static <A extends Window> A onWindowClosed(final A w, fO r) {
  if (w != null) swing {
    w.addWindowListener(new WindowAdapter {
      public void windowClosed(WindowEvent e) {
        temp tempRememberListener(w, 'removeWindowListener, this);
        pcallF(r);
      }
    });
  }
  ret w;
}

Began life as a copy of #1009661