[xmonad] Trying to code jump-or-execute

I'm a former sawfish user, and I used to have this really awesome keyboard shortcut called "jump-or-exec". I would press for example Super+F, and if Firefox was not running, it would be executed, and if it was already running, then it would be given focus. I had similar shortcuts for emacs, terminals, etc. I'm a bit of a haskell newb -- I can tell that I can simply use 'spawn' to launch a process, and if I had a list of current windows I would know how to iterate through them and find out whether one currently exists, but I don't know how to get such a list. Ideally I'd like to be able to match against window title or class. Is there a way to do this with xmonad?