static <A> Collection<A> pnlStruct(Collection<A> l) {
  int i = 0;
  if (l != null) for (A a : l) print((++i) + ". " + struct_noStringSharing(a));
  ret l;
}

static <A> A[] pnlStruct(A[] l) {
  pnlStruct(asList(l));
  ret l;
}

static <A, B> Map<A, B> pnlStruct(Map<A, B> map) {
  pnlStruct(mapToLines(map));
  ret map;
}