Edward Kmett wrote:
Indeed. A proper "EitherT" was added, but due to bikeshedding turned into ExceptT in the process complicating the migration story a fair bit. To get a version of ExceptT for older transformers versions you can use transformers-compat, so there is at least some migration story. =/
Thanks Ed. I'm really only interested in GHC 7.10 and later, but there are a number of combinators in Control.Monad.Trans.Either that seem to be missing from Control.Monad.Trans.Except and in my day job we have a extended version of Control.Monad.Trans.Either that has yet more combinators that I miss whenever I write code outside the work environment. 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 -- really just an alias for EitherT constructor hoistEither :: Monad m => Either e a -> EitherT e m a Combinators which I am used to using at work include: firstEitherT :: Functor m => (x -> y) -> EitherT x m a -> EitherT y m a secondEitherT :: Functor m => (a -> b) -> EitherT e m a -> EitherT e m b tryEitherT :: (Functor m, MonadCatch m, Exception e) => (e -> x) -> m a -> EitherT x m a There are probably others which I can't remember just now. Whats the right place for these, the C.M.T.Except or somewhere else? I'd prefer not to have to carry them from project to project. Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/