That's not just an application for procedural cities, that's Houdini (http://www.sidefx.com/), a relatively well-known 3D modeling, animation and rendering tool based on the node-based (a.k.a. functional) approach. I investigated them, and while I found the tool itself very powerful, its language is not a proper general-purpose functional language, and I don't think it's turing-complete (if you exclude their integrated Python scripting).