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bug#34852: 26.1; seq-intersection ignores nil as element


From: Miguel V. S. Frasson
Subject: bug#34852: 26.1; seq-intersection ignores nil as element
Date: Fri, 15 Mar 2019 13:08:50 -0300

Hi

I was convinced by the discussions here that changing seq-contains is a bad idea.

I had the false premise that ELT=nil makes seq-contains return nil.

If I could make a suggestion, it would be include an &optional NOT-FOUND to be the value returned in case of not finding any element matching TESTFN.

Cheers 

Miguel 

Em sex, 15 de mar de 2019 12:56, Basil L. Contovounesios <address@hidden> escreveu:
Michael Heerdegen <address@hidden> writes:

> "Miguel V. S. Frasson" <address@hidden> 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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