Z Combinator for D and C++

zcomb.cpp

#include <iostream>
#include <functional>

template <typename R, typename... Args>
std::function<R(Args...)> Z(std::function<R(std::function<R(Args...)>, Args...)> f) {
  return [&](const Args&... args) { return f(Z(f), args...); };
}

int main(int argc, char const* argv[]) {
  std::cout << 
  Z(
    (std::function<long(std::function<long(long)>, long)>)
    [](std::function<long(long)> factorial, long n) {
      return n <= 1 ? 1 : n * factorial(n - 1);        
    }
  )(5)
  << std::endl;
}

zcomb.d

import std.stdio;

R delegate(Args) Z(R, Args...)(R delegate(R delegate(Args), Args) f){
  return (Args args) => f(Z(f), args);
}

void main(){
  writeln(Z((ulong delegate(ulong) factorial, ulong n) => n <= 1 ? 1 : n * factorial(n - 1))(5));
}