template<class T>
class BST {
public:
    inorderTraverse(void visit(T&)) const;
};

template<class KeyT, class ItemT>
class Entry {
    ItemT item;
    KeyT key;
};

template<class KeyT, class ItemT>
class Dictionary {
    BST< Entry<KeyT, ItemT> > itemTree;
public:
    traverse(void visit(ItemT&)) const;
};