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) if arg1 == 0 then return 1 end return 0 end becomes: s(:defn, :conditional1, s(:args, :arg1), s(:scope, s(:block, s(:if, s(:call, s(:lvar, :arg1), :==, s(:arglist, s(:lit, 0))), s(:return, s(:lit, 1)), nil), s(:return, s(:lit, 0)))))