avl-tree-stack is a compiled Lisp function in `avl-tree.el'.

(avl-tree-stack TREE &optional REVERSE)

Return an object that behaves like a sorted stack
of all elements of TREE.

If REVERSE is non-nil, the stack is sorted in reverse order.
(See also `avl-tree-stack-pop').

Note that any modification to TREE *immediately* invalidates all
avl-tree-stacks created before the modification (in particular,
calling `avl-tree-stack-pop' will give unpredictable results).

Operations on these objects are significantly more efficient than
constructing a real stack with `avl-tree-flatten' and using
standard stack functions. As such, they can be useful in
implementing efficient algorithms of AVL trees. However, in cases
where mapping functions `avl-tree-mapc', `avl-tree-mapcar' or
`avl-tree-mapf' would be sufficient, it is better to use one of
those instead.