-- Code of Figure 9.10, page 379 from
-- Kenneth C. Louden, Programming Languages
-- Principles and Practice 2nd Edition
-- Copyright (C) Brooks-Cole/ITP, 2003

generic
  type T is private;
package Queues is
  type Queue is private;
  function createq return Queue;
  function enqueue(q:Queue;elem:T) return Queue;
  function frontq(q:Queue) return T;
  function dequeue(q:Queue) return Queue;
  function emptyq(q:Queue) return Boolean;
private
  type Queuerep;
  type Queue is access Queuerep;
end Queues;