``self.config.replacer_function``(``Callable[[str], str]``) must exists.

def _result(self) -> ResultLazyType:
        """
        ``self.config.replacer_function``(``Callable[[str], str]``) must exists.
        """
        config = cast(IntervalsCollectionBasedReplacerConfig, self.config)

        diff_acc = 0
        for interval, aggregated_mark in self.continuous_intervals():
            start, end = interval
            processed_start = start + diff_acc
            processed_end = end + diff_acc

            segment = self.input_sequence[start:end]

            if aggregated_mark is not None:
                processed_segment = config.labeler2repl[cast(Type[workflow.IntervalLabeler],
                                                             aggregated_mark)](segment)

                if not processed_segment:
                    # segment is removed.
                    processed_end = processed_start
                else:
                    processed_end = processed_start + len(processed_segment)

                diff_acc += len(processed_segment) - len(segment)
                segment = processed_segment

            yield segment, (interval, (processed_start, processed_end), aggregated_mark is not None)