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