eyepl
Eyepl
Eyepl is a small reasoning language for turning facts and rules into answers and proofs.
Prolog-like syntax. Small core. Inspectable results.
Quick start
Install the published CLI globally:
npm install --global eyepl
eyepl --version
printf 'query(works(stdin, true)).\nworks(stdin, true) :- eq(ok, ok).\n' | eyepl -
Eyepl has no build step. From a source checkout, install its RDF parser dependencies and run the CLI directly with Node.js 18 or newer:
npm install
node bin/eyepl.js examples/ancestor.pl
node bin/eyepl.js --proof examples/socrates.pl
node bin/eyepl.js --warnings test/conformance/warnings/negation/unstratified_mutual.pl
printf 'query(works(stdin, true)).\nworks(stdin, true) :- eq(ok, ok).\n' | node bin/eyepl.js -
For one-off local CLI use from the checkout, npm can run the package bin without a manual symlink:
npm exec --yes --package=. -- eyepl --version
npm exec --yes --package=. -- eyepl examples/ancestor.pl
To install the checkout’s eyepl command on your PATH, use npm’s package link:
npm link
eyepl --version
For local browser use, run python3 -m http.server from the checkout and open
http://localhost:8000/playground.html.
JavaScript API
import { run, Program, Solver } from 'eyepl';
const result = run(`
query(answer(X0)).
answer(ok) :- eq(ok, ok).
`);
console.log(result.stdout);
Rules headed by false are inference fuses. A matching fuse aborts before
queries run; the CLI exits with code 65, while the JavaScript API throws an
InferenceFuseError carrying the same code and a matched-rule diagnostic.
STEM showcase: evidence-backed diagnosis
The spacecraft battery example combines sensor telemetry, the physical relation
P = I²R, engineering limits, redundant measurements, and causal rules to
derive a diagnosis and safety action:
node bin/eyepl.js examples/spacecraft-battery-diagnosis.pl
node bin/eyepl.js -p examples/spacecraft-battery-diagnosis.pl
The normal output reports computed metrics, a thermal-runaway precursor, and an
isolate_and_cool action. With -p, every conclusion carries machine-readable
evidence back to telemetry facts, arithmetic operations, threshold comparisons,
and the independent temperature channel.
How it works
The name Eyepl combines EYE with pl, reflecting EYE-style reasoning expressed with Prolog-like syntax.
Its default execution is automatically hybrid: ordinary goals use indexed depth-first resolution, while recursive helper predicate groups are detected and tabled automatically.
Clause selection combines compact any-argument scalar indexes with demand-driven multi-argument indexes. SWI-Prolog-inspired quality checks avoid building indexes for small, weakly selective, or variable-heavy clause groups.
RDF 1.2 files
The tools convert standard RDF files to ordinary Eyepl rdf/4 facts, run
Eyepl rules, and serialize query answers as RDF 1.2 N-Quads:
node tools/rdf-to-eyepl.mjs --rules rules.pl data.ttl -o program.pl
node bin/eyepl.js program.pl > derived.pl
node tools/eyepl-to-rdf.mjs derived.pl -o derived.nq
The input format is detected from the filename. Supported inputs include RDF
1.2 Turtle, TriG, N-Triples, N-Quads and RDF/XML, as well as JSON-LD, RDFa,
Microdata, Notation3 and SHACL Compact Syntax. For stdin, provide the format;
use --base when relative IRIs need an explicit base:
node tools/rdf-to-eyepl.mjs --format turtle --base https://example/ -
RDF IRIs, scoped blank nodes, literals, directional language strings, nested
triple terms, named graphs and the default graph all have lossless Eyepl term
encodings. The
RDF 1.2 chapter
in The Art of Eyepl covers the mapping and --include-source behavior.
Tests
npm test
npm run test:conformance
node test/run-conformance-report.mjs
# release preparation writes conformance-report.md via the preversion script
npm run test:examples
npm run test:regression