type F = (v: L) => L<any>;

export type L<T extends F = F> = T & { run: () => T };

const defer: <T extends F>(run: () => T) => L<T> = <T extends F>(run: () => T) =>
  Object.assign(((p: Parameters<T>[0]): ReturnType<T> => {
    let v: F;
    return defer(() => run()(defer(() => v ??= p.run())).run());
  }) as T, { run });

export const _ = <T extends F>(v: T): L<T> => defer(() => v);

export const fromNative: <T>(v: T) => L<any>
  = v => defer(() => v as any);
export const toNative: <T>(v: L<any>) => T
  = <T>(v: L<any>) => v.run() as T;

export const y = (f: () => L<F>) => defer(() => f().run());

export const undef: any = defer(() => { throw new Error('undefined'); });

export const id: L<<T extends L>(v: T) => T>
  = _(v => v);
export const cnst: L<<T extends L>(v: T) => L<(_: unknown) => T>>
  = _(v => _(_ => v)) as L<<T extends L>(v: T) => L<(_: unknown) => T>>;
export const pipe: L<<A extends L, B extends L, C extends L>(f: L<(v: B) => C>) => L<(g: L<(v: A) => B>) => L<(v: A) => C>>>
  = _(<A extends L, B extends L, C extends L>(f: L<(v: B) => C>) =>
    _((g: L<(v: A) => B>) =>
      _((v: A) => f(g(v)))));