postorder
ret = postorder (dfa->str_tree, lower_subexps, preg);
ret = postorder (dfa->str_tree, calc_first, dfa);
postorder (tree, free_tree, NULL);
postorder (tree, free_tree, NULL);
postorder (expr, free_tree, NULL);
postorder (tree, free_tree, NULL);
postorder (tree, free_tree, NULL);
postorder (tree, free_tree, NULL);
postorder (tree, free_tree, NULL);
postorder (elem, free_tree, NULL);
postorder (elem, mark_opt_subexp, (void *) subidx);
static reg_errcode_t postorder (bin_tree_t *root,
action(r, postorder, d);