Re: [Haskell-beginners] monads do not fit together?

Kim, I simplified the problem by removing the if then. After that I desugared the do block to what I think is the equivalent with >> and >>=. I get the same message (Couldn't match expected type `CGIT IO a0' with actual type `IO [String]'). I think I do understand where this message is coming from. But what can I do to fix it? Kees module Main( main ) where import Network.CGI import Text.XHtml import Text.XHtml.Transitional import Data.Maybe runRefreshFirewall :: String -> IO [String] runRefreshFirewall un = do return ["test" ] inputCgiOkPage :: String -> [String] -> Html inputCgiOkPage un msgs = body << h1 << ("Un: " ++ un) {-- cgiMain :: CGI CGIResult cgiMain = do maybeUn <- getInput "un" do msgs <-runRefreshFirewall (fromJust maybeUn) output $ renderHtml $ (inputCgiOkPage (fromJust maybeUn) msgs) --} cgiMain :: CGI CGIResult cgiMain = (getInput "un") >>= \maybeUn -> (runRefreshFirewall (fromJust maybeUn) >>= \msgs -> (output $ renderHtml $ inputCgiOkPage (fromJust maybeUn) msgs)) main :: IO () main = runCGI $ handleErrors cgiMain Van: Beginners [mailto:beginners-bounces@haskell.org] Namens Kim-Ee Yeoh Verzonden: maandag 14 oktober 2013 14:58 Aan: The Haskell-Beginners Mailing List - Discussion of primarily beginner-level topics related to Haskell Onderwerp: Re: [Haskell-beginners] monads do not fit together? On Mon, Oct 14, 2013 at 6:51 PM, Kees Bleijenberg wrote: The error at the problem line is: parse error on input `<-' If I move the line above the 'if' I get: Couldn't match expected type `CGIT IO t0' with actual type `IO [String]'. Looks like you're missing a "do". You're writing code like this: if blah then x <- foo bar x else quux when you need to write if blah then do x <- foo bar x else quux Recommended exercises: * can you see in your mind's eye the desugaring of do-syntax? * how would you write it in a single line, i.e. without using indentation a.k.a. "layout" -- hint: look up curly braces -- Kim-Ee