Subject kbd_driver;
 Observer kbd_observer;
 void key_pressed(int event, void *_param)
 {
     char *param = (char *)_param;
     if (event == EVENT_KBD_PRESSED)
         printf("You pressed %c\n", *param);
 }
 void register_kbd_listener(void)
 {
     observer_SetEvent(&kbd_observer, key_pressed);
     observer_Subscribe(&kbd_driver, &kbd_observer);
 }