I second that too. I have "obviously" (due to my studies) some experience with TeX, and in particular with LaTeX which are markup languages, but to a large extent less "static" than more common *ML ones. I also tried MetaPost to draw some graphs, and I noticed it has some declarative features, e.g. a point can be defined implicitly in terms of the intersection of two straigh lines. Quite a niche application, but interesting indeed...