On Feb 13, 2017 10:25 AM, "Christof Donat via Boost" <boost@lists.boost.org> wrote: In a hobby project, I am using Spirit Karma generators. As far as I have understood Spirit Karma, it is not designed to work lazily in the iterator based interface. It takes an output iterator and writes to it until it has finished. What I am thinking of is a kind of generating range. E.g.: for(auto& char: generator_range(double_ << " + " << double_ << "i", context, c.real(), c.imag())) { // do whatever with the single characters returned by the generator } Is there something like that, which I simply have not found? You should be able to build that with Boost.Coroutine. Launch the Karma generator in a pull_type coroutine, which accepts a (corresponding) push_type coroutine as its argument. A push_tyoe coroutine can be used as an output iterator. Pass that iterator to Karma, and then lazily retrieve characters from the pull_type coroutine.