bug#49407: Request: Specify default values in `map-let` in Map.el

[Lars Ingebrigtsen]

Okam <okamsn@protonmail.com> writes:

> `map-let` allows one to conveniently bind variables using `map-elt`, but
> does not provide a way specify a default value if a key is missing.
>
> With `map-elt`, one can use the optional third argument to specify this
> value.  It would be good to have this in `map-let` as well.
>
> For example, maybe it could look something like
>
>      ;; As just a third value in the list:
>      (let ((map '(:a 1 :b 2)))
>        (map-let ((:a a)
>                  (:b b)
>                  (:c c 3))
>            map
>          (+ a b c)))

Hm...  I guess that could be useful.  I've added Nicolas to the CCs;
perhaps he has an opinion here.

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