static <A> ItIt<A> iterateUpdatingProgressBar(JProgressBar progressBar, Collection<A> l) {
  if (progressBar == null) ret iterator(l);
  ret iteratorFromFunction_withEndMarker_f0(new F0 {
    int i;
    Iterator<A> it = iterator(l);
    NotTooOften nto = onlyTenTimesASecond();
    
    public O get() {
      if (!it.hasNext()) ret endMarker();
      if (i > 0 && nto.yo())
        setProgressBarValue(progressBar, i);
      ++i;
      ret it.next();
    }
  });
}