import Control.Monad.Trans.Identity (IdentityT,runIdentityT)
import Control.Monad.Trans.State    (State, get, runState)
import Control.Monad.Trans.Class    (lift)

withoutIdentityT :: State () ()
withoutIdentityT = do 
  x <- get 
  return x 

withIdentityT :: IdentityT (State ()) ()
withIdentityT = do 
  x <- lift get 
  return x

withIdentityT2 :: IdentityT (IdentityT (State ())) ()
withIdentityT2 = do 
  x <- lift $ lift get 
  return x

main = do 
  let x = runState                             withoutIdentityT   ()
  let y = runState               (runIdentityT withIdentityT    ) ()
  let z = runState (runIdentityT (runIdentityT withIdentityT2  )) ()
  print x
  print y
  print z