CALL-NEXT-METHOD example

[Gregor.pa@Xerox.COM]

    Date: Thu, 5 Nov 87 22:27 EST
    From: David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>

    I don't see why (collect '(a b c)) isn't invalid for the same
    reason.  The list method becomes inapplicable in the recursive call.


Oops, your right.  What I spaced on at the time was that I wasn't change
the applicable set of next methods so it was OK.  Should that in fact be
the rule?

If not, here is a corrected example.

(defmethod collect (thing) thing)

(defmethod collect ((n number))
  (let ((l ()))
    (dotimes (i n)
      (push (call-next-method) l))
    (reverse l)))

(defmethod collect ((l list))
  (mapcar #'call-next-method l))


(collect 5) ==> (5 5 5 5 5)

(collect '(() () ())) ==> (() () ())

;;; But note the following erroneous use of call-next-method.
;;; This example would cause an error to be signalled because
;;; the argument which is supplied to call-next-method would
;;; cause a different set of methods to be applicable.

(collect '(1 2 3))
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