[Haskell-cafe] Strange behaviour with writeFile

Hi, I am observing some rather strange behaviour with writeFile. Say I have the following code: answer <- AbstractIO.readFile "filename" let (answer2, remainder) = parseAnswer answer if remainder == "" && answer2 == "" then do AbstractIO.putStrLn $ "completed" else do AbstractIO.putStrLn answer2 AbstractIO.writeFile "filename" remainder With the above I get an error saying the resources to "filename" are locked. If I add the line "AbstractIO.putStrLn $ show (answer2, remainder) before I call writeFile it suddenly magically works! Has anyone seen strange behaviour like this before? Regards, Chris.