GENERIC
 
  TYPE Element IS PRIVATE;
 
PACKAGE Queues_Generic IS
------------------------------------------------------------------------
--| Specification for Generic FIFO Queues Package
--| Author: Michael B. Feldman, The George Washington University
--| Last Modified: January 1996
------------------------------------------------------------------------
  -- type definition
 
  TYPE Queue (Capacity: Positive) IS LIMITED PRIVATE;
 
  -- exported exceptions
 
  QueueFull  : EXCEPTION;
  QueueEmpty : EXCEPTION;
 
  -- constructors
 
  PROCEDURE MakeEmpty (Q : IN OUT Queue);
  -- Pre:    Q is defined
  -- Post:   Q is empty
 
  PROCEDURE Enqueue (Q : IN OUT Queue; E : IN Element);
  -- Pre:    Q and E are defined
  -- Post:   Q is returned with E as the top Element
  -- Raises: QueueFull if Q already contains Capacity Elements
 
  PROCEDURE Dequeue (Q : IN OUT Queue);
  -- Pre:    Q is defined
  -- Post:   Q is returned with the top Element discarded
  -- Raises: QueueEmpty if Q contains no Elements
 
  -- selector
 
  FUNCTION First (Q : IN Queue) RETURN Element;
  -- Pre:    Q is defined
  -- Post:   The first Element of Q is returned
  -- Raises: QueueEmpty if Q contains no Elements
 
  -- inquiry operations
 
  FUNCTION IsEmpty (Q : IN Queue) RETURN Boolean;
  -- Pre:    Q is defined
  -- Post:   returns True if Q is empty, False otherwise
 
  FUNCTION IsFull  (Q : IN Queue) RETURN Boolean;
  -- Pre:    Q is defined
  -- Post:   returns True if Q is full, False otherwise
 
PRIVATE
 
  TYPE List IS ARRAY (Positive RANGE <>) OF Element;
  TYPE Queue (Capacity: Positive) IS RECORD
    Tail  : Natural := 0;
    Store : List(1..Capacity);
  END RECORD;
 
END Queues_Generic;