role.rb

  ...
  def self.available_controllers(name)
    roles = Role.all(:name => name, :authorizable_type.not => nil)
    exists_controllers = roles.collect{|r| r.authorizable_type}
    controllers = Application.subclasses_list.to_a.sort
    controllers - exists_controllers
  end

  def authorizable_class
    return nil if authorizable_type.nil?

    klass = begin
      authorizable_type.split("::").inject(Object){|x, y| x.const_get(y)}
    rescue NameError => e
      msg = "Class not found: `#{authorizable_type}'"
      Merb.logger.warn!(msg)
      nil
    end
  end
  ...
  def callable_actions
    klass = authorizable_class
    # make sure is a controller
    return [] if klass.nil? || !klass.respond_to?(:callable_actions) 

    # get the supper class's actions out your way
    actions = klass.callable_actions.keys - klass.superclass.callable_actions.keys 
    actions.sort
  end