anchor.diff:  ;;; @return Returns the top element from the queue if possible.
   (defun peek (queue)
     (if (is-empty? queue)
  -      '()
  -    (car (reverse (car queue)))))
  +    NIL
  +    (car (queue-elements queue))))
   
   ;;; Pretty-prints the queue
   ;;; 
   ;;; @param queue
   ;;;         The queue to pretty-print.
   (defun print-queue (queue)
  -  (format t "~a~%" (car queue)))
  +  (format t "~a~%" (queue-elements queue)))
  +
  
positive.code: ;;;; Copyright (c) 2015, Thomas Lang. All rights reserved.
  ;;;; 
  ;;;; This program is free software: you can redistribute it and/or modify
  ;;;; it under the terms of the GNU General Public License as published by
  
negative.code: ;;;; You should have received a copy of the GNU General Public License
  ;;;; along with this program.  If not, see <http://www.gnu.org/licenses/>
  
  ;;; Struct describing a very basic queue.
  ;;; A queue is basically a list that allows the insertion of elements at the one
  ;;; and the removal of elements at the other end only.
  ;;;
  ;;; In this specific implementation, elements can be added at the very rear of it
  ;;; and removal only takes place at the front.
  (defstruct queue
    (elements NIL)
    ;; For efficiency purposes we save a pointer to the very last element of the
    ;; queue here.
    (qlast NIL)
  )
  
  ;;; Checks if the queue is empty or not.
  ;;;
  