TypeScript taggedUnion pattern match

tagged-union-pattern-match.ts

class TaggedUnionValue<
  TaggedUnion extends { [K in keyof TaggedUnion]: any[] },
  Tag extends keyof TaggedUnion
> {
  constructor(
    private readonly tag: Tag,
    private readonly value: TaggedUnion[Tag],
  ) {}
}

function match<
  TaggedUnion extends { [K in keyof TaggedUnion]: any[] },
  Tag extends keyof TaggedUnion
>({ tag, value }: TaggedUnionValue<TaggedUnion, Tag>) {
  return <Result>(
    cases: { [K in keyof TaggedUnion]: (...args: TaggedUnion[K]) => Result },
  ) => cases[tag](value);
}

function unionConstructor<
  TaggedUnion extends { [K in keyof TaggedUnion]: any[] }
>() {
  return <Tag extends keyof TaggedUnion>(
    tag: Tag,
    ...value: TaggedUnion[Tag]
  ): Data<TaggedUnion> => new TaggedUnionValue(tag, value);
}

type Data<
  TaggedUnion extends { [K in keyof TaggedUnion]: any[] }
> = TaggedUnionValue<TaggedUnion, keyof TaggedUnion>;

interface Maybe<T> {
  Some: [T];
  None: [];
}
const Maybe = <T>() => unionConstructor<Maybe<T>>();

const v = Maybe<number>()("Some", 77);

const u = match(v)({
  Some: value => "hel",
  None: () => "hello",
});

function gotSweets(sweets: Data<Maybe<number>>) {
  return match(sweets)({
    Some: count => count,
    None: () => 10,
  });
}

interface Email {
  Valid: [string];
  Invalid: [string];
  Uncheck: [string];
}
const Email = unionConstructor<Email>();

const m = Email("Uncheck", "[email protected]");