# File lib/yadis/yadis.rb, line 99
  def filter_services(filter)
    # product a list of filtered ServiceEndpoint objects.  filtered
    # will contain a list of nil or ServiceEnpoint (subclasses) objects.
    filtered = self.services.collect {|s| filter.call(s)}
    
    # return all object in filtered that are not nil
    return filtered.find_all {|s| s}
  end