struct Null
{
};

template <class Car, class Cdr>
struct Cons
{
	Car car;
	Cdr cdr;
};

constexpr Null null = Null {};

template <class Car, class Cdr>
constexpr Cons<Car,Cdr> cons(const Car &car, const Cdr &cdr)
{
	return Cons<Car,Cdr> {car, cdr};
}


constexpr int length(const Null &p)
{
	return 0;
}

template <class Car, class Cdr>
constexpr int length(const Cons<Car, Cdr> &p)
{
	return 1 + length(p.cdr);
}

constexpr auto foo = length(cons(3,cons(2,null)));

#include <iostream>
int main()
{
	std::cout << foo << std::endl;
}