peano plus

peano.cpp

#include <stdio.h>
#include <functional>

struct zero;

template <typename V>
struct signtype
{
	using value = typename signtype<V>::value;
};

template <>
struct signtype<zero>
{
    using value = zero;
};

template <int v>
struct num
{
    using name = signtype<typename num<v-1>::name>;
};
template <>
struct num<0>
{
    using name = zero;
};

using one = signtype<zero>;
using two = signtype<one>;
using three = signtype<two>;

template <typename V1, typename V2>
struct plus;

template <typename V2>
struct plus<zero,V2>
{
    using sum = V2;
};

template <typename V1, typename V2>
struct plus<signtype<V1>,V2>
{
    using sum = signtype< typename plus<V1,V2>::sum >;
};

using result = plus<one,two>::sum;

int main()
{
    printf("Hello World");
    printf(" => %d\n",std::is_same<three,num<3>::name>::value);
    printf(" => %d\n",std::is_same<result,three>::value);
    return 0;
}