anchor.diff:  
   
   (defun queue-pop (queue &key wait-p)
  -  "Pop the next item from the queue QUEUE, returning as values the
  -item which was popped and whether the queue was empty.  If WAIT-P is a
  -number, busy-wait up to that many seconds to pop an item.  If WAIT-P
  -is otherwise non-nil, busy-wait forever."
  +  "Pop the next item from QUEUE, returning as values the item which
  +was popped and whether the queue was empty.  If WAIT-P is a number,
  +busy-wait up to that many seconds to pop an item.  If WAIT-P is
  +otherwise non-nil, busy-wait forever."
     (cond
      (wait-p
       (let ((end-time (when (numberp wait-p)
  
positive.code: 
  
  (defun queue-dequeue (queue)
    (symbol-macrolet
        ((head (queue-head queue)))
      (with-cas-retry
  
negative.code:           (multiple-value-bind (item empty-p)
                (queue-dequeue queue)
              (unless empty-p
                #+with-assertions (assert (not (eq +empty+ item)))
                (return (values item empty-p))))
            (when (and end-time
                       (>= (get-internal-real-time) end-time))
  