using namespace std;
using namespace conduit;
using namespace conduit::operators;
auto fib = []() -> seq<int> {
  auto a = 0; 
  auto b = 1;
  while ( true ) {
    co_yield a;
    tie(a, b) = tuple{a + b, a};
  }
};
auto items = fib() 
  >> take(5)
  >> zipWith(range, [](auto x, auto y) { 
    return tuple{x, y};
  });
int vals[] = { 0, 1, 1, 2, 3, 5 };
for(auto [i, n] : items) {
  EXPECT_EQ(vals[i], n);
}

#define RET(X) { return X; }
// sieve of eratosthenes
auto primes = [] {
  return range()
    >> map([](auto i) RET(3+i*2) ) // create a seqence of odd nums > 2
    >> flatMap([primes = vector<int>()](auto c) mutable RET ( 
      primes // divide each candidate by the primes we encountered
        >> find([c](auto p) RET (c % p == 0)) // search and stop if divisible
        >> count() // find yields at most 1 element, count how many we got (starts with zero)
        >> orElse(just(c)) // if we didn't find any, its a prime. yield it
        >> find([](auto x) RET (x)) // filter out zeros yielded by find+count or take prime
        >> forEach([&](auto p) {
          primes.push_back(p);  // update list of primes
        }) // Note: lifetime of primes-vector is bound to the coroutine  
    )) >> startsWith(just(2)); // two is the only even prime
};