[xmonad] Automatic switch to external monitor?

Hey all, I have a dock at work where I plop my laptop each day; used to be that as soon as I woke it, it would switch to using the external monitor only and never turn on the laptop screen. Now it turns on both even though the laptop is closed, and it takes me opening it and running my "dock" script (uses xrandr to turn off laptop display and enable external), shutting the laptop (which sleeps it), then waking it again. Quite irritating! Until recently this seemed to be automatic for me, but since switching monitors it isn't. I'm sure there's some way to do this via ACPI or whatever, but I'm not familiar enough with it to know. Basically i need an action for "docked" that will try running "dock on" and see what happens. Any thoughts?