You can use this module with the following in your ~/.xmonad/xmonad.hs file:

 import XMonad.Actions.CopyWindow

Then add something like this to your keybindings:

 -- 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 x, k), windows $ f i)
     | (i, k) <- zip (workspaces x) [xK_1 ..]
     , (f, m) <- [(W.view, 0), (W.shift, shiftMask), (copy, shiftMask .|. controlMask)]]

To use the above key bindings you need also to import XMonad.StackSet:

 import qualified XMonad.StackSet as W

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 x .|. shiftMask, xK_c     ), kill1) -- @@ Close the focused window

Instead of copying a window from a workset to a workset maybe you don't want to have to remember where you placed it. For that consider:

  , ((modMask x, xK_b    ), runOrCopy "firefox" (className =? "Firefox")) -- @@ run or copy firefox

Another possibility which this extension provides is 'making window always visible' (i.e. always on current workspace), similar to corresponding metacity functionality. This behaviour is emulated through copying given window to all the workspaces and then removing it when it's unneeded on all workspaces any more.

Here is the example of keybindings which provide these actions:

  , ((modMask x, xK_v ), windows copyToAll) -- @@ Make focused window always visible
  , ((modMask x .|. shiftMask, xK_v ),  killAllOtherCopies) -- @@ Toggle window state back

For detailed instructions on editing your key bindings, see XMonad.Doc.Extending.

Kill all other copies of focused window (if they're present) 'All other' means here 'copies, which are not on current workspace'

TODO: Call this function after copyToAll?

Remove the focused 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)