//public Resp<U> Bind<U>(Func<T, Resp<U>> f) => HasResponse ? new Resp<U>(resp) : f(val);
 public Resp <T> If(Func <T, bool> check, Func <T, ICommonError> toResp) => HasResponse || check(val) ? this : Resp <T> .End(toResp(val));