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</o:shapelayout></xml><![endif]--></head><body lang=NL link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Kim,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>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 >>=.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>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?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Kees<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>module Main(<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> main<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>where <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>import Network.CGI<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>import Text.XHtml<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>import Text.XHtml.Transitional<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>import Data.Maybe<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>runRefreshFirewall :: String -> IO [String]<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>runRefreshFirewall un = do<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> return ["test" ] <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>inputCgiOkPage :: String -> [String] -> Html <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>inputCgiOkPage un msgs = body << h1 << ("Un: " ++ un) <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>{--<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>cgiMain :: CGI CGIResult <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>cgiMain = do<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> maybeUn <- getInput "un" <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> do <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> msgs <-runRefreshFirewall (fromJust maybeUn) <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> output $ renderHtml $ (inputCgiOkPage (fromJust maybeUn) msgs)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>--}<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>cgiMain :: CGI CGIResult <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>cgiMain = (getInput "un") >>= \maybeUn -> (runRefreshFirewall (fromJust maybeUn) >>= <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> \msgs -> (output $ renderHtml $ inputCgiOkPage (fromJust maybeUn) msgs))<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>main :: IO ()<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>main = runCGI $ handleErrors cgiMain<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>Van:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Beginners [mailto:beginners-bounces@haskell.org] <b>Namens </b>Kim-Ee Yeoh<br><b>Verzonden:</b> maandag 14 oktober 2013 14:58<br><b>Aan:</b> The Haskell-Beginners Mailing List - Discussion of primarily beginner-level topics related to Haskell<br><b>Onderwerp:</b> Re: [Haskell-beginners] monads do not fit together?<o:p></o:p></span></p></div><p class=MsoNormal><o:p> </o:p></p><div><div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>On Mon, Oct 14, 2013 at 6:51 PM, Kees Bleijenberg <<a href="mailto:k.bleijenberg@lijbrandt.nl" target="_blank">k.bleijenberg@lijbrandt.nl</a>> wrote:<o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>The error at the problem line is: parse error on input `<-' <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>If I move the line above the ’if’ I get: Couldn't match expected type `CGIT IO t0' with actual type `IO [String]'. <o:p></o:p></p></div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-bottom:12.0pt'>Looks like you're missing a "do". You're writing code like this:<o:p></o:p></p></div><div><p class=MsoNormal>if blah then<o:p></o:p></p></div><div><p class=MsoNormal> x <- foo<o:p></o:p></p></div><div><p class=MsoNormal> bar x<o:p></o:p></p></div><div><p class=MsoNormal>else<o:p></o:p></p></div><div><p class=MsoNormal style='margin-bottom:12.0pt'> quux<br><br>when you need to write<o:p></o:p></p></div><div><div><p class=MsoNormal>if blah then do<o:p></o:p></p></div><div><p class=MsoNormal> x <- foo<o:p></o:p></p></div><div><p class=MsoNormal> bar x<o:p></o:p></p></div><div><p class=MsoNormal>else<o:p></o:p></p></div><p class=MsoNormal> quux<o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Recommended exercises:<o:p></o:p></p></div><div><p class=MsoNormal><br>* can you see in your mind's eye the desugaring of do-syntax?<o:p></o:p></p></div><div><p class=MsoNormal><br>* how would you write it in a single line, i.e. without using indentation a.k.a. "layout" -- hint: look up curly braces<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>-- Kim-Ee<o:p></o:p></p></div></div></div></div></body></html>