#include <iostream>
#include <functional>

// Y-combinator for the A type -> B type
template <typename A, typename B>
std::function<B(A)> y(std::function<B(std::function<B(A)>, A)> f) {
  return std::bind(f,std::bind(&y<A,B>,f), std::placeholders::_1);
}

int fact(std::function<int(int)> f, int v) {
  if(v == 0)
    return 1;
  else
    return v * f(v -1);
}

int main(int argc, const char** argv) {
  auto factorial = y<int,int>(fact);
  std::cout << factorial(5) << std::endl;
  return 0;
}