+            (_, Ref::StackCell(..)) => {
+                Ordering::Less
+            }
         }
     }
 }
@@ -76,13 +118,13 @@ impl PartialEq<Ref> for Addr {
     }
 }
 
-// for use in MachineState::bind.
+// for use crate::in MachineState::bind.
 impl PartialOrd<Ref> for Addr {
     fn partial_cmp(&self, r: &Ref) -> Option<Ordering> {
         match self {
             &Addr::StackCell(fr, sc) => {
                 match *r {
-                    Ref::AttrVar(_) | Ref::HeapCell(_) | Ref::PStrTail(..) => {
+                    Ref::AttrVar(_) | Ref::HeapCell(_) => {
                         Some(Ordering::Greater)
                     }
                     Ref::StackCell(fr1, sc1) => {
@@ -104,22 +146,6 @@ impl PartialOrd<Ref> for Addr {
                     Ref::AttrVar(h1) | Ref::HeapCell(h1) => {
                         h.partial_cmp(h1)
                     }
-                    Ref::PStrTail(h1, _) => {
-                        h.partial_cmp(h1)
-                    }
-                }
-            }
-            &Addr::PStrTail(h, n) => {
-                match r {
-                    Ref::StackCell(..) => {
-                        Some(Ordering::Less)
-                    }
-                    Ref::AttrVar(h1) | Ref::HeapCell(h1) => {
-                        h.partial_cmp(h1)
-                    }
-                    Ref::PStrTail(h1, n1) => {
-                        Some(h.cmp(h1).then_with(|| n.cmp(n1)))
-                    }
                 }
             }
             _ => {
@@ -130,9 +156,24 @@ impl PartialOrd<Ref> for Addr {
 }
 
 impl Addr {
+    #[inline]
+    pub fn is_heap_bound(&self) -> bool {
+        match self {
+            Addr::Char(_) | Addr::EmptyList |
+            Addr::CutPoint(_) | Addr::Usize(_) | Addr::Fixnum(_) |
+            Addr::Float(_) => {
+                false
+            }
+            _ => {
+                true
+            }
+        }
+    }
+
+    #[inline]
     pub fn is_ref(&self) -> bool {
         match self {
-            Addr::HeapCell(_) | Addr::StackCell(_, _) | Addr::AttrVar(_) | Addr::PStrTail(..) => {
+            Addr::HeapCell(_) | Addr::StackCell(_, _) | Addr::AttrVar(_) => {
                 true
             }
             _ => {
@@ -141,16 +182,105 @@ impl Addr {
         }
     }
 
+    #[inline]
     pub fn as_var(&self) -> Option<Ref> {
         match self {
             &Addr::AttrVar(h) => Some(Ref::AttrVar(h)),
             &Addr::HeapCell(h) => Some(Ref::HeapCell(h)),
             &Addr::StackCell(fr, sc) => Some(Ref::StackCell(fr, sc)),
-            &Addr::PStrTail(h, n) => Some(Ref::PStrTail(h, n)),
             _ => None,
         }
     }
 
+    pub(super)
+    fn order_category(&self, heap: &Heap) -> Option<TermOrderCategory> {
+        match Number::try_from((*self, heap)) {
+            Ok(Number::Integer(_)) | Ok(Number::Fixnum(_)) | Ok(Number::Rational(_)) => {
+                Some(TermOrderCategory::Integer)
+            }
+            Ok(Number::Float(_)) => {
+                Some(TermOrderCategory::FloatingPoint)
+            }
+            _ => {
+                match self {
+                    Addr::HeapCell(_) | Addr::AttrVar(_) | Addr::StackCell(..) => {
+                        Some(TermOrderCategory::Variable)
+                    }
+                    Addr::Float(_) => {
+                        Some(TermOrderCategory::FloatingPoint)
+                    }
+                    &Addr::Con(h) => {
+                        match &heap[h] {
+                            HeapCellValue::Atom(..) => {
+                                Some(TermOrderCategory::Atom)
+                            }
+                            HeapCellValue::DBRef(_) => {
+                                None
+                            }
+                            _ => {
+                                unreachable!()
+                            }
+                        }
+                    }
+                    Addr::Char(_) | Addr::EmptyList => {
+                        Some(TermOrderCategory::Atom)
+                    }
+                    Addr::Fixnum(_) | Addr::Usize(_) => {
+                        Some(TermOrderCategory::Integer)
+                    }
+                    Addr::Lis(_) | Addr::PStrLocation(..) | Addr::Str(_) => {
+                        Some(TermOrderCategory::Compound)
+                    }
+                    Addr::CutPoint(_) | Addr::Stream(_) | Addr::TcpListener(_) => {
+                        None
+                    }
+                }
+            }
+        }
+    }
+
+    pub fn as_constant_index(&self, machine_st: &MachineState) -> Option<Constant> {
+        match self {
+            &Addr::Char(c) => {
+                Some(Constant::Char(c))
+            }
+            &Addr::Con(h) => {
+                match &machine_st.heap[h] {
+                    &HeapCellValue::Atom(ref name, _) if name.is_char() => {
+                        Some(Constant::Char(name.as_str().chars().next().unwrap()))
+                    }
+                    &HeapCellValue::Atom(ref name, _) => {
+                        Some(Constant::Atom(name.clone(), None))
+                    }
+                    &HeapCellValue::Integer(ref n) => {
+                        Some(Constant::Integer(n.clone()))
+                    }
+                    &HeapCellValue::Rational(ref n) => {
+                        Some(Constant::Rational(n.clone()))
+                    }
+                    _ => {
+                        None
+                    }
+                }
+            }
+            &Addr::EmptyList => {
+                Some(Constant::EmptyList)
+            }
+            &Addr::Fixnum(n) => {
+                Some(Constant::Fixnum(n))
+            }
+            &Addr::Float(f) => {
+                Some(Constant::Float(f))
+            }
+            &Addr::Usize(n) => {
+                Some(Constant::Usize(n))
+            }
+            _ => {
+                None
+            }
+        }
+    }
+
     pub fn is_protected(&self, e: usize) -> bool {
         match self {
             &Addr::StackCell(addr, _) if addr >= e => false,
@@ -164,12 +294,13 @@ impl Add<usize> for Addr {
 
     fn add(self, rhs: usize) -> Self::Output {
         match self {
+            Addr::Stream(h) => Addr::Stream(h + rhs),
+            Addr::Con(h) => Addr::Con(h + rhs),
             Addr::Lis(a) => Addr::Lis(a + rhs),
             Addr::AttrVar(h) => Addr::AttrVar(h + rhs),
             Addr::HeapCell(h) => Addr::HeapCell(h + rhs),
             Addr::Str(s) => Addr::Str(s + rhs),
             Addr::PStrLocation(h, n) => Addr::PStrLocation(h + rhs, n),
-            Addr::PStrTail(h, n) => Addr::PStrTail(h + rhs, n),
             _ => self,
         }
     }
@@ -181,11 +312,12 @@ impl Sub<i64> for Addr {
     fn sub(self, rhs: i64) -> Self::Output {
         if rhs < 0 {
             match self {
+                Addr::Stream(h) => Addr::Stream(h + rhs.abs() as usize),
+                Addr::Con(h) => Addr::Con(h + rhs.abs() as usize),
                 Addr::Lis(a) => Addr::Lis(a + rhs.abs() as usize),
                 Addr::AttrVar(h) => Addr::AttrVar(h + rhs.abs() as usize),
                 Addr::HeapCell(h) => Addr::HeapCell(h + rhs.abs() as usize),
                 Addr::Str(s) => Addr::Str(s + rhs.abs() as usize),
-                Addr::PStrTail(h, n) => Addr::PStrTail(h + rhs.abs() as usize, n),
                 Addr::PStrLocation(h, n) => Addr::PStrLocation(h + rhs.abs() as usize, n),
                 _ => self,
             }
@@ -200,11 +332,12 @@ impl Sub<usize> for Addr {
 
     fn sub(self, rhs: usize) -> Self::Output {
         match self {
+            Addr::Stream(h) => Addr::Stream(h - rhs),
+            Addr::Con(h) => Addr::Con(h - rhs),
             Addr::Lis(a) => Addr::Lis(a - rhs),
             Addr::AttrVar(h) => Addr::AttrVar(h - rhs),
             Addr::HeapCell(h) => Addr::HeapCell(h - rhs),
             Addr::Str(s) => Addr::Str(s - rhs),
-            Addr::PStrTail(h, n) => Addr::PStrTail(h - rhs, n),
             Addr::PStrLocation(h, n) => Addr::PStrLocation(h - rhs, n),
             _ => self,
         }
@@ -217,7 +350,7 @@ impl SubAssign<usize> for Addr {
     }
 }
 
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub enum TrailRef {
     Ref(Ref),
     AttrVarHeapLink(usize),
@@ -230,30 +363,87 @@ impl From<Ref> for TrailRef {
     }
 }
 
-#[derive(Clone, PartialEq)]
+#[derive(Debug)]
 pub enum HeapCellValue {
     Addr(Addr),
+    Atom(ClauseName, Option<SharedOpDesc>),
+    DBRef(DBRef),
+    Integer(Rc<Integer>),
     NamedStr(usize, ClauseName, Option<SharedOpDesc>), // arity, name, precedence/Specifier if it has one.
-    PartialString(PartialString),
+    Rational(Rc<Rational>),
+    PartialString(PartialString, bool), // the partial string, a bool indicating whether it came from a Constant.
+    Stream(Stream),
+    TcpListener(TcpListener),
 }
 
 impl HeapCellValue {
+    #[inline]
     pub fn as_addr(&self, focus: usize) -> Addr {
         match self {
             HeapCellValue::Addr(ref a) => {
-                a.clone()
+                *a
+            }
+            HeapCellValue::Atom(..) | HeapCellValue::DBRef(..) | HeapCellValue::Integer(..) |
+            HeapCellValue::Rational(..) => {
+                Addr::Con(focus)
             }
             HeapCellValue::NamedStr(_, _, _) => {
                 Addr::Str(focus)
             }
-            HeapCellValue::PartialString(_) => {
+            HeapCellValue::PartialString(..) => {
                 Addr::PStrLocation(focus, 0)
             }
+            HeapCellValue::Stream(_) => {
+                Addr::Stream(focus)
+            }
+            HeapCellValue::TcpListener(_) => {
+                Addr::TcpListener(focus)
+            }
+        }
+    }
+
+    #[inline]
+    pub fn context_free_clone(&self) -> HeapCellValue {
+        match self {
+            &HeapCellValue::Addr(addr) => {
+                HeapCellValue::Addr(addr)
+            }
+            &HeapCellValue::Atom(ref name, ref op) => {
+                HeapCellValue::Atom(name.clone(), op.clone())
+            }
+            &HeapCellValue::DBRef(ref db_ref) => {
+                HeapCellValue::DBRef(db_ref.clone())
+            }
+            &HeapCellValue::Integer(ref n) => {
+                HeapCellValue::Integer(n.clone())
+            }
+            &HeapCellValue::NamedStr(arity, ref name, ref op) => {
+                HeapCellValue::NamedStr(arity, name.clone(), op.clone())
+            }
+            &HeapCellValue::Rational(ref r) => {
+                HeapCellValue::Rational(r.clone())
+            }
+            &HeapCellValue::PartialString(ref pstr, has_tail) => {
+                HeapCellValue::PartialString(pstr.clone(), has_tail)
+            }
+            &HeapCellValue::Stream(ref stream) => {
+                HeapCellValue::Stream(stream.clone())
+            }
+            &HeapCellValue::TcpListener(_) => {
+                HeapCellValue::Atom(clause_name!("$tcp_listener"), None)
+            }
         }
     }
 }
 
-#[derive(Clone, Copy, Eq, PartialEq, Ord, PartialOrd)]
+impl From<Addr> for HeapCellValue {
+    #[inline]
+    fn from(value: Addr) -> HeapCellValue {
+        HeapCellValue::Addr(value)
+    }
+}
+
+#[derive(Debug, Clone, Copy, Eq, PartialEq, Ord, PartialOrd)]
 pub enum IndexPtr {
     DynamicUndefined, // a predicate, declared as dynamic, whose location in code is as yet undefined.
     Undefined,
@@ -263,7 +453,7 @@ pub enum IndexPtr {
     UserTermExpansion
 }
 
-#[derive(Clone, Ord, PartialOrd, Eq, PartialEq)]
+#[derive(Debug, Clone, Ord, PartialOrd, Eq, PartialEq)]
 pub struct CodeIndex(pub Rc<RefCell<(IndexPtr, ClauseName)>>);
 
 impl CodeIndex {
@@ -318,7 +508,7 @@ impl From<(usize, ClauseName)> for CodeIndex {
     }
 }
 
-#[derive(Clone, Copy, PartialEq)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub enum DynamicAssertPlace {
     Back,
     Front,
@@ -342,7 +532,7 @@ impl DynamicAssertPlace {
     }
 }
 
-#[derive(Clone, Copy, PartialEq)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub enum DynamicTransactionType {
     Abolish,
     Assert(DynamicAssertPlace),
@@ -352,7 +542,7 @@ pub enum DynamicTransactionType {
     Retract, // dynamic index of the clause to remove.
 }
 
-#[derive(Clone, Copy, PartialOrd, Ord, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialOrd, Ord, PartialEq, Eq)]
 pub enum REPLCodePtr {
     CompileBatch,
     UseModule,
@@ -361,7 +551,7 @@ pub enum REPLCodePtr {
     UseQualifiedModuleFromFile
 }
 
