[xmonad] How to swap screen in a multihead environment?

[Felix Bou]

I have just started to use xmonad, and it seems to me a great software
for multihead screens.

At his moment, I am using two physical screens and I would like to use
a key binding to do the following thing: "swap screens".

By swap screens I mean moving from
  -the configuration [1 2] to the configuration [2 1]
  -the configuration [1 3] to the configuration [3 1]
  -the configuration [4 2] to the configuration [2 4]
etc
When I say configuration [1 2] I mean that workspace 1 is on left
screen and workspace2 in on right screen; and the same idea for [2 1],
[1 3], etc

Does anybody know how to do this?