static void upgradeModuleVar(fS moduleVar, fS programID, final bool callMain) {
  S name = snippetWithTitle(programID);
  infoBox("Upgrading module " + name);
  O module = get(mc(), moduleVar);
  cleanUp(module);
  set(mc(), moduleVar, null);
  module = hotwire(programID);
  if (callMain) callMain(module);
  set(mc(), moduleVar, module);
  infoBox("Upgraded module " + name);
}