Rather than golfing your questions (which seems popular), I'll try to
give you some concrete answers.
First off, I agree with Bulat that this is probably too large of a
first project; doing it in pieces seems like it would be a lot
simpler. In particular "if the file changes, ..." isn't a requirement
I'd put on the project for a "first attempt". And just getting the
non-GUI version to work is a good start; then you can go about
learning a GUI library, which can be a project all by itself :)
2008/5/20 Yann Golanski
2- Get a random element from a list and remove it: Okay, this I understand less well. I looked at the solutions of problems 23 and 20 in http://www.haskell.org/haskellwiki/99_questions so there is a skeleton there. However, my list is IO [String].... Hum, monads.
There's nothing tricky about that, though (although 'and remove it' is a bit odd from a Haskeller's point of view; you would instead make a new list without that element). Lets break this out into some a function to solve the problem. I'll leave the implementation to you. removeElement :: [String] -> Int -> (String, [String]) This is a pure function, but you are, as you mentioned, inside IO. But that's no problem; in your higher level code (where you call parseImageFile) you should also be inside IO: main = do images <- parseImageFile path -- now, images :: [String] -- simple! you are living inside of IO here, so you can get at the values returned! n <- getRandomNumber (length images) let (image, rest) = removeElement images n changeDesktop image Note the difference between the lines with "<-" and the line with "let"; "x <- m" takes "m :: IO a" and gives you an "x :: a". Whereas "let x = z" takes "z :: a" and gives "x :: a"; it just labels the result of a non-IO call. Now you just have to write the other functions: getRandomNumber :: Int -> IO Int changeDesktop :: String -> IO () path :: String -- not really a function! To loop, you can write an IO action that calls itself as the last element of the "do" statement. -- ryan