From: Kim Minh Kaplan
Subject: How do you use APPLY with CALL-NEXT-METHOD ?
Date: Sun, 23 Jul 2006 14:27:23 +0000
Message-ID: <1153664843.773481.213600@i42g2000cwa.googlegroups.com>

I am trying tu modify the behaviour of a method like this :

    (defgeneric foo (this &rest args))

    (defmethod foo (this &rest args)
      (cons this args))

    (defclass bar () ())

    (defmethod foo ((this bar) &rest args)
      (apply 'call-next-method :bar args))

Un fortunately this does not work :

    (foo (make-instance 'bar) 1 2)

    Error: attempt to call `CALL-NEXT-METHOD' which is an undefined
	   function.
      [condition type: UNDEFINED-FUNCTION]

How should I do such a modification of arguments to CALL-NEXT-METHOD?
-- 
Kim Minh.
http://www.kim-minh.com/

• Re: How do you use APPLY with CALL-NEXT-METHOD ? Pascal Costanza
  • Re: How do you use APPLY with CALL-NEXT-METHOD ? Kim Minh Kaplan

From: Pascal Costanza
Subject: Re: How do you use APPLY with CALL-NEXT-METHOD ?
Date: Sun, 23 Jul 2006 14:41:50 +0000
Message-ID: <4ihg5eF3qb79U1@individual.net>

Kim Minh Kaplan wrote:
> I am trying tu modify the behaviour of a method like this :
> 
>     (defgeneric foo (this &rest args))
> 
>     (defmethod foo (this &rest args)
>       (cons this args))
> 
>     (defclass bar () ())
> 
>     (defmethod foo ((this bar) &rest args)
>       (apply 'call-next-method :bar args))
> 
> Un fortunately this does not work :
> 
>     (foo (make-instance 'bar) 1 2)
> 
>     Error: attempt to call `CALL-NEXT-METHOD' which is an undefined
> 	   function.
>       [condition type: UNDEFINED-FUNCTION]
> 
> How should I do such a modification of arguments to CALL-NEXT-METHOD?


If you apply or funcall a function by its quoted name, like you do when 
you say (apply 'call-next-method ...), Lisp attempts to find a global 
definition of that function, as if it were defined by defun or defgeneric.

However, call-next-method is typically implemented as a local function 
(as if by flet or labels), so (apply 'call-next-method ...) cannot see 
this local function. You should instead call (apply #'call-next-method 
...), which will look up the function locally.

I hope this helps.


Pascal

-- 
My website: http://p-cos.net
Closer to MOP & ContextL:
http://common-lisp.net/project/closer/

From: Kim Minh Kaplan
Subject: Re: How do you use APPLY with CALL-NEXT-METHOD ?
Date: Sun, 23 Jul 2006 14:47:39 +0000
Message-ID: <1153666059.662364.41810@i3g2000cwc.googlegroups.com>

Pascal Costanza wrote:

> If you apply or funcall a function by its quoted name, like you do when
> you say (apply 'call-next-method ...), Lisp attempts to find a global
> definition of that function, as if it were defined by defun or defgeneric.
>
> However, call-next-method is typically implemented as a local function
> (as if by flet or labels), so (apply 'call-next-method ...) cannot see
> this local function. You should instead call (apply #'call-next-method
> ...), which will look up the function locally.
>
> I hope this helps.

Ah, silly me, I should have thought about it.   Works now, thank you.
-- 
Kim Minh
http://www.kim-minh.com/