Fix -Wnoncanonical-monoid-instances warnings

XMonad/Hooks/FadeWindows.hs

@@ -138,13 +138,12 @@ import           Graphics.X11.Xlib.Extras                (Event(..))
 -- to make it obay the monoid laws
 data Opacity = Opacity Rational | OEmpty
 
+instance Semigroup Opacity where
+  r <> OEmpty = r
+  _ <> r      = r
+
 instance Monoid Opacity where
   mempty                  = OEmpty
-  r      `mappend` OEmpty = r
-  _      `mappend` r      = r
-
-instance Semigroup Opacity where
-  (<>) = mappend
 
 -- | A FadeHook is similar to a ManageHook, but records window opacity.
 type FadeHook = Query Opacity

XMonad/Hooks/Focus.hs

@@ -373,7 +373,6 @@ instance Semigroup a => Semigroup (FocusQuery a) where
     (<>)            = liftM2 (<>)
 instance Monoid a => Monoid (FocusQuery a) where
     mempty          = return mempty
-    mappend         = (<>)
 
 runFocusQuery :: FocusQuery a -> Focus -> Query a
 runFocusQuery (FocusQuery m)    = runReaderT m

XMonad/Hooks/WallpaperSetter.hs

@@ -74,13 +74,12 @@ data Wallpaper = WallpaperFix FilePath -- ^ Single, fixed wallpaper
 newtype WallpaperList = WallpaperList [(WorkspaceId, Wallpaper)]
   deriving (Show,Read)
 
-instance Monoid WallpaperList where
-  mempty = WallpaperList []
-  mappend (WallpaperList w1) (WallpaperList w2) =
+instance Semigroup WallpaperList where
+  WallpaperList w1 <> WallpaperList w2 =
     WallpaperList $ M.toList $ M.fromList w2 `M.union` M.fromList w1
 
-instance Semigroup WallpaperList where
-  (<>) = mappend
+instance Monoid WallpaperList where
+  mempty = WallpaperList []
 
 -- | Complete wallpaper configuration passed to the hook
 data WallpaperConf = WallpaperConf {