-#[derive(Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq)]
 pub enum CodePtr {
     BuiltInClause(BuiltInClauseType, LocalCodePtr), // local is the successor call.
     CallN(usize, LocalCodePtr, bool),               // arity, local, last call.
@@ -428,37 +618,31 @@ impl LocalCodePtr {
             LocalCodePtr::DirEntry(p) => {
                 heap.append(functor!(
                     "dir_entry",
-                    1,
-                    [heap_integer!(Integer::from(*p))]
+                    [integer(*p)]
                 ));
             }
             LocalCodePtr::InSituDirEntry(p) => {
                 heap.append(functor!(
                     "in_situ_dir_entry",
-                    1,
-                    [heap_integer!(Integer::from(*p))]
+                    [integer(*p)]
                 ));
             }
             LocalCodePtr::TopLevel(chunk_num, offset) => {
                 heap.append(functor!(
                     "top_level",
-                    2,
-                    [heap_integer!(Integer::from(*chunk_num)),
-                     heap_integer!(Integer::from(*offset))]
+                    [integer(*chunk_num), integer(*offset)]
                 ));
             }
             LocalCodePtr::UserGoalExpansion(p) => {
                 heap.append(functor!(
                     "user_goal_expansion",
-                    1,
-                    [heap_integer!(Integer::from(*p))]
+                    [integer(*p)]
                 ));
             }
             LocalCodePtr::UserTermExpansion(p) => {
                 heap.append(functor!(
                     "user_term_expansion",
-                    1,
-                    [heap_integer!(Integer::from(*p))]
+                    [integer(*p)]
                 ));
             }
         }
@@ -470,8 +654,12 @@ impl LocalCodePtr {
 impl PartialOrd<CodePtr> for CodePtr {
     fn partial_cmp(&self, other: &CodePtr) -> Option<Ordering> {
         match (self, other) {
-            (&CodePtr::Local(ref l1), &CodePtr::Local(ref l2)) => l1.partial_cmp(l2),
-            _ => Some(Ordering::Greater),
+            (&CodePtr::Local(ref l1), &CodePtr::Local(ref l2)) => {
+                l1.partial_cmp(l2)
+            }
+            _ => {
+                Some(Ordering::Greater)
+            }
         }
     }
 }
@@ -486,8 +674,12 @@ impl PartialOrd<LocalCodePtr> for LocalCodePtr {
           | (&LocalCodePtr::TopLevel(_, p1), &LocalCodePtr::TopLevel(_, ref p2)) => {
                 p1.partial_cmp(p2)
             }
-            (_, &LocalCodePtr::TopLevel(_, _)) => Some(Ordering::Less),
-            _ => Some(Ordering::Greater),
+            (_, &LocalCodePtr::TopLevel(_, _)) => {
+                Some(Ordering::Less)
+            }
+            _ => {
+                Some(Ordering::Greater)
+            }
         }
     }
 }
@@ -578,7 +770,7 @@ impl AddAssign<usize> for CodePtr {
 pub type HeapVarDict = IndexMap<Rc<Var>, Addr>;
 pub type AllocVarDict = IndexMap<Rc<Var>, VarData>;
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub struct DynamicPredicateInfo {
     pub(super) clauses_subsection_p: usize, // a LocalCodePtr::DirEntry value.
 }
@@ -598,6 +790,7 @@ pub type DynamicCodeDir = IndexMap<(ClauseName, ClauseName, usize), DynamicPredi
 
 pub type GlobalVarDir = IndexMap<ClauseName, (Ball, Option<usize>)>;
 
+#[derive(Debug)]
 pub(crate) struct ModuleStub {
     pub(crate) atom_tbl: TabledData<Atom>,
     pub(crate) in_situ_code_dir: InSituCodeDir,
@@ -613,17 +806,22 @@ impl ModuleStub {
 }
 
 pub(crate) type ModuleStubDir = IndexMap<ClauseName, ModuleStub>;
+pub(crate) type StreamAliasDir = IndexMap<ClauseName, Stream>;
+pub(crate) type StreamDir = BTreeSet<Stream>;
 
+#[derive(Debug)]
 pub struct IndexStore {
     pub(super) atom_tbl: TabledData<Atom>,
     pub(super) code_dir: CodeDir,
-    pub(super) module_dir: ModuleDir,
     pub(super) dynamic_code_dir: DynamicCodeDir,
     pub(super) global_variables: GlobalVarDir,
     pub(super) in_situ_code_dir: InSituCodeDir,
     pub(super) in_situ_module_dir: ModuleStubDir,
+    pub(super) module_dir: ModuleDir,
     pub(super) modules: ModuleDir,
     pub(super) op_dir: OpDir,
+    pub(super) streams: StreamDir,
+    pub(super) stream_aliases: StreamAliasDir,
 }
 
 impl IndexStore {
@@ -710,6 +908,8 @@ impl IndexStore {
             in_situ_module_dir: ModuleStubDir::new(),
             op_dir: default_op_dir(),
             modules: ModuleDir::new(),
+            stream_aliases: StreamAliasDir::new(),
+            streams: StreamDir::new(),
         }
     }
 
@@ -740,13 +940,13 @@ impl IndexStore {
         let r_w_h = clause_name!("run_cleaners_with_handling");
         let r_wo_h = clause_name!("run_cleaners_without_handling");
 
-        let non_iso = clause_name!("non_iso");
+        let iso_ext = clause_name!("iso_ext");
 
         let r_w_h = self
-            .get_internal(r_w_h, 0, non_iso.clone())
+            .get_internal(r_w_h, 0, iso_ext.clone())
             .and_then(|item| item.local());
         let r_wo_h = self
-            .get_internal(r_wo_h, 1, non_iso)
+            .get_internal(r_wo_h, 1, iso_ext)
             .and_then(|item| item.local());
 
         if let Some(r_w_h) = r_w_h {
@@ -762,6 +962,7 @@ impl IndexStore {
 pub type CodeDir = BTreeMap<PredicateKey, CodeIndex>;
 pub type TermDir = IndexMap<PredicateKey, (Predicate, VecDeque<TopLevel>)>;
 
+#[derive(Debug)]
 pub struct TermDirQuantumEntry {
     pub old_terms: (Predicate, VecDeque<TopLevel>),
     pub new_terms: (Predicate, VecDeque<TopLevel>),
@@ -790,6 +991,7 @@ impl TermDirQuantumEntry {
     }
 }
 
+#[derive(Debug)]
 pub struct TermDirQuantum(IndexMap<PredicateKey, TermDirQuantumEntry>);
 
 impl TermDirQuantum {
@@ -833,7 +1035,7 @@ impl TermDirQuantum {
     }
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Ord, PartialOrd)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Ord, PartialOrd)]
 pub enum CompileTimeHook {
     GoalExpansion,
     TermExpansion,
@@ -887,6 +1089,16 @@ pub enum RefOrOwned<'a, T: 'a> {
     Owned(T),
 }
 
+impl<'a, T: 'a + fmt::Debug> fmt::Debug for RefOrOwned<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            &RefOrOwned::Borrowed(ref borrowed) =>
+                write!(f, "Borrowed({:?})", borrowed),
+            &RefOrOwned::Owned(ref owned) => write!(f, "Owned({:?})", owned),
+        }
+    }
+}
+
 impl<'a, T> RefOrOwned<'a, T> {
     pub fn as_ref(&'a self) -> &'a T {
         match self {

src/machine/mod.rs

@@ -1,12 +1,12 @@
-use prolog_parser::ast::*;
-use prolog_parser::tabled_rc::*;
+use crate::prolog_parser::ast::*;
+use crate::prolog_parser::tabled_rc::*;
 
-use crate::prolog::clause_types::*;
-use crate::prolog::forms::*;
-use crate::prolog::heap_print::*;
-use crate::prolog::instructions::*;
-use crate::prolog::machine::heap::*;
-use crate::prolog::read::*;
+use crate::clause_types::*;
+use crate::forms::*;
+use crate::heap_print::*;
+use crate::instructions::*;
+use crate::machine::heap::*;
+use crate::read::*;
 
 mod attributed_variables;
 pub(super) mod code_repo;
@@ -19,37 +19,41 @@ pub mod machine_errors;
 pub mod machine_indices;
 pub(super) mod machine_state;
 pub mod modules;
-mod partial_string;
+pub mod partial_string;
 mod raw_block;
 mod stack;
+pub(crate) mod streams;
 pub(super) mod term_expansion;
 pub mod toplevel;
 
+#[macro_use]
+mod arithmetic_ops;
 #[macro_use]
 mod machine_state_impl;
 mod system_calls;
 
-use crate::prolog::machine::attributed_variables::*;
-use crate::prolog::machine::code_repo::*;
-use crate::prolog::machine::compile::*;
-use crate::prolog::machine::machine_errors::*;
-use crate::prolog::machine::machine_indices::*;
-use crate::prolog::machine::machine_state::*;
-use crate::prolog::machine::modules::*;
-use crate::prolog::machine::toplevel::*;
-use crate::prolog::read::PrologStream;
+use crate::machine::attributed_variables::*;
+use crate::machine::code_repo::*;
+use crate::machine::compile::*;
+use crate::machine::machine_errors::*;
+use crate::machine::machine_indices::*;
+use crate::machine::machine_state::*;
+use crate::machine::modules::*;
+use crate::machine::streams::*;
+use crate::machine::toplevel::*;
 
-use indexmap::IndexMap;
+use crate::indexmap::IndexMap;
 
 use std::collections::VecDeque;
+use std::convert::TryFrom;
 use std::fs::File;
-use std::io::Read;
 use std::mem;
 use std::ops::Index;
 use std::path::PathBuf;
 use std::rc::Rc;
 use std::sync::atomic::AtomicBool;
 
+#[derive(Debug)]
 pub struct MachinePolicies {
     call_policy: Box<dyn CallPolicy>,
     cut_policy: Box<dyn CutPolicy>,
@@ -69,6 +73,14 @@ impl MachinePolicies {
     }
 }
 
+impl Default for MachinePolicies {
+    #[inline]
+    fn default() -> Self {
+        MachinePolicies::new()
+    }
+}
+
+#[derive(Debug)]
 pub struct Machine {
     pub(super) machine_st: MachineState,
     pub(super) inner_heap: Heap,
@@ -76,7 +88,8 @@ pub struct Machine {
     pub(super) indices: IndexStore,
     pub(super) code_repo: CodeRepo,
     pub(super) toplevel_idx: usize,
-    pub(super) prolog_stream: ParsingStream<Box<dyn Read>>,
+    pub(super) current_input_stream: Stream,
+    pub(super) current_output_stream: Stream,
 }
 
 impl Index<LocalCodePtr> for CodeRepo {
@@ -149,7 +162,15 @@ impl SubModuleUser for IndexStore {
     fn insert_dir_entry(&mut self, name: ClauseName, arity: usize, idx: CodeIndex) {
         if let Some(ref code_idx) = self.code_dir.get(&(name.clone(), arity)) {
             if !code_idx.is_undefined() {
-                println!("Warning: overwriting {}/{}", &name, arity);
+                match (name.as_str(), arity) {
+                    ("term_expansion", 2) => {
+                    }
+                    ("goal_expansion", 2) => {
+                    }
+                    _ => {
+                        println!("Warning: overwriting {}/{}", &name, arity);
+                    }
+                }
             }
 
             let (p, module_name) = idx.0.borrow().clone();
@@ -191,13 +212,6 @@ impl SubModuleUser for IndexStore {
     }
 }
 
-#[inline]
-fn current_dir() -> std::path::PathBuf {
-    let mut path_buf = std::path::PathBuf::from(file!());
-    path_buf.pop();
-    path_buf
-}
-
 include!(concat!(env!("OUT_DIR"), "/libraries.rs"));
 
 static TOPLEVEL: &str = include_str!("../toplevel.pl");
@@ -205,14 +219,13 @@ static TOPLEVEL: &str = include_str!("../toplevel.pl");
 impl Machine {
     fn compile_special_forms(&mut self)
     {
-        let current_dir = current_dir();
+        let verify_attrs_src = ListingSource::User;
 
-        let verify_attrs_src = ListingSource::from_file_and_path(
-            clause_name!("attributed_variables.pl"),
-            current_dir.clone(),
-        );
-
-        match compile_special_form(self, parsing_stream(VERIFY_ATTRS.as_bytes()), verify_attrs_src)
+        match compile_special_form(
+            self,
+            Stream::from(VERIFY_ATTRS),
+            verify_attrs_src,
+        )
         {
             Ok(p) => {
                 self.machine_st.attr_var_init.verify_attrs_loc = p;
@@ -221,12 +234,13 @@ impl Machine {
                 panic!("Machine::compile_special_forms() failed at VERIFY_ATTRS"),
         }
 
-        let project_attrs_src = ListingSource::from_file_and_path(
-            clause_name!("project_attributes.pl"),
-            current_dir,
-        );
+        let project_attrs_src = ListingSource::User;
 
-        match compile_special_form(self, parsing_stream(PROJECT_ATTRS.as_bytes()), project_attrs_src)
+        match compile_special_form(
+            self,
+            Stream::from(PROJECT_ATTRS),
+            project_attrs_src,
+        )
         {
             Ok(p) => {
                 self.machine_st.attr_var_init.project_attrs_loc = p;
@@ -240,17 +254,11 @@ impl Machine {
     {
         self.toplevel_idx = self.code_repo.code.len();
 
-        let mut current_dir = current_dir();
-        current_dir.pop();
-
-        let top_lvl_src = ListingSource::from_file_and_path(
-            clause_name!("toplevel.pl"),
-            current_dir,
-        );
+        let top_lvl_src = ListingSource::User;
 
         compile_user_module(
             self,
-            parsing_stream(TOPLEVEL.as_bytes()),
+            Stream::from(TOPLEVEL),
             true,
             top_lvl_src,
         );
@@ -264,7 +272,11 @@ impl Machine {
 
             Ok(self.indices.insert_module(module))
         } else {
-            Err(SessionError::ModuleNotFound)
+            let err = ExistenceError::ModuleSource(ModuleSource::File(
+                clause_name!("$toplevel"),
+            ));
+
+            Err(SessionError::ExistenceError(err))
         }
     }
 
@@ -278,7 +290,10 @@ impl Machine {
 
         if path.is_file() {
             let file_src = match File::open(&path) {
-                Ok(file_handle) => parsing_stream(file_handle),
+                Ok(file_handle) => Stream::from_file_as_input(
+                    clause_name!(".scryerrc"),
+                    file_handle,
+                ),
                 Err(_) => return,
             };
 
@@ -293,47 +308,46 @@ impl Machine {
 
     #[cfg(test)]
     pub fn reset(&mut self) {
-        self.prolog_stream = readline::input_stream();
+        self.current_input_stream = readline::input_stream();
         self.policies.cut_policy = Box::new(DefaultCutPolicy {});
         self.machine_st.reset();
     }
 
     pub fn run_init_code(&mut self, code: Code) -> bool {
-	let old_machine_st = self.sink_to_snapshot();
-	self.machine_st.reset();
+	    let old_machine_st = self.sink_to_snapshot();
+	    self.machine_st.reset();
 
-	self.code_repo.cached_query = code;
-	self.run_query();
+	    self.code_repo.cached_query = code;
+	    self.run_query();
 
         let result = self.machine_st.fail;
-	self.absorb_snapshot(old_machine_st);
+	    self.absorb_snapshot(old_machine_st);
 
         !result
     }
 
     pub fn run_top_level(&mut self) {
-	use std::env;
+        use std::env;
 
-	let mut filename_atoms = vec![];
+        let mut arg_pstrs = vec![];
 
-	// the first of these is the path to the scryer-prolog executable, so skip
-	// it.
-	for filename in env::args().skip(1) {
-	    let atom = atom!(filename, self.indices.atom_tbl);
-	    filename_atoms.push(Addr::Con(atom));
-	}
+        for arg in env::args() {
+            arg_pstrs.push(self.machine_st.heap.put_complete_string(&arg));
+        }
 
-	let list_addr =
-	    Addr::HeapCell(self.machine_st.heap.to_list(filename_atoms.into_iter()));
+        let list_addr = Addr::HeapCell(self.machine_st.heap.to_list(arg_pstrs.into_iter()));
+        self.machine_st[temp_v!(1)] = list_addr;
 
