static AutoCloseable tempOnFrameClose(JFrame f, Runnable r) {
  if (f == null || r == null) null;
  ret swing(-> {
    var listener = new WindowAdapter {
      public void windowClosing(WindowEvent e) {
        pcall-messagebox { r.run(); }
      }
    };
    f.addWindowListener(listener);
    ret -> swing { f.removeWindowListener(listener); };
  });
}