static Throwable pcall(Runnable r) {
  try {
    r.run();
    return null;
  } catch (Throwable e) {
    return e;
  }
}

static O pcall(O o, S method, O... args) null on exception {
  ret call(o, method, args);
}

static <A> A pcall(IF0<A> f) null on exception {
  ret f == null ? null : f!;
}