248 lines
9.1 KiB
TypeScript
248 lines
9.1 KiB
TypeScript
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import type { Assertion, Bindings, Handle, Ref, Turn } from "./actor.js";
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import { Dictionary, IdentityMap, is, Record, Tuple, Value } from "preserves";
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export type Attenuation = Array<RewriteStage>; // array of stages, each a list of alternatives
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export type RewriteStage = Array<Rewrite>;
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export type Rewrite = { pattern: Pattern, template: Template };
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export const _CRec = Symbol.for('rec');
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export const CRec = Record.makeConstructor<{label: Value<never>, arity: number}, never>()(
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_CRec, ['label', 'arity']);
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export const _CArr = Symbol.for('arr');
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export const CArr = Record.makeConstructor<{arity: number}, never>()(
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_CArr, ['arity']);
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export const _CDict = Symbol.for('dict');
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export const CDict = Record.makeConstructor<{}, never>()(
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_CDict, []);
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export type ConstructorSpec =
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| Record<typeof _CRec, [Value<never>, number], never>
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| Record<typeof _CArr, [number], never>
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| Record<typeof _CDict, [], never>;
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export const _PDiscard = Symbol.for('_');
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export const PDiscard = Record.makeConstructor<{}, never>()(
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_PDiscard, []);
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export const _PBind = Symbol.for('bind');
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export const PBind = Record.makeConstructor<{name: string, pattern: Pattern}, never>()(
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_PBind, ['name', 'pattern']);
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export const _PAnd = Symbol.for('and');
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export const PAnd = Record.makeConstructor<{patterns: Array<Pattern>}, never>()(
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_PAnd, ['patterns']);
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export const _PNot = Symbol.for('not');
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export const PNot = Record.makeConstructor<{pattern: Pattern}, never>()(
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_PNot, ['pattern']);
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export const _Lit = Symbol.for('lit');
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export const Lit = Record.makeConstructor<{value: Value<never>}, never>()(
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_Lit, ['value']);
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export const _PCompound = Symbol.for('compound');
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export const PCompound =
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Record.makeConstructor<{ctor: ConstructorSpec, members: Dictionary<Pattern, never>}, never>()(
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_PCompound, ['ctor', 'members']);
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export type Pattern =
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| Record<typeof _PDiscard, [], never>
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| Record<typeof _PBind, [string, Pattern], never>
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| Record<typeof _PAnd, [Pattern[]], never>
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| Record<typeof _PNot, [Pattern], never>
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| Record<typeof _Lit, [Value<never>], never>
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| Record<typeof _PCompound, [ConstructorSpec, Dictionary<Pattern, never>], never>;
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export const _TRef = Symbol.for('ref');
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export const TRef = Record.makeConstructor<{name: string}, never>()(
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_TRef, ['name']);
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export const _TCompound = Symbol.for('compound');
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export const TCompound =
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Record.makeConstructor<{ctor: ConstructorSpec, members: Dictionary<Template, never>}, never>()(
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_TCompound, ['ctor', 'members']);
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export type Template =
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| Record<typeof _TRef, [string], never>
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| Record<typeof _Lit, [Value<never>], never>
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| Record<typeof _TCompound, [ConstructorSpec, Dictionary<Template, never>], never>;
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export function match(p: Pattern, v: Assertion): Bindings | null {
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let bindings: Bindings = {};
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function walk(p: Pattern, v: Assertion): boolean {
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switch (p.label) {
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case _PDiscard:
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return true;
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case _PBind:
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if (walk(PBind._.pattern(p), v)) {
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bindings[PBind._.name(p)] = v;
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return true;
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}
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return false;
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case _PAnd:
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for (const pp of PAnd._.patterns(p)) {
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if (!walk(pp, v)) return false;
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}
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return true;
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case _PNot: {
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const savedBindings = bindings;
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bindings = {};
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const result = !walk(PNot._.pattern(p), v)
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bindings = savedBindings;
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return result;
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}
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case _Lit:
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return is(Lit._.value(p), v);
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case _PCompound: {
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const ctor = PCompound._.ctor(p);
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const members = PCompound._.members(p);
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switch (ctor.label) {
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case _CRec:
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if (!Record.isRecord<Assertion, Tuple<Assertion>, Ref>(v)) return false;
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if (!is(CRec._.label(ctor), v.label)) return false;
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if (CRec._.arity(ctor) !== v.length) return false;
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for (const [key, pp] of members) {
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if (typeof key !== 'number') return false;
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if (!walk(pp, v[key])) return false;
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}
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return true;
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case _CArr:
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if (!Array.isArray(v)) return false;
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if ('label' in v) return false;
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if (CArr._.arity(ctor) !== v.length) return false;
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for (const [key, pp] of members) {
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if (typeof key !== 'number') return false;
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if (!walk(pp, v[key])) return false;
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}
