add CopyWindow module, to support sticky/tagged windows.

This module allows dwm-style tagging (as I understand dwm).  You can have a
given window visible in multiple workspaces.  If it's visible in two
workspaces both of which are visible, a gap will show up in one of them
(which is something that needs fixing in xmonad core).  Also defines a
kill1 which is like kill, but only removes from the current workspace a
window if it's in multiple workspaces.

CopyWindow.hs

@@ -0,0 +1,89 @@
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  XMonadContrib.CopyWindow
+-- Copyright   :  (c) David Roundy <droundy@darcs.net>
+-- License     :  BSD3-style (see LICENSE)
+--
+-- Maintainer  :  David Roundy <droundy@darcs.net>
+-- Stability   :  unstable
+-- Portability :  unportable
+--
+-- Provides a binding to duplicate a window on multiple workspaces,
+-- providing dwm-like tagging functionality.
+--
+-----------------------------------------------------------------------------
+
+module XMonadContrib.CopyWindow (
+                                 -- * Usage
+                                 -- $usage
+                                 copy, kill1
+                                ) where
+
+import Prelude hiding ( filter )
+import Control.Monad.State ( gets )
+import qualified Data.List as L
+import XMonad
+import Operations ( windows, kill )
+import StackSet
+
+-- $usage
+-- You can use this module with the following in your Config.hs file:
+-- 
+-- > import XMonadContrib.CopyWindow
+--
+-- > -- mod-[1..9] @@ Switch to workspace N
+-- > -- mod-shift-[1..9] @@ Move client to workspace N
+-- > -- mod-control-shift-[1..9] @@ Copy client to workspace N
+-- > [((m .|. modMask, k), f i)
+-- >     | (i, k) <- zip [0..fromIntegral (workspaces-1)] [xK_1 ..]
+-- >     , (f, m) <- [(view, 0), (shift, shiftMask), (copy, shiftMask .|. controlMask)]]
+--
+-- you may also wish to redefine the binding to kill a window so it only
+-- removes it from the current workspace, if it's present elsewhere:
+--
+-- >  , ((modMask .|. shiftMask, xK_c     ), kill1) -- @@ Close the focused window
+
+-- | copy. Copy a window to a new workspace.
+copy :: WorkspaceId -> X ()
+copy n = windows (copy' n)
+
+copy' :: (Ord a, Eq s, Integral i) => i -> StackSet i a s -> StackSet i a s
+copy' n s = if n `tagMember` s && n /= tag (workspace (current s))
+            then maybe s go (peek s)
+            else s
+    where go w = view (tag (workspace (current s))) $ insertUp' w $ view n s
+
+ 
+-- |
+-- /O(n)/. (Complexity due to check if element is in current stack.) Insert
+-- a new element into the stack, above the currently focused element.
+--
+-- The new element is given focus, and is set as the master window.
+-- The previously focused element is moved down.  The previously
+-- 'master' element is forgotten. (Thus, 'insert' will cause a retiling).
+--
+-- If the element is already in the current stack, it is shifted to the
+-- focus position, as if it had been removed and then added.
+--
+-- Semantics in Huet's paper is that insert doesn't move the cursor.
+-- However, we choose to insert above, and move the focus.
+
+insertUp' :: Eq a => a -> StackSet i a s -> StackSet i a s
+insertUp' a s = modify (Just $ Stack a [] [])
+                (\(Stack t l r) -> Just $ Stack a (L.delete a l) (L.delete a (t:r))) s
+
+delete' :: Ord a => a -> StackSet i a s -> StackSet i a s
+delete' w = sink w . modify Nothing (filter (/= w))
+
+-- | Remove the focussed window from this workspace.  If it's present in no
+-- other workspace, then kill it instead. If we do kill it, we'll get a
+-- delete notify back from X.
+--
+-- There are two ways to delete a window. Either just kill it, or if it
+-- supports the delete protocol, send a delete event (e.g. firefox)
+--
+kill1 :: X ()
+kill1 = do ss <- gets windowset
+           whenJust (peek ss) $ \w -> if member w $ delete' w ss
+                                      then windows $ delete' w
+                                      else kill

MetaModule.hs

@@ -25,6 +25,7 @@ import XMonadContrib.Anneal ()
 import XMonadContrib.Circle ()
 -- TODO commented because it requires hs-boot modifications import XMonadContrib.Commands ()
 import XMonadContrib.Combo ()
+import XMonadContrib.CopyWindow ()
 import XMonadContrib.Decoration ()
 import XMonadContrib.Dmenu ()
 import XMonadContrib.DwmPromote ()