[Xmonad] haskell style in x window programming

8 Aug 2007

      Hi,

today I was refreshing my memories about arrows and I thought to
rewrite the minimal example of X selections I've sent a couple of days
ago.

It was written in a strict C style, as Dons observed, so I thought to
rewrite it with a simple Kleisli arrow to force myself to use another
coding paradigm.

It's a mess, and, I think, not only for my personal lack of
programming style. Arguments of functions are disposed in a convenient
way for imperative programming, but when it comes to function
composition it just gets very difficult for me.

I would like to have you suggestions. This could help me improve my
style, and perhaps contribute to introducing the Haskell community to
X programming by making the code we produce within this project more
adherent to the Haskell way of doing things.

Thanks for your kind attention.

Andrea

the code below requires my last patch to X11-extras available here:

http://www.haskell.org/pipermail/xmonad/2007-August/001661.html

module Main where
import Graphics.X11.Xlib
import Graphics.X11.Xlib.Extras
import System.Exit (exitWith, ExitCode(..))

import Data.Maybe
import Data.Char

import Control.Arrow

dpyWin :: Kleisli IO String (Display, Window)
dpyWin = Kleisli openDisplay
      >>>
      arr id &&& arr defaultScreen
      >>>
      arr fst &&& Kleisli (uncurry rootWindow) 
      >>>
      arr fst &&& cw
      where cw = Kleisli (uncurry $ cw' 0 0 200 100 0 0 0)
            cw' x y wh ht back border i d rw = 
                createSimpleWindow d rw x y wh ht back border i            

atoms :: Kleisli IO (Display, Window) ((Display, Window),(Atom, Atom))
atoms = arr id
        &&& 
        (arr fst >>>
         Kleisli (atom "PRIMARY" True)
         &&&
         Kleisli (atom "BLITZ_SEL_STRING" False))
    where atom t b d = internAtom d t b

convertSel :: ((Display, Window),(Atom, Atom)) -> IO ()
convertSel ((d,w),(a,b)) = 
    xConvertSelection d a sTRING b w currentTime

-- ok I'm giving up
getSel :: ((Display, Window), (t, Atom)) -> IO ()
getSel ((d,w),(p,clp)) = do
  allocaXEvent $ \e -> do
    nextEvent d e
    ev <- getEvent e
    if ev_event_type ev == selectionNotify 
       then do res <- getWindowProperty8 d clp w
               putStrLn $ map (chr . fromIntegral)  . fromMaybe [] $ res
       else do putStrLn "Failed!"
  destroyWindow d w

doRun = dpyWin 
        >>> 
        atoms 
        >>>
        Kleisli convertSel &&& Kleisli getSel
        >>> 
        Kleisli (\_ -> exitWith ExitSuccess) 

main :: IO ()
main = runKleisli doRun ""

[Xmonad] haskell style in x window programming

Andrea Rossato