Wm -> W, all good monads have single capital letter names. comment the W.hs file

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+-----------------------------------------------------------------------------
+-- |
+-- Module      :  W.hs
+-- Copyright   :  (c) Spencer Janssen 2007
+-- License     :  BSD3-style (see LICENSE)
+-- 
+-- Maintainer  :  sjanssen@cse.unl.edu
+-- Stability   :  unstable
+-- Portability :  not portable, uses cunning newtype deriving
+--
+-----------------------------------------------------------------------------
+--
+-- The W monad, a state monad transformer over IO, for the window manager state.
+--
+
+module W where
+
+import Data.Sequence
+import Control.Monad.State
+import System.IO (hFlush, hPutStrLn, stderr)
+import Graphics.X11.Xlib
+
+--
+-- | WState, the window manager state.
+-- Just the display, width, height and a window list
+--
+data WState = WState
+    { display       :: Display
+    , screenWidth   :: !Int
+    , screenHeight  :: !Int
+    , windows       :: Seq Window
+    }
+
+-- | The W monad, a StateT transformer over IO encapuslating the window
+-- manager state
+--
+newtype W a = W (StateT WState IO a)
+    deriving (Functor, Monad, MonadIO)
+
+-- | Run the W monad, given a chunk of W monad code, and an initial state
+-- Return the result, and final state
+--
+runW :: W a -> WState -> IO (a, WState)
+runW (W m) = runStateT m
+
+withIO :: (forall b. (a -> IO b) -> IO b) -> (a -> W c) -> W c
+withIO f g = do
+    s <- W get
+    (y, t) <- io (f (flip runW s . g))
+    W (put t)
+    return y
+
+--
+-- | Lift an IO action into the W monad
+--
+io :: IO a -> W a
+io = liftIO
+
+--
+-- | Lift an IO action into the W monad, discarding any result
+--
+io_ :: IO a -> W ()
+io_ f = liftIO f >> return ()
+
+--
+-- | A 'trace' for the W monad
+--
+trace :: String -> W ()
+trace msg = io $ do
+    hPutStrLn stderr msg
+    hFlush stderr
+
+-- ---------------------------------------------------------------------
+-- Getting at the window manager state
+
+-- | Return the current dispaly
+getDisplay          :: W Display
+getDisplay          = W (gets display)
+
+-- | Return the current windows
+getWindows          :: W (Seq Window)
+getWindows          = W (gets windows)
+
+-- | Return the screen width
+getScreenWidth      :: W Int
+getScreenWidth      = W (gets screenWidth)
+
+-- | Return the screen height
+getScreenHeight     :: W Int
+getScreenHeight     = W (gets screenHeight)
+
+-- | Set the current window list
+setWindows          :: Seq Window -> W ()
+setWindows x        = W (modify (\s -> s {windows = x}))
+
+-- | Modify the current window list
+modifyWindows       :: (Seq Window -> Seq Window) -> W ()
+modifyWindows f     = W (modify (\s -> s {windows = f (windows s)}))