Prolog

An experimental Prolog-like interpreter written in OCaml with Dune and Menhir.

It provides an interactive REPL for entering queries, asserting clauses into an in-memory database, and exploring solutions through backtracking.

Features

• Interactive command-line REPL.
• Facts and rules with atoms, variables, and compound terms.
• assertz(...) for adding clauses to the database at runtime.
• Query solving with substitution display for variable bindings.
• Backtracking through multiple solutions with ;.

Requirements

• OCaml
• Dune 3.10 or newer
• Menhir

Install project dependencies with opam before building.

Build

opam install . --deps-only
dune build

Run

dune exec prolog

Using the REPL

The prompt accepts simple Prolog-style queries.

Example session:

prolog ?- assertz(parent(john, mary)).
Saved

prolog ?- parent(john, X).
X = mary

If a query has more than one solution, press ; to ask for the next solution or . to stop.

Syntax

• Atoms start with a lowercase letter, such as john or parent.
• Variables start with an uppercase letter, such as X or Person.
• Compound terms look like parent(john, mary).
• Queries end with a period.

Project layout

• bin/ - executable entry point and REPL.
• lib/ast/ - term, clause, and query types.
• lib/database/ - in-memory clause storage.
• lib/errors/ - parse and runtime error types.
• lib/evaluator/ - goal solving and backtracking.
• lib/lexer/ - tokenization rules.
• lib/parser/ - grammar definition.
• lib/parser_interface/ - helpers for parsing strings and files.
• lib/unify/ - unification logic.
• test/ - test entry point.

What should be on GitHub

Commit the source and project metadata:

• bin/
• lib/
• test/
• dune-project
• prolog.opam
• README.md
• LICENSE
• .gitignore

Do not commit generated or local-only files:

• _build/
• .prolog_history
• editor swap files or machine-specific caches

Notes

The current dune-project and generated opam metadata still contain placeholder values for the package synopsis, description, homepage, documentation, and maintainer. Replace those before publishing the project publicly.