Reduce head usage

XMonad/Actions/CycleSelectedLayouts.hs

@@ -39,8 +39,9 @@ cycleToNext lst a = do
 -- | If the current layout is in the list, cycle to the next layout. Otherwise,
 --   apply the first layout from list.
 cycleThroughLayouts :: [String] -> X ()
-cycleThroughLayouts lst = do
+cycleThroughLayouts []         = pure ()
+cycleThroughLayouts lst@(x: _) = do
     winset <- gets windowset
     let ld = description . S.layout . S.workspace . S.current $ winset
-    let newld = fromMaybe (head lst) (cycleToNext lst ld)
+    let newld = fromMaybe x (cycleToNext lst ld)
     sendMessage $ JumpToLayout newld

XMonad/Actions/OnScreen.hs

@@ -27,7 +27,7 @@ module XMonad.Actions.OnScreen (
     ) where
 
 import XMonad
-import XMonad.Prelude (fromMaybe, guard)
+import XMonad.Prelude (fromMaybe, guard, empty)
 import XMonad.StackSet hiding (new)
 
 
@@ -140,10 +140,9 @@ toggleOrView' f i st = fromMaybe (f i st) $ do
     let st' = hidden st
     -- make sure we actually have to do something
     guard $ i == (tag . workspace $ current st)
-    guard $ not (null st')
-    -- finally, toggle!
-    return $ f (tag . head $ st') st
-
+    case st' of
+      []      -> empty
+      (h : _) -> return $ f (tag h) st  -- finally, toggle!
 
 -- $usage
 --

XMonad/Hooks/CurrentWorkspaceOnTop.hs

@@ -22,11 +22,12 @@ module XMonad.Hooks.CurrentWorkspaceOnTop (
     currentWorkspaceOnTop
     ) where
 
+import qualified Data.List.NonEmpty as NE (nonEmpty)
+import qualified Data.Map as M
 import XMonad
+import XMonad.Prelude (NonEmpty ((:|)), when)
 import qualified XMonad.StackSet as S
 import qualified XMonad.Util.ExtensibleState as XS
-import XMonad.Prelude (unless, when)
-import qualified Data.Map as M
 
 -- $usage
 -- You can use this module with the following in your @~\/.xmonad\/xmonad.hs@:
@@ -63,7 +64,9 @@ currentWorkspaceOnTop = withDisplay $ \d -> do
             wins = fltWins ++ map fst rs  -- order: first all floating windows, then the order the layout returned
         -- end of reimplementation
 
-        unless (null wins) $ do
-            io $ raiseWindow d (head wins)  -- raise first window of current workspace to the very top,
-            io $ restackWindows d wins      -- then use restackWindows to let all other windows from the workspace follow
+        case NE.nonEmpty wins of
+            Nothing         -> pure ()
+            Just (w :| ws') -> do
+                io $ raiseWindow d w            -- raise first window of current workspace to the very top,
+                io $ restackWindows d (w : ws') -- then use restackWindows to let all other windows from the workspace follow
         XS.put(CWOTS curTag)

XMonad/Hooks/InsertPosition.hs

@@ -82,5 +82,7 @@ insertDown :: (Eq a) => a -> W.StackSet i l a s sd -> W.StackSet i l a s sd
 insertDown w = W.swapDown . W.insertUp w
 
 focusLast' ::  W.Stack a -> W.Stack a
-focusLast' st = let ws = W.integrate st
-    in W.Stack (last ws) (drop 1 $ reverse ws) []
+focusLast' st =
+  case reverse (W.integrate st) of
+    []       -> st
+    (l : ws) -> W.Stack l ws []

XMonad/Hooks/StatusBar/PP.hs

@@ -401,7 +401,7 @@ dzenStrip = strip [] where
     strip keep x
       | null x              = keep
       | "^^" `isPrefixOf` x = strip (keep ++ "^") (drop 2 x)
-      | '^' == head x       = strip keep (drop 1 . dropWhile (/= ')') $ x)
+      | "^"  `isPrefixOf` x = strip keep (drop 1 . dropWhile (/= ')') $ x)
       | otherwise           = let (good,x') = span (/= '^') x
                               in strip (keep ++ good) x'
 

XMonad/Hooks/WallpaperSetter.hs

@@ -140,7 +140,7 @@ getPicPath conf (WallpaperDir dir) = do
   direxists <- doesDirectoryExist $ wallpaperBaseDir conf </> dir
   if direxists
     then do files <- getDirectoryContents $ wallpaperBaseDir conf </> dir
-            let files' = filter ((/='.').head) files
+            let files' = filter (not . ("." `isPrefixOf`)) files
             file <- pickFrom files'
             return $ Just $ wallpaperBaseDir conf </> dir </> file
     else return Nothing

XMonad/Hooks/WorkspaceHistory.hs

@@ -34,7 +34,7 @@ import Control.DeepSeq
 import Prelude
 import XMonad
 import XMonad.StackSet hiding (delete, filter, new)
-import XMonad.Prelude (delete, find, foldl', groupBy, nub, sortBy)
+import XMonad.Prelude (delete, find, foldl', groupBy, nub, sortBy, listToMaybe)
 import qualified XMonad.Util.ExtensibleState as XS
 
 -- $usage
@@ -90,7 +90,7 @@ workspaceHistoryWithScreen = XS.gets history
 
 workspaceHistoryByScreen :: X [(ScreenId, [WorkspaceId])]
 workspaceHistoryByScreen =
-  map (\wss -> (fst $ head wss, map snd wss)) .
+  map (\wss -> (maybe 0 fst (listToMaybe wss), map snd wss)) .
   groupBy (\a b -> fst a == fst b) .
   sortBy (\a b -> compare (fst a) $ fst b)<$>
   workspaceHistoryWithScreen

XMonad/Layout/CenteredMaster.hs

@@ -80,11 +80,9 @@ applyPosition :: (LayoutClass l a, Eq a) =>
 applyPosition pos wksp rect = do
   let stack = W.stack wksp
   let ws = W.integrate' stack
-  if null ws then
-     runLayout wksp rect
-     else do
-       let firstW = head ws
-       let other  = drop 1 ws
+  case ws of
+    []               -> runLayout wksp rect
+    (firstW : other) -> do
        let filtStack = stack >>= W.filter (firstW /=)
        wrs <- runLayout (wksp {W.stack = filtStack}) rect
        return $ first ((firstW, place pos other rect) :) wrs

XMonad/Layout/Combo.hs

@@ -91,7 +91,7 @@ instance (LayoutClass l (), LayoutClass l1 a, LayoutClass l2 a, Read a, Show a,
                                          handleMessage super (SomeMessage ReleaseResources)
                                return ([(w,rinput)], Just $ C2 [w] [w] super' l1' l2')
               arrange origws =
-                  do let w2' = case origws `intersect` w2 of [] -> [head origws]
+                  do let w2' = case origws `intersect` w2 of [] -> take 1 origws
                                                              [x] -> [x]
                                                              x -> case origws \\ x of
                                                                   [] -> init x

XMonad/Prompt/Shell.hs

@@ -197,7 +197,7 @@ getCommands = do
     p  <- getEnv "PATH" `E.catch` econst []
     let ds = filter (/= "") $ split ':' p
     es <- forM ds $ \d -> getDirectoryContents d `E.catch` econst []
-    return . uniqSort . filter ((/= '.') . head) . concat $ es
+    return . uniqSort . filter (not . ("." `isPrefixOf`)) . concat $ es
 
 split :: Eq a => a -> [a] -> [[a]]
 split _ [] = []