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From: Alan Mackenzie <acm@muc.de>
To: Richard Stallman <rms@gnu.org>
Cc: ulm@gentoo.org, emacs-devel@gnu.org
Subject: Re: Why have a #if .... #else .... #endif construct in Emacs Lisp, when we could make the existing code DTRT unchanged?
Date: Tue, 5 Sep 2023 14:11:06 +0000	[thread overview]
Message-ID: <ZPc2-vg1dSTgIUST@ACM> (raw)
In-Reply-To: <E1qdJxZ-0005QO-Q2@fencepost.gnu.org>

Hello, Richard.

On Mon, Sep 04, 2023 at 20:30:25 -0400, Richard Stallman wrote:
> [[[ To any NSA and FBI agents reading my email: please consider    ]]]
> [[[ whether defending the US Constitution against all enemies,     ]]]
> [[[ foreign or domestic, requires you to follow Snowden's example. ]]]

>   > How about making the byte compiler recognize the construct
 
>   >  (if (< emacs-major-version NUMBER) ...)

>   > and do this optimization on it?

> People seem not to have considered this seriously, ....

It was actually the first thing I considered when the original problem
occurred to me.  We have a similar optimisation in place for (featurep
xemacs).  But then, the number of ways emacs-major-version (to say
nothing of emacs-minor-version) can be used is large (starting with <,
<=, >, >=, =, /=, eq, eql, equal, and extending to predicates involving
e-minor-v), that it would be at least somewhat difficult to apply in
practice.

> .... but I have not seen any serious discussion of a drawback.

I outlined some drawbacks in my post of yesterday evening (Monday
2022-09-04), European time.

> What flaw or drawback do people see in it?

The above.  Plus, some (possibly most) of the predicates we want to
optimise out are expressed in terms of present/absent features rather
than numeric version numbers.  There are  just 45 occurrences of
emacs-major-version in the Lisp sources, over 2000 occurrences of boundp
and fboundp.  We could convert (some of) those 45 to use static-if in
less time than it would take to amend the interpreter and byte-compiler
to handler emacs-major-version specially.

> It should optimize the existing the existing code with no change at
> all.  Isn't that just perfect?

Sadly, no it's not.  It would only do part of the job which is to be
done.  It would make some parts of Emacs more complicated.


> -- 
> Dr Richard Stallman (https://stallman.org)
> Chief GNUisance of the GNU Project (https://gnu.org)
> Founder, Free Software Foundation (https://fsf.org)
> Internet Hall-of-Famer (https://internethalloffame.org)

-- 
Alan Mackenzie (Nuremberg, Germany).



  parent reply	other threads:[~2023-09-05 14:11 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 [this message]
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
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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