Simplify duplicate/cloned screen logic

XMonad/Main.hs

@@ -26,7 +26,6 @@ import System.Environment (getArgs)
 
 import Graphics.X11.Xlib hiding (refreshKeyboardMapping)
 import Graphics.X11.Xlib.Extras
-import Graphics.X11.Xinerama    (getScreenInfo)
 
 import XMonad.Core
 import XMonad.StackSet (new, floating, member)
@@ -46,7 +45,7 @@ xmonad initxmc = do
     let dflt = defaultScreen dpy
 
     rootw  <- rootWindow dpy dflt
-    xinesc <- getScreenInfo dpy
+    xinesc <- getCleanedScreenInfo dpy
     nbc    <- initColor dpy $ normalBorderColor xmc
     fbc    <- initColor dpy $ focusedBorderColor xmc
     hSetBuffering stdout NoBuffering

XMonad/Operations.hs

@@ -246,34 +246,35 @@ tileWindow w r = withDisplay $ \d -> do
 
 -- ---------------------------------------------------------------------
 
--- | getCleanedScreenInfo. reads the list of screens and removes
--- duplicated or contained screens.
-getCleanedScreenInfo :: Display -> IO ([(ScreenId, Rectangle)])
-getCleanedScreenInfo dpy = do
-    xinesc' <- getScreenInfo dpy
-    let xinescN' = zip [0..] xinesc'
+-- | Returns True if the first rectangle is contained within, but not equal
+-- to the second.
 containedIn :: Rectangle -> Rectangle -> Bool
-        containedIn (Rectangle x1 y1 w1 h1) (Rectangle x2 y2 w2 h2) =
-                x1 >= x2 &&
-                y1 >= y2 &&
-                fromIntegral x1 + w1 <= fromIntegral x2 + w2 &&
-                fromIntegral y1 + h1 <= fromIntegral y2 + h2
-        -- remove all screens completely contained in another.
-        xinescS' = filter (\(_,r1) -> not (any (\r2 -> r1 `containedIn` r2 && r1 /= r2) xinesc')) xinescN'
-        -- removes all duplicate screens but the first
-        xinesc   = foldr (\r l -> if snd r `elem` map snd l then l else r:l) [] xinescS'
-    return xinesc
+containedIn r1@(Rectangle x1 y1 w1 h1) r2@(Rectangle x2 y2 w2 h2)
+ = and [ r1 /= r2
+       , x1 >= x2
+       , y1 >= y2
+       , fromIntegral x1 + w1 <= fromIntegral x2 + w2
+       , fromIntegral y1 + h1 <= fromIntegral y2 + h2 ]
 
+-- | Given a list of screens, remove all duplicated screens and screens that
+-- are entirely contained within another.
+nubScreens :: [Rectangle] -> [Rectangle]
+nubScreens xs = nub . filter (\x -> not $ any (x `containedIn`) xs) $ xs
+
+-- | Cleans the list of screens according to the rules documented for
+-- nubScreens.
+getCleanedScreenInfo :: MonadIO m => Display -> m [Rectangle]
+getCleanedScreenInfo = io .  fmap nubScreens . getScreenInfo
 
 -- | rescreen.  The screen configuration may have changed (due to
 -- xrandr), update the state and refresh the screen, and reset the gap.
 rescreen :: X ()
 rescreen = do
-    xinesc <- withDisplay (io . getCleanedScreenInfo)
+    xinesc <- withDisplay getCleanedScreenInfo
 
     windows $ \ws@(W.StackSet { W.current = v, W.visible = vs, W.hidden = hs }) ->
         let (xs, ys) = splitAt (length xinesc) $ map W.workspace (v:vs) ++ hs
-            (a:as)   = zipWith3 (\x (n,s) g -> W.Screen x n (SD s g)) xs xinesc gs
+            (a:as)   = zipWith3 W.Screen xs [0..] $ zipWith SD xinesc gs
             sgs      = map (statusGap . W.screenDetail) (v:vs)
             gs       = take (length xinesc) (sgs ++ repeat (0,0,0,0))
         in  ws { W.current = a