-	self.machine_st[temp_v!(1)] = list_addr;
-        self.machine_st.p = CodePtr::Local(LocalCodePtr::DirEntry(self.toplevel_idx));
-
-        self.run_query();
+        loop {
+            self.machine_st.p = CodePtr::Local(LocalCodePtr::DirEntry(self.toplevel_idx));
+            self.run_query();
+        }
     }
 
-    pub fn new(prolog_stream: PrologStream) -> Self
+    pub fn new(current_input_stream: Stream, current_output_stream: Stream) -> Self
     {
+        use crate::ref_thread_local::RefThreadLocal;
+
         let mut wam = Machine {
             machine_st: MachineState::new(),
             inner_heap: Heap::new(),
@@ -341,53 +355,64 @@ impl Machine {
             indices: IndexStore::new(),
             code_repo: CodeRepo::new(),
             toplevel_idx: 0,
-            prolog_stream,
+            current_input_stream,
+            current_output_stream,
         };
 
         let atom_tbl = wam.indices.atom_tbl.clone();
-        let mut lib_path = current_dir();
-
-        lib_path.pop();
-        lib_path.push("lib");
 
         wam.indices.add_term_and_goal_expansion_indices();
 
         compile_listing(
             &mut wam,
-            parsing_stream(BUILTINS.as_bytes()),
+            Stream::from(LIBRARIES.borrow()["builtins"]),
             default_index_store!(atom_tbl.clone()),
             true,
-            ListingSource::from_file_and_path(
-                clause_name!("builtins.pl"),
-                lib_path.clone(),
-            ),
+            ListingSource::User,
         );
 
         wam.compile_special_forms();
 
-        compile_user_module(&mut wam, parsing_stream(ERROR.as_bytes()), true,
-                            ListingSource::from_file_and_path(
-                                clause_name!("error"),
-                                lib_path.clone(),
-                            )
+        compile_user_module(
+            &mut wam,
+            Stream::from(LIBRARIES.borrow()["error"]),
+            true,
+            ListingSource::User,
         );
-        compile_user_module(&mut wam, parsing_stream(LISTS.as_bytes()), true,
-                            ListingSource::from_file_and_path(
-                                clause_name!("lists"),
-                                lib_path.clone(),
-                            ),
+
+        compile_user_module(
+            &mut wam,
+            Stream::from(LIBRARIES.borrow()["pairs"]),
+            true,
+            ListingSource::User,
         );
-        compile_user_module(&mut wam, parsing_stream(NON_ISO.as_bytes()), true,
-                            ListingSource::from_file_and_path(
-                                clause_name!("non_iso"),
-                                lib_path.clone(),
-                            )
+
+        compile_user_module(
+            &mut wam,
+            Stream::from(LIBRARIES.borrow()["lists"]),
+            true,
+            ListingSource::User,
         );
-        compile_user_module(&mut wam, parsing_stream(SI.as_bytes()), true,
-                            ListingSource::from_file_and_path(
-                                clause_name!("si"),
-                                lib_path.clone(),
-                            )
+
+        compile_user_module(
+            &mut wam,
+            Stream::from(LIBRARIES.borrow()["iso_ext"]),
+            true,
+            ListingSource::User,
+        );
+
+        compile_user_module(
+            &mut wam,
+            Stream::from(LIBRARIES.borrow()["si"]),
+            true,
+            ListingSource::User,
+        );
+
+        compile_user_module(
+            &mut wam,
+            Stream::from(LIBRARIES.borrow()["charsio"]),
+            true,
+            ListingSource::User,
         );
 
         if wam.compile_top_level().is_err() {
@@ -395,10 +420,35 @@ impl Machine {
         }
 
         wam.compile_scryerrc();
+        wam.configure_streams();
 
         wam
     }
 
+    pub fn configure_streams(&mut self) {
+        self.current_input_stream.options.alias = Some(clause_name!("user_input"));
+
+        self.indices.stream_aliases.insert(
+            clause_name!("user_input"),
+            self.current_input_stream.clone(),
+        );
+
+        self.indices.streams.insert(
+            self.current_input_stream.clone()
+        );
+
+        self.current_output_stream.options.alias = Some(clause_name!("user_output"));
+
+        self.indices.stream_aliases.insert(
+            clause_name!("user_output"),
+            self.current_output_stream.clone(),
+        );
+
+        self.indices.streams.insert(
+            self.current_output_stream.clone()
+        );
+    }
+
     #[inline]
     pub fn machine_flags(&self) -> MachineFlags {
         self.machine_st.flags
@@ -504,53 +554,57 @@ impl Machine {
 
     fn extract_module_export_list(&mut self) -> Result<Vec<ModuleExport>, ParserError>
     {
-	let mut export_list = self.machine_st[temp_v!(2)].clone();
-	let mut exports = vec![];
+	    let mut export_list = self.machine_st[temp_v!(2)].clone();
+	    let mut exports = vec![];
 
-	while let Addr::Lis(l) = self.machine_st.store(self.machine_st.deref(export_list)) {
-	    match &self.machine_st.heap[l] {
-		&HeapCellValue::Addr(Addr::Str(s)) => {
+	    while let Addr::Lis(l) = self.machine_st.store(self.machine_st.deref(export_list)) {
+	        match &self.machine_st.heap[l] {
+		        &HeapCellValue::Addr(Addr::Str(s)) => {
                     match &self.machine_st.heap[s] {
                         HeapCellValue::NamedStr(arity, ref name, _)
                             if *arity == 2 && name.as_str() == "/" => {
-		                let name = match &self.machine_st.heap[s+1] {
-			            &HeapCellValue::Addr(Addr::Con(Constant::Atom(ref name, _))) =>
-			                name.clone(),
-			            _ =>
-			                unreachable!()
-		                };
+		                        let name = match &self.machine_st.heap[s+1] {
+			                        &HeapCellValue::Atom(ref name, _) =>
+			                            name.clone(),
+			                        _ =>
+			                            unreachable!()
+		                        };
 
-		                let arity = match &self.machine_st.heap[s+2] {
-			            &HeapCellValue::Addr(Addr::Con(Constant::Integer(ref arity))) =>
-			                arity.to_usize().unwrap(),
-			            _ =>
-			                unreachable!()
-		                };
+		                        let arity = match &self.machine_st.heap[s+2] {
+			                        &HeapCellValue::Integer(ref arity) =>
+			                            arity.to_usize().unwrap(),
+                                    &HeapCellValue::Addr(Addr::Fixnum(n)) =>
+                                        usize::try_from(n).unwrap(),
+			                        _ =>
+			                            unreachable!()
+		                        };
 
-		                exports.push(ModuleExport::PredicateKey((name, arity)));
+		                        exports.push(ModuleExport::PredicateKey((name, arity)));
                             }
                         HeapCellValue::NamedStr(arity, ref name, _)
                             if *arity == 3 && name.as_str() == "op" => {
                                 let name = match &self.machine_st.heap[s+3] {
-			            &HeapCellValue::Addr(Addr::Con(Constant::Atom(ref name, _))) =>
-			                name.clone(),
-			            _ =>
-			                unreachable!()
-		                };
+			                        &HeapCellValue::Atom(ref name, _) =>
+			                            name.clone(),
+			                        _ =>
+			                            unreachable!()
+		                        };
 
                                 let spec = match &self.machine_st.heap[s+2] {
-			            &HeapCellValue::Addr(Addr::Con(Constant::Atom(ref name, _))) =>
-			                name.clone(),
-			            _ =>
-			                unreachable!()
-		                };
+			                        &HeapCellValue::Atom(ref name, _) =>
+			                            name.clone(),
+			                        _ =>
+			                            unreachable!()
+		                        };
 
-		                let prec = match &self.machine_st.heap[s+1] {
-			            &HeapCellValue::Addr(Addr::Con(Constant::Integer(ref arity))) =>
-			                arity.to_usize().unwrap(),
-			            _ =>
-			                unreachable!()
-		                };
+		                        let prec = match &self.machine_st.heap[s+1] {
+			                        &HeapCellValue::Integer(ref arity) =>
+			                            arity.to_usize().unwrap(),
+                                    &HeapCellValue::Addr(Addr::Fixnum(n)) =>
+                                        usize::try_from(n).unwrap(),
+			                        _ =>
+			                            unreachable!()
+		                        };
 
                                 exports.push(ModuleExport::OpDecl(to_op_decl(
                                     prec,
@@ -560,43 +614,58 @@ impl Machine {
                             }
                         _ => unreachable!()
                     }
-		}
-		_ => unreachable!()
+		        }
+		        _ => unreachable!()
+	        }
+
+	        export_list = self.machine_st.heap[l+1].as_addr(l+1);
 	    }
 
-	    export_list = self.machine_st.heap[l+1].as_addr(l+1);
-	}
-
-	Ok(exports)
+	    Ok(exports)
     }
 
     fn use_module<ToSource>(&mut self, to_src: ToSource)
 	where ToSource: Fn(ClauseName) -> ModuleSource
     {
-	// the term expander will overwrite the cached query, so save it here.
-	let cached_query = mem::replace(&mut self.code_repo.cached_query, vec![]);
+	    // the term expander will overwrite the cached query, so save it here.
+	    let cached_query = mem::replace(&mut self.code_repo.cached_query, vec![]);
 
-	let module_spec = self.machine_st[temp_v!(1)].clone();
-	let name = match self.machine_st.store(self.machine_st.deref(module_spec)) {
-	    Addr::Con(Constant::Atom(name, _)) => name,
-	    _ => unreachable!()
-	};
+	    let module_spec = self.machine_st[temp_v!(1)].clone();
+	    let name = {
+            let addr = self.machine_st.store(self.machine_st.deref(module_spec));
 
-	let load_result = match to_src(name) {
-	    ModuleSource::Library(name) =>
+            match self.machine_st.heap.index_addr(&addr).as_ref() {
+                HeapCellValue::Atom(name, _) =>
+                    name.clone(),
+                HeapCellValue::Addr(Addr::Char(c)) =>
+                    clause_name!(c.to_string(), self.indices.atom_tbl),
+                HeapCellValue::Addr(addr @ Addr::PStrLocation(..)) => {
+                    let mut heap_pstr_iter =
+                        self.machine_st.heap_pstr_iter(*addr);
+                    clause_name!(
+                        heap_pstr_iter.to_string(),
+                        self.indices.atom_tbl
+                    )
+                }
+                _ => unreachable!(),
+            }
+	    };
+
+	    let load_result = match to_src(name) {
+	        ModuleSource::Library(name) =>
                 if let Some(module) = self.indices.take_module(name.clone()) {
                     self.indices.remove_module(clause_name!("user"), &module);
                     self.indices.modules.insert(name.clone(), module);
 
-		    Ok(name)
-		} else {
-		    load_library(self, name, false)
-		},
-	    ModuleSource::File(name) =>
+		            Ok(name)
+		        } else {
+		            load_library(self, name, false)
+		        },
+	        ModuleSource::File(name) =>
                 load_module_from_file(self, PathBuf::from(name.as_str()), false)
-	};
+	    };
 
-	let result = load_result.and_then(|name| {
+	    let result = load_result.and_then(|name| {
             let module = self.indices.take_module(name.clone()).unwrap();
 
             if !module.is_impromptu_module {
@@ -606,26 +675,34 @@ impl Machine {
             Ok(self.indices.insert_module(module))
         });
 
-	self.code_repo.cached_query = cached_query;
+	    self.code_repo.cached_query = cached_query;
 
-	if let Err(e) = result {
-	    self.throw_session_error(e, (clause_name!("use_module"), 1));
-	}
+	    if let Err(e) = result {
+	        self.throw_session_error(e, (clause_name!("use_module"), 1));
+	    }
     }
 
     fn use_qualified_module<ToSource>(&mut self, to_src: ToSource)
 	where ToSource: Fn(ClauseName) -> ModuleSource
     {
-	// the term expander will overwrite the cached query, so save it here.
-	let cached_query = mem::replace(&mut self.code_repo.cached_query, vec![]);
+	    // the term expander will overwrite the cached query, so save it here.
+	    let cached_query = mem::replace(&mut self.code_repo.cached_query, vec![]);
 
-	let module_spec = self.machine_st[temp_v!(1)].clone();
-	let name = match self.machine_st.store(self.machine_st.deref(module_spec)) {
-	    Addr::Con(Constant::Atom(name, _)) => name,
-	    _ => unreachable!()
-	};
+	    let module_spec = self.machine_st[temp_v!(1)].clone();
+	    let name = {
+            let addr = self.machine_st.store(self.machine_st.deref(module_spec));
 
-	let exports = match self.extract_module_export_list() {
+            match self.machine_st.heap.index_addr(&addr).as_ref() {
+                HeapCellValue::Atom(name, _) =>
+                    name.clone(),
+                HeapCellValue::Addr(Addr::Char(c)) =>
+                    clause_name!(c.to_string(), self.indices.atom_tbl),
+	            _ =>
+                    unreachable!(),
+            }
+	    };
+
+	    let exports = match self.extract_module_export_list() {
             Ok(exports) => exports,
             Err(e) => {
                 self.throw_session_error(SessionError::from(e), (clause_name!("use_module"), 2));
@@ -633,38 +710,38 @@ impl Machine {
             }
         };
 
-	let load_result = match to_src(name) {
-	    ModuleSource::Library(name) =>
+	    let load_result = match to_src(name) {
+	        ModuleSource::Library(name) =>
                 if let Some(module) = self.indices.take_module(name.clone()) {
                     self.indices.remove_module(clause_name!("user"), &module);
                     self.indices.modules.insert(name.clone(), module);
 
-		    Ok(name)
-		} else {
-		    load_library(self, name, false)
-		},
-	    ModuleSource::File(name) =>
+		            Ok(name)
+		        } else {
+		            load_library(self, name, false)
+		        },
+	        ModuleSource::File(name) =>
                 load_module_from_file(self, PathBuf::from(name.as_str()), false)
-	};
+	    };
 
-	let result = load_result.and_then(|name| {
-	    let module = self.indices.take_module(name.clone()).unwrap();
+	    let result = load_result.and_then(|name| {
+	        let module = self.indices.take_module(name.clone()).unwrap();
 
             if !module.is_impromptu_module {
-	        self.indices.use_qualified_module(&mut self.code_repo,
-					          self.machine_st.flags,
-					          &module,
-					          &exports)?;
+	            self.indices.use_qualified_module(&mut self.code_repo,
+					                              self.machine_st.flags,
+					                              &module,
+					                              &exports)?;
             }
 
-	    Ok(self.indices.insert_module(module))
+	        Ok(self.indices.insert_module(module))
         });
 
-	self.code_repo.cached_query = cached_query;
+	    self.code_repo.cached_query = cached_query;
 
