Changelog

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All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog, and this project adheres to Semantic Versioning.

[0.1.0] - 2026-08-04

Added

  • Initial extraction from Aletheia: term representation, clause database, SLD-resolution engine (with a genuine clause-scoped cut), and the arithmetic/exceptions/lists/io builtin predicates, split out into their own package so they're usable without Aletheia's reader/syntax layer.
  • A dynamic database: assert/1, asserta/1, assertz/1, retract/1, retractall/1. Effects persist across separate Episteme.query/2 calls against the same Database.t(), not just within one.
  • Solution aggregation: findall/3, forall/2.
  • between/3 in Episteme.Builtins.Arithmetic.
  • Pluggable clause storage via the new Episteme.Database.Backend behaviour: Episteme.Database.Backends.Ets (the default, in-memory, indexed by {name, arity}) and Episteme.Database.Backends.Dets (the same shape, persisted to disk). Database.new/1 takes a :backend option; Database.close/1 and Database.sync/1 are new.
  • TUTORIAL.md (a from-scratch walkthrough), REFERENCE.md (every control construct, comparison, type check, arithmetic feature, and exception/database/list/I/O predicate, in full detail with a verified example each), EXAMPLES.md (complete, verified-runnable programs), CHEATSHEET.md (a one-page predicate/function reference), and CONTRIBUTING.md.

Changed

  • Breaking: control constructs and comparison operators are now spelled as plain English words instead of ISO Prolog's punctuation operators, since Episteme has no reader of its own for that punctuation to be conventional syntax against:
    • , → and/2, ; → or/2, ! → cut, \+ → not/1
    • (Cond -> Then ; Else) → if_then_else/3 (new, explicit 3-arity goal, replacing the old "; wrapping a ->" nested-pattern special case); (Cond -> Then) → if_then/2
    • = → unify/2, \= → not_unify/2, == → equal/2, \== → not_equal/2
    • =:= → numeric_equal/2, =\= → numeric_not_equal/2, =< → less_or_equal/2, >= → greater_or_equal/2
    • +, -, *, /, <, > are unchanged — ordinary math notation, not Prolog-specific punctuation, and arithmetic expression functors (+, -, *, /, //, mod, rem, **, ^, abs, sign, min, max, sqrt) are entirely unaffected, since those were never goals to begin with. No aliases: the old symbol-based names are gone, not deprecated.
  • Breaking: Database.t() now wraps a mutable backend resource (an ETS table by default) rather than being a plain immutable struct — assert/retract need a database whose mutations are visible to every holder of the same value. add_clause/2, add_fact/2, clauses_for/3, defined?/3, indicator/1, and consult_forms/2 keep their existing signatures and behavior; Database.new/0 still works exactly as before (now sugar for Database.new([])).
  • The precommit alias now runs sobelow --skip, honoring the # sobelow_skip [...] justification comment on Episteme.query_once/2 (a documented low-confidence false positive) instead of only silencing it by happenstance of sobelow's own default exit code.
  • ichor_runtime requirement bumped from ~> 0.1.0 to ~> 0.2, resolving to 0.2.0. That release's breaking change (raw_captures becoming an ordered list of pairs instead of a map) is confined to Ichor.Actions/Ichor.Capture/the grammar runtime, none of which Episteme touches — it only uses Ichor.Backtrack.* and Ichor.Toolkit.TermWalk, both unaffected, so this is a no-op for Episteme's own behavior.

Fixed

  • Episteme.query/2 (and query_once/2/query_lazy/2) no longer crashes with a raw FunctionClauseError when a partial list (one ending in a variable or other non-list, non-[] tail, e.g. [1 | X]) appears anywhere in the top-level goal — the internal walk that finds which variables to report in the answer used Enum.reduce/3, which only works on proper (nil-terminated) lists.
  • length/2 with an unbound list and a bound count built one fresh variable and duplicated the same one that many times instead of generating independent fresh variables, so e.g. and(length(L, 3), unify(L, [a, b, c])) wrongly failed (the shared variable couldn't unify with two different values at once).
  • The package description in mix.exs exceeded Hex's 300-character limit, so mix hex.build (and thus mix hex.publish, and the CI job that runs hex.build to verify the package assembles) failed outright. Trimmed to fit while keeping the same content.