Thanks for the tips.
(There's also the obvious syntax error of not quoting the string "int.hex", but I suspect you would have caught that one.)
In fact it was supposed to be there. Just a typo I guess
After the catch, you have another instance of the readFile command you would have just run, which you probably don't want.
Typo :)
It's important that getLine is aligned with putStrLn and the rest of the do block, if you use something like the emacs haskell-mode, you can have your editor align this automatically, or semi-automatically for you.
Sure did the trick by aligning it. Well after getting all the tips from you and the other answers I came up with a working version below: main :: IO() main =do ex <- doesFileExist "./newint.hex" when ex (catch (removeFile "./newint.hex") (\_ -> do putStrLn "Not possible to remove newint.hex, Please close all programs using this file.\nPress RETURN (ENTER) to quit." getLine exitWith ExitSuccess)) hexFile <- catch (readFile "int.hex") (\_ -> do putStrLn "File int.hex not found.\nPress RETURN (ENTER) to quit." getLine exitWith ExitSuccess) putStr "What is the key number (0 or 1)?\n" keyno <- getLine when ((length keyno /= 1) && (keyno /= "1") && (keyno /= "0")) (error "Please input either 0 or 1 as key number") putStr "Input key.\n" key <- getLine newLine <- outputLine keyno key (lines(hexFile)) putStrLn ("newint.hex created with key " ++ key ++ ". Press RETURN (Enter) to quit") getLine return() Now I have one problem (Well 2 really but the second one is just me not having programmed in haskell for so long that I forgot). getLine is used for the sole purpous of stopping the program and allowing the user to read the error message before the window closes but error does not allow me to do that and aparently using a lambda function (As shown below) does not work (It gives error upon compilation when ((length keyno /= 1) && (keyno /= "1") && (keyno /= "0")) (\_ -> putStrLn "Please input either 0 or 1 as key number" getLine exitWith ExitSuccess) So is there anyway to fix that? The second error is that apparenlty (keyno /= "1") and (keyno /= "0") do not work, but I suspect that, like Java, one can't compare strings using = sign or am I wrong?
Check out the wiki: http://www.haskell.org/hawiki/HaskellNewbie -- lots of beginner questions and answers have been accumulated there.
Also, to really understand what's going on with the do-notation, it would be best that you learn what monads are about. I'll direct you at the "All About Monads" tutorial: http://www.nomaware.com/monads/html/ And of course, my own take on them: :) http://www.haskell.org/hawiki/MonadsAsContainers
Mostly appreciated
Hope this helps,
Surelly did. Don't know what I would do without you guys. Best Regards NooK