[xmonad] Xmonad trashed?

[Matthew]

I'm on arch linux, 64 bit.  I recently auto-upgraded a bunch of packages, and now even the simplest xmonad.hs file fails to compile.
Given this xmonad.hs :

import XMonad
 
main = xmonad defaultConfig
        { modMask = mod4Mask
        , terminal = "lxterminal"
        -- more changes
        }


I get the error:
xmonad.hs:1:7:
      Could not find module Xmonad
      it is not a module in the current program or in any known package.

Apparently  the XMonad module is not in the current ghc path or something.  It's been a while since I've used ghc so I'm not sure how to fix this.