make DwmPromote compile

DwmPromote.hs

@@ -8,7 +8,7 @@
 --
 -----------------------------------------------------------------------------
 --
--- Dwm-like promote function for xmonad.
+-- Dwm-like swap function for xmonad.
 --
 -- Swaps focused window with the master window. If focus is in the
 -- master, swap it with the next window in the stack. Focus stays in the
@@ -27,20 +27,13 @@ module XMonadContrib.DwmPromote (dwmpromote) where
 
 import XMonad
 import Operations (windows)
-import StackSet hiding (promote)
+import StackSet hiding (swap)
 import qualified Data.Map as M
 
 dwmpromote :: X ()
-dwmpromote = windows promote
+dwmpromote = windows swap
 
-promote :: (Integral i, Integral j, Ord a) => StackSet i j a -> StackSet i j a
-promote w = maybe w id $ do
-    a <- peek w -- fail if null
-    stack <- index (current w) w
-    let newstack = swap a (next stack a) stack
-    return . raiseFocus (head newstack) $
-        w { stacks = M.adjust (\(f,_) -> (f, newstack)) (current w) (stacks w) }
-  where
-    next s a | head s /= a = head s -- focused is not master
-             | length s > 1 = s !! 1
-             | otherwise = a
+swap :: StackSet i a s -> StackSet i a s
+swap = modify Empty $ \c -> case c of
+    Node t [] (x:rs) -> Node x [] (t:rs)
+    Node t ls rs     -> Node t [] (ys ++ x : rs) where (x:ys) = reverse ls