-- This is the generic specification for a stack abstract data type.
-- Usage: Put these lines in the client (in the appropriate place):

--    with StackPkg;   -- this statement precedes client procedure declaration
-- 
--                     -- the next 2 statements go inside the client procedure
--                     -- the next 2 statements go after MyType is declared
--    package MyStkPkg is new StackPkg(Size => 100; ItemType => MyType);
--    use  MyStkPkg;

generic  -- Generic parameters are declared here

	Size : Positive;            -- Size of stack to create

	type ItemType is private;   -- Type of elements that stack will contain

package StackPkg is

	type Stack is limited private;

	Stack_Empty: exception; -- Raised if do top or pop on an empty stack
	Stack_Full : exception; -- Raised if push onto full stack

        -- Determine if stack is empty or full
	function isEmpty (s : Stack) return Boolean;
	function isFull  (s : Stack) return Boolean;

        -- Put element Item onto Stack s
	procedure push (item : ItemType; s : in out Stack)
      with pre => not isFull(s) or else raise Stack_Full;

        -- Remove an element from Stack s
	procedure pop  (s : in out Stack)
      with pre => not isEmpty(s) or else raise Stack_Empty;

        -- Return top element from Stack s
	function  top   (s : Stack) return ItemType
      with pre => not isEmpty(s) or else raise Stack_Empty;

private

	type StackElements is array(1 .. Size) of ItemType;

	type Stack is record
		Elements : StackElements;
		Top : Natural range 0 .. Size := 0;
	end record;

end StackPkg;