With MonadReader (and other mtl classes), one thing you can't do is polymorphically reach "under" a given part of the transformer stack. For example, there's no polymorphic way to say "I want to run `ask`, but not the outer-most `ask`, the next one down". Here's an idea for how to have that possibility.

reader-alt

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE KindSignatures #-}
import Control.Monad.Reader (ReaderT)
import Control.Monad.State (StateT)
import qualified Control.Monad.Reader as R
import qualified Control.Monad.State as S

class Monad m => DmwitMonadReader m where
	type Env m
	type Wrapped m :: * -> *
	ask :: m (Env m)
	liftReader :: Wrapped m a -> m a

instance Monad m => DmwitMonadReader (ReaderT r m) where
	type Env (ReaderT r m) = r
	type Wrapped (ReaderT r m) = m
	ask = R.ask
	liftReader = R.lift

instance DmwitMonadReader m => DmwitMonadReader (StateT s m) where
	type Env (StateT s m) = Env m
	type Wrapped (StateT s m) = Wrapped m
	ask = S.lift ask
	liftReader = S.lift . liftReader