Add deleteSubmap

[QuietJoon]

Could you add this new function?

I've been used bytestring-trie for many use case, and I implement a function for myself like

deleteSubmap' key trie =
    foldr
        (\k t -> delete k t)
        trie
        (keys $ submap key trie)

However, because it traverses every deleting target entries, this version is too slow.

Could you add my implementation in the Data.Trie.Internal?

I'm not sure that the function's name and actual implementation is proper for your package.
If you care, please rename&change it.

[wrengr]

You can actually already get this efficiently via:

deleteSubmap q = alterBy_ (\_ _ _ _ -> (Nothing, empty)) q undefined

Granted the need for the undefined value there is a bit unsightly. I can adjust the type of alterBy_ to avoid that