On 11/18/07, Benja Fallenstein
Hi Radosław,
You should be able to write this with MaybeT as follows:
Correction, sorry. The code in my original mail doesn't take care of converting the 'Maybe's returned by the functions you're calling into 'MaybeT's. The following should work, but is a little annoying: getStrip :: IO ( Maybe String ) getStrip = runMaybeT $ do pageContent <- MaybeT $ downloadFile mainPageAddress z <- MaybeT $ return $ patternForStrip pageContent MaybeT $ downloadFile $ mainPageAddress ++ z Something like the following might feel cleaner, though: maybeT :: Maybe a -> MaybeT m a maybeT = MaybeT . return downloadFile :: String -> MaybeT IO String downloadFile s = maybeT (parseURI s) >>= liftIO . httpGet getStrip :: MaybeT IO String getStrip = do pageContent <- downloadFile mainPageAddress z <- maybeT $ patternForStrip pageContent downloadFile $ mainPageAddress ++ z Best, - Benja