ruby_parser (RP) is a ruby parser written in pure ruby (utilizing racc--which does by default use a C extension). RP's output is the same as ParseTree's output: s-expressions using ruby's arrays and base types. As an example: def conditional1 arg1 return 1 if arg1 == 0 return 0 end becomes: s(:defn, :conditional1, s(:args, :arg1), s(:if, s(:call, s(:lvar, :arg1), :==, s(:lit, 0)), s(:return, s(:lit, 1)), nil), s(:return, s(:lit, 0))) Tested against 801,039 files from the latest of all rubygems (as of 2013-05): * 1.8 parser is at 99.9739% accuracy, 3.651 sigma * 1.9 parser is at 99.9940% accuracy, 4.013 sigma * 2.0 parser is at 99.9939% accuracy, 4.008 sigma