On Thu, Apr 29, 2004 at 06:27:32PM -0500, Ben_Yu@asc.aon.com wrote:
Hi, While writing monad programs, I sometimes want to do a return as it is in imperative program. i.e., do{return 1; return 2} is same as return 1
Is this possible at all?
Someone already proposed an Error monad, but I think that Continuation monad is more appropriate, as it's easier to ,,return'' values of different types. It also allows you to choose the place you want to ,,return'' to. You'll probably want to use features of other monad, so use a ContT monad transformer. Here's an example: import Control.Monad.Cont code = (\m -> runContT m return) $ do x <- callCC $ \exit -> do exit 1 return 2 lift (print x) This will print 1, not 2. Best regards, Tom -- .signature: Too many levels of symbolic links