#include <iostream>
#include <typeinfo>

// mapping :: TYPE -> TYPE
// ---------------------------------------------------------
// ?? --> int (default "value")
template<typename X> struct mapping {
  using type = int;
};
// if instead you want it to be undefined for unknown types:
//template<typename X> struct mapping;
// bool --> double
template<> struct mapping<bool> {
  using type = double;
};



// map :: ([T] -> T) -> (T -> T) -> ([T] -> T)
//         "List"       "Mapping"   result "type" (also a "List")
// --------------------------------------------------------
template<template<typename...> class List,
         template<typename> class Mapping>
struct map {
  template<typename... Elements>
  using type = List<typename Mapping<Elements>::type...>;
};


template<typename...> struct Example {};



template<typename... S>
using MappedExample = map<Example, mapping>::type<S...>;

template<typename... S>
MappedExample<S...> f() {
  return MappedExample<S...>{};
}


int main() {
  std::cout
    << typeid(Example<bool,int,char,double>).name()
    << std::endl
    << typeid(decltype(f<bool, int, char, double>())).name()
    << std::endl;
}