-----------------------------------------------------------------------------
-- |
-- 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, and support routines.
--
module W where
import Control.Monad.State
import System.IO
import Graphics.X11.Xlib (Display,Window)
-- | WState, the window manager state.
-- Just the display, width, height and a window list
data WState = WState
{ display :: Display
, screenWidth :: !Int
, screenHeight :: !Int
, windows :: !Windows
}
--
-- Multithreaded issues:
--
-- We'll want a status bar, it will probably read from stdin
-- but will thus need to run in its own thread, and modify its status
-- bar window
--
type Windows = [Window]
-- | The W monad, a StateT transformer over IO encapuslating the window
-- manager state
newtype W a = W { unW :: StateT WState IO a }
deriving (Functor, Monad, MonadIO, MonadState WState)
-- | Run the W monad, given a chunk of W monad code, and an initial state
-- Return the result, and final state
runW :: WState -> W a -> IO (a, WState)
runW st a = runStateT (unW a) st
-- | 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. Logs a string to stderr. The result may
-- be found in your .xsession-errors file
trace :: String -> W ()
trace msg = io $ do
hPutStrLn stderr msg
hFlush stderr
-- ---------------------------------------------------------------------
-- Getting at the window manager state
-- | Modify the current window list
modifyWindows :: (Windows -> Windows) -> W ()
modifyWindows f = modify $ \s -> s {windows = f (windows s)}
-- ---------------------------------------------------------------------
-- Generic utilities
-- | Run an action forever
forever :: (Monad m) => m a -> m b
forever a = a >> forever a
-- | Rotate a list by 'n' elements.
--
-- for xs = [5..8] ++ [1..4]
--
-- rotate 0
-- [5,6,7,8,1,2,3,4]
--
-- rotate 1
-- [6,7,8,1,2,3,4,5]
--
-- rotate (-1)
-- [4,5,6,7,8,1,2,3]
--
rotate n xs = take l . drop offset . cycle $ xs
where
l = length xs
offset | n < 0 = l + n
| otherwise = n
