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bug#71120: 29.3; buglet in cl-loop
From: |
Andrea Corallo |
Subject: |
bug#71120: 29.3; buglet in cl-loop |
Date: |
Wed, 29 May 2024 17:33:49 -0400 |
User-agent: |
Gnus/5.13 (Gnus v5.13) |
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.
BTW Philippe, you can workaround the bug with:
(cl-loop repeat 100 collect (random 6))
Bests
Andrea
- bug#71120: 29.3; buglet in cl-loop, Philippe Schnoebelen, 2024/05/22
- bug#71120: 29.3; buglet in cl-loop, Philip Kaludercic, 2024/05/29
- bug#71120: 29.3; buglet in cl-loop,
Andrea Corallo <=
- bug#71120: 29.3; buglet in cl-loop, Mattias Engdegård, 2024/05/30
- bug#71120: 29.3; buglet in cl-loop, Andrea Corallo, 2024/05/30
- bug#71120: 29.3; buglet in cl-loop, Stefan Monnier, 2024/05/30
- bug#71120: 29.3; buglet in cl-loop, Andrea Corallo, 2024/05/30
- bug#71120: 29.3; buglet in cl-loop, Mattias Engdegård, 2024/05/30
- bug#71120: 29.3; buglet in cl-loop, Andrea Corallo, 2024/05/30
- bug#71120: 29.3; buglet in cl-loop, Mattias Engdegård, 2024/05/30
- bug#71120: 29.3; buglet in cl-loop, Andrea Corallo, 2024/05/30