static L map_printProgress(O f, Collection l) {
  L x = emptyList(l);
  int i = 0, n = l(l);
  S desc = null;
  NotTooOften nto = onlyEverySecond();
  if (l != null) for (O o : l) {
    x.add(callF(f, o));
    ++i;
    if (nto.yo()) {
      if (desc == null) desc = shorten(str(f), 20);
      print(desc + ": " + i + "/" + n);
    }
  }
  ret x;
}