Hi,
It doesn't use State monad anymore and it returns Maybe. This seems to be the common preference, is it? Feel free to vote against. Should we change Data.Map also? There is another proposal for changes in findMin/findMax so it is better to make this two breaking changes together rather than in a later release.
The standard libraries proposal thingy is to go via the libraries list, create tickets etc. What reason is there to make this part of the base libraries, rather than a separate package on hackage? I can't see much reason to make Data.Tree part of the base libraries, other than the fact it already is, and it could easily get moved out at a future date. We've seen there is some advantage in leaving the implementation outside the base library, as its already changed several times in the past few days. Thnanks Neil