anchor.diff:  (defmethod keys ((item null))
     nil)
   
  -(defun plist-set (plist key val) ;; FIX: use this to add keys to plists so that their order isn't changed
  +(defun plist-set (plist key val)
     (if (getf plist key)
         (progn
           (setf (getf plist key) val)
  
positive.code:     result))
  
  (defun play-test (item)
    (format t "Playing ~s at ~f.~%" item (/ (get-internal-real-time) internal-time-units-per-second)))
  
  (defparameter *event-output-function* 'play-test
  
negative.code:   (:documentation "Class representing a musical event."))
  
  (defun event (&rest params)
    "Create an event, using the PARAMS as its keys/values."
    (let ((ev (make-instance 'event)))
      (labels ((accumulator (pairs)
                 (when (not (null (car pairs)))
  