eyeling

A Notation3 (N3) reasoner in JavaScript.

eyeling is:

• a single self-contained file (eyeling.js, no external deps)
• a practical N3/Turtle superset (enough for lots of real rulesets)
• supports forward (=>) + backward (<=) chaining over Horn-style rules
• prints only newly derived forward facts, optionally preceded by compact proof comments
• “pass-only-new” style output (we never want to leak raw input data; backward rules can act like “functions” over raw data)
• works fully client-side (browser) and in Node.js

Playground

Try it here:

• Eyeling playground

The playground runs eyeling client-side. You can:

• edit an N3 program directly
• load an N3 program from a URL (in the "Load N3 from URL" box or as ?url=...)
• share a link with the program encoded in the URL fragment (#...)

Quick start

Requirements

• Node.js >= 18 (anything modern with BigInt support is fine)

Install

npm i eyeling

CLI

Run on a file:

npx eyeling examples/socrates.n3

(Or install globally: npm i -g eyeling and run eyeling ....)

JavaScript API

const { reason } = require("eyeling");

const input = `
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>.
@prefix : <http://example.org/socrates#>.

:Socrates a :Human.
:Human rdfs:subClassOf :Mortal.

{ ?S a ?A. ?A rdfs:subClassOf ?B } => { ?S a ?B }.
`;

const output = reason({ proofComments: false }, input);
console.log(output);

ESM:

import eyeling from "eyeling";
const output = eyeling.reason({ proofComments: false }, input);
console.log(output);

Note: the API currently shells out to the bundled eyeling.js CLI under the hood (simple + robust).

Testing

From a repo checkout:

npm test

Or run individual suites:

npm run test:api
npm run test:examples
npm run test:package
npm run test:packlist

• test:api runs an independent JS API test suite (does not rely on examples/).
• test:examples runs the examples in the examples directory and compares against the golden outputs in examples/output.
• test:package does a “real consumer” smoke test: npm pack → install tarball into a temp project → run API + CLI + examples.
• test:packlist sanity-checks what will be published in the npm tarball (and the CLI shebang/bin wiring).

Usage

Usage: eyeling [options] <file.n3>

Options:
  -h, --help              Show this help and exit.
  -v, --version           Print version and exit.
  -p, --proof-comments    Enable proof explanations.
  -n, --no-proof-comments Disable proof explanations (default).
  -s, --super-restricted  Disable all builtins except => and <=.
  -a, --ast               Print parsed AST as JSON and exit.
  --strings               Print log:outputString strings (ordered by key) instead of N3 output.

By default, eyeling:

1. parses the input (facts + rules)
2. runs forward chaining to a fixpoint
3. prints only newly derived forward facts (not the original input facts)
4. prints a compact per-triple explanation as # comments (can be disabled)

What output do I get?

For each newly derived triple, eyeling prints:

1. a proof-style comment block explaining why the triple holds (unless -n), and then
2. the triple itself in N3/Turtle syntax.

The proof comments are compact “local justifications” per derived triple (not a single exported global proof tree).

Reasoning model

Forward + backward chaining

• Forward chaining to fixpoint for forward rules written as { P } => { C } .
• Backward chaining (SLD-style) for backward rules written as { H } <= { B } . and for built-ins.

Forward rule premises are proved using:

• ground facts (input + derived)
• backward rules
• built-ins

The CLI prints only newly derived forward facts.

Performance notes

eyeling includes a few key performance mechanisms:

• facts are indexed for matching:
  • by predicate, and (when possible) by (predicate, object) (important for type-heavy workloads)
• IRIs/literals are interned to reduce allocations and speed up comparisons/lookups
• parsed numeric literals are cached, and rule standardization reuses unchanged subterms to cut repeated parsing/allocation
• duplicate detection uses a fast key path when a triple is fully IRI/Literal-shaped
• backward rules are indexed by head predicate
• the backward prover is iterative (explicit stack), so deep chains won’t blow the JS call stack
• for very deep backward chains, substitutions may be compactified (semantics-preserving) to avoid quadratic “copy a growing substitution object” behavior

Blank nodes and quantification

eyeling follows the usual N3 intuition:

1. blank nodes in facts are normal RDF blanks (_:b1, _:b2, … within a run)
2. blank nodes in rule premises behave like rule-scoped universals (similar to variables)
3. blank nodes only in rule conclusions behave like existentials: each rule firing generates fresh Skolem blanks (_:sk_0, _:sk_1, …)

Equal facts up to renaming of Skolem IDs are treated as duplicates and are not re-added.

Rule-producing rules aka meta-rules

eyeling understands the log:implies / log:impliedBy idiom.

Top level:

• { P } log:implies { C } . becomes a forward rule { P } => { C } .
• { H } log:impliedBy { B } . becomes a backward rule { H } <= { B } .

During reasoning:

• any derived log:implies / log:impliedBy triple with formula subject/object is turned into a new live forward/backward rule.

Inference fuse

Rules whose conclusion is false are treated as hard failures:

:stone :color :black .
:stone :color :white .

{ ?X :color :black . ?X :color :white . } => false.

As soon as the premise is provable, eyeling exits with status code 2.

Syntax + built-ins

eyeling’s parser targets (nearly) the full Notation3 Language grammar from the W3C N3 Community Group spec.

In practice this means: it’s a Turtle superset that also accepts quoted formulas, rules, paths, and the N3 “syntax shorthand” operators (=, =>, <=) described in the spec.

Commonly used N3/Turtle features:

• Prefix/base directives (@prefix / @base, and SPARQL-style PREFIX / BASE)
• Triples with ; and ,
• Variables (?x)
• Blank nodes ([], and [ :p :o; :q :r ])
• Collections ( ... )
• Quoted formulas { ... }
• Implications (=>, <=)
• Datatyped literals (^^) and language tags ("..."@en)
• Inverse predicate sugar (<- and keyword forms like is ... of)
• Resource paths (! and ^)
• # line comments

eyeling implements a pragmatic subset of common N3 builtin families and evaluates them during backward goal proving:

• crypto: crypto:md5 crypto:sha crypto:sha256 crypto:sha512
• list: list:append list:first list:firstRest list:in list:iterate list:last list:length list:map list:member list:memberAt list:notMember list:remove list:rest list:reverse list:sort
• log: log:collectAllIn log:content log:equalTo log:forAllIn log:impliedBy log:implies log:notEqualTo log:notIncludes log:semantics log:skolem log:uri
• math: math:absoluteValue math:acos math:asin math:atan math:cos math:cosh math:degrees math:difference math:equalTo math:exponentiation math:greaterThan math:integerQuotient math:lessThan math:negation math:notEqualTo math:notGreaterThan math:notLessThan math:product math:quotient math:remainder math:rounded math:sin math:sinh math:sum math:tan math:tanh
• string: string:concatenation string:contains string:containsIgnoringCase string:endsWith string:equalIgnoringCase string:format string:greaterThan string:jsonPointer string:lessThan string:matches string:notEqualIgnoringCase string:notGreaterThan string:notLessThan string:notMatches string:replace string:scrape string:startsWith
• time: time:localTime

License

MIT (see LICENSE).