turing machine, not sure where this is from I am not the origin author.

turing.cc

/*
 * =====================================================================================
 *
 *       Filename:  turing.cc
 *
 *    Description:  
 *
 *        Version:  1.0
 *        Created:  30/07/12 19:16:46
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  David Irvine (MaidSafe), david.irvine@maidsafe.net
 *   Organization:  
 *
 * =====================================================================================
 */
#include <iostream>
#include <vector>

using namespace std;

enum class Direction
{
  L,
  R
};

template<int Value>
struct repeat
{
  static const int head = Value;
  typedef repeat<Value> tail;
};

template<int Head, typename Tail>
struct cons
{
  static const int head = Head;
  typedef Tail tail;
};

template<Direction, typename Left, typename Right>
struct step { };

template<typename Left, typename Right>
struct step<Direction::L, Left, Right>
{
  typedef typename Left::tail left;
  typedef cons<Left::head, Right> right;
};

template<typename Left, typename Right>
struct step<Direction::R, Left, Right>
{
  typedef cons<Right::head, Left> left;
  typedef typename Right::tail right;
};

template<typename TuringMachine, typename Left, typename Right, typename State = typename TuringMachine::initial_state>
struct turing_machine
{
  typedef typename TuringMachine::template transition_table<Right::head, State> transition;
  typedef step<transition::direction, Left, cons<transition::symbol, typename Right::tail>> after;

  typedef turing_machine<TuringMachine, typename after::left, typename after::right, typename transition::state> next;

  typedef typename next::final_left final_left;
  typedef typename next::final_right final_right;
};

template<typename TuringMachine, typename Left, typename Right>
struct turing_machine<TuringMachine, Left, Right, typename TuringMachine::final_state>
{
  typedef Left final_left;
  typedef Right final_right;
};

struct busy_beaver
{
  struct A { };
  struct B { };
  struct H { };

  template<int Sym, typename State>
  struct transition_table { };

  typedef A initial_state;
  typedef H final_state;
};

template<>
struct busy_beaver::transition_table<0, busy_beaver::A>
{
  static const int symbol = 1;
  static const Direction direction = Direction::R;
  typedef B state;
};

template<>
struct busy_beaver::transition_table<0, busy_beaver::B>
{
  static const int symbol = 1;
  static const Direction direction = Direction::L;
  typedef A state;
};

template<>
struct busy_beaver::transition_table<1, busy_beaver::A>
{
  static const int symbol = 1;
  static const Direction direction = Direction::L;
  typedef B state;
};

template<>
struct busy_beaver::transition_table<1, busy_beaver::B>
{
  static const int symbol = 1;
  static const Direction direction = Direction::R;
  typedef H state;
};

template<typename T>
struct type_list_to_vector
{
  void operator()(std::vector<int> &output);
};

template<int Head, typename Tail>
struct type_list_to_vector<cons<Head, Tail>>
{
  void operator()(std::vector<int> &output)
  {
    output.push_back(Head);
    type_list_to_vector<Tail>()(output);
  }
};

template<int Value>
struct type_list_to_vector<repeat<Value>>
{
  void operator()(std::vector<int> &output)
  {
    output.push_back(Value);
  }
};

int main()
{

  typedef turing_machine<busy_beaver, repeat<0>, repeat<0>> tm;

  //cout << typeid(tm::next).name() << endl;
  //cout << typeid(tm::next::next).name() << endl;
  //cout << typeid(tm::next::next::next).name() << endl;
  //cout << typeid(tm::next::next::next::next).name() << endl;
  //cout << typeid(tm::next::next::next::next::next).name() << endl;
  //cout << typeid(tm::next::next::next::next::next::next).name() << endl;

  //cout << endl;

  vector<int> tape;
  type_list_to_vector<tm::final_left>()(tape);

  cout << ".. " << tape.back() << ' ';
  for (auto it = tape.crbegin(); it != tape.crend(); ++it)
    cout << *it << ' ';
  
  tape.clear();
  type_list_to_vector<tm::final_right>()(tape);
  cout << '*' << tape.front() << "* ";
  for (auto it = tape.cbegin() + 1; it != tape.cend(); ++it)
    cout << *it << ' ';
  cout << tape.back() << " .." << endl;

  //cout << typeid(tm::final_left).name() << endl;
  //cout << typeid(tm::final_right).name() << endl;
}