The code is here, and the API docs are here. It's not much, but it's enough to make blocking calls to BMPx's volume-control APIs.
Reading the DBUS API docs is very interesting, because it reminds me of how much effort the Cairo folks have put into their API. It's very difficult (I think especially difficult when you're intimate with the code) to figure out the simplest point to delineate library-internal from library-external, and for every function they've added to Cairo there's been a discussion of whether that's the right place for it, what effect it'll have on language bindings, etc., etc. The DBUS docs, by contrast, feel pretty overwhelming and feel somewhat incoherent.
With each project like this I learn something more, which is always the point. The two goals of this one are understanding DBUS better and (obviously) Haskell. So far the most noteworthy piece is how dynamic exceptions work, which I've long wondered about and still don't quite understand. In O'Caml, exceptions are specially handled by the langauge (with an
exnkeyword, as I recall), but in Haskell (of course) it's just some functions and some fancy typing. I'd explain more but I doubt there's even one reader of this who cares. :P