static class Confirm extends Status {
  O responder; // must contain an answer function
  
  *() {}
  *(O *responder) {}
  
  S answer(S s) {
    status(null); // always forget question after one line
    
    if (isYes(s))
      ret callAnswerMethod(responder, s);
    else if (isNo(s))
      ret "OK, cancelled";
    null;
  }
}

static S confirm(S msg, O responder) {
  status(new Confirm(responder));
  ret msg;
}