return recursive lambda

recursive_lambda.cpp

#include <iostream>
#include <functional>
using namespace std;

function<int(int)> foo() {
  return [](int n) -> int {
      function<int(int)> fac = [&](int n) -> int {
          return n == 0 ? 1 : n * fac(n-1);
      };
      return fac(n);
  };
}

int main(int, char*[]) {
  cout << foo()(4) << endl;
  return 0;
}