/*
 * This code is from "Algorithms in C, Third Edition,"
 * by Robert Sedgewick, Addison Wesley Longman, 1998.
 */
void traverse(link h, void (*visit)(link))
  {
    STACKinit(max); STACKpush(h);
    while (!STACKempty())
      {
        (*visit)(h = STACKpop());
        if (h->r != NULL) STACKpush(h->r); 
        if (h->l != NULL) STACKpush(h->l); 
      }
  }