X.U.Loggers: Add logTitlesOnScreen

This works like logTitles, but gets an explicit screen to log the window
titles on.  This may be useful when having status bars for each screen
that show all windows on their respective visible workspaces.

XMonad/Util/Loggers.hs

@@ -36,7 +36,7 @@ module XMonad.Util.Loggers (
     -- * XMonad: Screen-specific Loggers
     -- $xmonad-screen
     , logCurrentOnScreen, logLayoutOnScreen
-    , logTitleOnScreen, logWhenActive
+    , logTitleOnScreen, logWhenActive, logTitlesOnScreen
     -- * Formatting Utilities
     -- $format
     , onLogger
@@ -174,8 +174,8 @@ maildirNew mdir = logFileCount (mdir ++ "/new/") (not . isPrefixOf ".")
 logTitle :: Logger
 logTitle = withWindowSet $ traverse (fmap show . getName) . W.peek
 
--- | Get the titles of all windows on the current workspace and format
--- them according to the given functions.
+-- | Get the titles of all windows on the visible workspace of the given
+-- screen and format them according to the given functions.
 --
 -- ==== __Example__
 --
@@ -188,14 +188,14 @@ logTitle = withWindowSet $ traverse (fmap show . getName) . W.peek
 -- >   formatFocused   = wrap "[" "]" . xmobarColor "#ff79c6" "" . shorten 50 . xmobarStrip
 -- >   formatUnfocused = wrap "(" ")" . xmobarColor "#bd93f9" "" . shorten 30 . xmobarStrip
 --
-logTitles
-  :: (String -> String) -- ^ Formatting for the focused   window
+logTitlesOnScreen
+  :: ScreenId           -- ^ Screen to log the titles on
+  -> (String -> String) -- ^ Formatting for the focused   window
   -> (String -> String) -- ^ Formatting for the unfocused window
   -> Logger
-logTitles formatFoc formatUnfoc = do
-  winset <- gets windowset
-  let focWin = W.peek  winset
-      wins   = W.index winset
+logTitlesOnScreen sid formatFoc formatUnfoc = (`withScreen` sid) $ \screen -> do
+  let focWin = fmap W.focus . W.stack . W.workspace $ screen
+      wins   = maybe [] W.integrate . W.stack . W.workspace $ screen
   winNames <- traverse (fmap show . getName) wins
   pure . Just
        . unwords
@@ -203,6 +203,13 @@ logTitles formatFoc formatUnfoc = do
                  wins
                  winNames
 
+-- | Like 'logTitlesOnScreen', but directly use the "focused" screen
+-- (the one with the currently focused workspace).
+logTitles :: (String -> String) -> (String -> String) -> Logger
+logTitles formatFoc formatUnfoc = do
+  sid <- gets $ W.screen . W.current . windowset
+  logTitlesOnScreen sid formatFoc formatUnfoc
+
 -- | Get the name of the current layout.
 logLayout :: Logger
 logLayout = withWindowSet $ return . Just . ld