Symmetric difference for Set and IntSet

[Simon Jakobi]

I have opened https://github.com/haskell/containers/issues/732 to
track this idea.

Am Fr., 26. Juni 2020 um 19:27 Uhr schrieb David Feuer <david.feuer at gmail.com>:
>
> Map merges can do even more, because they work with arbitrary Applicative functors. So a functor like
>
>     data Triple a = Triple a a a
>     instance Applicative Triple where
>       pure a = Triple a a a
>       liftA2 f (Triple x y z) (Triple p q r) = Triple (f x p) (f y q) (f z r)
>
> can be used to calculate union, intersection, *and* symmetric difference all in one go. I should just bite the bullet and implement that for sets.
>
> On Fri, Jun 26, 2020, 1:16 PM Andrew Lelechenko <andrew.lelechenko at gmail.com> wrote:
>>
>> On 18 Jun 2020, at 23:42, Bardur Arantsson <spam at scientician.net> wrote:
>> > I think it's probably going to be useful, but I would suggest an
>> > algorithm which actually returns each of the terms here (as a tuple), i.e.
>> >
>> >   The "added" bits
>> >   The "removed" bits
>> >   The "common" bits
>> >
>> > This may not be *that* useful for sets per se, but I've lost count of
>> > how often I've had to implement a similar thing for maps.
>>
>>
>> This is probably orthogonal to my proposal here, because it does not improve the performance of symmetricDifference. Maps are more flexible in this aspect, because there are merge tactics, which allow to encode any set operation.
>>
>> Best regards,
>> Andrew
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