Re: MCL support for MOP

[bill@cambridge.apple.com (Bill St. Clair)]

At  9:07 PM 12/29/92 +0000, Donald H. Mitchell wrote:
>I saw an article in the lisp newsgroup that had one phrase that worried me.
>I'm considering using MCL for a large project that I've been doing on
>a set of Symbolics ivory boards.  I want to be certain that MCL will
>support my needs.
>
>That project requires the ability to define new metaclasses and 
>use them with defclass;
>it further requires the ability to define new methods for that metaclass for 
>direct-slot-definition-class, effective-slot-definition-class, and
>compute-effective-slot-definition;
>it requires the ability to create subclasses of standard-slot-definition
>to add "facets" to slots (really slots on the slots); and finally,
>to support the above, we define subclasses of standard-direct-slot... and
>standard-effective-slot...
>
>Does MCL support programmers making these modifications?

No. MCL does allow you to subclass standard-class and specify a :metaclass
to defclass, but it does not have the standard-slot-definition, standard-direct-slot, or standard-effective-slot classes, nor
does it support the direct-slot-definition-class,
effective-slot-definition-class, or compute-effective-slot-definition
generic functions. Adding more MOP support to MCL is on my list of
things to do, but it's not very near the top of the list so I'm not
likely to do it soon.

You may be able to do what you want with PCL. I have not tried PCL
with MCL 2.0 final, but Thomas Morgan said that the newest version
works:

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From: Thomas_E_Morgan@cup.portal.com
Newsgroups: comp.lang.lisp.mcl
Subject: Re: Taboo: MCL 2.0 and PCL (March 92 or newer)
Date: 29 Dec 92 23:46:09 GMT
Organization: The Portal System (TM)
Lines: 12

Omar,
The July-92-PCL-1d-tar.z version of PCL on 
parcftp.xerox.com in \pub\pcl can be compiled
with MCL 2.0 final.

You need to set the autoload lisp package flag
to true, before evaluating the defsys.lisp file.

I've been using it for some months, for reasons
similar to the ones you mention.

   ...Tom M