@suss/datalog

Part of suss, which reads both sides of every call in a repository and says where the two disagree.

A small semi-naïve Datalog evaluator with stratified negation. suss derives its program facts with it.

Why suss ships a Datalog engine

Extraction keeps running into problems that are fixpoints. One is which functions are reachable from an entry point. Another is what a bare throw err re-throw can raise, which is the union of everything the try block throws, transitively. A third is how a wrapper of a wrapper resolves to its underlying route. Written as rules over base facts, each one comes to a few lines you can check by reading them:

import { Database, evaluate, lit, rule, variable as v } from "@suss/datalog";

const db = new Database();
db.add("entry", ["main"]);
db.add("calls", ["main", "helper"]);
db.add("calls", ["helper", "util"]);

evaluate(db, [
  rule("reachable", [v("f")], [lit("entry", v("f"))]),
  rule(
    "reachable",
    [v("g")],
    [lit("reachable", v("f")), lit("calls", v("f"), v("g"))],
  ),
]);

db.facts("reachable"); // [["main"], ["helper"], ["util"]]

The engine guarantees termination and soundness, and those are proved once, for the engine. Negation (notLit) is stratified: a rule set with a negation cycle is a hard error at evaluation time. Because of that, you can check a rule on its own without thinking about the engine.

Rules are plain data, without DSL strings or embedded code, so the same rule set can later run on a faster external engine. An analysis written against a set of facts (calls, throws, handles, and so on) does not depend on the language. A second language adapter only has to emit the same facts.

More

• How the engine evaluates
• Documentation
• Source and issues

Apache 2.0. See LICENSE.