static void
traverse_recursive (struct bst_node *node, bst_item_func *action, void *param)
{
  if (node != NULL)
    {
      traverse_recursive (node->bst_link[0], action, param);
      action (node->bst_data, param);
      traverse_recursive (node->bst_link[1], action, param);
    }
}
void
walk (struct bst_table *tree, bst_item_func *action, void *param)
{
  assert (tree != NULL && action != NULL);
  traverse_recursive (tree->bst_root, action, param);
}