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- To: USERASMV%LNCC.BITNET@Forsythe.Stanford.EDU
- From: Gregor Kiczales <email@example.com>
- Date: Fri, 17 Aug 90 13:14:19 PDT
- Cc: COMMON-LISP-OBJECT-SYSTEM@SAIL.STANFORD.EDU
- In-reply-to: Andre de Souza Mello Valente
- Sender: firstname.lastname@example.org
's message of Fri, 17 Aug 90 15:13:26 AST <805@LNCC.BITNET>
Subject: Re: DISTRIBUTED CLOS IMPLEMENTATION: ASK FOR HELP
Date: Fri, 17 Aug 90 15:13:26 AST
From: Andre de Souza Mello Valente
I am implementing a distributed version of CLOS, and I have
some "silly" doubts about some implementation strategies and
techniques. Maybe someone can help me and suggest a solution:
A general comment is that you should get a copy of PCL, which may
provide a useful starting point for your work. PCL is a portable
implementation of (most of) CLOS. It is available for free from
Xerox (by anonymous FTP). For more information, send a message
a) How can I intercept the CL evaluation to use my own
dispatcher (the CLOS dispatcher, of course)? I thought
about using eval-hook or apply-hook, but there are some
problems. For instance, when you are using one of these
functions and get an error, the interpreter make a throw
that goes back to the interpreter top-level - and you should
reinitialize to use the desired eval or apply again.
If you look in PCL, you will see a technique which just makes the
individual functions which are generic use a special dispatcher.
At a lower level is an implementation of objects called funcallable
instances. These are functions which you can set the code of.
b) How can I intercept the printing system to use the CLOS
one (with "print-object")? We have to take care of two
major possibilities: calling explicitly one of print, write,
format, etc.; calling implicitly via the interpreter (in the
read-eval-print cycle). Although it seems not, the second is
very important because you have to print un-re-readable strings
for the CLOS objects (#<...).
In large part, this isn't possible without the sources of the underlying
Common Lisp. For objects defined by defstruct you can use
:print-function, but for most other things it is hard to get this to
work. This is one the the things PCL doesn't support properly about
c) How can I create the new versions of typep, type-of, etc.,
using the older ones? I tried to create a new package and shadow
the CL ones, but had no success. BTW, I tried the same with
print, but got nothing also.
This is very hard to get completely right without access to the sources
from the underlying lisp. PCL includes a version of this that works
mostly right, you should look at that.