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return true;
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case _CDict:
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if (!Dictionary.isDictionary<Assertion, Ref>(v)) return false;
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for (const [key, pp] of members) {
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const vv = v.get(key as Assertion);
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if (vv === void 0) return false;
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if (!walk(pp, vv)) return false;
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}
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return true;
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}
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}
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}
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}
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return walk(p, v) ? bindings : null;
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}
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export function instantiate(t: Template, b: Bindings): Assertion {
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function walk(t: Template): Assertion {
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switch (t.label) {
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case _TRef: {
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const v = b[TRef._.name(t)];
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if (v === void 0) throw new Error(`Unbound reference: ${TRef._.name(t)}`);
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return v;
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}
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case _Lit:
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return Lit._.value(t) as Assertion;
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case _TCompound: {
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const ctor = TCompound._.ctor(t);
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const members = TCompound._.members(t);
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switch (ctor.label) {
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case _CRec: {
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const v = Record<Assertion, any, Ref>(
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CRec._.label(ctor) as Assertion,
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[],
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);
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v.length = CRec._.arity(ctor);
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for (const [key, tt] of members) {
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v[key as number] = walk(tt);
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}
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return v;
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}
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case _CArr: {
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const v = [];
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v.length = CArr._.arity(ctor);
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for (const [key, tt] of members) {
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v[key as number] = walk(tt);
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}
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return v;
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}
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case _CDict: {
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const v = new Dictionary<Assertion, Ref>();
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for (const [key, tt] of members) {
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v.set(key as Assertion, walk(tt));
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}
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return v;
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}
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}
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}
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}
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}
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return walk(t);
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}
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export function rewrite(r: Rewrite, v: Assertion): Assertion | null {
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const bindings = match(r.pattern, v);
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if (bindings === null) return null;
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return instantiate(r.template, bindings);
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}
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export function examineAlternatives(alternatives: RewriteStage, v: Assertion): Assertion | null {
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for (const r of alternatives) {
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const w = rewrite(r, v);
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if (w !== null) return w;
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}
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return null;
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}
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export function runRewrites(a: Attenuation | undefined, v: Assertion): Assertion | null {
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if (a !== void 0) {
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for (const stage of a) {
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const w = examineAlternatives(stage, v);
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if (w === null) return null;
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v = w;
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}
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}
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return v;
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}
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export function rfilter(... patterns: Pattern[]): RewriteStage {
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return patterns.map(p => ({ pattern: PBind('a', p), template: TRef('a') }));
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}
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export function attenuate(ref: Ref, ... a: Attenuation): Ref {
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return { ... ref, attenuation: [... a, ... (ref.attenuation ?? [])] };
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}
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export function forwarder(t: Turn, ref: Ref): { proxy: Ref, revoker: Ref } {
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let underlying: Ref | null = ref;
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let handleMap = new IdentityMap<Handle, Handle>();
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let proxy = t.ref({
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assert(turn: Turn, assertion: Assertion, handle: Handle): void {
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if (underlying === null) return;
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handleMap.set(handle, turn.assert(underlying, assertion));
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},
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retract(turn: Turn, handle: Handle): void {
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if (underlying === null) return;
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turn.retract(handleMap.get(handle));
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handleMap.delete(handle);
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},
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message(turn: Turn, body: Assertion): void {
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if (underlying === null) return;
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turn.message(underlying, body);
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},
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sync(turn: Turn, peer: Ref): void {
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if (underlying === null) return;
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turn._sync(underlying, peer);
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},
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});
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let revoker = t.ref({
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message(turn: Turn, _body: Assertion): void {
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underlying = null;
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handleMap.forEach(h => turn.retract(h));
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},
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});
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return { proxy, revoker };
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}
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