ContinuationMonadとMonadTransformer

Haskell Wikiとモナドのすべてを見ながらContinuationモナドとMonadTransformerをお勉強(学習と言うべきなんだろう、きっと)。分かったような、分かんないような。今日はひとまず撤収。
Continuationモナドは何が「うれしい」のかな?一発でexitできるところ?Continuation Passing Styleがエレガントに書ける?そーなの?
(4/24 追記)
「継続」がちゃんと分かってないんだな、きっと。しっかり勉強してからもう一度挑戦。

import Control.Monad.Cont

execute :: Cont (IO ()) String -> IO ()
execute c = putStrLn "<<execute>> " >> runCont c putStrLn

executeT :: ContT () IO String -> IO ()
executeT c = putStrLn "<<executeT>> " >> runContT c putStrLn

myCont = callCC cont
  where
    cont :: (String -> Cont (IO ()) String) -> Cont (IO ()) String
    cont exit = do
      return $ "cont: " ++ (show 10)

myContT = callCC contT
  where
    contT :: (String -> ContT () IO String) -> ContT () IO String
    contT exit = do
      liftIO (readLn :: IO Int) >>= liftIO . return . (++) "contT: " . show
--    contT exit = liftIO $ do
--      readLn :: IO Int >>= return . (++) "contT: " . show

myExitT = callCC exitT
  where
    exitT :: (String -> ContT () IO String) -> ContT () IO String
    exitT exit = do
      n <- liftIO (readLn :: IO Int)
      if n == 0
        then exit "exited!!!"
        else return $ (++) "exitT: " $ show n

main = execute myCont >> executeT myContT >> executeT myExitT