To recover from my overly complex previous post, here is a much simply goto based on existing monad transformers:
goto :: Monad m => ContT r m r -> ContT r m a goto (ContT m) = ContT $ \_ -> m return
That doesn't actually work, though. Try running the following script: import Data.List import MonadLib goto :: Monad m => ContT r m r -> ContT r m a goto (ContT m) = ContT $ \_ -> m return myComp :: ContT () IO () myComp = do input <- inBase $ putStrLn "Print something (y/n)?" >> getLine unless ("y" `isPrefixOf` input) $ goto exit inBase $ putStrLn "Something." input <- inBase $ putStrLn "Print more (y/n)?" >> getLine unless ("y" `isPrefixOf` input) $ goto exit inBase $ putStrLn "More." where exit = do inBase $ putStrLn "Ok, I'm exiting." return () main :: IO () main = runContT return myComp