pyrites/haskell-experiments/CLAUDE.md

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Build Commands

cabal build          # Build the project
cabal test           # Run all tests
cabal repl           # Start interactive REPL

To run a single test file or specific test:

cabal test --test-option=--match="/DatalogParser/"

Architecture

This is an experimental Datalog implementation in Haskell with the following components:

Parsing Layer (src/Datalog/DatalogParser.hs)

Megaparsec-based parser that converts Datalog text into an AST:

• Term - Variables (Var), symbols (Sym), numbers (Num)
• Literal - Predicate with arguments, optionally negated
• Statement - Fact, Rule (with Head and body literals), or Query
• Entry points: parseDatalog, parseDatalogFile

Evaluation Engine (src/Datalog/InMemoryDB.hs)

In-memory database storing relations and rules:

• InMemoryDB - Contains relations map and constants set (Herbrand universe)
• Relation - Name, arity, tuples (facts), and associated rules
• RelationRule - Head variables and body constraints
• Key functions: withFacts, withFactsAndRules for building databases
• Query evaluation is not yet implemented

Data Flow

1. Text parsed into Statement (Fact/Rule/Query)
2. Facts populate relations with tuples; rules encode derivation logic via RuleContext and BodyConstraint
3. Variables are indexed during rule processing for efficient constraint matching

Other Modules

• SimpleParser / ArithmeticParser - Experimental arithmetic expression parsers
• Ologs - Categorical data structures (dots and arcs representing objects and morphisms)

Development Environment

Nix support via shell.nix provides HLS, cabal-install, and Hoogle. Use direnv allow for automatic environment loading.