Recursive
Preorder for Distinct Node/Poly Implementation
void poly::print_preorder
(void)
{
if (get_tag()==I) cout << ival() << "
";
else { // must be pointer to a
node
node<poly> * np = pval();
while (np != NULL){
(np->data).print_preorder();
np = np->next;
}
}
}