static PopupMenu makePopupMenu(O... x) {
  if (x == null) null;
  if (l(x) == 1 && x[0] instanceof PopupMenu)
    ret (PopupMenu) x[0];
  new PopupMenu m;
  for i over x: {
    O o = x[i];
    if (eqOneOf(o, "***", "---", "===", ""))
      m.addSeparator();
    else if (o instanceof S && get(x, i+1) instanceof Runnable)
      m.add(menuItem((S) o, get(x, ++i)));
    else if (o instanceof S || o instanceof Menu || o instanceof MenuItem)
      call(m, "add", o);
    else
      print("Unknown menu item: " + o);
  }
  ret m;
}