idris-lang/Idris-dev — pull request #1504 by Heather (2014-09-01 07:02:15+00:00)
Title: EitherErr Applicative for Functor-Applicative-Monad_Proposal

`EitherErr' is an instance of Monad but not Applicative - this will become an error in GHC 7.10, under the Applicative-Monad Proposal.

http://www.haskell.org/haskellwiki/Functor-Applicative-Monad_Proposal