-	if let Err(e) = result {
-	    self.throw_session_error(e, (clause_name!("use_module"), 2));
-	}
+	    if let Err(e) = result {
+	        self.throw_session_error(e, (clause_name!("use_module"), 2));
+	    }
     }
 
     fn handle_toplevel_command(&mut self, code_ptr: REPLCodePtr, p: LocalCodePtr) {
@@ -679,14 +756,14 @@ impl Machine {
                     self.throw_session_error(e, (clause_name!("repl"), 0));
                 }
             }
-	    REPLCodePtr::UseModule =>
-		self.use_module(ModuleSource::Library),
-	    REPLCodePtr::UseModuleFromFile =>
-		self.use_module(ModuleSource::File),
-	    REPLCodePtr::UseQualifiedModule =>
-		self.use_qualified_module(ModuleSource::Library),
-	    REPLCodePtr::UseQualifiedModuleFromFile =>
-		self.use_qualified_module(ModuleSource::File)
+	        REPLCodePtr::UseModule =>
+		        self.use_module(ModuleSource::Library),
+	        REPLCodePtr::UseModuleFromFile =>
+		        self.use_module(ModuleSource::File),
+	        REPLCodePtr::UseQualifiedModule =>
+		        self.use_qualified_module(ModuleSource::Library),
+	        REPLCodePtr::UseQualifiedModuleFromFile =>
+		        self.use_qualified_module(ModuleSource::File)
         }
 
         self.machine_st.p = CodePtr::Local(p);
@@ -699,7 +776,7 @@ impl Machine {
         snapshot.e = self.machine_st.e;
         snapshot.b = self.machine_st.b;
         snapshot.b0 = self.machine_st.b0;
-        snapshot.s = self.machine_st.s;
+        snapshot.s = self.machine_st.s.clone();
         snapshot.tr = self.machine_st.tr;
         snapshot.num_of_args = self.machine_st.num_of_args;
 
@@ -743,7 +820,7 @@ impl Machine {
     }
 
     pub(super) fn run_query(&mut self) {
-	self.machine_st.cp = LocalCodePtr::TopLevel(0, self.code_repo.size_of_cached_query());
+	    self.machine_st.cp = LocalCodePtr::TopLevel(0, self.code_repo.size_of_cached_query());
         let end_ptr = CodePtr::Local(self.machine_st.cp);
 
         while self.machine_st.p < end_ptr {
@@ -751,12 +828,16 @@ impl Machine {
                 &mut self.indices,
                 &mut self.policies,
                 &mut self.code_repo,
-                &mut self.prolog_stream,
+                &mut self.current_input_stream,
+                &mut self.current_output_stream,
             );
 
             match self.machine_st.p {
-                CodePtr::Local(LocalCodePtr::TopLevel(_, p)) if p > 0 => {}
-                CodePtr::REPL(code_ptr, p) => self.handle_toplevel_command(code_ptr, p),
+                CodePtr::Local(LocalCodePtr::TopLevel(_, p)) if p > 0 => {
+                }
+                CodePtr::REPL(code_ptr, p) => {
+                    self.handle_toplevel_command(code_ptr, p)
+                }
                 CodePtr::DynamicTransaction(trans_type, p) => {
                     // self.code_repo.cached_query is about to be overwritten by the term expander,
                     // so hold onto it locally and restore it after the compiler has finished.
@@ -784,29 +865,37 @@ impl MachineState {
         indices: &mut IndexStore,
         policies: &mut MachinePolicies,
         code_repo: &CodeRepo,
-        prolog_stream: &mut PrologStream,
+        current_input_stream: &mut Stream,
+        current_output_stream: &mut Stream,
     ) {
         match instr {
-            &Line::Arithmetic(ref arith_instr) => self.execute_arith_instr(arith_instr),
+            &Line::Arithmetic(ref arith_instr) => {
+                self.execute_arith_instr(arith_instr)
+            }
             &Line::Choice(ref choice_instr) => {
                 self.execute_choice_instr(choice_instr, &mut policies.call_policy)
             }
             &Line::Cut(ref cut_instr) => {
                 self.execute_cut_instr(cut_instr, &mut policies.cut_policy)
             }
-            &Line::Control(ref control_instr) => self.execute_ctrl_instr(
-                indices,
-                code_repo,
-                &mut policies.call_policy,
-                &mut policies.cut_policy,
-                prolog_stream,
-                control_instr,
-            ),
+            &Line::Control(ref control_instr) => {
+                self.execute_ctrl_instr(
+                    indices,
+                    code_repo,
+                    &mut policies.call_policy,
+                    &mut policies.cut_policy,
+                    current_input_stream,
+                    current_output_stream,
+                    control_instr,
+                )
+            }
             &Line::Fact(ref fact_instr) => {
                 self.execute_fact_instr(&fact_instr);
                 self.p += 1;
             }
-            &Line::Indexing(ref indexing_instr) => self.execute_indexing_instr(&indexing_instr),
+            &Line::Indexing(ref indexing_instr) => {
+                self.execute_indexing_instr(&indexing_instr)
+            }
             &Line::IndexedChoice(ref choice_instr) => {
                 self.execute_indexed_choice_instr(choice_instr, &mut policies.call_policy)
             }
@@ -822,14 +911,22 @@ impl MachineState {
         indices: &mut IndexStore,
         policies: &mut MachinePolicies,
         code_repo: &CodeRepo,
-        prolog_stream: &mut PrologStream,
+        current_input_stream: &mut Stream,
+        current_output_stream: &mut Stream,
     ) {
         let instr = match code_repo.lookup_instr(self.last_call, &self.p) {
             Some(instr) => instr,
             None => return,
         };
 
-        self.dispatch_instr(instr.as_ref(), indices, policies, code_repo, prolog_stream);
+        self.dispatch_instr(
+            instr.as_ref(),
+            indices,
+            policies,
+            code_repo,
+            current_input_stream,
+            current_output_stream,
+        );
     }
 
     fn backtrack(&mut self) {
@@ -880,7 +977,8 @@ impl MachineState {
         indices: &mut IndexStore,
         policies: &mut MachinePolicies,
         code_repo: &mut CodeRepo,
-        prolog_stream: &mut PrologStream,
+        current_input_stream: &mut Stream,
+        current_output_stream: &mut Stream,
     ) -> bool {
         loop {
             let instr = match code_repo.lookup_instr(self.last_call, &self.p) {
@@ -896,7 +994,14 @@ impl MachineState {
                 None => return false,
             };
 
-            self.dispatch_instr(instr.as_ref(), indices, policies, code_repo, prolog_stream);
+            self.dispatch_instr(
+                instr.as_ref(),
+                indices,
+                policies,
+                code_repo,
+                current_input_stream,
+                current_output_stream,
+            );
 
             if self.fail {
                 self.backtrack();
@@ -920,10 +1025,17 @@ impl MachineState {
         indices: &mut IndexStore,
         policies: &mut MachinePolicies,
         code_repo: &mut CodeRepo,
-        prolog_stream: &mut PrologStream,
+        current_input_stream: &mut Stream,
+        current_output_stream: &mut Stream,
     ) {
         loop {
-            self.execute_instr(indices, policies, code_repo, prolog_stream);
+            self.execute_instr(
+                indices,
+                policies,
+                code_repo,
+                current_input_stream,
+                current_output_stream,
+            );
 
             if self.fail {
                 self.backtrack();
@@ -939,7 +1051,13 @@ impl MachineState {
                     if !instigating_instr.as_ref().is_head_instr() {
                         let cp = self.p.local();
                         self.run_verify_attr_interrupt(cp);
-                    } else if !self.verify_attr_stepper(indices, policies, code_repo, prolog_stream) {
+                    } else if !self.verify_attr_stepper(
+                        indices,
+                        policies,
+                        code_repo,
+                        current_input_stream,
+                        current_output_stream,
+                    ) {
                         if self.fail {
                             break;
                         }

src/machine/modules.rs

@@ -1,10 +1,10 @@
-use prolog_parser::ast::*;
-use prolog_parser::tabled_rc::*;
+use crate::prolog_parser::ast::*;
+use crate::prolog_parser::tabled_rc::*;
 
-use crate::prolog::forms::*;
-use crate::prolog::machine::code_repo::*;
-use crate::prolog::machine::machine_errors::*;
-use crate::prolog::machine::machine_indices::*;
+use crate::forms::*;
+use crate::machine::code_repo::*;
+use crate::machine::machine_errors::*;
+use crate::machine::machine_indices::*;
 
 use std::collections::VecDeque;
 use std::mem;
@@ -48,6 +48,7 @@ impl Module {
             (te.0)
                 .0
                 .extend((self.user_term_expansions.0).0.iter().cloned());
+
             te.1.extend(self.user_term_expansions.1.iter().cloned());
         }
 
@@ -60,6 +61,7 @@ impl Module {
             (ge.0)
                 .0
                 .extend((self.user_goal_expansions.0).0.iter().cloned());
+
             ge.1.extend(self.user_goal_expansions.1.iter().cloned());
         }
 
@@ -166,7 +168,7 @@ pub trait SubModuleUser {
                                     }
                                 }
                             }
-                        }                    
+                        }
                         _ => {}
                     };
                 },
@@ -202,7 +204,7 @@ pub trait SubModuleUser {
         _: &Module,
         _: &Vec<ModuleExport>,
     ) -> Result<(), SessionError>;
-    
+
     fn use_module(
         &mut self,
         _: &mut CodeRepo,
@@ -232,7 +234,7 @@ where
 
                 if !user.import_decl(name.clone(), arity, submodule) {
                     let submodule_name = submodule.module_decl.name.clone();
-                    
+
                     return Err(SessionError::ModuleDoesNotContainExport(
                         submodule_name,
                         (name, arity)
@@ -250,12 +252,12 @@ where
 
                 let op_dir = user.op_dir();
                 let prec = op_decl.0;
-                
+
                 op_decl.insert_into_op_dir(
                     submodule.module_decl.name.clone(),
                     op_dir,
                     prec,
-                );                   
+                );
             }
         }
     }
@@ -282,12 +284,12 @@ pub fn use_module<User: SubModuleUser>(
             ModuleExport::OpDecl(op_decl) => {
                 let op_dir = user.op_dir();
                 let prec = op_decl.0;
-                
+
                 op_decl.insert_into_op_dir(
                     submodule.module_decl.name.clone(),
                     op_dir,
                     prec,
-                );                
+                );
             }
         }
     }

src/machine/partial_string.rs

@@ -0,0 +1,202 @@
+use core::marker::PhantomData;
+
+use std::alloc;
+use std::mem;
+use std::ptr;
+use std::ops::RangeFrom;
+use std::slice;
+use std::str;
+
+#[derive(Debug)]
+pub struct PartialString {
+    buf: *const u8,
+    len: usize,
+    _marker: PhantomData<[u8]>,
+}
+
+impl Drop for PartialString {
+    fn drop(&mut self) {
+        unsafe {
+            let layout = alloc::Layout::from_size_align_unchecked(self.len, mem::align_of::<u8>());
+            alloc::dealloc(self.buf as *mut u8, layout);
+
+            self.buf = ptr::null();
+            self.len = 0;
+        }
+    }
+}
+
+impl Clone for PartialString {
+    #[inline]
+    fn clone(&self) -> Self {
+        self.clone_from_offset(0)
+    }
+}
+
+fn scan_for_terminator<Iter: Iterator<Item = char>>(iter: Iter) -> usize {
+    let mut terminator_idx = 0;
+
+    for c in iter {
+        if c == '\u{0}' && terminator_idx != 0 {
+            return terminator_idx;
+        }
+
+        terminator_idx += c.len_utf8();
+    }
+
+    terminator_idx
+}
+
+#[derive(Debug)]
+pub struct PStrIter {
+    buf: *const u8,
+    len: usize,
+}
+
+impl PStrIter {
+    #[inline]
+    fn from(buf: *const u8, len: usize, idx: usize) -> Self {
+        PStrIter {
+            buf: (buf as usize + idx) as *const _,
+            len: len - idx,
+        }
+    }
+}
+
+impl Iterator for PStrIter {
+    type Item = char;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        unsafe {
+            let slice = slice::from_raw_parts(self.buf, self.len);
+            let s = str::from_utf8(slice).unwrap();
+
+            if let Some(c) = s.chars().next() {
+                self.buf = self.buf.offset(c.len_utf8() as isize);
+                self.len -= c.len_utf8();
+
+                Some(c)
+            } else {
+                None
+            }
+        }
+    }
+}
+
+impl PartialString {
+    #[inline]
+    pub(super)
+    fn new(src: &str) -> Option<(Self, &str)> {
+        let pstr = PartialString {
+            buf: ptr::null_mut(),
+            len: 0,
+            _marker: PhantomData,
+        };
+
+        unsafe {
+            pstr.append_chars(src)
+        }
+    }
+
+    unsafe fn append_chars(mut self, src: &str) -> Option<(Self, &str)> {
+        let terminator_idx = scan_for_terminator(src.chars());
+
+        let layout = alloc::Layout::from_size_align_unchecked(
+            terminator_idx + '\u{0}'.len_utf8(),
+            mem::align_of::<u8>(),
+        );
+
+        self.buf = alloc::alloc(layout) as *const _;
+        self.len = terminator_idx + '\u{0}'.len_utf8();
+
+        ptr::copy(
+            src.as_ptr(),
+            self.buf as *mut _,
+            terminator_idx,
+        );
+
+        self.write_terminator_at(terminator_idx);
+
+        Some(if terminator_idx != src.as_bytes().len() {
+            (self, &src[terminator_idx ..])
+        } else {
+            (self, "")
+        })
+    }
+
+    pub(super)
+    fn clone_from_offset(&self, n: usize) -> Self {
+        let len =
+            if self.len - '\u{0}'.len_utf8() > n {
+                self.len - n - '\u{0}'.len_utf8()
+            } else {
+                0
+            };
+
+        let mut pstr = PartialString {
+            buf: ptr::null_mut(),
+            len: len + '\u{0}'.len_utf8(),
+            _marker: PhantomData,
+        };
+
+        unsafe {
+            let layout = alloc::Layout::from_size_align_unchecked(
+                len + '\u{0}'.len_utf8(),
+                mem::align_of::<u8>(),
+            );
+
+            pstr.buf = alloc::alloc(layout);
+
+            if len > 0 {
+                ptr::copy(
+                    (self.buf as usize + n) as *const u8,
+                    pstr.buf as *mut _,
+                    len,
+                );
+            }
+
+            pstr.write_terminator_at(len);
+        }
+
+        pstr
+    }
+
+    #[inline]
+    pub(super)
+    fn write_terminator_at(&mut self, index: usize) {
+        unsafe {
+            ptr::write(
+                (self.buf as usize + index) as *mut u8,
+                0u8,
+            );
+        }
+    }
+
+    #[inline]
+    pub fn range_from(&self, index: RangeFrom<usize>) -> PStrIter {
+        if self.len >= '\u{0}'.len_utf8() {
+            PStrIter::from(self.buf, self.len - '\u{0}'.len_utf8(), index.start)
+        } else {
+            PStrIter::from(self.buf, 0, 0)
+        }
+    }
+
+    #[inline]
+    pub fn at_end(&self, end_n: usize) -> bool {
+        end_n + 1 == self.len
+    }
+
+    #[inline]
+    pub fn as_str_from(&self, n: usize) -> &str {
+        unsafe {
+            let slice = slice::from_raw_parts(
+                self.buf,
+                self.len - '\u{0}'.len_utf8(),
+            );
+
+            let s = str::from_utf8(slice).unwrap();
+
+            &s[n ..]
+        }
+    }
+}

src/machine/project_attributes.pl

@@ -1,3 +1,5 @@
+:- module('$project_atts', [copy_term/3]).
+
 '$attribute_goals_driver'(QueryVars, AttrVars) :-
     gather_modules(AttrVars, Modules0, _),
     sort(Modules0, Modules),
@@ -99,7 +101,7 @@ call_attribute_goals_with_module_prefix([Module | Modules], GoalCaller, AttrVars
     call_attribute_goals_with_module_prefix(Modules, GoalCaller, AttrVars, Gs).
 
