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From: "B. Pym" <No_spamming@noWhere_7073.org>
Newsgroups: comp.lang.lisp
Subject: Re: How do you insert declarations into loops?
Date: Tue, 2 Jul 2024 10:24:36 -0000 (UTC)
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Thomas A. Russ wrote:

>  > Example:  This function loops over a list of associations
>  > collecting the cdrs.
>  >
>  >    (defun list-cdrs (list)
>  >      (loop for (unwanted-var . wanted-var) in list
>  >            collect wanted-var))
>  >
>  > When I compile list-cdrs, I get an "unused lexical variable, UNWANTED-VAR"
>  > message (this is fine.).  Normally, if I wanted to inhibit this
>  > warning I would stick a (declare (ignore unwanted-var)) in the
>  > beginning of the function body immediately following the declaration.
>  > It doesn't seem that you can do this using loop.
> 
> The solution is not to introduce an ignore declartion, but instead to
> use a hack in the destructuring pattern matcher:
> 
>     (defun list-cdrs (list)
>       (loop for (NIL . wanted-var) in list
>             collect wanted-var))


(map cdr '((a . 2) (b . 3)))
 ===>
(2 3)