Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!mit-eddie!CS.ROCHESTER.EDU!quiroz
From: quiroz@CS.ROCHESTER.EDU
Newsgroups: comp.emacs
Subject: Re: hooks in Gnumacs
Message-ID: <8709190514.AA07697@procyon.cs.rochester.edu>
Date: Sat, 19-Sep-87 01:17:19 EDT
Article-I.D.: procyon.8709190514.AA07697
Posted: Sat Sep 19 01:17:19 1987
Date-Received: Sun, 20-Sep-87 13:23:23 EDT
Sender: daemon@eddie.MIT.EDU
Reply-To: quiroz@ROCHESTER.UUCP (Cesar Quiroz)
Organization: U of Rochester, CS Dept, Rochester, NY
Lines: 29
Summary: Please don't define c[ad]+r as macros.

In a recent article, <280@hrc63.co.uk>, Ciaran Byrne contributes
some functions to add hooks to code that originally didn't have
them. 

That posting contained some definitions of the classic c[ad]+r
functions, only as macros.  I want to make a plea so other Emacs
contributors consider for a moment that those macros make it hard
to implement the standardly accepted meanings of those functions.
(Byrne's code is by no means unique in this respect, by the way,
just the most recent one to provide c[ad]+r as macros.)

As to why it could be good to approximate standardly accepted Lisp
behavior, you could see the notes that accompany cl.el in recent
releases of GNU Emacs (I understand it was in 18.47, cannot confirm
right now).  As to why redefining them as macros causes trouble,
imagine an implementation of defstruct that uses list structure to
represent a struct and apply-ies c[ad]+r to instances in order to
retrieve the slot values.  (The one in cl.el uses vectors, so it
doesn't have this problem, but others might easily occur.)

It can be argued that the language should have included these
functions as primitives.  However, it is so easy to define them
"correctly", that it should be done the right way.  (Notice that in
18.47 and later, if cl.el is available, just (require 'cl) should be
enough.) 

By the way, if someone wants to discuss language extensions for
Emacs Lisp or implementation/design questions, that could be a nice
thing to do in this group.  Ideas anyone?