Scryer Prolog

Benchmarks in Scryer Prolog are centered around running queries against a Prolog module file.

Lifecycle:

1. benchmark.setup() is called, which reads a specified .pl module file.
2. A new scryer_prolog::machine::Machine is initialized.
3. The query is executed against that machine.

Execution differences:

• Criterion: Runs the query many times to gather statistical data.
• iai: Runs the query exactly once to count instructions.

Scryer Prolog uses a strategy called first instantiated argument indexing. It indexes on the leftmost argument of a predicate that is not a variable in all clauses of that predicate's definition.

This is particularly useful for meta-predicates like maplist/N and foldl/N. Even if the first argument is a variable (the goal), Scryer will automatically use the second argument (the list) for indexing, preventing unnecessary choicepoints and ensuring deterministic goals.

Scryer Prolog uses a compact UTF-8 internal representation for strings, providing up to a 24-fold reduction in memory usage compared to traditional WAM implementations.

Key Behaviors:

• The default value for the double_quotes flag is chars. This means double-quoted strings like "abc" are treated as lists of characters: [a,b,c].
• Partial Strings: You can use partial_string/3 from library(iso_ext) to construct partial strings that behave like partial lists of characters while maintaining the efficient internal encoding.

?- partial_string("abc", Ls0, Ls).
Ls0 = [a,b,c|Ls].

Scryer Prolog can be installed using several methods depending on your environment and requirements:

Binaries

Pre-compiled binaries are available for quick installation.

Native Compilation

You can compile the project from source using the following methods:

• From a local git checkout: Clone the repository and build it locally.
• Via cargo install: Use the Rust package manager to install it directly.

Building WebAssembly

Scryer Prolog supports building for WebAssembly targets.

Caveats for Windows

Note that there are specific caveats when installing or running on Windows environments.

Clone the repository and use cargo build with the --release flag to produce an optimized, faster executable. The resulting binary will be located in target/release/scryer-prolog.

$> git clone https://github.com/mthom/scryer-prolog
$> cd scryer-prolog
$> cargo build --release

On Windows, it is recommended to build within an MSYS2 environment to handle native C compilation requirements. The resulting binary does not require MSYS2 to run. For execution, use an advanced shell like Windows Terminal instead of the default mintty.

To create a Windows Installer (MSI) using the WiX Toolset, compile in release mode and then run:

candle.exe scryer-prolog.wxs
light.exe scryer-prolog.wixobj

Precompiled binaries for various platforms can be downloaded directly from the GitHub releases page. This is the fastest way to get started without a local build environment.

https://github.com/mthom/scryer-prolog/releases/latest

After consulting a program, you can query its predicates.

Querying and Results:

• To see further answers for a query, press SPACE.
• To abort a search and return to the top-level prompt, press RETURN or ..
• To see the next 5 answers, press f.
• To see all answers, press a.
• To show a help message, press h.

Navigation and Completion:

• Use TAB to complete atoms and predicate names. Pressing TAB repeatedly cycles through alternative completions.

For declarative debugging, use predicates from library(debug):

• (*)/1: "Generalize away" a goal. Place * in front of a goal to ignore it during debugging to see if the rest of the predicate succeeds.
• ($)/1: Emit a trace of the execution, showing when a goal is invoked and when it succeeds.