Lambda the Ultimate

Hi,

I'm trying to find out about languages/papers which deal with modifying the PL's syntax within itself. For example: incorporating EBNF so it can dynamically extend it's grammar. I'm not sure, but I was wondering if this is covered by the term "syntactic abstraction"?

My background is very much imperative languages, but I've done a fair bit with parsers, and I'm learning some Lisp. My web searches have only yielded "Boo" and S-expression langages so far.

Any help gratefully received.