class PluginInvocation():
    _plugins = {}

    def __init__(self, name, data):
        super().__init__()
        if name not in self._plugins:
            raise KeyError(f'No such plugin function: {name}')
        self._name = name
        self._data = data

    def __call__(self):
        return self._plugins[self._name](**self._data)

    @classmethod
    def register_plugin(cls, name, fn):
        cls._plugins[name] = fn


def plugin_constructor(loader, node):
    data = loader.construct_mapping(node)
    return PluginInvocation(node.tag[1:], data)


def render_traverse(obj):
    """
    Walk through a complex, JSON-serializable data structure, and
    invoke plugins if for custom tags.
    :param obj: The object to traverse.
    """
    if isinstance(obj, list):
        # list -> recurse into each item
        return [render_traverse(x) for x in obj]
    elif isinstance(obj, dict):
        # dict -> recurse into the value of each (key, value)
        return {k: render_traverse(v) for k, v in obj.items()}
    elif isinstance(obj, PluginInvocation):
        # PluginTag -> invoke the plugin with the stored arguments
        return obj()
    else:
        # anything else -> return as-is
        return obj