// A function that returns the value of a lambda expression - a closure.
// The closure refers a global variable, seed, instead of a dangling local variable in f.
// This compiles and runs. But it is rather primitive seen from a functional programming point of view.

#include <iostream>     
#include <string>
#include <functional>     // std::function

int seed; 

std::function<int(int)> f(const int seed0){
  seed = seed0;      // Assigning global variable

  return [](int i){  
     seed++;              
     return i + seed;
  };

}

int main () {
  using namespace std;
  auto g = f(5);          // f(5) returns a function that can access the 
                          // global seed. OK. But not that interesting.

  for(int i = 1; i <= 5; i++)
    cout << "g(" << i << ") = " << g(i) << endl;    // 7, 9, 11, 13, 15
}