Re: containers: symmetricDifference for Set and HashSet

A few months ago we briefly discussed a function with a slightly different type: symmetricDifference :: Set a -> Set a -> Set a symmetricDifference x y = (x \\ y) <> (y \\ x) See https://mail.haskell.org/pipermail/libraries/2020-June/030632.html. Am Di., 1. Dez. 2020 um 10:19 Uhr schrieb 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 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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