From: Andrea Corallo <acorallo@gnu.org>
To: Philip Kaludercic <philipk@posteo.net>
Cc: 71120@debbugs.gnu.org, "Mattias Engdegård" <mattiase@acm.org>,
"Stefan Monnier" <monnier@iro.umontreal.ca>,
"Philippe Schnoebelen" <phs@lmf.cnrs.fr>
Subject: bug#71120: 29.3; buglet in cl-loop
Date: Wed, 29 May 2024 17:49:10 -0400 [thread overview]
Message-ID: <yp1bk4os2zt.fsf@fencepost.gnu.org> (raw)
In-Reply-To: <yp1fru0s3pe.fsf@fencepost.gnu.org> (Andrea Corallo's message of "Wed, 29 May 2024 17:33:49 -0400")
Andrea Corallo <acorallo@gnu.org> writes:
> Philip Kaludercic <philipk@posteo.net> writes:
>
>> Philippe Schnoebelen <phs@lmf.cnrs.fr> writes:
>>
>>> When I need a list of 100 random dice throws I write
>>>
>>> (cl-loop for i from 1 to 100 collect (random 6))
>>>
>>> It compiles just fine.
>>>
>>> If instead I use
>>>
>>> (cl-loop for _i from 1 to 100 collect (random 6))
>>>
>>> then I get a compilation warning:
>>>
>>> foo.el:1:18: Warning: variable ‘_i’ not left unused
>>>
>>> It should be the other way around.
>>
>> The issue here is that the warning describes an issue in the output, in
>> the latter case
>>
>> (let* ((_i 1) (--cl-var-- nil))
>> (while (<= _i 100)
>> (setq --cl-var-- (cons (random 6) --cl-var--))
>> (setq _i (+ _i 1)))
>> (nreverse --cl-var--))
>>
>> As you see, _i is both evaluated in (+ _i 1) and updated.
>>
>> Here you have a minimal working example of the warning:
>>
>> (byte-compile (lambda () (let ((_x 3)) _x)))
>>
>> ;; Warning: variable ‘_x’ not left unused
>>
>> My guess is that fixing this would require cl-loop to notice that the
>> counter is prefixed with a "_" and then use some other variable, but
>> that might lead to issues with existing code. Perhaps this
>> transformation might be safe in that case:
>>
>> (let* ((<fresh-variable> 1) (--cl-var-- nil))
>> (while (<= <fresh-variable> 100)
>> (let ((_i <fresh-variable>))
>> (setq --cl-var-- (cons (random 6) --cl-var--))
>> (setq <fresh-variable> (+ <fresh-variable> 1))))
>> (nreverse --cl-var--))
>>
>> I have added Mattias and Stefan to the CCs, as they'll probably have
>> more qualified comments to add.
>
> This is the same transformation that came to my mind reading the orginal
> report, I think it should be safe.
As a datapoint, SBCL does expands this with inside a
(declare (ignore i))
Unfortuantelly we don't support it :/ and our 'ignore' doesn't work here
as goes in the opposite direction :(
Andrea
next prev parent reply other threads:[~2024-05-29 21:49 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-22 8:43 bug#71120: 29.3; buglet in cl-loop Philippe Schnoebelen via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-05-29 20:47 ` Philip Kaludercic
2024-05-29 21:33 ` Andrea Corallo
2024-05-29 21:49 ` Andrea Corallo [this message]
2024-05-30 1:45 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-05-30 9:25 ` Mattias Engdegård
2024-05-30 13:14 ` Andrea Corallo
2024-05-30 14:51 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-05-30 15:41 ` Andrea Corallo
2024-05-30 15:45 ` Mattias Engdegård
2024-05-30 17:15 ` Andrea Corallo
2024-05-30 17:18 ` Mattias Engdegård
2024-05-30 17:42 ` Andrea Corallo
2024-05-31 4:30 ` Gerd Möllmann
2024-05-31 8:29 ` Mattias Engdegård
2024-06-03 15:24 ` Andrea Corallo
2024-06-03 15:32 ` Mattias Engdegård
2024-06-03 15:42 ` Andrea Corallo
2024-06-03 16:24 ` Mattias Engdegård
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