containers: symmetricDifference for Set and HashSet

[David Feuer]

This has been raised before. I'm going to try to look at implementation
within the next week or so.

On Tue, Dec 1, 2020, 4:17 AM Ben Franksen <ben.franksen at online.de> wrote:

> Would it make sense to add a function like the following to containers:
>
>   symmetricDifference :: Set a -> Set a -> (Set a, Set a, Set a)
>   symmetricDifference a b = (a \\ b, a `intersection` b, b \\ a)
>
> with the idea that this can be implemented more efficiently as a
> primitive than the above specification? (And similarly for HashSet.)
>
> If this is the case, then perhaps difference and intersection could be
> defined in terms of this new primitive:
>
>   difference a b = let (r, _, _) = symmetricDifference in r
>   intersection a b = let (_, r, _) = symmetricDifference in r
>
> *if* it turns out that this does not degrade performance.
>
> Cheers
> Ben
>
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