novy-syndicate/src/runtime/rewrite.ts

import type { Assertion, Handle, Ref, Turn } from "./actor.js";
import { Bytes, Dictionary, DoubleFloat, IdentityMap, is, isPointer, Record, SingleFloat, Tuple } from "@preserves/core";

import {
    Alts,
    Attenuation,
    CArr,
    CDict,
    CRec,
    Caveat,
    ConstructorSpec,
    Lit,
    PAnd,
    PAtom,
    PBind,
    PCompound,
    PCompoundMembers,
    PDiscard,
    PNot,
    PPointer,
    Pattern,
    Rewrite,
    TRef,
    Template,
    _val,
} from '../gen/sturdy.js';
export * from '../gen/sturdy.js';

export type Bindings = { [name: string]: Assertion };

export function match(p: Pattern, v: Assertion): Bindings | null {
    let bindings: Bindings = {};

    function walk(p: Pattern, v: Assertion): boolean {
        switch (p._variant) {
            case 'PDiscard':
                return true;
            case 'PAtom':
                switch (p.value._variant) {
                    case 'Boolean': return typeof v === 'boolean';
                    case 'ByteString': return Bytes.isBytes(v);
                    case 'Double': return DoubleFloat.isDouble(v);
                    case 'Float': return SingleFloat.isSingle(v);
                    case 'SignedInteger': return typeof v === 'number';
                    case 'String': return typeof v === 'string';
                    case 'Symbol': return typeof v === 'symbol';
                }
            case 'PPointer':
                return isPointer(v);
            case 'PBind':
                if (walk(p.value.pattern, v)) {
                    bindings[p.value.name.asPreservesText()] = v;
                    return true;
                }
                return false;
            case 'PAnd':
                for (const pp of p.value.patterns) {
                    if (!walk(pp, v)) return false;
                }
                return true;
            case 'PNot': {
                const savedBindings = bindings;
                bindings = {};
                const result = !walk(p.value.pattern, v)
                bindings = savedBindings;
                return result;
            }
            case 'Lit':
                return is(p.value.value, v);
            case 'PCompound': {
                const ctor = p.value.ctor;
                const members = p.value.members;
                switch (ctor._variant) {
                    case 'CRec':
                        if (!Record.isRecord<Assertion, Tuple<Assertion>, Ref>(v)) return false;
                        if (!is(ctor.value.label, v.label)) return false;
                        if (ctor.value.arity !== v.length) return false;
                        for (const [key, pp] of members) {
                            if (typeof key !== 'number') return false;
                            if (!walk(pp, v[key])) return false;
                        }
                        return true;
                    case 'CArr':
                        if (!Array.isArray(v)) return false;
                        if ('label' in v) return false;
                        if (ctor.value.arity !== v.length) return false;
                        for (const [key, pp] of members) {
                            if (typeof key !== 'number') return false;
                            if (!walk(pp, v[key])) return false;
                        }
                        return true;
                    case 'CDict':
                        if (!Dictionary.isDictionary<Assertion, Ref>(v)) return false;
                        for (const [key, pp] of members) {
                            const vv = v.get(key as Assertion);
                            if (vv === void 0) return false;
                            if (!walk(pp, vv)) return false;
                        }
                        return true;
                }
            }
            default:
                ((_p : never) => {})(p);
                return false;
        }
    }

    return walk(p, v) ? bindings : null;
}

export function instantiate(t: Template, b: Bindings): Assertion {
    function walk(t: Template): Assertion {
        switch (t._variant) {
            case 'TRef': {
                const n = t.value.name.asPreservesText()
                const v = b[n];
                if (v === void 0) throw new Error(`Unbound reference: ${n}`);
                return v;
            }
            case 'Lit':
                return t.value.value as Assertion;
            case 'TCompound': {
                const ctor = t.value.ctor;
                const members = t.value.members;
                switch (ctor._variant) {
                    case 'CRec': {
                        const v = [] as unknown as Record<Assertion, Assertion[], Ref>;
                        v.length = ctor.value.arity;
                        v.label = ctor.value.label;
                        for (const [key, tt] of members) {
                            v[key as number] = walk(tt);
                        }
                        return v;
                    }
                    case 'CArr': {
                        const v = [];
                        v.length = ctor.value.arity;
                        for (const [key, tt] of members) {
                            v[key as number] = walk(tt);
                        }
                        return v;
                    }
                    case 'CDict': {
                        const v = new Dictionary<Ref, Assertion>();
                        for (const [key, tt] of members) {
                            v.set(key as Assertion, walk(tt));
                        }
                        return v;
                    }
                }
            }
        }
    }

