On Mon, Jan 2, 2017 at 2:14 AM, Erik de Castro Lopo <mle+hs at mega-nerd.com> wrote: > Combinators in C.M.T.Either but not in C.M.T.Except: > > bimapEitherT :: Functor m => (e -> f) -> (a -> b) -> EitherT e m a -> EitherT f m b It's not a very pretty substitute, but note that bimapEitherT f g = mapExceptT (fmap (bimap f g))