use new StackSet api

Main.hs

@@ -144,7 +144,10 @@ handle e = trace (eventName e)
 -- | refresh. Refresh the currently focused window. Resizes to full
 -- screen and raises the window.
 refresh :: W ()
-refresh = whenJust W.peek $ \w -> withScreen $ \(d,sw,sh) -> io $ do
+refresh = do
+    ws <- gets workspace
+    whenJust (W.peek ws) $ \w ->
+        withScreen $ \(d,sw,sh) -> io $ do
             moveResizeWindow d w 0 0 (fromIntegral sw) (fromIntegral sh) -- fullscreen
             raiseWindow d w
 
@@ -167,7 +170,8 @@ windows f = modifyWorkspace f >> refresh
 -- | manage. Add a new window to be managed in the current workspace. Bring it into focus.
 -- If the window is already under management, it is just raised.
 manage :: Window -> W ()
-manage w = do withDisplay $ \d -> io $ mapWindow d w
+manage w = do
+    withDisplay $ io . flip mapWindow w
     windows $ W.push w
 
 -- | unmanage. A window no longer exists, remove it from the window
@@ -186,25 +190,30 @@ focus = windows . W.rotate
 
 -- | Kill the currently focused client
 kill :: W ()
-kill = withDisplay $ \d -> whenJust W.peek $ io_ . killClient d
+kill = withDisplay $ \d -> do
+    ws <- gets workspace
+    whenJust (W.peek ws) $ io_ . killClient d
 
 -- | tag. Move a window to a new workspace
 tag :: Int -> W ()
 tag o = do
     ws <- gets workspace
-    when (n /= W.cursor ws) $
-        whenJust W.peek $ \w -> do
+    let m = W.current ws
+    when (n /= m) $
+        whenJust (W.peek ws) $ \w -> do
             hide w
             windows $ W.shift n
-    where n = o -1
+    where n = o-1
 
 -- | view. Change the current workspace to workspce at offset 'n-1'.
 view :: Int -> W ()
 view o = do
     ws <- gets workspace
-    when (n /= W.cursor ws) $
-        whenJust (flip W.index n) $ \new -> do
-            mapM_ hide (W.stack ws)
+    let m = W.current ws
+    when (n /= m) $
+        whenJust (W.index n ws) $ \new ->
+        whenJust (W.index m ws) $ \old -> do
+            mapM_ hide   old
             mapM_ reveal new
             windows $ W.view n
     where n = o-1

WMonad.hs

@@ -16,7 +16,7 @@
 
 module WMonad where
 
-import StackSet
+import StackSet (StackSet)
 
 import Control.Monad.State
 import System.IO
@@ -87,11 +87,6 @@ modifyWorkspace f = do
     trace (show ws) -- log state changes to stderr
 
 -- | Run a side effecting action with the current workspace. Like 'when' but
--- for (WorkSpace -> Maybe a).
-whenJust :: (WorkSpace -> Maybe a) -> (a -> W ()) -> W ()
-whenJust mg f = do
-    ws <- gets workspace
-    case mg ws of
-        Nothing -> return ()
-        Just w  -> f w
+whenJust :: Maybe a -> (a -> W ()) -> W ()
+whenJust mg f = maybe (return ()) f mg