 copy_term(Source, Dest, Goals) :-
-    term_variables(Source, Vars),
+    '$term_attributed_variables'(Source, Vars),
     gather_modules(Vars, Modules0, _),
     sort(Modules0, Modules),
     call_attribute_goals_with_module_prefix(Modules, call_query_var_goals, Vars, Goals0),

src/machine/raw_block.rs

@@ -5,7 +5,7 @@ use std::mem;
 use std::ptr;
 
 pub(crate) trait RawBlockTraits {
-    fn init_size() -> usize;    
+    fn init_size() -> usize;
     fn align() -> usize;
 
     #[inline]
@@ -14,6 +14,7 @@ pub(crate) trait RawBlockTraits {
     }
 }
 
+#[derive(Debug)]
 pub(crate) struct RawBlock<T: RawBlockTraits> {
     pub(crate) size: usize,
     pub(crate) base: *const u8,
@@ -36,20 +37,6 @@ impl<T: RawBlockTraits> RawBlock<T> {
         block
     }
 
-    pub(crate)
-    fn with_capacity(cap: usize) -> Self {
-        let mut block = RawBlock { size: 0,
-                                   base: ptr::null(),
-                                   top: ptr::null(),
-                                   _marker: PhantomData };
-
-        unsafe {
-            block.init_at_size(cap);
-        }
-
-        block
-    }
-
     unsafe fn init_at_size(&mut self, cap: usize) {
         let layout = alloc::Layout::from_size_align_unchecked(cap, T::align());
 
@@ -86,7 +73,6 @@ impl<T: RawBlockTraits> RawBlock<T> {
         mem::replace(self, Self::empty_block())
     }
 
-
     #[inline]
     fn free_space(&self) -> usize {
         debug_assert!(self.top >= self.base,

src/machine/stack.rs

@@ -1,12 +1,13 @@
-use crate::prolog::machine::machine_indices::*;
-use crate::prolog::machine::raw_block::*;
-
 use core::marker::PhantomData;
 
+use crate::machine::machine_indices::*;
+use crate::machine::raw_block::*;
+
 use std::mem;
 use std::ops::{Index, IndexMut};
 use std::ptr;
 
+#[derive(Debug)]
 struct StackTraits {}
 
 impl RawBlockTraits for StackTraits {
@@ -35,6 +36,7 @@ const fn prelude_size<Prelude>() -> usize {
     (size & !(align - 1)) + align
 }
 
+#[derive(Debug)]
 pub struct Stack {
     buf: RawBlock<StackTraits>,
     _marker: PhantomData<Addr>,
@@ -47,12 +49,12 @@ impl Drop for Stack {
     }
 }
 
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct FramePrelude {
-    is_or_frame: u8,
     pub num_cells: usize,
 }
 
+#[derive(Debug)]
 pub struct AndFramePrelude {
     pub univ_prelude: FramePrelude,
     pub e: usize,
@@ -60,9 +62,9 @@ pub struct AndFramePrelude {
     pub interrupt_cp: LocalCodePtr,
 }
 
+#[derive(Debug)]
 pub struct AndFrame {
     pub prelude: AndFramePrelude,
-    _marker: PhantomData<Addr>,
 }
 
 impl AndFrame {
@@ -101,24 +103,7 @@ impl IndexMut<usize> for AndFrame {
     }
 }
 
-impl Drop for AndFrame {
-    fn drop(&mut self) {
-        let prelude_offset = prelude_size::<AndFramePrelude>();
-
-        unsafe {
-            let ptr = mem::transmute::<&mut AndFrame, *const u8>(self);
-            let ptr = ptr as usize + prelude_offset;
-
-            for idx in 0 .. self.prelude.univ_prelude.num_cells {
-                let index_offset = idx * mem::size_of::<Addr>();
-                let ptr = (ptr + index_offset) as *mut Addr;
-
-                ptr::drop_in_place(ptr);
-            }
-        }
-    }
-}
-
+#[derive(Debug)]
 pub struct OrFramePrelude {
     pub univ_prelude: FramePrelude,
     pub e: usize,
@@ -133,9 +118,9 @@ pub struct OrFramePrelude {
     pub attr_var_init_bindings_b: usize,
 }
 
+#[derive(Debug)]
 pub struct OrFrame {
     pub prelude: OrFramePrelude,
-    _marker: PhantomData<Addr>
 }
 
 impl Index<usize> for OrFrame {
@@ -170,24 +155,6 @@ impl IndexMut<usize> for OrFrame {
     }
 }
 
-impl Drop for OrFrame {
-    fn drop(&mut self) {
-        let prelude_offset = prelude_size::<OrFramePrelude>();
-
-        unsafe {
-            let ptr = mem::transmute::<&mut OrFrame, *const u8>(self);
-            let ptr = ptr as usize + prelude_offset;
-
-            for idx in 0 .. self.prelude.univ_prelude.num_cells {
-                let index_offset = idx * mem::size_of::<Addr>();
-                let ptr = (ptr + index_offset) as *mut Addr;
-
-                ptr::drop_in_place(ptr);
-            }
-        }
-    }
-}
-
 impl OrFrame {
     pub fn size_of(num_cells: usize) -> usize {
         prelude_size::<OrFramePrelude>() + num_cells * mem::size_of::<Addr>()
@@ -204,18 +171,19 @@ impl Stack {
 
         unsafe {
             let new_top = self.buf.new_block(frame_size);
+            let e = self.buf.top as usize - self.buf.base as usize;
 
             for idx in 0 .. num_cells {
                 let offset = prelude_size::<AndFramePrelude>() + idx * mem::size_of::<Addr>();
-                ptr::write((self.buf.top as usize + offset) as *mut Addr, Addr::StackCell(0,0));
+                ptr::write(
+                    (self.buf.top as usize + offset) as *mut Addr,
+                    Addr::StackCell(e, idx + 1),
+                );
             }
 
             let and_frame = &mut *(self.buf.top as *mut AndFrame);
-
-            and_frame.prelude.univ_prelude.is_or_frame = 0;
             and_frame.prelude.univ_prelude.num_cells = num_cells;
 
-            let e = self.buf.top as usize - self.buf.base as usize;
             self.buf.top = new_top;
 
             e
@@ -227,18 +195,19 @@ impl Stack {
 
         unsafe {
             let new_top = self.buf.new_block(frame_size);
+            let b = self.buf.top as usize - self.buf.base as usize;
 
             for idx in 0 .. num_cells {
                 let offset = prelude_size::<OrFramePrelude>() + idx * mem::size_of::<Addr>();
-                ptr::write((self.buf.top as usize + offset) as *mut Addr, Addr::StackCell(0,0));
+                ptr::write(
+                    (self.buf.top as usize + offset) as *mut Addr,
+                    Addr::StackCell(b, idx),
+                );
             }
 
             let or_frame = &mut *(self.buf.top as *mut OrFrame);
-
-            or_frame.prelude.univ_prelude.is_or_frame = 1;
             or_frame.prelude.univ_prelude.num_cells = num_cells;
 
-            let b = self.buf.top as usize - self.buf.base as usize;
             self.buf.top = new_top;
 
             b
@@ -281,6 +250,7 @@ impl Stack {
         Stack { buf: self.buf.take(), _marker: PhantomData }
     }
 
+    #[inline]
     pub fn truncate(&mut self, b: usize) {
         if b == 0 {
             self.inner_truncate(mem::align_of::<Addr>());
@@ -289,40 +259,12 @@ impl Stack {
         }
     }
 
+    #[inline]
     fn inner_truncate(&mut self, b: usize) {
-        let mut b = b + self.buf.base as usize;
-        let base  = b;
+        let base = b + self.buf.base as usize;
 
-        unsafe {
-            while b as *const _ < self.buf.top {
-                let univ_prelude = ptr::read(b as *const FramePrelude);
-
-                let offset = if univ_prelude.is_or_frame == 0 {
-                    let frame_ptr = b as *mut AndFrame;
-                    let frame = &mut *frame_ptr;
-                    let size_of_frame = AndFrame::size_of(frame.prelude.univ_prelude.num_cells);
-
-                    ptr::drop_in_place(frame_ptr);
-
-                    b + size_of_frame
-                } else {
-                    debug_assert!(univ_prelude.is_or_frame == 1);
-
-                    let frame_ptr = b as *mut OrFrame;
-                    let frame = &mut *frame_ptr;
-                    let size_of_frame = OrFrame::size_of(frame.prelude.univ_prelude.num_cells);
-
-                    ptr::drop_in_place(frame_ptr);
-
-                    b + size_of_frame
-                };
-
-                b = offset;
-            }
-
-            if base < self.buf.top as usize {
-                self.buf.top = base as *const _;
-            }
+        if base < self.buf.top as usize {
+            self.buf.top = base as *const _;
         }
     }
 

src/machine/term_expansion.rs

@@ -1,42 +1,16 @@
-use prolog_parser::ast::*;
-use prolog_parser::parser::*;
+use crate::prolog_parser::ast::*;
+use crate::prolog_parser::parser::*;
 
-use crate::prolog::machine::machine_indices::HeapCellValue;
-use crate::prolog::machine::*;
-use crate::prolog::rug::ops::Pow;
-use crate::prolog::rug::Integer;
+use crate::machine::machine_indices::HeapCellValue;
+use crate::machine::*;
+use crate::rug::ops::Pow;
+use crate::rug::Integer;
 
 use std::cell::Cell;
 use std::collections::VecDeque;
-use std::io::Read;
 use std::iter::Rev;
 use std::vec::IntoIter;
 
-fn unfold_by_str_once(term: &mut Term, s: &str) -> Option<(Term, Term)> {
-    if let &mut Term::Clause(_, ref name, ref mut subterms, _) = term {
-        if name.as_str() == s && subterms.len() == 2 {
-            let snd = *subterms.pop().unwrap();
-            let fst = *subterms.pop().unwrap();
-
-            return Some((fst, snd));
-        }
-    }
-
-    None
-}
-
-pub fn unfold_by_str(mut term: Term, s: &str) -> Vec<Term> {
-    let mut terms = vec![];
-
-    while let Some((fst, snd)) = unfold_by_str_once(&mut term, s) {
-        terms.push(fst);
-        term = snd;
-    }
-
-    terms.push(term);
-    terms
-}
-
 pub fn fold_by_str<I>(terms: I, mut term: Term, sym: ClauseName) -> Term
 where
     I: DoubleEndedIterator<Item = Term>,
@@ -53,7 +27,11 @@ where
     term
 }
 
-fn extract_from_list(head: Box<Term>, tail: Box<Term>) -> Result<Rev<IntoIter<Term>>, ParserError> {
+fn extract_from_list(
+    head: Box<Term>,
+    tail: Box<Term>,
+) -> Result<Rev<IntoIter<Term>>, ParserError>
+{
     let mut terms = vec![*head];
     let mut tail = *tail;
 
@@ -69,16 +47,18 @@ fn extract_from_list(head: Box<Term>, tail: Box<Term>) -> Result<Rev<IntoIter<Te
     }
 }
 
-pub struct TermStream<'a, R: Read> {
+#[derive(Debug)]
+pub struct TermStream<'a> {
     stack: Vec<Term>,
     pub(crate) wam: &'a mut Machine,
-    parser: Parser<'a, R>,
+    parser: Parser<'a, Stream>,
     pub(crate) flags: MachineFlags,
     term_expansion_lens: (usize, usize),
     goal_expansion_lens: (usize, usize),
     top_level_terms: Vec<(Term, usize, usize)>, // term, line_num, col_num.
 }
 
+#[derive(Debug)]
 pub struct ExpansionAdditionResult {
     term_expansion_additions: (Predicate, VecDeque<TopLevel>),
     goal_expansion_additions: (Predicate, VecDeque<TopLevel>),
@@ -100,7 +80,7 @@ impl ExpansionAdditionResult {
     }
 }
 
-impl<'a, R: Read> Drop for TermStream<'a, R> {
+impl<'a> Drop for TermStream<'a> {
     fn drop(&mut self) {
         self.wam.indices.in_situ_code_dir.clear();
         self.wam.indices.in_situ_module_dir.clear();
@@ -110,9 +90,9 @@ impl<'a, R: Read> Drop for TermStream<'a, R> {
     }
 }
 
-impl<'a, R: Read> TermStream<'a, R> {
+impl<'a> TermStream<'a> {
     pub fn new(
-        src: &'a mut ParsingStream<R>,
+        src: &'a mut ParsingStream<Stream>,
         atom_tbl: TabledData<Atom>,
         flags: MachineFlags,
         wam: &'a mut Machine,
@@ -185,7 +165,7 @@ impl<'a, R: Read> TermStream<'a, R> {
 
     #[inline]
     pub fn eof(&mut self) -> Result<bool, ParserError> {
-	self.parser.devour_whitespace()?; // eliminate dangling comments before checking for EOF.
+	    self.parser.devour_whitespace()?; // eliminate dangling comments before checking for EOF.
         Ok(self.stack.is_empty() && self.parser.eof()?)
     }
 
