It's similar to this already. But this isn't flexible enough to implement methods etc which abop expands towards. My goal was to do almost everything all other browser based lsystems are doing while keeping it fast which most tools are not.
you'll probably be pleasantly surprised by how easy it is to write a parser using a parser generator; unfortunately i don't know which one to recommend for js (i've used yacc, ocamlyacc, hammer, and a few i've written myself, but i don't recommend using the js one i wrote)
if you aren't pleasantly surprised, maybe try a different parser generator
