def class_defined(filename, class_name, superclass_name)
      @definition_graph[filename] ||= {}
      @definition_graph[filename][class_name] = superclass_name
      class_encountered(filename, class_name)
      class_encountered(filename, superclass_name) if superclass_name
    end
def class_defined(filename, class_name, superclass_name)
      @definition_graph[filename] ||= {}
      @definition_graph[filename][class_name] = superclass_name
      class_encountered(filename, class_name)
      class_encountered(filename, superclass_name) if superclass_name
    end
definition_graph:  { "faster_car.riml" => { "s:FasterCar" => "s:Car" }, "car.riml" => { "s:Car" => nil } }
 encountered_graph: { "faster_car.riml" => ["s:FasterCar", "s:Car"], "car.riml" => ["s:Car"] }