-- This is the generic specification for a dynamic queue abstract data type.

generic
    type ItemType is private;
package queue_pkg is

    type Queue is limited private;

    Queue_Empty, Queue_Full: exception;

    function  is_Empty(Q: Queue) return Boolean;
    function  is_Full(Q: Queue) return Boolean;

    function  front(Q: Queue) return ItemType;

    procedure enqueue (Item: ItemType; Q: in out Queue);
    procedure dequeue (Q: in out Queue);

private

    type QueueNode;

    type QueueNodePointer is access QueueNode;

    type QueueNode is record
        Data: ItemType;
        Prev: QueueNodePointer;
        Next: QueueNodePointer;
    end record;

    type Queue is record
        Front: QueueNodePointer := NULL;
        Back: QueueNodePointer := NULL;
    end record;

end queue_pkg;