[xmonad] multi-head bindings

[Brian Lewis]

I have two monitors, left and right, and workspaces 1-6.

I'd like to configure xmonad so that when I go to workspace 1, I see
workspace 1 on the left, focused, and workspace 2 on the right.

When I go to workspace 2, I'd like to see workspace 1 on the left, and
workspace 2 on the right, focused.

When I go to workspace 3, I'd like to see workspace 3 on the left,
focused, and workspace 4 on the right. And so on.

How can I do it? Thank you.