Hi all, I wrote a simple interpreter that can be run in the console: data Interaction a b = Exit b | Output b (Interaction a b) | Input (a -> Interaction a b) runConsole :: Interaction String String -> IO () runConsole (Exit b) = putStrLn $ "Finished. Result: " ++ b runConsole (Output s cont) = putStrLn s >> runConsole cont runConsole (Input f) = putStr "> " >> getLine >>= runConsole . f interpreter :: Int -> Interaction String String interpreter i = interaction where interaction = Input input input "exit" = Exit (show i) input "inc" = Output "ok" $ interpreter (i+1) input "show" = Output (show i) interaction input "hello"= Output "Hello World!" interaction input s = Output ("Whas's '" ++ s ++ "' ?") interaction main = runConsole . Output "Known commands: show, inc, hello, exit" $ interpreter 5 I have not yet gained a good understanding of the continuation monad, but I wonder if it could be used here. What would a clean solution look like? Perhaps there are other things that need to be changed as well? Regards, Tim