generic
	type Item is private;
package stacks is
	type stack is limited private;
	function newstack return Stack; -- "new" is reserved.
	function pop( the_stack:Stack) return Stack;
	function push( the_stack:Stack; an_item:Item) return Stack;
	function top( the_stack: Stack) return Item;
	function empty( the_stack:Stack) return Boolean;

	stack_empty: exception;	
private
	type stack_node;
	type stack is access stack_node;
end stacks;