struct card_inserted {
  std::string account;
};
class atm {
  messaging::receiver incoming;
  messaging::sender bank;
  messaging::sender interface_hardware;
  void (atm::*state)();
  std::string account;
  std::string pin;
  void waiting_for_card()
  {
    interface_hardware.send(display_enter_card());
    incoming.wait().handle<card_inserted>([&](card_inserted const& msg) {
      account = msg.account;
      pin     = "";
      interface_hardware.send(display_enter_pin());
      state = &atm::getting_pin;
    });
  }
  void getting_pin();

public:
  void run()
  {
    state = &atm::waiting_for_card;
    try {
      for (;;) {
        (this->*state)();
      }
    }
    catch (messaging::close_queue const&) {
    }
  }
};