#include <functional>
#include <iostream>


std::function<int()> generator = []{
    int i = 0;
      return [=]() mutable {
        return i < 10 ? i++ : -1;
      };
}();

int main(void)
{
int ret = 0; while ((ret = generator()) != -1) std::cout << "generator: " << ret << std::endl;
}