Re: pcase-dolist

[Tassilo Horn <tsdh@gnu.org>]

Thierry Volpiatto <thierry.volpiatto@gmail.com> 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.

Bye,
Tassilo