// f modifies original content pane
// f: Component -> Component
static JSplitPane addToWindowSplitLeft_f(Component c, Component toAdd, O f) {
  JFrame frame = getFrame(c);
  JSplitPane sp;
  setContentPane(frame, sp = jhsplit(toAdd, (Component) callF(f, frame.getContentPane())));
  ret sp;
}