bug#58278: Add new function seq-keep

[Robert Pluim]

>>>>> On Tue, 04 Oct 2022 12:42:50 +0200, Lars Ingebrigtsen <larsi@gnus.org> 
>>>>> said:

    Lars> Robert Pluim <rpluim@gmail.com> writes:
    >> Well, cl-mapcan applies a function to the elements of a sequence and
    >> discards 'nil' results. Looks pretty similar to me.

    Lars> No, it concatenates the results, so the values returned by the 
function
    Lars> has to be lists.

Thatʼs why I said "apart from the syntactic sugar" 😀

Robert
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