Lint some pieces of code

Closes: https://github.com/xmonad/xmonad/pull/401

src/XMonad/Config.hs

@@ -218,7 +218,7 @@ keys conf@(XConfig {XMonad.modMask = modMask}) = M.fromList $
     , ((modMask              , xK_period), sendMessage (IncMasterN (-1))) -- %! Deincrement the number of windows in the master area
 
     -- quit, or restart
-    , ((modMask .|. shiftMask, xK_q     ), io (exitWith ExitSuccess)) -- %! Quit xmonad
+    , ((modMask .|. shiftMask, xK_q     ), io exitSuccess) -- %! Quit xmonad
     , ((modMask              , xK_q     ), spawn "if type xmonad; then xmonad --recompile && xmonad --restart; else xmessage xmonad not in \\$PATH: \"$PATH\"; fi") -- %! Restart xmonad
 
     , ((modMask .|. shiftMask, xK_slash ), helpCommand) -- %! Run xmessage with a summary of the default keybindings (useful for beginners)

src/XMonad/Core.hs

@@ -41,11 +41,11 @@ import Control.Applicative ((<|>), empty)
 import Control.Monad.Fail
 import Control.Monad.State
 import Control.Monad.Reader
+import Control.Monad (void)
 import Data.Semigroup
 import Data.Traversable (for)
 import Data.Time.Clock (UTCTime)
 import Data.Default.Class
-import Data.List (isInfixOf)
 import System.FilePath
 import System.IO
 import System.Info
@@ -60,7 +60,7 @@ import System.Exit
 import Graphics.X11.Xlib
 import Graphics.X11.Xlib.Extras (getWindowAttributes, WindowAttributes, Event)
 import Data.Typeable
-import Data.List ((\\))
+import Data.List (isInfixOf, (\\))
 import Data.Maybe (isJust,fromMaybe)
 
 import qualified Data.Map as M
@@ -431,7 +431,7 @@ catchIO f = io (f `E.catch` \(SomeException e) -> hPrint stderr e >> hFlush stde
 --
 -- Note this function assumes your locale uses utf8.
 spawn :: MonadIO m => String -> m ()
-spawn x = spawnPID x >> return ()
+spawn x = void $ spawnPID x
 
 -- | Like 'spawn', but returns the 'ProcessID' of the launched application
 spawnPID :: MonadIO m => String -> m ProcessID

src/XMonad/Layout.hs

@@ -39,7 +39,7 @@ import Data.Maybe (fromMaybe)
 data Resize     = Shrink | Expand
 
 -- | Increase the number of clients in the master pane.
-data IncMasterN = IncMasterN !Int
+newtype IncMasterN = IncMasterN Int
 
 instance Message Resize
 instance Message IncMasterN
@@ -199,8 +199,8 @@ choose (Choose d l r) d' ml      mr = f lr
                     (CL, CR) -> (hide l'  , return r')
                     (CR, CL) -> (return l', hide r'  )
                     (_ , _ ) -> (return l', return r')
-    f (x,y)  = fmap Just $ liftM2 (Choose d') x y
-    hide x   = fmap (fromMaybe x) $ handle x Hide
+    f (x,y)  = Just <$> liftM2 (Choose d') x y
+    hide x   = fromMaybe x <$> handle x Hide
 
 instance (LayoutClass l a, LayoutClass r a) => LayoutClass (Choose l r) a where
     runLayout (W.Workspace i (Choose CL l r) ms) =

src/XMonad/Main.hs

@@ -87,14 +87,14 @@ usage :: IO ()
 usage = do
     self <- getProgName
     putStr . unlines $
-        concat ["Usage: ", self, " [OPTION]"] :
-        "Options:" :
-        "  --help                       Print this message" :
-        "  --version                    Print the version number" :
-        "  --recompile                  Recompile your xmonad.hs" :
-        "  --replace                    Replace the running window manager with xmonad" :
-        "  --restart                    Request a running xmonad process to restart" :
-        []
+        [ "Usage: " <> self <> " [OPTION]"
+        , "Options:"
+        , "  --help                       Print this message"
+        , "  --version                    Print the version number"
+        , "  --recompile                  Recompile your xmonad.hs"
+        , "  --replace                    Replace the running window manager with xmonad"
+        , "  --restart                    Request a running xmonad process to restart"
+        ]
 
