From: Noam Postavsky <npostavs@gmail.com>
To: "Omar Antolín Camarena" <omar@matem.unam.mx>
Cc: 40827@debbugs.gnu.org, Stefan Monnier <monnier@iro.umontreal.ca>
Subject: bug#40827: 28.0.50; Macroexpansion at runtime
Date: Sat, 25 Apr 2020 10:49:03 -0400 [thread overview]
Message-ID: <87sggrfwo0.fsf@gmail.com> (raw)
In-Reply-To: <874kt8snsq.fsf@matem.unam.mx> ("Omar Antolín Camarena"'s message of "Fri, 24 Apr 2020 14:09:57 -0500")
Omar Antolín Camarena <omar@matem.unam.mx> writes:
> It seems that now, most of the time both the intepreter and the
> byte-compiler, whether using lexical binding or not, will expand macros
> at function definition time. This trick of combining an illegal (rx ...
> (eval ...) ...), with lexical binding, and with eval-defun is the only
> way I've found to trigger macro expansion at runtime.
[...]
> I discovered this during an interesting discussion on reddit, which you
> can read here:
>
> https://www.reddit.com/r/emacs/comments/g5bat3/weekly_tipstricketc_thread/fo362s8
[...]
> (info "(elisp) Repeated Expansion") says:
>
>> 14.5.5 How Many Times is the Macro Expanded?
>
>> Occasionally problems result from the fact that a macro call is
>> expanded each time it is evaluated in an interpreted function, but is
>> expanded only once (during compilation) for a compiled function. If
>> the macro definition has side effects, they will work differently
>> depending on how many times the macro is expanded.
Also further down:
[...] But in interpreted execution, the macro is expanded each
time the macro call runs
[...]
If `initialize' is interpreted, a new list `(nil)' is constructed each
time `initialize' is called.
(elisp "(elisp) Expansion") does mention that uncompiled macro calls
(usually) also get expanded just once:
Note that Emacs tries to expand macros when loading an uncompiled
Lisp file. This is not always possible, but if it is, it speeds up
subsequent execution. *Note How Programs Do Loading::.
Ccing Stefan M, since you made the eager macroexpansion changes as far
as I recall.
next prev parent reply other threads:[~2020-04-25 14:49 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-24 19:09 bug#40827: 28.0.50; Macroexpansion at runtime Omar Antolín Camarena
2020-04-25 14:49 ` Noam Postavsky [this message]
2020-04-25 20:04 ` Stefan Monnier
2021-08-10 16:05 ` Lars Ingebrigtsen
2020-04-26 3:28 ` Richard Stallman
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