static L map_printProgress(Collection l, O f) {
  ret map_printProgress(f, l);
}

static L map_printProgress(O f, Collection l) {
  L x = emptyList(l);
  if (nempty(l)) {
    int i = 0, n = l(l);
    S desc = null;
    NotTooOften nto = onlyEverySecond();
    nto.yo(); // wait 1 second before printing
    bool printed = false;
    for (O o : l) {
      x.add(callF(f, o));
      ++i;
      if (nto.yo()) {
        printed = true;
        if (desc == null) desc = shorten(str(f), 20);
        print(desc + ": " + i + "/" + n);
      }
    }
    if (printed)
      print(desc + ": " + n + " done");
  }
  ret x;
}