library:	queue
module:		queue
author: 	Peter Hinely <phinely@hawaii.edu>
copyright: 	1998

/* 
  A queue class and associated methods

  A linked-list implementation of a queue.  A reference is kept to
  the last pair of the linked list.  This is used to add elements
  (actually pairs) to the end of the list.
  
  The relevant methods provided here should be more efficient than 
  those specialized on the <dequeue> class.  Note that this is not
  a dequeue so not all methods of a dequeue are supported.
  
  push-last! and pop! are the most relevant methods to the class.
  I would have liked to use names without the exclamation points,
  but can't because the generic functions in the <dequeue> class
  aren't open (this bug has been fixed).

  A <queue> does not maintain its size explicity.
  
  Obviously queue's can be implemented in different ways.  A circular 
  stretchy vector might be a better choice.
*/