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