What was that programming language based on creating new grammar rules?
mbrubeck: I've seen a few of these recently...My favorite, OMeta is a pattern/grammar-oriented language (and one of the most interesting papers I read last year).  This comes from Alessandro Warth at VPRI, where Alan Kay and others are doing some really great research: http://tinlizzie.org/ometa/there's the Bondi language and its "pattern calculus": http://lambda-the-ultimate.org/node/3695and the one that's most like you describe is π (Pi): http://www.pi-programming.org/What.html