@@ -201,6 +181,7 @@ impl<'a, R: Read> TermStream<'a, R> {
             te_len,
             te_queue_len,
         );
+
         let goal_expansion_additions = self.wam.code_repo.truncate_terms(
             (clause_name!("goal_expansion"), 2),
             ge_len,
@@ -240,7 +221,7 @@ impl<'a, R: Read> TermStream<'a, R> {
         term_string: &str,
         op_dir: &OpDir,
     ) -> Result<Term, ParserError> {
-        let mut stream = parsing_stream(term_string.trim().as_bytes());
+        let mut stream = parsing_stream(term_string.trim().as_bytes())?;
         let mut parser = Parser::new(&mut stream, self.parser.get_atom_tbl(), self.flags);
 
         parser.read_term(composite_op!(
@@ -257,7 +238,7 @@ impl<'a, R: Read> TermStream<'a, R> {
 
         while let Some(term) = self.stack.pop() {
             match machine_st.try_expand_term(self.wam, &term, CompileTimeHook::TermExpansion) {
-                Some(term_string) => {                        
+                Some(term_string) => {
                     let term = self.parse_expansion_output(term_string.as_str(), op_dir)?;
                     self.enqueue_term(term)?;
                 }
@@ -269,7 +250,7 @@ impl<'a, R: Read> TermStream<'a, R> {
 
         unreachable!()
     }
-    
+
     pub fn read_term(&mut self, op_dir: &OpDir) -> Result<Term, ParserError> {
         loop {
             if let Some(term) = self.stack.pop() {
@@ -326,7 +307,8 @@ impl<'a, R: Read> TermStream<'a, R> {
 }
 
 impl MachineState {
-    pub(super) fn print_with_locs(&self, addr: Addr, op_dir: &OpDir) -> PrinterOutputter {
+    pub(super)
+    fn print_with_locs(&self, addr: Addr, op_dir: &OpDir) -> PrinterOutputter {
         let output = PrinterOutputter::new();
         let mut printer = HCPrinter::from_heap_locs(&self, op_dir, output);
         let mut max_var_length = 0;
@@ -337,12 +319,16 @@ impl MachineState {
 
         printer.quoted = true;
         printer.numbervars = true;
-        // the purpose of the offset is to avoid clashes with variable names that might
-        // occur after the addresses in the expanded term are substituted with the variable
-        // names in the pre-expansion term. This formula ensures that all generated "numbervars"-
-        // style variable names will be longer than the keys of the var_dict, and therefore
-        // not equal to any of them.
+
+        // the purpose of the offset is to avoid clashes with variable
+        // names that might occur after the addresses in the expanded
+        // term are substituted with the variable names in the
+        // pre-expansion term. This formula ensures that all generated
+        // "numbervars"- style variable names will be longer than the
+        // keys of the var_dict, and therefore not equal to any of
+        // them.
         printer.numbervars_offset = Integer::from(10).pow(max_var_length as u32) * 26;
+        printer.print_strings_as_strs = true;
         printer.drop_toplevel_spec();
 
         printer.see_all_locs();
@@ -354,8 +340,8 @@ impl MachineState {
     }
 
     // reset the machine, but keep the heap contents as they were.
-    // this prevents clashes between underscored variable names
-    // in the same query.
+    // this prevents clashes between underscored variable names in the
+    // same query.
     fn reset_with_heap_preservation(&mut self) {
         let heap = self.heap.take();
         self.reset();
@@ -379,13 +365,16 @@ impl MachineState {
         wam.code_repo.cached_query = code;
 
         self.cp = LocalCodePtr::TopLevel(0, 0);
+
         self.at_end_of_expansion = false;
+        self.flags.double_quotes = DoubleQuotes::Chars;
 
         self.query_stepper(
             &mut wam.indices,
-            &mut wam.policies,
+            &mut MachinePolicies::default(),
             &mut wam.code_repo,
             &mut readline::input_stream(),
+            &mut Stream::stdout(),
         );
 
         if self.fail || self.at_end_of_expansion {
@@ -398,6 +387,7 @@ impl MachineState {
             let output = self.print_with_locs(Addr::HeapCell(h), &wam.indices.op_dir);
 
             self.reset_with_heap_preservation();
+
             Some(output.result())
         }
     }

src/machine/toplevel.rs

@@ -1,19 +1,20 @@
-use prolog_parser::ast::*;
-use prolog_parser::tabled_rc::*;
+use crate::prolog_parser::ast::*;
+use crate::prolog_parser::tabled_rc::*;
 
-use crate::prolog::forms::*;
-use crate::prolog::iterators::*;
-use crate::prolog::machine::machine_errors::*;
-use crate::prolog::machine::machine_indices::*;
-use crate::prolog::machine::term_expansion::*;
-use crate::prolog::machine::*;
+use crate::forms::*;
+use crate::iterators::*;
+use crate::machine::machine_errors::*;
+use crate::machine::machine_indices::*;
+use crate::machine::term_expansion::*;
+use crate::machine::*;
 
-use indexmap::{IndexMap, IndexSet};
+use crate::indexmap::{IndexMap, IndexSet};
 
 use std::borrow::BorrowMut;
 use std::cell::Cell;
 use std::collections::VecDeque;
-use std::io::Read;
+use std::convert::TryFrom;
+use std::fmt;
 use std::mem;
 use std::ops::DerefMut;
 use std::rc::Rc;
@@ -23,6 +24,15 @@ enum IndexSource<'a, T> {
     Local(&'a mut T)
 }
 
+impl<'a, T: fmt::Debug> fmt::Debug for IndexSource<'a, T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            IndexSource::TermStream => write!(fmt, "TermStream"),
+            IndexSource::Local(ref local) => write!(fmt, "Local({:?})", local),
+        }
+    }
+}
+
 fn op_dir<'a, 'b: 'a>(from: &'b IndexSource<'a, IndexStore>) -> RefOrOwned<'a, OpDir> {
     match from {
         IndexSource::TermStream => RefOrOwned::Owned(OpDir::new()),
@@ -30,15 +40,16 @@ fn op_dir<'a, 'b: 'a>(from: &'b IndexSource<'a, IndexStore>) -> RefOrOwned<'a, O
     }
 }
 
-struct CompositeIndices<'a, 'b, 'c, R: Read> {
-    term_stream: &'b mut TermStream<'a, R>,
+#[derive(Debug)]
+struct CompositeIndices<'a, 'b, 'c> {
+    term_stream: &'b mut TermStream<'a>,
     index_src: IndexSource<'c, IndexStore>,
     static_code_dir: Option<IndexSource<'c, CodeDir>>
 }
 
-impl<'a, 'b, 'c, R: Read> CompositeIndices<'a, 'b, 'c, R> {
+impl<'a, 'b, 'c> CompositeIndices<'a, 'b, 'c> {
     fn new(
-        term_stream: &'b mut TermStream<'a, R>,
+        term_stream: &'b mut TermStream<'a>,
         index_src: IndexSource<'c, IndexStore>,
         static_code_dir: Option<IndexSource<'c, CodeDir>>,
     ) -> Self {
@@ -212,8 +223,8 @@ fn setup_op_decl(
     };
 
     let prec = match *terms.pop().unwrap() {
-        Term::Constant(_, Constant::Integer(bi)) => match bi.to_usize() {
-            Some(n) if n <= 1200 => n,
+        Term::Constant(_, Constant::Fixnum(bi)) => match usize::try_from(bi) {
+            Ok(n) if n <= 1200 => n,
             _ => return Err(ParserError::InconsistentEntry),
         },
         _ => return Err(ParserError::InconsistentEntry),
@@ -225,16 +236,21 @@ fn setup_op_decl(
 fn setup_predicate_indicator(term: &mut Term) -> Result<PredicateKey, ParserError>
 {
     match term {
-        Term::Clause(_, ref name, ref mut terms, Some(_))
-            if name.as_str() == "/" && terms.len() == 2 =>
+        Term::Clause(_, ref slash, ref mut terms, Some(_))
+            if (slash.as_str() == "/" || slash.as_str() == "//") && terms.len() == 2 =>
         {
             let arity = *terms.pop().unwrap();
             let name  = *terms.pop().unwrap();
 
             let arity = arity
                 .to_constant()
-                .and_then(|c| c.to_integer())
-                .and_then(|n| n.to_usize())
+                .and_then(|c| {
+                    match c {
+                        Constant::Integer(n) => n.to_usize(),
+                        Constant::Fixnum(n) => usize::try_from(n).ok(),
+                        _ => None
+                    }
+                })
                 .ok_or(ParserError::InvalidModuleExport)?;
 
             let name  = name
@@ -242,7 +258,11 @@ fn setup_predicate_indicator(term: &mut Term) -> Result<PredicateKey, ParserErro
                 .and_then(|c| c.to_atom())
                 .ok_or(ParserError::InvalidModuleExport)?;
 
-            Ok((name, arity))
+            if slash.as_str() == "/" {
+                Ok((name, arity))
+            } else {
+                Ok((name, arity + 2))
+            }
         }
         _ => Err(ParserError::InvalidModuleExport),
     }
@@ -320,16 +340,37 @@ fn setup_module_decl(
     }
 }
 
-fn setup_use_module_decl(mut terms: Vec<Box<Term>>) -> Result<ModuleSource, ParserError> {
+fn read_library_path(
+    term: Term,
+    atom_tbl: TabledData<Atom>,
+) -> Option<ClauseName> {
+    match term {
+        Term::Constant(_, Constant::Atom(atom, _)) => {
+            Some(atom.defrock_brackets())
+        }
+        _ => {
+            let mut atoms = vec![];
+
+            for term in unfold_by_str(term, "/") {
+                match term {
+                    Term::Constant(_, Constant::Atom(atom, _)) => {
+                        atoms.push(atom.as_str().to_owned());
+                    }
+                    _ => return None,
+                }
+            }
+
+            Some(clause_name!(atoms.join("/"), atom_tbl))
+        }
+    }
+}
+
+fn setup_use_module_decl(mut terms: Vec<Box<Term>>, atom_tbl: TabledData<Atom>) -> Result<ModuleSource, ParserError> {
     match *terms.pop().unwrap() {
         Term::Clause(_, ref name, ref mut terms, None)
             if name.as_str() == "library" && terms.len() == 1 =>
         {
-            terms
-                .pop()
-                .unwrap()
-                .to_constant()
-                .and_then(|c| c.to_atom())
+            read_library_path(*terms.pop().unwrap(), atom_tbl)
                 .map(|c| ModuleSource::Library(c))
                 .ok_or(ParserError::InvalidUseModuleDecl)
         }
@@ -339,6 +380,32 @@ fn setup_use_module_decl(mut terms: Vec<Box<Term>>) -> Result<ModuleSource, Pars
     }
 }
 
+fn setup_double_quotes(mut terms: Vec<Box<Term>>) -> Result<DoubleQuotes, ParserError> {
+    let dbl_quotes = *terms.pop().unwrap();
+
+    match terms[0].as_ref() {
+        Term::Constant(_, Constant::Atom(ref name, _))
+            if name.as_str() == "double_quotes" => {
+                match dbl_quotes {
+                    Term::Constant(_, Constant::Atom(name, _)) => {
+                        match name.as_str() {
+                            "atom"  => Ok(DoubleQuotes::Atom),
+                            "chars" => Ok(DoubleQuotes::Chars),
+                            "codes" => Ok(DoubleQuotes::Codes),
+                            _ => Err(ParserError::InvalidDoubleQuotesDecl),
+                        }
+                    }
+                    _ => {
+                        Err(ParserError::InvalidDoubleQuotesDecl)
+                    }
+                }
+            },
+        _ => {
+            Err(ParserError::InvalidDoubleQuotesDecl)
+        }
+    }
+}
+
 type UseModuleExport = (ModuleSource, Vec<ModuleExport>);
 
 fn setup_qualified_import(
@@ -350,11 +417,7 @@ fn setup_qualified_import(
         Term::Clause(_, ref name, ref mut terms, None)
             if name.as_str() == "library" && terms.len() == 1 =>
         {
-            terms
-                .pop()
-                .unwrap()
-                .to_constant()
-                .and_then(|c| c.to_atom())
+            read_library_path(*terms.pop().unwrap(), atom_tbl.clone())
                 .map(|c| ModuleSource::Library(c))
                 .ok_or(ParserError::InvalidUseModuleDecl)
         }
@@ -551,8 +614,8 @@ fn draw_from_term_dir_impl(
     }
 }
 
-fn draw_from_term_dir<R: Read>(
-    indices: &CompositeIndices<R>,
+fn draw_from_term_dir(
+    indices: &CompositeIndices,
     intra_module_term_dirs: &mut IndexMap<ClauseName, TermDirQuantum>,
     top_level_term_dirs: &mut TermDirQuantum,
     key: &PredicateKey,
@@ -589,8 +652,8 @@ fn draw_from_term_dir<R: Read>(
     );
 }
 
-fn setup_declaration<'a, 'b, 'c, R: Read>(
-    indices: &mut CompositeIndices<'a, 'b, 'c, R>,
+fn setup_declaration<'a, 'b, 'c>(
+    indices: &mut CompositeIndices<'a, 'b, 'c>,
     flags: MachineFlags,
     mut terms: Vec<Box<Term>>,
     line_num: usize,
@@ -600,54 +663,62 @@ fn setup_declaration<'a, 'b, 'c, R: Read>(
 
     match term {
         Term::Clause(_, name, mut terms, _) =>
-	    match (name.as_str(), terms.len()) {
-		("dynamic", 1) => {
-		    let (name, arity) = setup_predicate_indicator(&mut *terms.pop().unwrap())?;
-		    Ok(Declaration::Dynamic(name, arity))
-		}
-		("initialization", 1) => {
-		    let mut rel_worker = RelationWorker::new(flags, line_num, col_num);
-		    let query_terms = rel_worker.setup_query(indices, terms, false)?;
-		    let queue = rel_worker.parse_queue(indices)?;
+	        match (name.as_str(), terms.len()) {
+		        ("dynamic", 1) => {
+		            let (name, arity) = setup_predicate_indicator(&mut *terms.pop().unwrap())?;
+		            Ok(Declaration::Dynamic(name, arity))
+		        }
+		        ("initialization", 1) => {
+		            let mut rel_worker = RelationWorker::new(flags, line_num, col_num);
+		            let (query_terms, _) = rel_worker.setup_query(indices, terms, false, false)?;
+		            let queue = rel_worker.parse_queue(indices)?;
 
-		    Ok(Declaration::ModuleInitialization(query_terms, queue))
-		}
-		("module", 2) =>
-		    Ok(Declaration::Module(setup_module_decl(terms, indices.atom_tbl())?)),
-		("op", 3) =>
-		    Ok(Declaration::Op(setup_op_decl(terms, indices.atom_tbl())?)),
-		("non_counted_backtracking", 1) => {
-		    let (name, arity) = setup_predicate_indicator(&mut *terms.pop().unwrap())?;
-		    Ok(Declaration::NonCountedBacktracking(name, arity))
-		}
+		            Ok(Declaration::ModuleInitialization(query_terms, queue))
+		        }
+		        ("module", 2) =>
+		            Ok(Declaration::Module(setup_module_decl(terms, indices.atom_tbl())?)),
+		        ("op", 3) =>
+		            Ok(Declaration::Op(setup_op_decl(terms, indices.atom_tbl())?)),
+		        ("non_counted_backtracking", 1) => {
+		            let (name, arity) = setup_predicate_indicator(&mut *terms.pop().unwrap())?;
+		            Ok(Declaration::NonCountedBacktracking(name, arity))
+		        }
+                ("set_prolog_flag", 2) => {
+                    Ok(Declaration::SetPrologFlag(setup_double_quotes(terms)?))
+                }
                 ("multifile", 1) => {
                     let mut term = *terms.pop().unwrap();
 
                     match setup_predicate_indicator(&mut term) {
-                        Ok((name, arity)) =>
-                            Ok(Declaration::MultiFile(MultiFileIndicator::LocalScoped(name, arity))),
-                        _ =>
+                        Ok((name, arity)) => {
+                            Ok(Declaration::MultiFile(MultiFileIndicator::LocalScoped(name, arity)))
+                        }
+                        _ => {
                             setup_scoped_predicate_indicator(&mut term)
                                 .map(|key| {
                                     Declaration::MultiFile(MultiFileIndicator::ModuleScoped(key))
                                 })
+                        }
                     }
                 }
-		("use_module", 1) => {
-		    Ok(Declaration::UseModule(setup_use_module_decl(terms)?))
+		        ("use_module", 1) => {
+		            Ok(Declaration::UseModule(setup_use_module_decl(terms, indices.atom_tbl())?))
                 }
-		("use_module", 2) => {
-		    let (name, exports) = setup_qualified_import(terms, indices.atom_tbl())?;
-		    Ok(Declaration::UseQualifiedModule(name, exports))
-		}
-		_ => {
-		    Err(ParserError::InconsistentEntry)
+		        ("use_module", 2) => {
+		            let (name, exports) = setup_qualified_import(terms, indices.atom_tbl())?;
+		            Ok(Declaration::UseQualifiedModule(name, exports))
+		        }
+		        _ => {
+		            Err(ParserError::InconsistentEntry)
                 }
-	    },
-        _ => Err(ParserError::InconsistentEntry),
+	        },
+        _ => {
+            Err(ParserError::InconsistentEntry)
+        }
     }
 }
 
