static <B, A extends Cl<B>> A printLines(S msg default "", A c) {
  for (O o : unnull(c))
    print(msg, o);
  ret c;
}

svoid <A> printLines(Iterable<A> l, IF1<A, S> f) {
  for (S s : mapI(l, f))
    print(s);
}