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Re: cc-vars.el
From: |
Dave Love |
Subject: |
Re: cc-vars.el |
Date: |
19 Nov 2002 16:55:47 +0000 |
User-agent: |
Gnus/5.09 (Gnus v5.9.0) Emacs/21.2 |
Martin Stjernholm <address@hidden> writes:
> True, but it's more valid within different versions of the same
> branch, e.g. between Emacs 20 and 21,
You definitely can't rely on Emacs 21 byte code running in Emacs 20.
> and even more so between minor versions.
There's no guarantee of that either, particularly if macro expansions
change to use new features.
> I had at one point a simple macro system that tested all
> this at compile time and made completely tailored byte code, and I got
> a complaint from a user then.
I don't understand that. I wouldn't worry about details of the
compiled code.
> The only way to avoid compiler warnings cleanly (in some sense) is to
> do the tests with macros at compile time,
I don't think that's true. Definitely not if compilation is done in
batch, file-by-file so that stuff in `eval-when-compile' doesn't
affect other compilations.
> Don't you rather mean code like this?
>
> (if (fboundp 'fred)
> (fred ...))
Yes, sorry.
> It'd be cool if the compiler did enough flow analysis to cope with
> that, but it might be hard to get it to work well, and if it doesn't
> work well then I'd prefer to have the possibility to control the
> warnings explicitly with some pragma-like system.
It doesn't do data-flow analysis, and doesn't need to in order to do
this sort of thing usefully. It was a simple change to the function
that compiles `if'.
> An interesting angle is if something like the following can be used
> (although I'd consider this too a workaround rather than a solution):
>
> (if (boundp 'fido)
> (symbol-value 'fido))
> (if (fboundp 'fred)
> (funcall 'fred ...))
>
> Someone with insight in the inner workings of the compiler can perhaps
> advice on how effectively it manages to optimize such things.
(equal (byte-compile (lambda () (if (fboundp 'fred) (funcall 'fred))))
(byte-compile (lambda () (if (fboundp 'fred) (fred)))))
=> t
I think CL used such a trick, but it's not (now) effective.
> Anyway, this is besides the point regarding cc-bytecomp, since that
> one is necessary to keep it working and compiling without warnings on
> both Emacs and XEmacs.
I don't see what the real difference is between cc-mode and Gnus in
this respect, but then I'm not maintaining cc-mode.
- Re: cc-vars.el, (continued)
- Re: cc-vars.el, Dave Love, 2002/11/20
- Re: cc-vars.el, Dave Love, 2002/11/20
- Re: cc-vars.el, Dave Love, 2002/11/19
- Re: cc-vars.el, Richard Stallman, 2002/11/20
- Re: cc-vars.el, Dave Love, 2002/11/24
- Re: cc-vars.el, Miles Bader, 2002/11/20
- Re: cc-vars.el, Dave Love, 2002/11/24
- Re: cc-vars.el, Kai Großjohann, 2002/11/19
- Re: cc-vars.el,
Dave Love <=
- Re: cc-vars.el, Martin Stjernholm, 2002/11/19
- Re: cc-vars.el, Kai Großjohann, 2002/11/20
- Re: cc-vars.el, Richard Stallman, 2002/11/21
- Re: cc-vars.el, Dave Love, 2002/11/20
Re: cc-vars.el, Stefan Monnier, 2002/11/18