Oh this brings a lot of memories. I remember writing a DSL for visualization of logs that we collected when we were working in a hyper local geographical search engine. I was fresh out of college and this was when Google maps had yet to penetrate my country.

I started out with pylex, yacc and then what was supposed to be a quite simple DSL with a few keywords and a few nodes, very quickly exploded to a very complicated endeavor. Alas, I'll never be able to prove that it was Turing Complete. But that doesn't stop me from believing it.