On Tue, May 20, 2008 at 09:15:57AM +0100, Yann Golanski wrote:
1- Get a list out of a file: I managed to do that using the following:
parseImageFile :: FilePath -> IO [String] parseImageFile file = do inpStr <- readFile file return $ filter (/="") (breaks (=='\n') inpStr)
Note that there is a standard function "lines" which splits a string into lines.
Nice, simple and I understand what it is doing.
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.
Any pointers as to how to do that?
import System.Random removeRandomElement :: [a] -> IO (a, [a]) removeRandomElement l = do i <- randomRIO (0, length l - 1) return (removeAt i l) where removeAt is from problem 20 above. And you use it like anything else in the IO monad: do ... images <- parseImageFile ... ... (chosen, rest) <- removeRandomElement images ...
3- Wait and do something later.... How, I have no idea how to do that! Help?
Control.Concurrent.threadDelay is the simplest way to make a thread sleep for a while. However, if you're using some GUI library, you may want to use the library's own timers.
4- I guess that progress bars and updating text will be somewhere in the GUI (I chose wxHaskell)... Again, no idea where.
I'm not familiar with wxHaskell, sorry.
5- How do you call an external program in Haskell? Either xv or Esetroot will do the job of displaying the image. Is there a Haskell native way to do that?
There is a direct X11 library for Haskell, but you're probably better off just calling an external program. See the System.Process module. Hope this helps. Lauri