Function mismatch

include/boost/parser/parser.hpp:2802–2816

            typename Sentinel2,
            typename Pred>
        std::pair<Iter1, Iter2> mismatch(
            Iter1 first1,
            Sentinel1 last1,
            Iter2 first2,
            Sentinel2 last2,
            Pred pred)
        {
            std::pair<Iter1, Iter2> retval{first1, first2};
            while (retval.first != last1 && retval.second != last2 &&
                   pred(*retval.first, *retval.second)) {
                ++retval.first;
                ++retval.second;
            }
            return retval;
        }

        template<
            typename Iter1,