functionalTemplates.cpp

#import <stdio.h>

template<int i>
class Integer {
public:
    static const int value = i;
};

template<class Left, class Right>
class Add {
public:
    static const int value = Left::value + Right::value;
};

template<class Item, class Next>
class List {
public:
    using value = Item;
    using next = Next;
};

class Nil {};

template<class List>
class head {
public:
    using value = typename List::value;
};

template<class List>
class tail {
public:
    using value = typename List::next;
};

template<class List>
class sum {
    using lhs = typename head<List>::value;
    using rhs = typename sum<typename tail<List>::value >::value;
    using tot = Add<lhs, rhs>;
public:
    using value = Integer<tot::value>;
};

template<>
class sum<Nil> {
public:
    using value = Integer<0>;
};

using aa = List<Integer<10>, List<Integer<2>, List<Integer<8>, Nil> > >;

int main() {
    printf("%d", sum<aa>::value::value);
}