mp.ts

class MP<T> extends Promise<T> {
  filter<T>(pred: (v: T) => boolean): MP<T> {
    return this.then((v) => { return pred(v) ? v : new Error() })
  }
}

p.ts

function filter<T>(promise: Promise<T>, pred: (v: T) => boolean): Promise<T> {
  return promise.then((v) => {
    return pred(v) ? v : new Error('Promise cannot satisfy precondition');
  });
}