curry.cpp

// apply を利用した実装メモ

// primary
template <typename Ret, typename Args>
struct RetType;

template <typename Ret>
struct RetType<Ret, tuple<>> {
  typedef Ret type;
};

template <typenamea Ret, typename Arg, typename ...Args>
struct RetType<Ret, tuple<Arg, Args...>> {
  typedef typename RetType<Ret, tuple<Args...>>::type Partial;
  typedef function<Partial (Arg)> type;
};

template <typename T>
struct curry_impl;

template <>
struct curry_impl<tuple<>> {
  template <typename Ret, typename ...Args>
  static auto impl(Ret (*fun)(Args...), tuple<Args...> t) -> Ret {
    return apply(fun, t);
  }
};

template <typename UnBoundArgsHead, typename ...UnBoundArgsTail>
struct curry_impl<tuple<UnBoundArgsHead, UnBoundArgsTail...>> {
  template <typename Ret, typename ...Args, typename ...BoundArgs>
  static auto impl(Ret (*fun)(Args...), tuple<BoundArgs...> t) -> typename RetType<Ret, tuple<UnBoundArgsHead, UnBoundArgsTail...>>::type {
    return [](UnBoundArgsHead arg){ return curry_impl<tuple<UnBoundArgsTail...>>::impl(fun, tuple_cat(t, make_tuple(arg));
  }
};

template <typename Ret, typename ...Args>
auto curry(Ret (*fun)(Args...)) -> typename RetType<Ret, tuple<Args...>>::type {
  return curry_impl<tuple<Args...>>::impl(fun, make_tuple());
}

// 職場からなのでコンパイル試せてないけれど、こんな感じで…
// RetType は (Arg1 -> Arg2 ... -> ArgN) -> Ret な型を Arg1 -> (Arg2 -> ... (ArgN -> Ret) ... ) に変換する type function
// decltype(self) が無理なら返値型を計算してやろうの発想。