bug#58278: Add new function seq-keep

[Robert Pluim]

>>>>> On Tue, 04 Oct 2022 13:23:02 +0200, Lars Ingebrigtsen <larsi@gnus.org> 
>>>>> said:

    Lars> Robert Pluim <rpluim@gmail.com> writes:
    >> I never meant that. I meant defining `seq-keep' in terms of `'cl-mapcan',
    >> with the appropriate converting elements to lists done for you (or
    >> even using `mapcan' if youʼre willing to give up the &rest behaviour
    >> of `cl-mapcan')

    Lars> Oh, OK.  I don't think that would be particularly efficient, though.

Iʼve measured it: itʼs not (even when using mapcan) :-)

Robert
--