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Re: [nongnu] elpa/racket-mode 363246ac70 1/2: Fix cl-loop byte-compiler

From: Stefan Monnier
Subject: Re: [nongnu] elpa/racket-mode 363246ac70 1/2: Fix cl-loop byte-compiler warnings
Date: Mon, 18 Sep 2023 16:36:00 -0400
User-agent: Gnus/5.13 (Gnus v5.13)

> If instead of `setq` cl-loop expanded to use `let`
>          (lambda
>            (--cl-var1-- --cl-var2--)
>            (let ((i (cons --cl-var1-- --cl-var2--))
>              (racket--region-set-face
>               (car i)
>               (cdr i)
>               (funcall func
>                        (or
>                         (get-text-property
>                          (car i)
>                          'face)
>                         'default))
>               'force))))

Yes, that's pretty much what Emacs-30 generates now.

> would that avoid the byte-compiler warning?


> If not, can it add an `ignore`?

Yes and no:

- It can add one within the `let` but that would be useless
  because the internal `i` *is* used already.
- It can't really add one outside the `let` because that would cause
  warnings again if the surrounding code doesn't use an extra `let` to
  define that (external) `i`.

> I guess my general question is: If I can hand-write code to avoid the
> warning, and macros can write any code that I can write by hand, why
> can't cl-loop do so for me?

Because as human you get to make a decision based on more information
than the macro so you'd sometimes put an `ignore` and sometimes not but
the macro can't guess when to put one and when not to.


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