Set: A variant of insert that tells whether the element was already inside

[nh2]

Would it make sense to add this?

Analog to insertLookupWithKey from Data.Map, saving one traversal.

insertLookup :: Ord a => a -> Set a -> (Bool, Set a)

or

insertLookup :: Ord a => a -> Set a -> Maybe (Set a)

[foxik]

My personal opinion is "It is not worth it". The API is wide enough as it is and I believe the speed difference between two calls lookup+insert and lookup+maybe insert is not so big.

Nevertheless, if you feel differently, do not hesitate to open a discussion at libraries@haskell, see http://www.haskell.org/haskellwiki/Library_submissions#Guidance_for_proposers.

Cheers,
Milan

[foxik]

Closing for now, please feel free to reopen if interested in it.