Multi step reasoner in c++ templates -

i looking simple implementation of planner/search algorithm implemented compile time c++ templates. application such thing partly academic, partly driven practical needs code verification.

here essence of looking for: imagine search algorithm plan actions 'start' state 'end' state.

template<a, b> struct step{    //all steps have:    static void doaction(); }   struct start{}; struct state1{}; struct state2{}; struct end{};   //transition between neighbor-states known:  template<> struct<start, state1>{      static void doaction(){          std::cout << "start -> state1" << std::endl;      } };  template<> struct<state1, state2>{      static void doaction(){          std::cout << "state1 -> state2" << std::endl;      } };  template<> struct<state2, end>{      static void doaction(){          std::cout << "state2 -> end" << std::endl;      } }; 

now use magic of templates find sequence of steps (using sfinae or other tricks). how can following achieved?

 //todo: implement reasoner:  template<typename a, typename b, typename c> struct step<a,c>{     typedef step<a,b> s1;     typedef step<b,c> s2;      static void doaction(){          s1::doaction();          s2::doaction();     }  };   // code using it: step<start, state1>::doaction(); //expect: "start -> state1"   step<start, state2>::doaction(); // expect: "start -> state1"                                   //         "state1 -> state2"  step<start, end>::doaction();    // expect: "start -> state1"                                  //         "state1 -> state2"                                  //         "state2 -> end" 

this best solved backwards. define path<end>::cost == 0 , reasoning backwards path<state2,end>::cost==path<end>::cost + 1 because there's step<state2,end>.

your pathfinder algorithm need list of states consider, though: can't discover them given definition of states , step<>