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A confusing title for a confusing question! I understand a) monads, b) the IO monad, c) the Cont monad ( Control.Monad.Cont ), and d) the ContT continuation transformer monad. (And I vaguely understand monad transformers in general -- though not enough to answer this question.) I understand how to write a program where all the functions are in the Cont monad ( Cont r a ), and I understand how to write a program where all the functions are in the combined Cont/IO monad ( ContT r IO a ). But I'm wondering how I might write a program where some functions are in a combined Cont/IO monad ( ContT r IO a ) and other functions are just in the Cont monad ( Cont r a ). Basically, I want to write the whole program in continuation style, but only use the IO monad where necessary (much like in "regular" Haskell code, I only use the IO monad where necessary). For example consider these two functions, in non-continuation style: foo :: Int -> IO Int foo n = do let x = n + 1 print x return $ bar x bar :: Int -> Int bar m = m * 2 Note that foo requires IO but bar is pure. Now I figured out how to write this code fully using the continuation monad, but I needed to thread IO through bar as well: foo :: Int -> ContT r IO Int foo n = do let x = n + 1 liftIO $ print x bar x bar :: Int -> ContT r IO Int bar m = return $ m * 2 I do want all my code in continuation style, but I don't want to have to use the IO monad on functions that don't require it. Basically, I would like to define bar like this: bar

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