enum UpDown {
  up(true), down(false);
  
  bool bit;
  
  private *(bool *bit) {}
  
  static UpDown fromBool(bool bit) { ret bit ? up : down; }
  
  bool isUp() { ret bit; }
  bool isDown() { ret !bit; }
  
  int direction() { ret isUp() ? 1 : -1; }
}