This is to advertise the proposal (https://gitlab.haskell.org/ghc/ghc/-/issues/19922) to add a superclass to the MonadTrans type class in Control.Monad.Trans. A Monad transformer 'trans' lifts a 'Monad m' to a 'Monad (trans m)'. This proposal code-ifies that with a superclass constraint: class (forall m. Monad m => Monad (trans m)) => MonadTrans trans where .. This is the main motiviating example of the Quantified Class Constraints paper https://gkaracha.github.io/papers/quantcs.pdf Without it composition (·) as described in the paper can't be defined. Uses include deriving MonadTrans via the composition of two MonadTransformers: type Ok :: MonadTransformer newtype Ok m a = Ok (Int -> Int -> m a) deriving (Functor, Applicative, Monad) via (ReaderT Int · ReaderT Int) m :: Type -> Type deriving MonadTrans via ReaderT Int · ReaderT Int :: MonadTransformer