Using nonstandard method-class in generic-functions

[Martin Boyer <gamin@Moe.McRCIM.McGill.EDU>]

I am trying to define my own class of methods
using Victoria Day PCL on Lucid 3.0.2.

I am having a problem using DEFMETHOD on generic functions when the method
class (defined through GENERIC-FUNCTION-METHOD-CLASS) is not STANDARD-METHOD.
It may be a PCL bug somewhere, but I'm not really good enough to tell.

From the following transcript, perhaps some kind soul can tell me what is
going wrong:

;;; Given the following definitions:

(defclass widget
   ()
   ( (position :accessor widget-position
	       :initform nil) )
)

;;;; ACTION-METHOD
;;; This is simply a standard method with additional slots.
;;;
(defclass action-method
   (standard-method)
   ( (type	 :reader action-type) )
)

;;; The following is an edited transcript:

> (setq gf (ensure-generic-function 'hello :lambda-list '(object)))
#<Compiled-Function HELLO 75491F>

> (setf (pcl::generic-function-method-class gf) (find-class 'action-method))
#<Standard-Class ACTION-METHOD 34362573>

> (describe gf)

#<Compiled-Function HELLO 75491F> is an instance of class 
    #<Funcallable-Standard-Class PCL::STANDARD-GENERIC-FUNCTION 73606503>:
 The following slots have :INSTANCE allocation:
 NAME                      HELLO
 METHODS                   NIL
 DISCRIMINATOR-CODE        NIL
 CLASSICAL-METHOD-TABLE    NIL
 COMBINED-METHODS          NIL
 CACHE                     NIL
 VALID-P                   NIL
 PRETTY-ARGLIST            NIL
 METHOD-CLASS              #<Standard-Class ACTION-METHOD 34362573>
 DISPATCH-ORDER            :DEFAULT

> (defmethod hello
   ( (self widget) )

   (format t "~A (a widget) says hello.~%" self)
)
>>Error: The value of ARRAY, NIL, should be of type (ARRAY * (*))

LUCID-RUNTIME-SUPPORT:1DIM-AREF-SUBR:
   Required arg 0 (ARRAY): NIL
   Required arg 1 (I): 3
:C  0: Use a new value
:A  1: Abort to Lisp Top Level

-> :a
Abort to Lisp Top Level
Back to Lisp Top Level

> (quit)


Note that if I use 
(setf (pcl::generic-function-method-class gf) (find-class 'standard-method))
instead, I don't get the error.

By the way, many thanks to kanderso@DINO.BBN.COM for the
ENSURE-GENERIC-FUNCTION and GET-METHOD tricks that allowed me to get
this far.

Thanks,

Martin

--
Martin Boyer                           
McGill Research Centre for Intelligent Machines
McGill University, Montreal, QC

gamin@larry.mcrcim.mcgill.edu
gamin@mcgill-vision.uucp