[Haskell-cafe] Using catch and errors

[Alexandre Weffort Thenorio]

I am trying to get catch to work but I guess I am total newbie on this one.

main :: IO()
main =  do
  removeFile "./newint.hex"
  hexFile <- catch (readFile int.hex)  (\_ -> do putStrLn "Cannot find
int.hex"
        getLine --Simply stop program so user can read error message
        return() --Quit)
 hexFile <- readFile "int.hex"
--res of program goes here
getLine
return()


But it keeps giving me error on getLine. How can I quit a program in case of
an error giving an error message?

Also I tried something like

main :: IO()
main =  do
            ex <- doesFileExist "./newint.hex"
             if ex then removeFile "./newint.hex"

But that won't work either. Any ideas? I'd like to catch different errors
and quit program giving different error messages

Last but not least I have the function

outputLine keyno key orgFile = do
    let part1 = getLeft keyno (orgFile!!1)
    let part2 = getRight keyno (orgFile!!1)
    let total = part1 ++ (map toUpper key) ++ part2
    let checks = checksum (drop 1 total)
    let final = total ++ checks ++ "\n"
    newHexFile <- openFile "newint.hex" WriteMode
     hPutStrLn newHexFile (orgFile!!0 ++ "\n" ++ final ++ unlines (drop 2
orgFile))

I'd like to be able to check for stuff such as size of key and wheter keyno
is only 1 or 0 and quit program with error message otherwise but again
couldn't quite get catch to work.

Any reading tips about subject would be appreciated.

Best Regards

NooK