better instance Hashable IntSet? about containers HOT 8 OPEN

for a given set of elements, the IntSet representation is unique? E.g., "the mask is the largest position ..." https://github.com/haskell/containers/blob/master/containers/src/Data/IntSet/Internal.hs#L261

Then a hash function could just use structure and contents of the internal representation generically?

from containers.

@jwaldmann Correct.

from containers.

Correct, but it would be wasteful. The Tips contain all the elements, it would be sufficient to just hash the contents of those (ignoring Bins).

from containers.

Correct, but it would be wasteful. The Tips contain all the elements, it would be sufficient to just hash the contents of those (ignoring Bins).

Oh yeah, I think there is redundant info there. I'd have to review the representation; it's been a little while.

from containers.

Ah yes, the Tip includes the prefix.

from containers.

We could offer

serialize :: (Word -> r -> r) -> r -> IntSet -> r

This could be used to hash efficiently, with serialize written so it can inline. What would be a good matching deserialize type though?

from containers.

• serialize: could we write instance Ord IntSet with that? (#787 #470)
• deserialize: don't know. what would be the use case?

from containers.

I doubt that's quite what we'd want for Ord, but maybe close. The use case is that I'd be more comfortable with "publicly" exporting serialize/deserialize than a function that's only good for writing the Hashable instance.

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