generator pipeline and accumulate

#include "stdafx.h"
#include <experimental\generator>
#include <experimental\coroutine>
#include <iostream>
#include <string>
#include <numeric>

using namespace std;
using namespace std::experimental;

std::experimental::generator<int> gen()
{
 for (int i = 0;; ++i)
  co_yield i;
};

std::experimental::generator<int> take_until(std::experimental::generator<int> g, int sentinel)
{
 for (auto v : g)
 {
  if (v == sentinel)
   break;
  co_yield v;
 }
}


int main()
{
 auto g1 = take_until(gen(), 10);
 auto a = std::accumulate(g1.begin(), g1.end(), 0);
  cout << a << endl;

 std::string s;
 getline(cin, s);
    return 0;
}