    return walk(t);
}

export function rewrite(r: Rewrite, v: Assertion): Assertion | null {
    const bindings = match(r.pattern, v);
    if (bindings === null) return null;
    return instantiate(r.template, bindings);
}

export function examineAlternatives(cav: Caveat, v: Assertion): Assertion | null {
    if (cav._variant === 'Alts') {
        for (const r of cav.value.alternatives) {
            const w = rewrite(r, v);
            if (w !== null) return w;
        }
        return null;
    } else {
        return rewrite(cav.value, v);
    }
}

export function runRewrites(a: Attenuation | undefined, v: Assertion): Assertion | null {
    if (a !== void 0) {
        for (const stage of a) {
            const w = examineAlternatives(stage, v);
            if (w === null) return null;
            v = w;
        }
    }
    return v;
}

const _a = Symbol.for('a');

export function rfilter(... patterns: Pattern[]): Caveat {
    const ps = patterns.map(p => Rewrite({
        pattern: Pattern.PBind(PBind({ name: _a, pattern: p })),
        template: Template.TRef(TRef(_a))
    }));
    return ps.length === 1 ? Caveat.Rewrite(ps[0]) : Caveat.Alts(Alts(ps));
}

export function attenuate(ref: Ref, ... a: Attenuation): Ref {
    if (a.length === 0) return ref;
    return { ... ref, attenuation: [... a, ... (ref.attenuation ?? [])] };
}

export function forwarder(t: Turn, ref: Ref): { proxy: Ref, revoker: Ref } {
    let underlying: Ref | null = ref;
    let handleMap = new IdentityMap<Handle, Handle>();
    let proxy = t.ref({
        assert(turn: Turn, assertion: Assertion, handle: Handle): void {
            if (underlying === null) return;
            handleMap.set(handle, turn.assert(underlying, assertion));
        },
        retract(turn: Turn, handle: Handle): void {
            if (underlying === null) return;
            turn.retract(handleMap.get(handle));
            handleMap.delete(handle);
        },
        message(turn: Turn, body: Assertion): void {
            if (underlying === null) return;
            turn.message(underlying, body);
        },
        sync(turn: Turn, peer: Ref): void {
            if (underlying === null) return;
            turn._sync(underlying, peer);
        },
    });
    let revoker = t.ref({
        message(turn: Turn, _body: Assertion): void {
            underlying = null;
            handleMap.forEach(h => turn.retract(h));
        },
    });
    return { proxy, revoker };
}

export function pRec(label: _val, ... members: Array<Pattern>): Pattern {
    return Pattern.PCompound(PCompound({
        ctor: ConstructorSpec.CRec(CRec({ label: label, arity: members.length })),
        members: PCompoundMembers(new Dictionary<Ref, Pattern>(
            members.map((p, i) => [i, p] as const).filter(e => e[1]._variant !== 'PDiscard')))}));
}

export function pArr(... members: Array<Pattern>): Pattern {
    return Pattern.PCompound(PCompound({
        ctor: ConstructorSpec.CArr(CArr(members.length)),
        members: PCompoundMembers(new Dictionary<Ref, Pattern>(
            members.map((p, i) => [i, p] as const).filter(e => e[1]._variant !== 'PDiscard')))}));
}

export function pDict(... entries: [_val, Pattern][]): Pattern {
    return Pattern.PCompound(PCompound({
        ctor: ConstructorSpec.CDict(CDict()),
        members: PCompoundMembers(new Dictionary<Ref, Pattern>(entries))}));
}

export function pLit(value: _val): Pattern {
    return Pattern.Lit(Lit(value));
}

export function pNot(p: Pattern): Pattern {
    return Pattern.PNot(PNot(p));
}

export function pAnd(... ps: Pattern[]): Pattern {
    return Pattern.PAnd(PAnd(ps));
}

export function pBind(name: symbol, pattern: Pattern): Pattern {
    return Pattern.PBind(PBind({ name, pattern }));
}

export function pPointer(): Pattern {
    return Pattern.PPointer(PPointer());
}

export function pSymbol(): Pattern {
    return Pattern.PAtom(PAtom.Symbol());
}

export function pByteString(): Pattern {
    return Pattern.PAtom(PAtom.ByteString());
}

export function pString(): Pattern {
    return Pattern.PAtom(PAtom.String());
}

export function pSignedInteger(): Pattern {
    return Pattern.PAtom(PAtom.SignedInteger());
}

export function pDouble(): Pattern {
    return Pattern.PAtom(PAtom.Double());
}

export function pFloat(): Pattern {
    return Pattern.PAtom(PAtom.Float());
}

export function pBoolean(): Pattern {
    return Pattern.PAtom(PAtom.Boolean());
}

export function pDiscard(): Pattern {
    return Pattern.PDiscard(PDiscard());
}