:m + XMonad

$> ghc-pkg list | ack xmonad
    xmonad-0.10.1
    xmonad-contrib-0.10.1
    xmonad-extras-0.10.1.1

$> ghci
GHCi, version 7.6.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.

> :m + XMonad

<no location info>:
    Could not find module `XMonad'
    It is not a module in the current program, or in any known package.