// isSep: func(A) -> bool
static <A> L<L<A>> groupNonEmpty(L<A> l, O isSep) {
  new L<L<A>> out;
  int j = 0;
  for (int i = 0; i < l(l); i++) {
    bool sep = isTrue(callF(isSep, l.get(i)));
    if (sep) {
      if (i > j)
        out.add(newSubList(l, j, i));
      j = i+1;
    }
  }
  if (l(l) > j)
    out.add(newSubList(l, j));
  ret out;
}