Re: [Emacs-diffs] map 988d721: Add a pcase pattern for maps and `map-let' based on it

[Nicolas Petton]

Stefan Monnier writes:

>> +  "pcase pattern matching map elements.
>> +Matches if the object is a map (list, hash-table or array), and
>> +binds values from ARGS to the corresponding element of the map.
>> +
>> +ARGS can be an alist of key/binding pairs of a list of keys."
>
> I think this would benefit from a bit more detail.  E.g. you could say
> "ARGS is a list of elements of the form (KEY PAT)" or something
> like that.

Yes, and there's a typo. It should be "[...] or a list of keys.".

>
>> +  (seq-map (lambda (elt)
>> +             (if (consp elt)
>> +                 `(app (pcase--flip map-elt ',(car elt)) ,(cdr elt))
>> +               `(app (pcase--flip map-elt ',elt) ,elt)))
>> +           args))
>
> Hmm... It looks like it's actually elements of the form (KEY . PAT) or
> elements of the form SYMBOL which stands for (SYMBOL . SYMBOL).

Yes, exactly.

> Some alternatives to consider:
> - Use (KEY PAT) instead of (KEY . PAT).  This makes the source code
>   a bit more concise, so I'm in favor of the (KEY PAT) form.

Why not, I don't have a strong opinion, and I think both would work.

> - Use a plist rather than an alist.  I like alists better in general, so
>   I'm fine with this choice.

Yes, I think it's better than a plist.

> - let KEY be evaluated rather than having it be quoted.  I.e. require
>   the programmer to write 'a when looking up the key `a'.  It costs an
>   extra quote in some/many cases, but does give you extra power.

Do you think it would be worth it? I'm not sure.

Cheers,
Nico
-- 
Nicolas Petton
http://nicolas-petton.fr

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