Re: Semantic of pcase `seq' and `map' patterns (was: pcase-setq)

[Nicolas Petton <nicolas@petton.fr>]

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Michael Heerdegen <michael_heerdegen@web.de> writes:

> After reading the doc of the `seq' pcase pattern:
>
> --8<---------------cut here---------------start------------->8---
> -- (seq &rest ARGS)
>
> pcase pattern matching sequence elements.
> Matches if the object is a sequence (list, string or vector), and
> binds each element of ARGS to the corresponding element of the
> sequence.
> --8<---------------cut here---------------end--------------->8---
>
> it was not obvious to me how this example would look like using pcase -
> especially, what "are" the "ARGS"?
>
> AFAIU the "ARGS" are just normal (pcase) patterns - they are not limited
> to variables, and matching can fail for them as well even if the number
> of sequence arguments would match.
>
> I think the semantic would be better described like this:
>
> --8<---------------cut here---------------start------------->8---
> -- (seq &rest PATTERNS)
>
> pcase pattern matching sequence elements.
> Matches if the object is a sequence (list, string or vector), and
> each PATTERN matches the corresponding element of the
> sequence.
> --8<---------------cut here---------------end--------------->8---
>
> Does that make sense?  Likewise `map', I guess.

Yes, it does. You could for example do:

    (pcase [1 2 3 4]
      ...
      ((seq (pred oddp) (pred evenp)) 'matched)
      ...)

I will update the documentation, thanks!

Nico

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