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Re: pcase-dolist

From: Tassilo Horn
Subject: Re: pcase-dolist
Date: Thu, 09 Jul 2015 12:17:46 +0200
User-agent: Gnus/5.130014 (Ma Gnus v0.14) Emacs/25.0.50 (gnu/linux)

Thierry Volpiatto <address@hidden> writes:

>>> So you'd want the above to signal an error in the case of:
>>>    (pcase-let ((`(,w ,x) '(1 2 3)))
>>>      (message "%s %s" w x))
>>> ?
>> Yes, if you want to pick the first two elements of a list with 2 or
>> more elements, you should use `(,w ,x . ,_).  I see that the above is
>> slightly more convenient and concise but I'd value consistency more.
> This would be a regression IMHO, what if you want to do e.g:
> (pcase-let ((`(,a ,b) (file-attributes "foo")))
>   (list a b))
> It would be inconvenient to have to bind the 10 unused remaining
> elements.

As I've said, you can use cdr-matching with a don't-care-pattern, e.g.,

  (pcase-let ((`(,a ,b . ,_) (file-attributes "~/.emacs")))
    (list a b))

which clearly states that you know that the list returned by
`file-attributes' has more than two elements but you are only interested
in the first two.


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