// show popup menu on right click only when a condition is met
svoid makePopupMenuConditional(JComponent c, F0<Bool> condition) {
  if (c != null && condition != null) swing {
    componentPopupMenu_Adapter adapter = firstInstanceOf(c.getMouseListeners(), componentPopupMenu_Adapter);
    c.removeMouseListener(adapter);
    c.addMouseListener(new MouseAdapter {
      public void mousePressed(MouseEvent e) {
        if (!callF(condition)) adapter.mousePressed(e);
      }
      public void mouseReleased(MouseEvent e) {
        if (!callF(condition)) adapter.mouseReleased(e);
      }
    });
  }
}