does-not-understand.lisp

(defclass animal ()
  ())
(defclass bear (animal)
  ((height :initarg :height)))
(defgeneric noise (animal))
(defmethod noise ((animal bear))
  (format t "ROAR~%"))
(defgeneric run (machine))
(defgeneric does-not-understand (object message))
(defmethod does-not-understand ((object bear) message)
  (format t "object ~s does not understand message ~s~%" object message))
(defmethod no-applicable-method :around (gf &rest args)
  (format t "args: ~s~%" args)
  (format t "first: ~s~%" (first args))
  (format t "class-of: ~s~%" (class-of (first args)))
  (if (find-method #'does-not-understand nil (list (class-of (first args)) (find-class t)) nil)
      (apply #'does-not-understand (first args) (cons gf (rest args)))
      (call-next-method)))