+#[derive(Debug)]
 struct RelationWorker {
     flags: MachineFlags,
     dynamic_clauses: Vec<(Term, Term)>, // Head, Body.
@@ -767,9 +838,9 @@ impl RelationWorker {
         self.fabricate_rule(fold_by_str(prec_seq.into_iter(), body_term, comma_sym))
     }
 
-    fn to_query_term<'a, 'b, 'c, R: Read>(
+    fn to_query_term<'a, 'b, 'c>(
         &mut self,
-        indices: &mut CompositeIndices<'a, 'b, 'c, R>,
+        indices: &mut CompositeIndices<'a, 'b, 'c>,
         term: Term,
     ) -> Result<QueryTerm, ParserError> {
         match term {
@@ -818,6 +889,7 @@ impl RelationWorker {
                     let term = Term::Clause(Cell::default(), clause_name!(";"), terms, None);
                     let (stub, clauses) = self.fabricate_disjunct(term);
 
+                    debug_assert!(clauses.len() > 0);
                     self.queue.push_back(clauses);
                     Ok(QueryTerm::Jump(stub))
                 }
@@ -843,9 +915,9 @@ impl RelationWorker {
         }
     }
 
-    fn pre_query_term<'a, 'b, 'c, R: Read>(
+    fn pre_query_term<'a, 'b, 'c>(
         &mut self,
-        indices: &mut CompositeIndices<'a, 'b, 'c, R>,
+        indices: &mut CompositeIndices<'a, 'b, 'c>,
         term: Term,
     ) -> Result<QueryTerm, ParserError> {
         match term {
@@ -864,16 +936,19 @@ impl RelationWorker {
         }
     }
 
-    fn setup_query<'a, 'b, 'c, R: Read>(
+    fn setup_query<'a, 'b, 'c>(
         &mut self,
-        indices: &mut CompositeIndices<'a, 'b, 'c, R>,
+        indices: &mut CompositeIndices<'a, 'b, 'c>,
         terms: Vec<Box<Term>>,
         blocks_cuts: bool,
-    ) -> Result<Vec<QueryTerm>, ParserError> {
+        assume_dyn: bool,
+    ) -> Result<(Vec<QueryTerm>, Term), ParserError> {
         let mut query_terms = vec![];
         let mut work_queue = VecDeque::from(terms);
         let mut machine_st = MachineState::new();
 
+        let mut dynamic_clause_terms = vec![];
+
         while let Some(term) = work_queue.pop_front() {
             let term = *term;
             let op_dir = op_dir(&indices.index_src);
@@ -892,7 +967,7 @@ impl RelationWorker {
                 let mut term = *term;
 
                 if let Term::Clause(cell, name, terms, op_spec) = term {
-                    if name.as_str() == "," {
+                    if name.as_str() == "," && terms.len() == 2 {
                         let term = Term::Clause(cell, name, terms, op_spec);
                         let mut subterms = unfold_by_str(term, ",");
 
@@ -910,17 +985,28 @@ impl RelationWorker {
                     mark_cut_variable(&mut term);
                 }
 
+                if assume_dyn {
+                    dynamic_clause_terms.push(term.clone());
+                }
+
                 query_terms.push(self.pre_query_term(indices, term)?);
             }
         }
 
-        Ok(query_terms)
+        let dynamic_clause_body =
+            if let Some(term) = dynamic_clause_terms.pop() {
+                fold_by_str(dynamic_clause_terms.into_iter(), term, clause_name!(","))
+            } else {
+                Term::Constant(Cell::default(), Constant::Atom(clause_name!("true"), None))
+            };
+
+        Ok((query_terms, dynamic_clause_body))
     }
 
-    fn setup_hook<'a, 'b, 'c, R: Read>(
+    fn setup_hook<'a, 'b, 'c>(
         &mut self,
         hook: CompileTimeHook,
-        indices: &mut CompositeIndices<'a, 'b, 'c, R>,
+        indices: &mut CompositeIndices<'a, 'b, 'c>,
         term: Term,
     ) -> Result<CompileTimeHookCompileInfo, ParserError> {
         match flatten_hook(term) {
@@ -941,24 +1027,24 @@ impl RelationWorker {
         }
     }
 
-    fn setup_rule<'a, 'b, 'c, R: Read>(
+    fn setup_rule<'a, 'b, 'c>(
         &mut self,
-        indices: &mut CompositeIndices<'a, 'b, 'c, R>,
+        indices: &mut CompositeIndices<'a, 'b, 'c>,
         mut terms: Vec<Box<Term>>,
         blocks_cuts: bool,
         assume_dyn: bool,
     ) -> Result<Rule, ParserError> {
-        let head = *terms.first().cloned().unwrap();
-        let post_head_terms: Vec<_> = terms.drain(1..).collect();
+        let dynamic_term_head = *terms.first().cloned().unwrap();
+        let post_head_terms: Vec<_> = terms.drain(1 ..).collect();
 
-        let tail = *post_head_terms.first().cloned().unwrap();
+        let (mut query_terms, dynamic_term_body) =
+            self.setup_query(indices, post_head_terms, blocks_cuts, assume_dyn)?;
 
         if assume_dyn {
-            self.dynamic_clauses.push((head, tail));
+            self.dynamic_clauses.push((dynamic_term_head, dynamic_term_body));
         }
 
-        let mut query_terms = self.setup_query(indices, post_head_terms, blocks_cuts)?;
-        let clauses = query_terms.drain(1..).collect();
+        let clauses = query_terms.drain(1 ..).collect();
         let qt = query_terms.pop().unwrap();
 
         match *terms.pop().unwrap() {
@@ -974,23 +1060,26 @@ impl RelationWorker {
         }
     }
 
-    fn try_term_to_query<'a, 'b, 'c, R: Read>(
+    fn try_term_to_query<'a, 'b, 'c>(
         &mut self,
-        indices: &mut CompositeIndices<'a, 'b, 'c, R>,
+        indices: &mut CompositeIndices<'a, 'b, 'c>,
         terms: Vec<Box<Term>>,
         blocks_cuts: bool,
     ) -> Result<TopLevel, ParserError> {
-        Ok(TopLevel::Query(self.setup_query(
+        let (result, _) = self.setup_query(
             indices,
             terms,
             blocks_cuts,
-        )?))
+            false,
+        )?;
+
+        Ok(TopLevel::Query(result))
     }
 
-    fn compact_module_scoped_head<'a, 'b, 'c, R: Read>(
+    fn compact_module_scoped_head<'a, 'b, 'c>(
         &self,
         term: &mut Term,
-        indices: &mut CompositeIndices<'a, 'b, 'c, R>,
+        indices: &mut CompositeIndices<'a, 'b, 'c>,
     ) {
         let inner_term = match term {
             Term::Clause(_, ref name, ref mut inner_terms, _)
@@ -1015,9 +1104,9 @@ impl RelationWorker {
         *term = inner_term;
     }
 
-    fn try_term_to_tl<'a, 'b, 'c, R: Read>(
+    fn try_term_to_tl<'a, 'b, 'c>(
         &mut self,
-        indices: &mut CompositeIndices<'a, 'b, 'c, R>,
+        indices: &mut CompositeIndices<'a, 'b, 'c>,
         term: Term,
         blocks_cuts: bool,
     ) -> Result<TopLevel, ParserError> {
@@ -1051,19 +1140,20 @@ impl RelationWorker {
                     Ok(TopLevel::Fact(self.setup_fact(term, true)?, self.line_num, self.col_num))
                 }
             }
-            term =>
-                Ok(TopLevel::Fact(self.setup_fact(term, true)?, self.line_num, self.col_num)),
+            term => {
+                Ok(TopLevel::Fact(self.setup_fact(term, true)?, self.line_num, self.col_num))
+            }
         }
     }
 
-    fn try_terms_to_tls<'a, 'b, 'c, I, R>(
+    fn try_terms_to_tls<'a, 'b, 'c, I>(
         &mut self,
-        indices: &mut CompositeIndices<'a, 'b, 'c, R>,
+        indices: &mut CompositeIndices<'a, 'b, 'c>,
         terms: I,
         blocks_cuts: bool,
     ) -> Result<VecDeque<TopLevel>, ParserError>
     where
-        I: IntoIterator<Item = Term>, R: Read
+        I: IntoIterator<Item = Term>
     {
         let mut results = VecDeque::new();
 
@@ -1074,9 +1164,9 @@ impl RelationWorker {
         Ok(results)
     }
 
-    fn parse_queue<'a, 'b, 'c, R: Read>(
+    fn parse_queue<'a, 'b, 'c>(
         &mut self,
-        indices: &mut CompositeIndices<'a, 'b, 'c, R>,
+        indices: &mut CompositeIndices<'a, 'b, 'c>,
     ) -> Result<VecDeque<TopLevel>, ParserError> {
         let mut queue = VecDeque::new();
 
@@ -1090,8 +1180,7 @@ impl RelationWorker {
 
     fn absorb(&mut self, other: RelationWorker) {
         self.queue.extend(other.queue.into_iter());
-        self.dynamic_clauses
-            .extend(other.dynamic_clauses.into_iter());
+        self.dynamic_clauses.extend(other.dynamic_clauses.into_iter());
     }
 }
 
@@ -1099,8 +1188,9 @@ pub type DynamicClause = Vec<(Term, Term)>;
 
 pub type DynamicClauseMap = IndexMap<(ClauseName, usize), DynamicClause>;
 
-pub struct TopLevelBatchWorker<'a, R: Read> {
-    pub(crate) term_stream: TermStream<'a, R>,
+#[derive(Debug)]
+pub struct TopLevelBatchWorker<'a> {
+    pub(crate) term_stream: TermStream<'a>,
     rel_worker: RelationWorker,
     pub(crate) results: Vec<(Predicate, VecDeque<TopLevel>)>,
     pub(crate) dynamic_clause_map: DynamicClauseMap,
@@ -1110,14 +1200,14 @@ pub struct TopLevelBatchWorker<'a, R: Read> {
     pub(crate) non_counted_bt_preds: IndexSet<PredicateKey>,
 }
 
-impl<'a, R: Read> TopLevelBatchWorker<'a, R> {
+impl<'a> TopLevelBatchWorker<'a> {
     pub fn new(
-        inner: &'a mut ParsingStream<R>,
+        stream: &'a mut ParsingStream<Stream>,
         atom_tbl: TabledData<Atom>,
         flags: MachineFlags,
         wam: &'a mut Machine,
     ) -> Self {
-        let term_stream = TermStream::new(inner, atom_tbl, flags, wam);
+        let term_stream = TermStream::new(stream, atom_tbl, flags, wam);
 
         let line_num = term_stream.line_num();
         let col_num  = term_stream.col_num();
@@ -1201,7 +1291,7 @@ impl<'a, R: Read> TopLevelBatchWorker<'a, R> {
         match self.dynamic_clause_map.get_mut(&(name.clone(), arity)) {
             Some(ref mut entry) => {
                 entry.clear(); // don't treat dynamic predicates as if they're discontiguous.
-                entry.extend(self.rel_worker.dynamic_clauses.drain(0..));
+                entry.extend(self.rel_worker.dynamic_clauses.drain(0 ..));
             }
             _ => {
                 self.rel_worker.dynamic_clauses.clear();
@@ -1217,7 +1307,7 @@ impl<'a, R: Read> TopLevelBatchWorker<'a, R> {
 
         while !self.term_stream.eof()? {
             let term = self.term_stream.read_term(&indices.op_dir)?;
-            
+
             // if is_consistent is false, preds is non-empty.
             let term = if !term.is_consistent(&preds) {
                 self.process_result(indices, &mut preds)?;
@@ -1248,7 +1338,7 @@ impl<'a, R: Read> TopLevelBatchWorker<'a, R> {
                 TopLevel::Declaration(decl) =>
                     return Ok(Some(decl)),
                 TopLevel::Query(_) =>
-                    return Err(SessionError::NamelessEntry),
+                    return Err(SessionError::QueryCannotBeDefinedAsFact),
             }
         }
 

