XMonad 0.13

main = do
   ...
    xmproc <- spawnPipe "xmobar ~/.xmonad/xmobar.hs"
...

gaps [(U,20)]

[(U,20)]

main = do

myWorkspaces !! n-1

main = do
         xmproc <- spawnPipe "xmobar"
         xmonad $ defaults {
         logHook =  dynamicLogWithPP $ def {
         ppOutput = System.IO.hPutStrLn xmproc
         , ppTitle = ( \ str -> "")
         , ppCurrent = xmobarColor xmobarCurrentWorkspaceColor "" . wrap "[""]"
         , ppSep = "  "
         , ppWsSep = "  "
         , ppLayout = (\ x -> case x of
            "Spacing 6 Minimize Tall"                 -> "[<icon=circle.xbm/>]"
            "Spacing 6 Minimize Full"                 -> "[<icon=monocle.xbm/>]"
            "Spacing 6 Minimize Mosaic"               -> "[<icon=bstack2.xbm/>]"
            "Spacing 6 Minimize Magnifier Tall"       -> "[<icon=corner_left.xbm/>]"
            _                                         -> x )
  }
 }

main = do
    spawn "feh --bg-center /usr/share/backgrounds/003.jpg"
    xmproc <- spawnPipe "xmobar ~/.xmonad/xmobar.hs"
    xmonad  =<< xmobar def {
    manageHook = myManageHook <+> manageDocks

Morisson
xmonad $ defaults {

s-ugra@ya.ru
А у меня при такой конструкции окна перекрывали бар и пришлось делать гапс.

, ((mod4Mask, xK_b), sendMessage ToggleStruts)

 myLayoutHook = spacing 6 $ avoidStruts
                $ toggleLayouts (noBorders Full)
                $ smartBorders
                $ minimize
                $ tiled ||| mosaic 2 [3,2] ||| Full ||| magnifier (Tall 1 0.3 0.5)
                     where
                     tiled   = Tall nmaster delta ratio
                     nmaster = 1
                     delta   = 0.01
                     ratio   = 0.5

Morisson
mod4Mask, xK_b

, ((0, xK_F11), sendMessage $ ToggleGap U) -- toggle the top gap

s-ugra@ya.ru
Посмотри в ~/.xmonad/xmonad.errors как компилятор ругается)