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From: Alan Mackenzie <acm@muc.de>
To: Stefan Kangas <stefankangas@gmail.com>
Cc: emacs-devel@gnu.org, "Mattias Engdegård" <mattiase@acm.org>
Subject: Re: Why shouldn't we have a #if .... #else .... #endif construct in Emacs Lisp?
Date: Wed, 30 Aug 2023 18:03:08 +0000	[thread overview]
Message-ID: <ZO-EXPYHUs6Dh2aC@ACM> (raw)
In-Reply-To: <CADwFkm=x4qRaMxPnndiUeBCycrY5Ux=WXJOycg5rXC6X96WiOw@mail.gmail.com>

Hello, Stefan.

On Wed, Aug 30, 2023 at 19:36:20 +0200, Stefan Kangas wrote:
> Alan Mackenzie <acm@muc.de> writes:

> > > 1. Would it be hard to make the byte-compiler not warn in the
> > > situation you describe?
> >
> > (That situation being where an obsolete function/variable is tested for,
> > and is used or not used according to the result of the test.)  It would
> > not be too hard, and the scheme I'm proposing (with help from Philip K.)
> > is one way of doing this.

> I'm asking because we already have special casing in place for
> (featurep 'xemacs) -- we just constant fold it -- so I'm wondering if
> it would make sense to do the same here.  See bytecomp.el:5671.

I looked at that, and came to the conclusion it doesn't make sense.  The
mechanics there would be to evaluate (if some-condition FOO BAR) at
compilation time and replace it with either FOO or BAR.  The problem is
some-condition can vary at run time, for example by setting an option,
so it would be more trouble than it's worth.

> It's not the same situation exactly though, as we will often be able
> to run bytecode from Emacs N+1 on Emacs N, whereas XEmacs/Emacs
> byte-code compatibility is both long gone and in all likelihood not
> coming back.

Indeed, not.

> > It may be, but it's clumsy.  We would need such an alias for _each_
> > function/variable which has been declared obsolete.  In my proposed
> > mechanism, by contrast, one would just need to replace an `if' form by a
> > `hash-if'.

> Right.  I guess this has been the state of the art in Emacs Lisp so
> far, though.  And then `hash-if' itself won't exist in Emacs 24
> either, of course, so depending on how ambitious people are with
> backwards-compatibility they'll have to lug around compatibility
> boiler-plate for that too.

The current size of hash-if, including doc-string, is 10 lines.  Add in
an extra line for (if (not fboundp 'hash-if) ....), and we come to 11
lines.  I think, given the heartaches and headaches suffered by package
maintainers when variables/functions become obsolete or vanish, this
would not be much of a hardship.

> If we do go with a new macro, I'd propose naming it `static-if' (as in
> APEL) instead of `hash-if', because the latter name seems to wrongly
> suggest that it has to do with hashing.

I looked at APEL, and its code was near identical to what I (with help
from PK) wrote.  I'd have nothing against the name static-if instead.
As long as this doesn't raise copyright assignment problems, assuming
the authors of APEL haven't assigned copyright to the FSF.

> Our legacy is also older than even the C preprocessor.

:-)

-- 
Alan Mackenzie (Nuremberg, Germany).



  reply	other threads:[~2023-08-30 18:03 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-08-28 19:37 Why shouldn't we have a #if .... #else .... #endif construct in Emacs Lisp? Alan Mackenzie
2023-08-28 19:47 ` Ulrich Mueller
2023-08-28 20:06   ` Alan Mackenzie
2023-08-28 21:01     ` Ulrich Mueller
2023-08-28 21:46       ` Alan Mackenzie
2023-08-31  2:07         ` Richard Stallman
2023-08-31  7:50           ` Alan Mackenzie
2023-09-04  1:34             ` Richard Stallman
2023-09-04 10:50               ` Alan Mackenzie
2023-09-04 11:02                 ` tomas
2023-09-04 15:19                   ` Emanuel Berg
2023-09-04 18:57                     ` tomas
2023-09-06  0:58                   ` Richard Stallman
2023-09-06  0:58                 ` Richard Stallman
2023-09-06  7:28                   ` Andreas Schwab
2023-09-06  9:31                     ` Alan Mackenzie
2023-09-06  9:56                   ` Alan Mackenzie
2023-09-09  0:39                     ` Richard Stallman
2023-09-09 10:32                       ` Ihor Radchenko
2023-09-10  0:22                         ` Richard Stallman
2023-09-10  8:36                           ` Ihor Radchenko
2023-09-13 23:53                             ` Richard Stallman
2023-09-20 12:59                               ` Ihor Radchenko
2023-09-05  0:30           ` Why have a #if .... #else .... #endif construct in Emacs Lisp, when we could make the existing code DTRT unchanged? Richard Stallman
2023-09-05  0:41             ` Emanuel Berg
2023-09-08 17:54               ` Emanuel Berg
2023-09-05  4:37             ` tomas
2023-09-05  5:53               ` Ihor Radchenko
2023-09-05  6:28                 ` tomas
2023-09-05 11:06             ` Adam Porter
2023-09-05 11:26             ` Lynn Winebarger
2023-09-05 14:11             ` Alan Mackenzie
2023-09-08  1:01               ` Richard Stallman
2023-09-08  2:45                 ` Po Lu
2023-09-10  0:24                   ` Richard Stallman
2023-09-05  8:14         ` Why shouldn't we have a #if .... #else .... #endif construct in Emacs Lisp? Ulrich Mueller
2023-08-28 19:53 ` Emanuel Berg
2023-08-29  9:19   ` Alan Mackenzie
2023-08-29 10:36   ` João Távora
2023-08-29 11:09     ` Ihor Radchenko
2023-08-29 11:20       ` João Távora
2023-08-30 20:48         ` Sean Whitton
2023-08-30 20:59           ` João Távora
2023-09-02 23:12     ` Stefan Monnier via Emacs development discussions.
2023-09-03  0:18       ` Emanuel Berg
2023-09-03 12:27       ` João Távora
2023-08-29 12:54 ` Philip Kaludercic
2023-08-29 13:23   ` Alan Mackenzie
2023-09-02 23:09   ` Stefan Monnier via Emacs development discussions.
2023-08-29 16:28 ` LdBeth
2023-08-29 20:09 ` Stefan Kangas
2023-08-30 10:31   ` Alan Mackenzie
2023-08-30 17:36     ` Stefan Kangas
2023-08-30 18:03       ` Alan Mackenzie [this message]
2023-08-30 18:17         ` Stefan Kangas
2023-09-02 15:06           ` Alan Mackenzie
2023-09-02 15:17             ` Eli Zaretskii
2023-09-02 19:43               ` Alan Mackenzie
2023-09-03  4:42                 ` Eli Zaretskii
2023-09-03 10:48                   ` Alan Mackenzie
2023-09-03 11:02                     ` Eli Zaretskii
2023-09-03 13:24                       ` Alan Mackenzie
2023-09-02 19:20             ` Philip Kaludercic
2023-09-02 19:37               ` Stefan Kangas
2023-09-02 19:58               ` Alan Mackenzie
2023-09-04 11:12                 ` Lynn Winebarger

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