[xmonad] Module for evaluating Haskell expressions in xmonad

[Daniel Schoepe]

I wrote a module that uses hint[1] to manipulate the state of xmonad
using normal Haskell expressions during runtime(like emacs' eval
feature), which is available here:
http://code.haskell.org/~asgaroth/xmonad-eval
I've put this in a separate package instead of using a contrib-module,
since that'd introduce hint as another dependency which should be
avoided, if someone doesn't want that feature and it should be a simpler
solution for the user than to add another flag to xmonad-contrib.cabal.

The expressions are typechecked and can return an result whose type is
an instance of Show(The expressions to be interpreted have to be
monomorphic and this approach seems better than having the user supply a
type witness or such all the time). The error handler and the
module/imports context of the expressions can be customized. It might be
possible to somehow wreck xmonad by some expressions, but only to that
extent to which it is already possible in xmonad.hs.
Anyhow, I'm not sure whether this could cause any other instabilities,
so any comments on that would be appreciated. After that I will prepare
a package and upload it to hackage for easier installation.

[1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hint