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 {

XMonad/Layout/Mosaic.hs

@@ -190,14 +190,13 @@ instance Functor Tree where
    fmap f (Branch l r) = Branch (fmap f l) (fmap f r)
    fmap _ Empty = Empty
 
+instance Semigroup (Tree a) where
+    Empty <> x = x
+    x <> Empty = x
+    x <> y = Branch x y
+
 instance Monoid (Tree a) where
     mempty = Empty
-    mappend Empty x = x
-    mappend x Empty = x
-    mappend x y = Branch x y
-
-instance Semigroup (Tree a) where
-    (<>) = mappend
 
 makeTree ::  (Num a1, Ord a1) => (a -> a1) -> [a] -> Tree a
 makeTree _ [] = Empty

XMonad/Util/PureX.hs

@@ -115,7 +115,6 @@ instance Semigroup a => Semigroup (PureX a) where
   (<>) = liftA2 (<>)
 
 instance Monoid a => Monoid (PureX a) where
-  mappend = liftA2 mappend
   mempty  = return mempty
 
 -- | The @XLike@ typeclass over monads reading @XConf@ values and tracking