 -- | Build the xmonad configuration file with ghc, then execute it.
 -- If there are no errors, this function does not return.  An
@@ -330,7 +330,7 @@ handle e@(DestroyWindowEvent {ev_window = w}) = do
 -- it is synthetic or we are not expecting an unmap notification from a window.
 handle (UnmapEvent {ev_window = w, ev_send_event = synthetic}) = whenX (isClient w) $ do
     e <- gets (fromMaybe 0 . M.lookup w . waitingUnmap)
-    if (synthetic || e == 0)
+    if synthetic || e == 0
         then unmanage w
         else modify (\s -> s { waitingUnmap = M.update mpred w (waitingUnmap s) })
  where mpred 1 = Nothing
@@ -428,7 +428,7 @@ handle event@(PropertyEvent { ev_event_type = t, ev_atom = a })
 
 handle e@ClientMessageEvent { ev_message_type = mt } = do
     a <- getAtom "XMONAD_RESTART"
-    if (mt == a)
+    if mt == a
         then restart "xmonad" True
         else broadcastMessage e
 

src/XMonad/ManageHook.hs

@@ -65,7 +65,7 @@ infixr 3 <&&>, <||>
 
 -- | '||' lifted to a 'Monad'.
 (<||>) :: Monad m => m Bool -> m Bool -> m Bool
-(<||>) x y = ifM x (pure True) y
+(<||>) x = ifM x (pure True)
 
 -- | If-then-else lifted to a 'Monad'.
 ifM :: Monad m => m Bool -> m a -> m a -> m a
@@ -98,7 +98,7 @@ className = ask >>= (\w -> liftX $ withDisplay $ \d -> fmap resClass $ io $ getC
 -- | A query that can return an arbitrary X property of type 'String',
 --   identified by name.
 stringProperty :: String -> Query String
-stringProperty p = ask >>= (\w -> liftX $ withDisplay $ \d -> fmap (fromMaybe "") $ getStringProperty d w p)
+stringProperty p = ask >>= (\w -> liftX $ withDisplay $ \d -> fromMaybe "" <$> getStringProperty d w p)
 
 getStringProperty :: Display -> Window -> String -> X (Maybe String)
 getStringProperty d w p = do

src/XMonad/Operations.hs

@@ -66,6 +66,7 @@ import qualified Data.Set as S
 import Control.Arrow (second)
 import Control.Monad.Reader
 import Control.Monad.State
+import Control.Monad (void)
 import qualified Control.Exception as C
 
 import System.IO
@@ -136,7 +137,7 @@ killWindow w = withDisplay $ \d -> do
                 setEventType ev clientMessage
                 setClientMessageEvent ev w wmprot 32 wmdelt currentTime
                 sendEvent d w False noEventMask ev
-        else killClient d w >> return ()
+        else void (killClient d w)
 
 -- | Kill the currently focused client.
 kill :: X ()
@@ -417,7 +418,7 @@ setFocusX w = withWindowSet $ \ws -> do
     currevt <- asks currentEvent
     let inputHintSet = wmh_flags hints `testBit` inputHintBit
 
-    when ((inputHintSet && wmh_input hints) || (not inputHintSet)) $
+    when (inputHintSet && wmh_input hints || not inputHintSet) $
       io $ do setInputFocus dpy w revertToPointerRoot 0
     when (wmtf `elem` protocols) $
       io $ allocaXEvent $ \ev -> do
@@ -425,7 +426,7 @@ setFocusX w = withWindowSet $ \ws -> do
         setClientMessageEvent ev w wmprot 32 wmtf $ maybe currentTime event_time currevt
         sendEvent dpy w False noEventMask ev
         where event_time ev =
-                if (ev_event_type ev) `elem` timedEvents then
+                if ev_event_type ev `elem` timedEvents then
                   ev_time ev
                 else
                   currentTime
@@ -515,7 +516,7 @@ cleanMask km = do
 -- | Get the 'Pixel' value for a named color.
 initColor :: Display -> String -> IO (Maybe Pixel)
 initColor dpy c = C.handle (\(C.SomeException _) -> return Nothing) $
-    (Just . color_pixel . fst) <$> allocNamedColor dpy colormap c
+    Just . color_pixel . fst <$> allocNamedColor dpy colormap c
     where colormap = defaultColormap dpy (defaultScreen dpy)
 
 ------------------------------------------------------------------------
@@ -535,7 +536,7 @@ writeStateToFile = do
         maybeShow _ = Nothing
 
         wsData   = W.mapLayout show . windowset
-        extState = catMaybes . map maybeShow . M.toList . extensibleState
+        extState = mapMaybe maybeShow . M.toList . extensibleState
 
     path <- asks $ stateFileName . directories
     stateData <- gets (\s -> StateFile (wsData s) (extState s))
@@ -598,7 +599,7 @@ floatLocation w =
     catchX go $ do
       -- Fallback solution if `go' fails.  Which it might, since it
       -- calls `getWindowAttributes'.
-      sc <- W.current <$> gets windowset
+      sc <- gets $ W.current . windowset
       return (W.screen sc, W.RationalRect 0 0 1 1)
 
   where fi x = fromIntegral x

src/XMonad/StackSet.hs

@@ -240,7 +240,7 @@ view i s
 
     | otherwise = s -- not a member of the stackset
 
-  where equating f = \x y -> f x == f y
+  where equating f x y = f x == f y
 
     -- 'Catch'ing this might be hard. Relies on monotonically increasing
     -- workspace tags defined in 'new'