num_tokens = length_func(result_docs, **kwargs)
        async def _collapse_docs_func(docs: List[Document], **kwargs: Any) -> str:
            return await self._collapse_chain.arun(
                input_documents=docs, callbacks=callbacks, **kwargs
            )
        _token_max = token_max or self.token_max
        while num_tokens is not None and num_tokens > _token_max:
            new_result_doc_list = _split_list_of_docs(
                result_docs, length_func, _token_max, **kwargs
            )
            result_docs = []
            for docs in new_result_doc_list:
                new_doc = await _acollapse_docs(docs, _collapse_docs_func, **kwargs)
                result_docs.append(new_doc)
            num_tokens = length_func(result_docs, **kwargs)
        return result_docs, {}
    @property
    def _chain_type(self) -> str:
        return "reduce_documents_chain"