GNU bug report logs - #34852
26.1; seq-intersection ignores nil as element

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From: "Basil L. Contovounesios" <contovob <at> tcd.ie>
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: 34852 <at> debbugs.gnu.org, Nicolas Petton <nicolas <at> petton.fr>, Stefan Monnier <monnier <at> iro.umontreal.ca>, "Miguel V. S. Frasson" <mvsfrasson <at> gmail.com>
Subject: bug#34852: 26.1; seq-intersection ignores nil as element
Date: Fri, 15 Mar 2019 15:56:19 +0000

Michael Heerdegen <michael_heerdegen <at> web.de> writes:

> "Miguel V. S. Frasson" <mvsfrasson <at> gmail.com> writes:
>
>> In any case, of another implementation for seq-intersection or not, I
>> think that the solution from Stefan should be implemented anyway
>> because
>>
>> * it makes seq-contains provide a useful return value when ELT=nil, so
>> it is a good exception; If ELT=nil, seq-contains currently returns nil
>> anyway;
>>
>> * it makes seq-contains become a real predicate function, making it
>> more useful;
>>
>> * since seq-contains has been used as predicate before, it is
>> unpredictable which code uses it out of official repositories, so this
>> fix potentially fixes other code.
>
> BTW, another (alternative) alternative would be to make it return
> (list ELT).  That would be a bit less backward-compatible, but a
> bit more consistent.

+1, either this or returning a boolean is fine with me.

-- 
Basil

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