I started building something similar a while back called music compojure. Anyone who is interested in algorithmic composition in Clojure may wish to look at the notation I came up with for comparison (see the examples directory on github). Though not perfect, it's very flexible and I'm quite pleased with some of the ideas in it. The code is perhaps maybe nearly useful. It produces midi files.

https://github.com/mhowlett/music-compojure