gistfile1.txt

(defclass plane (moving-object graphics-object)
     ((altitude :initform 0 :accessor plane-altitude)
      (speed))
  (:default-initargs :engine *jet*))

(ensure-class 'plane
  ':direct-superclasses '(moving-object graphics-object)
  ':direct-slots (list (list ':name 'altitude
                             ':initform '0
                             ':initfunction #'(lambda () 0)
                             ':readers '(plane-altitude)
                             ':writers '((setf plane-altitude)))
                       (list ':name 'speed))
  ':direct-default-initargs (list (list ':engine
                                        '*jet*
                                        #'(lambda () *jet*))))