concrete functor and monad transformers
#74Alternative instance for Either
There is still an Alternative instance for Either that uses a class from deprecated Control.Monad.Trans.Error module. This means that people can unintentionally or unknowingly use deprecated Control.Monad.Trans.Error.Error class as well as nonsensical Alternative orphan instance, if it happens to get into scope.
This issue also applies to MonadPlus instance for Either.