src/macros.rs

@@ -0,0 +1,431 @@
+macro_rules! interm {
+    ($n: expr) => {
+        ArithmeticTerm::Interm($n)
+    };
+}
+
+/* A simple macro to count the arguments in a variadic list
+ * of token trees.
+ */
+macro_rules! count_tt {
+    () => { 0 };
+    ($odd:tt $($a:tt $b:tt)*) => { (count_tt!($($a)*) << 1) | 1 };
+    ($($a:tt $even:tt)*) => { count_tt!($($a)*) << 1 };
+}
+
+macro_rules! functor {
+    ($name:expr, $fixity:expr, [$($dt:ident($($value:expr),*)),+], [$($aux:ident),*]) => ({
+        {
+            #[allow(unused_variables, unused_mut)]
+            let mut addendum = Heap::new();
+            let arity = count_tt!($($dt) +);
+            let aux_lens = [$($aux.len()),*];
+
+            let mut result =
+                vec![ HeapCellValue::NamedStr(arity, clause_name!($name), Some($fixity)),
+                      $(functor_term!( $dt($($value),*), arity, aux_lens, addendum ),)+ ];
+
+            $(
+                result.extend($aux.into_iter());
+            )*
+
+            result.extend(addendum.into_iter());
+            result
+        }
+    });
+    ($name:expr, $fixity:expr, [$($dt:ident($($value:expr),*)),+]) => ({
+        {
+            #[allow(unused_variables, unused_mut)]
+            let mut addendum = Heap::new();
+            let arity = count_tt!($($dt) +);
+
+            let mut result =
+                vec![ HeapCellValue::NamedStr(arity, clause_name!($name), Some($fixity)),
+                      $(functor_term!( $dt($($value),*), arity, [], addendum ),)+ ];
+
+            result.extend(addendum.into_iter());
+            result
+        }
+    });
+    ($name:expr, [$($dt:ident($($value:expr),*)),+], [$($aux:ident),*]) => ({
+        {
+            #[allow(unused_variables, unused_mut)]
+            let mut addendum = Heap::new();
+            let arity = count_tt!($($dt) +);
+            let aux_lens = [$($aux.len()),*];
+
+            let mut result =
+                vec![ HeapCellValue::NamedStr(arity, clause_name!($name), None),
+                      $(functor_term!( $dt($($value),*), arity, aux_lens, addendum ),)+ ];
+
+            $(
+                result.extend($aux.into_iter());
+            )*
+
+            result.extend(addendum.into_iter());
+            result
+        }
+    });
+    ($name:expr, [$($dt:ident($($value:expr),*)),+]) => ({
+        {
+            let arity = count_tt!($($dt) +);
+
+            vec![ HeapCellValue::NamedStr(arity, clause_name!($name), None),
+                  $(functor_term!( $dt($($value),*), arity, [], addendum ),)+ ]
+        }
+    });
+    ($name:expr, $fixity:expr) => (
+        vec![ HeapCellValue::Atom(clause_name!($name), Some($fixity)) ]
+    );
+    (clause_name($name:expr)) => (
+        vec![ HeapCellValue::Atom($name, None) ]
+    );
+    ($name:expr) => (
+        vec![ HeapCellValue::Atom(clause_name!($name), None) ]
+    );
+}
+
+macro_rules! functor_term {
+    (aux(0), $arity:expr, $aux_lens:expr, $addendum:ident) => ({
+        HeapCellValue::Addr(Addr::HeapCell($arity + 1))
+    });
+    (aux($e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => ({
+        let len: usize = $aux_lens[0 .. $e].iter().sum();
+        HeapCellValue::Addr(Addr::HeapCell($arity + 1 + len))
+    });
+    (aux($h:expr, 0), $arity:expr, $aux_lens:expr, $addendum:ident) => ({
+        HeapCellValue::Addr(Addr::HeapCell($arity + $h + 1))
+    });
+    (aux($h:expr, $e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => ({
+        let len: usize = $aux_lens[0 .. $e].iter().sum();
+        HeapCellValue::Addr(Addr::HeapCell($arity + $h + 1 + len))
+    });
+    (addr($e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => (
+        HeapCellValue::Addr($e)
+    );
+    (constant($h:expr, $e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => (
+        from_constant!($e, $h, $arity, $aux_lens, $addendum)
+    );
+    (constant($e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => (
+        from_constant!($e, 0, $arity, $aux_lens, $addendum)
+    );
+    (number($e:expr), $arity:expr, $aux_lens:expr, $addendum:ident) => (
+        $e.into()
+    );
+    (integer($e:expr), $arity:expr, $aux_lens:expr, $addendum: ident) => (
+        HeapCellValue::Integer(Rc::new(Integer::from($e)))
+    );
+    (clause_name($e:expr), $arity:expr, $aux_lens:expr, $addendum: ident) => (
+        HeapCellValue::Atom($e, None)
+    );
+    (atom($e:expr), $arity:expr, $aux_lens:expr, $addendum: ident) => (
+        HeapCellValue::Atom(clause_name!($e), None)
+    );
+    (value($e:expr), $arity:expr, $aux_lens:expr, $addendum: ident) => (
+        $e
+    );
+    (string($h:expr, $e:expr), $arity:expr, $aux_lens:expr, $addendum: ident) => ({
+        let len: usize = $aux_lens.iter().sum();
+        let h = len + $arity + 1 + $addendum.h() + $h;
+
+        $addendum.put_complete_string(&$e);
+
+        HeapCellValue::Addr(Addr::PStrLocation(h, 0))
+    });
+    (boolean($e:expr), $arity:expr, $aux_lens:expr, $addendum: ident) => ({
+        if $e {
+            functor_term!(atom("true"), $arity, $aux_lens, $addendum)
+        } else {
+            functor_term!(atom("false"), $arity, $aux_lens, $addendum)
+        }
+    });
+    ($e:expr, $arity:expr, $aux_lens:expr, $addendum:ident) => (
+        $e
+    );
+}
+
+macro_rules! from_constant {
+    ($e:expr, $over_h:expr, $arity:expr, $aux_lens:expr, $addendum:ident) => ({
+        match $e {
+            &Constant::Atom(ref name, ref op) => {
+                HeapCellValue::Atom(name.clone(), op.clone())
+            }
+            &Constant::Char(c) => {
+                HeapCellValue::Addr(Addr::Char(c))
+            }
+            &Constant::Fixnum(n) => {
+                HeapCellValue::Addr(Addr::Fixnum(n))
+            }
+            &Constant::Integer(ref n) => {
+                HeapCellValue::Integer(n.clone())
+            }
+            &Constant::Rational(ref r) => {
+                HeapCellValue::Rational(r.clone())
+            }
+            &Constant::Float(f) => {
+                HeapCellValue::Addr(Addr::Float(f))
+            }
+            &Constant::String(ref s) => {
+                let len: usize = $aux_lens.iter().sum();
+                let h = len + $arity + 1 + $addendum.h() + $over_h;
+
+                $addendum.put_complete_string(&s);
+
+                HeapCellValue::Addr(Addr::PStrLocation(h, 0))
+            }
+            &Constant::Usize(u) => {
+                HeapCellValue::Addr(Addr::Usize(u))
+            }
+            &Constant::EmptyList => {
+                HeapCellValue::Addr(Addr::EmptyList)
+            }
+        }
+    })
+}
+
+macro_rules! is_atom {
+    ($r:expr) => {
+        call_clause!(ClauseType::Inlined(InlinedClauseType::IsAtom($r)), 1, 0)
+    };
+}
+
+macro_rules! is_atomic {
+    ($r:expr) => {
+        call_clause!(ClauseType::Inlined(InlinedClauseType::IsAtomic($r)), 1, 0)
+    };
+}
+
+macro_rules! is_integer {
+    ($r:expr) => {
+        call_clause!(ClauseType::Inlined(InlinedClauseType::IsInteger($r)), 1, 0)
+    };
+}
+
+macro_rules! is_compound {
+    ($r:expr) => {
+        call_clause!(ClauseType::Inlined(InlinedClauseType::IsCompound($r)), 1, 0)
+    };
+}
+
+macro_rules! is_float {
+    ($r:expr) => {
+        call_clause!(ClauseType::Inlined(InlinedClauseType::IsFloat($r)), 1, 0)
+    };
+}
+
+macro_rules! is_rational {
+    ($r:expr) => {
+        call_clause!(ClauseType::Inlined(InlinedClauseType::IsRational($r)), 1, 0)
+    };
+}
+
+macro_rules! is_nonvar {
+    ($r:expr) => {
+        call_clause!(ClauseType::Inlined(InlinedClauseType::IsNonVar($r)), 1, 0)
+    };
+}
+
+macro_rules! is_var {
+    ($r:expr) => {
+        call_clause!(ClauseType::Inlined(InlinedClauseType::IsVar($r)), 1, 0)
+    };
+}
+
+macro_rules! call_clause {
+    ($ct:expr, $arity:expr, $pvs:expr) => {
+        Line::Control(ControlInstruction::CallClause(
+            $ct, $arity, $pvs, false, false,
+        ))
+    };
+    ($ct:expr, $arity:expr, $pvs:expr, $lco:expr) => {
+        Line::Control(ControlInstruction::CallClause(
+            $ct, $arity, $pvs, $lco, false,
+        ))
+    };
+}
+
+macro_rules! call_clause_by_default {
+    ($ct:expr, $arity:expr, $pvs:expr) => {
+        Line::Control(ControlInstruction::CallClause(
+            $ct, $arity, $pvs, false, true,
+        ))
+    };
+    ($ct:expr, $arity:expr, $pvs:expr, $lco:expr) => {
+        Line::Control(ControlInstruction::CallClause(
+            $ct, $arity, $pvs, $lco, true,
+        ))
+    };
+}
+
+macro_rules! proceed {
+    () => {
+        Line::Control(ControlInstruction::Proceed)
+    };
+}
+
+macro_rules! is_call {
+    ($r:expr, $at:expr) => {
+        call_clause!(ClauseType::BuiltIn(BuiltInClauseType::Is($r, $at)), 2, 0)
+    };
+}
+
+macro_rules! is_call_by_default {
+    ($r:expr, $at:expr) => {
+        call_clause_by_default!(ClauseType::BuiltIn(BuiltInClauseType::Is($r, $at)), 2, 0)
+    };
+}
+
+macro_rules! set_cp {
+    ($r:expr) => {
+        call_clause!(ClauseType::System(SystemClauseType::SetCutPoint($r)), 1, 0)
+    };
+}
+
+macro_rules! succeed {
+    () => {
+        call_clause!(ClauseType::System(SystemClauseType::Succeed), 0, 0)
+    };
+}
+
+macro_rules! fail {
+    () => {
+        call_clause!(ClauseType::System(SystemClauseType::Fail), 0, 0)
+    };
+}
+
+macro_rules! compare_number_instr {
+    ($cmp: expr, $at_1: expr, $at_2: expr) => {{
+        let ct = ClauseType::Inlined(InlinedClauseType::CompareNumber($cmp, $at_1, $at_2));
+        call_clause!(ct, 2, 0)
+    }};
+}
+
+macro_rules! jmp_call {
+    ($arity:expr, $offset:expr, $pvs:expr) => {
+        Line::Control(ControlInstruction::JmpBy($arity, $offset, $pvs, false))
+    };
+}
+
+macro_rules! try_eval_session {
+    ($e:expr) => {
+        match $e {
+            Ok(result) => result,
+            Err(e) => return EvalSession::from(e),
+        }
+    };
+}
+macro_rules! return_from_clause {
+    ($lco:expr, $machine_st:expr) => {{
+        if let CodePtr::VerifyAttrInterrupt(_) = $machine_st.p {
+            return Ok(());
+        }
+
+        if $lco {
+            $machine_st.p = CodePtr::Local($machine_st.cp);
+        } else {
+            $machine_st.p += 1;
+        }
+
+        Ok(())
+    }};
+}
+
+macro_rules! dir_entry {
+    ($idx:expr) => {
+        LocalCodePtr::DirEntry($idx)
+    };
+}
+
+macro_rules! set_code_index {
+    ($idx:expr, $ip:expr, $mod_name:expr) => {{
+        let mut idx = $idx.0.borrow_mut();
+
+        idx.0 = $ip;
+        idx.1 = $mod_name.clone();
+    }};
+}
+
+macro_rules! index_store {
+    ($atom_tbl:expr, $code_dir:expr, $op_dir:expr, $modules:expr) => {
+        IndexStore {
+            atom_tbl: $atom_tbl,
+            code_dir: $code_dir,
+            module_dir: ModuleDir::new(),
+            dynamic_code_dir: DynamicCodeDir::new(),
+            global_variables: GlobalVarDir::new(),
+            in_situ_code_dir: InSituCodeDir::new(),
+            in_situ_module_dir: ModuleStubDir::new(),
+            op_dir: $op_dir,
+            modules: $modules,
+            stream_aliases: StreamAliasDir::new(),
+            streams: StreamDir::new(),
+        }
+    };
+}
+
+macro_rules! default_index_store {
+    ($atom_tbl:expr) => {
+        index_store!($atom_tbl, CodeDir::new(), default_op_dir(), IndexMap::new())
+    };
+}
+
+macro_rules! put_constant {
+    ($lvl:expr, $cons:expr, $r:expr) => {
+        QueryInstruction::PutConstant($lvl, $cons, $r)
+    };
+}
+
+macro_rules! get_level_and_unify {
+    ($r: expr) => {
+        Line::Cut(CutInstruction::GetLevelAndUnify($r))
+    };
+}
+
+macro_rules! unwind_protect {
+    ($e: expr, $protected: expr) => {
+        match $e {
+            Err(e) => {
+                $protected;
+                return Err(e);
+            }
+            _ => {}
+        }
+    };
+}
+
+macro_rules! discard_result {
+    ($f: expr) => {
+        match $f {
+            _ => (),
+        }
+    };
+}
+
+macro_rules! ar_reg {
+    ($r: expr) => {
+        ArithmeticTerm::Reg($r)
+    };
+}
+
+macro_rules! atom_from {
+    ($self:expr, $indices:expr, $e:expr) => {
+        match $e {
+            Addr::Con(h) if $self.heap.atom_at(h) => {
+                match &$self.heap[h] {
+                    HeapCellValue::Atom(ref atom, _) => {
+                        atom.clone()
+                    }
+                    _ => {
+                        unreachable!()
+                    }
+                }
+            }
+            Addr::Char(c) => {
+                clause_name!(c.to_string(), $indices.atom_tbl.clone())
+            }
+            _ => {
+                unreachable!()
+            }
+        }
+    }
+}

src/main.rs

@@ -1,29 +1,62 @@
+extern crate blake2;
+extern crate chrono;
+extern crate cpu_time;
+extern crate crossterm;
+extern crate divrem;
 #[macro_use]
 extern crate downcast;
+extern crate git_version;
+extern crate hostname;
 extern crate indexmap;
 #[macro_use]
 extern crate lazy_static;
 extern crate libc;
+extern crate native_tls;
 extern crate nix;
+extern crate openssl;
+extern crate ordered_float;
 #[macro_use]
 extern crate prolog_parser;
 #[macro_use]
 extern crate ref_thread_local;
-extern crate termion;
+extern crate ring;
+extern crate ripemd160;
+extern crate rug;
+extern crate rustyline;
+extern crate sha3;
+extern crate unicode_reader;
 
-use nix::sys::signal;
+use crate::nix::sys::signal;
 
-mod prolog;
+#[macro_use]
+mod macros;
+mod allocator;
+mod arithmetic;
+mod codegen;
+mod clause_types;
+mod debray_allocator;
+mod fixtures;
+mod forms;
+mod heap_iter;
+mod heap_print;
+mod indexing;
+mod instructions;
+mod iterators;
+mod machine;
+mod read;
+mod targets;
+mod write;
 
-use crate::prolog::machine::*;
-use crate::prolog::read::*;
+use machine::*;
+use machine::streams::*;
+use read::*;
 
 use std::sync::atomic::Ordering;
 
 extern fn handle_sigint(signal: libc::c_int) {
     let signal = signal::Signal::from_c_int(signal).unwrap();
     if signal == signal::Signal::SIGINT {
-	INTERRUPT.store(true, Ordering::Relaxed);
+        INTERRUPT.store(true, Ordering::Relaxed);
     }
 }
 
@@ -31,6 +64,6 @@ fn main() {
     let handler = signal::SigHandler::Handler(handle_sigint);
     unsafe { signal::signal(signal::Signal::SIGINT, handler) }.unwrap();
 
-    let mut wam = Machine::new(readline::input_stream());
+    let mut wam = Machine::new(readline::input_stream(), Stream::stdout());
     wam.run_top_level();
 }