I wrote (in summary):
The thing I'm most missing from ratpoison and wmii is an external api, which makes them extensible from external programs (and any language.)
Are there any plans to offer such an interface in Xmonad in the future?
Donald Bruce Stewart
There's the Command.hs interface in the contrib module, used for some of this. At the moment I don't think there's any plan to embed a scripting language directly in xmonad: far better to extend Commands.hs to say, use ghc-api, to allow arbitrary haskell extension if you want it.
I wasn't referring to an embedded scripting language, but a generic API that would allow external scripts to communicate with Xmonad, both to read its state and to issue commands, like ratpoison's and wmii's APIs do. This would open up scripting in any language. Ease of scripting is what I find to be one of the attractions of those languages, and it'd be great to be able to script Xmonad in a language I already know (thought it's also nice to have the excuse to learn Haskell...)