static <A> ItIt<Pair<Int, A>> iterateListWithIndex(Iterable<A> l, int startAt default 0) {
  ret iff(new O {
    Iterator it = iterator(l);
    int i = startAt;
    
    public O get() {
      if (!it.hasNext()) ret endMarker();
      ret pair(i++, it.next());
    }
  });
}