Using partials with builder in Sinatra

builder_partial.rb

module Sinatra
  module BuilderHelper
    def helper_modules
      @helper_mods ||= Sinatra::Application.ancestors.select{|m| m.name =~ /Helper/} 
    end

    def builder_partial(template, xml, locals = {}, helper_mods = nil)
      template = "#{template}.builder" unless "#{template}" =~ /[.]builder$/
      helper_mods ||= self.helper_modules
            
      class << (context = OpenStruct.new({:xml => xml}.merge(locals))); self; end.send(:include, *helper_mods)
            
      File.open(File.join(settings.views, "#{template}")) do |f|
        eval f.read, context.send(:binding)
      end
    end
  end

  helpers BuilderHelper
end