Planning for the 7.12 release

[Ryan Scott]

Something I wanted to try to implement before GHC 7.12 are extensions
to DeriveFunctor, DeriveFoldable, and DeriveTraversable which would
allow for automatic derivation of Bifunctor, Bifoldable, and
Bitraversable. (This has already been implemented using Template
Haskell in an unreleased version of the bifunctors package [1], so
implementing it in GHC should be straightforward.)

I haven't made an issue for this yet since I was waiting on the
results of #10448 [2] (which would put Bifoldable and Bitraversable in
base, in addition to Bifunctor, which was added in 7.10). Currently,
Edward Kmett is listed as the owner of that issue, but I would be
happy to tackle it if it means we could get it in time for GHC 7.12.


Ryan S.
-----
[1] https://github.com/ekmett/bifunctors/tree/8e975aead363802610dedccf414b884f9b39b1f4
[2] https://ghc.haskell.org/trac/ghc/ticket/10448