Two popular parser generators have or will have ruby support: ANTLR 3.0 (still in alpha and likely to remain so for another year or two) will have ruby support too apparently: http://split-s.blogspot.com/2005/12/antlr-for-ruby.html They are even working on an antlr 3.0 grammar for ruby itself: http://rubyforge.org/projects/rubygrammar Also (not in alpha), there is a ruby version of Coco: http://www.ssw.uni-linz.ac.at/Research/Projects/Coco/ http://www.zenspider.com/ZSS/Products/CocoR/ http://rubyforge.org/projects/coco-ruby/