#console
sudo gem install ruby_parser

#irb
require 'rubygems' ; require 'ruby_parser' ; require 'pp'

pp RubyParser.new.parse "class C
                           def meth(arg)
                             arg * 2
                           end
                         end"

#=> 
s(:class,
 :C,
 nil,
 s(:scope,
  s(:defn,
   :meth,
   s(:args, :arg),
   s(:scope,
    s(:block,
     s(:return, s(:call, s(:lvar, :arg), :*, s(:arglist, s(:lit, 2)))))))))