Seeking views before a new major release of transformers package. The docs are here: http://code.haskell.org/~ross/transformers/dist/doc/html/transformers/ The source is here: darcs get http://code.haskell.org/~ross/transformers The major changes from version 0.2.2.0 are: * Foldable and Traversable instances for transformers that support them. * extra Monad instances: instance (MonadFix m) => MonadFix (MaybeT m) instance (MonadFix m) => MonadFix (IdentityT m) instance (Monad f, Monad g) => Monad (Product f g) instance (MonadPlus f, MonadPlus g) => MonadPlus (Product f g) instance (MonadFix f, MonadFix g) => MonadFix (Product f g) * new functors Backwards and Reverse * a new Lift transformer, a generalization of Errors * generalized constructor functions: state :: Monad m => (s -> (a, s)) -> StateT s m a reader :: Monad m => (r -> a) -> ReaderT r m a writer :: Monad m => (a, w) -> WriterT w m a Another issue that has been raised is: should the instance instance Monad (ContT r m) have a Monad constraint so that it can define fail?