unionWith of different value types

[BebeSparkelSparkel]

unionWith seems like it would be more useful and could be used in folds if it had the type

unionWith :: (Eq k, Hashable k) => (a -> b -> c) -> HashMap k a -> HashMap k b -> HashMap k c

Would you consider changing the type or adding it as unionWith'?

[treeowl]

That type doesn't work. You'd need two more function arguments: a -> c and b -> c. I'd rather add a containers-like merge mechanism.

[BebeSparkelSparkel]

http://hackage.haskell.org/package/containers-0.6.2.1/docs/Data-Map-Merge-Strict.html#v:merge
merge definitely seems better

[sjakobi]

Since there seems to be a consensus that a containers-style merge function as requested in #226 would be the better addition, I'll tentatively close this as a duplicate. Please reopen, if you disagree.