static S makeResponder_callAnswerMethod(O bot, S s, L<S> history) {
  S answer = (S) callOpt(bot, "answer", s, history);
  if (answer == null)
    answer = (S) callOpt(bot, "answer", s);
  return answer;
}

static Responder makeResponder(final O bot) {
  if (bot instanceof Responder) ret (Responder) bot;
  
  if (bot instanceof S) {
    S f = cast bot;
    ret new Responder {
      public S answer(S s, L<S> history) {
        S answer = (S) callOptMC((S) bot, s, history);
        if (answer == null)
          answer = (S) callOptMC((S) bot, s);
        return answer;
      }
    };
  }
  
  ret new Responder {
    public S answer(S s, L<S> history) {
      return makeResponder_callAnswerMethod(bot, s, history);
    }
  };
}