gistfile1.rb

require 'rubygems'
require 'parse_tree'
require 'ruby2ruby'
require 'sexp_processor'
require 'ruby_parser'

class Codes
  def super_awesome
    foo = 10
    foo + 10 * 20
  end
end

class RubyMutator < SexpProcessor
  def rewrite_lvar exp
    s(:call, exp, :+, s(:lit, 42))
  end
end

codes = ParseTree.new.parse_tree(Codes)
puts Ruby2Ruby.new.process(RubyMutator.new.process(codes.first))