~subsetpark/the-brzozowski-variations

3bc81c857a3f4c1233da02051f1171de01c26f85 — Zach Smith a month ago 58727c2 master
Use enums for literal discriminants
4 files changed, 47 insertions(+), 30 deletions(-)

M impls/ts/brzo.ts
M impls/ts/package-lock.json
M impls/ts/package.json
A impls/ts/tsconfig.json
M impls/ts/brzo.ts => impls/ts/brzo.ts +40 -30
@@ 1,86 1,96 @@
const enum languageKind {
        Empty,
        Epsilon,
        Char,
        Cat,
        Alt,
        Rep
};

interface Empty {
        kind: "empty";
        kind: languageKind.Empty;
}

function empty(): Empty { return { kind: "empty" } }
function empty(): Empty { return { kind: languageKind.Empty } }

interface Epsilon {
        kind: "epsilon";
        kind: languageKind.Epsilon;
}

function epsilon(): Epsilon { return { kind: languageKind.Epsilon } }

interface Char {
        kind: "char"
        kind: languageKind.Char
        value: string;
}

function char(value: string): Char { return { kind: "char", value } }
function char(value: string): Char { return { kind: languageKind.Char, value } }

interface Cat {
        kind: "cat"
        kind: languageKind.Cat
        left: Language
        right: Language
}

function cat(left: Language, right: Language): Cat {
        return { kind: "cat", left, right }
        return { kind: languageKind.Cat, left, right }
}

interface Alt {
        kind: "alt"
        kind: languageKind.Alt
        left: Language
        right: Language
}

function alt(left: Language, right: Language): Alt {
        return { kind: "alt", left, right }
        return { kind: languageKind.Alt, left, right }
}

interface Rep {
        kind: "rep";
        kind: languageKind.Rep;
        value: Language;
}

function rep(value: Language): Rep { return { kind: "rep", value: value } }
function rep(value: Language): Rep { return { kind: languageKind.Rep, value } }

type Language = Empty | Epsilon | Rep | Cat | Alt | Char

function is_nullable(l: Language): boolean {
        switch (l.kind) {
                case "empty":
                case languageKind.Empty:
                        return false;
                case "epsilon":
                case languageKind.Epsilon:
                        return true;
                case "char":
                case languageKind.Char:
                        return false;
                case "alt":
                case languageKind.Alt:
                        return is_nullable(l.left) || is_nullable(l.right);
                case "cat":
                case languageKind.Cat:
                        return is_nullable(l.left) && is_nullable(l.right);
                case "rep":
                case languageKind.Rep:
                        return true;
        }
}

function derive(pat: Language, char: string): Language {
        switch (pat.kind) {
                case "epsilon":
                case "empty":
                case languageKind.Empty:
                case languageKind.Epsilon:
                        return empty();
                case "char":
                case languageKind.Char:
                        if (pat.value == char) {
                                return { kind: "epsilon" };
                                return epsilon();
                        } else {
                                return { kind: "empty" };
                                return empty();
                        }
                case "rep":
                case languageKind.Rep:
                        return cat(derive(pat.value, char), pat);
                case "alt":
                        return {
                                kind: "alt",
                                left: derive(pat.left, char),
                                right: derive(pat.right, char)
                        };
                case "cat":
                case languageKind.Alt:
                        return alt(
                                derive(pat.left, char),
                                derive(pat.right, char)
                        );
                case languageKind.Cat:
                        const base = cat(derive(pat.left, char), pat.right);
                        if (is_nullable(pat.left)) {
                                return alt(derive(pat.right, char), base);

M impls/ts/package-lock.json => impls/ts/package-lock.json +1 -0
@@ 5,6 5,7 @@
  "packages": {
    "": {
      "dependencies": {
        "@types/node": "^16.11.6",
        "jest": "^27.3.1",
        "mocha": "^9.1.3",
        "ts-jest": "^27.0.7",

M impls/ts/package.json => impls/ts/package.json +1 -0
@@ 1,5 1,6 @@
{
  "dependencies": {
    "@types/node": "^16.11.6",
    "jest": "^27.3.1",
    "mocha": "^9.1.3",
    "ts-jest": "^27.0.7",

A impls/ts/tsconfig.json => impls/ts/tsconfig.json +5 -0
@@ 0,0 1,5 @@
{
        "compilerOptions": {
                "strict": true
        }
}