I can write a stack push function in the reader monad like so:

import Control.Monad.Reader

push :: String -> Reader [String] a -> Reader [String] a

push s action = local (s :) action

How can I write a push that works inside a monad transformer?

push' :: MonadTrans t => String -> t (Reader [String]) a -> t (Reader [String]) a

push' s action = ???