thanos / ex_datalog / dbccd4e47aba42cbf799e466d85295047e348c24-PR-122

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Pull #122

github

v0.4.0: Schema DSL for declaring Datalog programs

Add Ecto-inspired macro DSL (use ExDatalog.Schema) with relation,
fact, facts, rule, query, and wildcard macros that compile into the
existing Program/Rule/Fact/Constraint/Knowledge builder APIs.

Generated functions: program/0, materialize/0,1, queries/0, query/2

New modules:
- ExDatalog.Schema — macro module with __before_compile__
- ExDatalog.DSL.CompileError — readable compile-time errors
- ExDatalog.UnsupportedFeature — forward-compatible aggregate stub

DSL features:
- relation/2: typed field schemas (:atom, :integer, :string, :any)
- fact/1, facts/2: single and bulk fact declaration
- rule/2: lowercase vars, :atom constants, _/wildcard(), not_ negation,
  16 named constraint predicates (gt, eq, add, member, etc.)
- query/2: post-materialization queries with find/where and projection
- Compile-time validation: undefined relations, unsafe variables,
  arity mismatches with descriptive error messages
- Aggregate syntax parsed but not executable (returns UnsupportedFeature)

Documentation:
- README updated with DSL quickstart
- docs/migration_dsl.md — builder API → DSL migration guide
- docs/articles/ — 5 educational articles
- livebooks/ex_datalog_dsl.livemd — interactive tutorial
- CHANGELOG.md — v0.4.0 entry
- mix.exs — extras for livebooks, articles, migration guide; DSL module group

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