From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Lars Ingebrigtsen <larsi@gnus.org>
Cc: 46834@debbugs.gnu.org, Pip Cet <pipcet@gmail.com>
Subject: bug#46834: 28.0.50; byte-compiling the standard counter closure fails
Date: Mon, 01 Mar 2021 09:34:21 -0500 [thread overview]
Message-ID: <jwv1rczrlz5.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <8735xf8154.fsf@gnus.org> (Lars Ingebrigtsen's message of "Mon, 01 Mar 2021 14:16:39 +0100")
>>> (byte-compile (let ((l 0)) (lambda () (cl-incf l))))
> Huh, that's such a standard example of using closures that it's
> surprising that we haven't tripped on this before... but I guess we
> don't really write code like that much in Emacs. (I can confirm that
> the test case doesn't work in Emacs 28.)
The problem is not in the way the actual byte compiler handles such code
(e.g. when you compile a whole file, which works just fine), it's just
for the special case where we pass to `byte-compile` a function *value*
rather than an *expression* (in which case, `byte-compile` first needs
to turn this value back into a corresponding expression).
This is a very special situation, whose main use case is when you
do `(byte-compile 'SYMBOL)` and which we don't handle 100%
correctly, anyway.
E.g. (using lexical-binding, of course):
M-: (let ((x 1))
(defun counter1 () (cl-incf x))
(defun counter2 () (cl-incf x))) RET
then do
M-x byte-compile RET counter1 RET
and then try
M-: (list (counter1) (counter2) (counter1) (counter2))
and notice that the counter is not shared between the two functions :-(
> I've added Stefan M to the CCs; perhaps he has some comments.
Thanks,
Stefan
next prev parent reply other threads:[~2021-03-01 14:34 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-28 15:04 bug#46834: 28.0.50; byte-compiling the standard counter closure fails Pip Cet
2021-02-28 19:57 ` Pip Cet
2021-02-28 20:34 ` Pip Cet
2021-03-01 14:23 ` Stefan Monnier
2021-03-01 15:01 ` Pip Cet
2021-03-01 16:02 ` Stefan Monnier
2021-03-02 7:00 ` Lars Ingebrigtsen
2021-03-02 7:31 ` Pip Cet
2021-03-02 7:34 ` Lars Ingebrigtsen
2021-03-02 7:36 ` Pip Cet
2021-03-02 13:16 ` Eli Zaretskii
2021-03-02 13:19 ` Pip Cet
2021-03-02 13:48 ` Eli Zaretskii
2021-03-01 13:16 ` Lars Ingebrigtsen
2021-03-01 14:34 ` Stefan Monnier [this message]
2021-03-01 15:16 ` Pip Cet
2021-03-01 16:15 ` Stefan Monnier
2021-03-01 16:41 ` Pip Cet
2021-03-01 17:01 ` Stefan Monnier
2021-03-01 17:13 ` Pip Cet
2021-03-01 16:31 ` Eli Zaretskii
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