# File lib/chef/run_list/versioned_recipe_list.rb, line 32
      def add_recipe(name, version=nil)
        if version && @versions.has_key?(name)
          unless Chef::Version.new(@versions[name]) == Chef::Version.new(version)
            raise Chef::Exceptions::CookbookVersionConflict, "Run list requires #{name} at versions #{@versions[name]} and #{version}"
          end
        end
        @versions[name] = version if version
        self << name unless self.include?(name)
      end