Peano numerals with C++ templates

peano.cpp

#include "stdafx.h"

class z { };

template<typename>
class s { };

template<typename, typename>
class add { };

template<typename n>
struct add<z, n>
{
	typedef n type;
};

template<typename m, typename n>
struct add<s<m>, n>
{
	typedef typename add<m, s<n>>::type type;
};

template<typename>
struct eval { };

template<>
struct eval<z>
{
	static const int value = 0;
};

template<typename n>
struct eval<s<n>>
{
	static const int value = 1 + eval<n>::value;
};

int main()
{
	printf("%d\n", eval<add<s<s<z>>, s<s<s<z>>>>::type>::value);
}