ajax77

  template< typename T >
  auto findRoots(T a, T b, T c) -> pair<maybe<complex<T>>, maybe<complex<T>>> {
    typedef complex<T>       C;
    typedef maybe<C>         Root;
    typedef pair<Root, Root> Roots;

    if (a == 0) {
      if (b == 0) 
        return Roots(nothing,      nothing);
      else
        return Roots(Root(-c / b), nothing);
    } else {
      auto d     = C(b*b - a*c*4);
      auto two_a = a*2;
      return Roots(Root((-b + sqrt(d)) / two_a), 
                   Root((-b - sqrt(d)) / two_a));
    }
  }
  

  let pi = [](unsigned samples) -> double {
      typedef std::pair<double,double> point;
      let dxs = map([](const point& p) { return p.first*p.first + p.second*p.second; },
                    zip(take(samples, rand_range(-1.0,1.0)),
                        take(samples, rand_range(-1.0,1.0))));
      return 4.0 * filter([](double d) { return d <= 1.0; }, dxs).size() / dxs.size();
  }
  EXPECT_NEAR(pi(10000), 3.14);