C++ Template Hanoi

hanoi.cpp

#include <iostream>
#include <utility>

template <int, typename T, T a, T b, T c>
struct hanoi;

template <typename seq1, typename seq2>
struct concat;

template <typename... Args>
struct sequence {};

template <typename T, T a, T b>
struct pair {
  static constexpr auto first = a;
  static constexpr auto second = b;
};

template <typename... Args1, typename... Args2>
struct concat<sequence<Args1...>, sequence<Args2...>> {
  using type = sequence<Args1..., Args2...>;
};

template <typename T, T a, T b, T c>
struct hanoi<1, T, a, b, c> {
  using type = sequence<pair<T, a, c>>;
};

template <int n, typename T, T a, T b, T c>
struct hanoi {
  using type = typename concat<
                 typename concat<typename hanoi<n - 1, T, a, c, b>::type,
                                 sequence<pair<T, a, c>>
                                >::type,
                 typename hanoi<n - 1, T, b, a, c>::type
               >::type;
};

// here we got type T for sequence<>
template <typename T>
void print(T) {}

template <typename T, typename... Args>
void print(sequence<T, Args...>) {
  std::cout << T::first << "->" << T::second << std::endl;
  print(sequence<Args...>());
}

int main(int, const char*[]) {
    print(typename hanoi<7, char, 'A', 'B', 'C'>::type());
}