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#include <iostream>
using namespace std;
 
template <typename HEAD, typename... TAIL>
struct List
{
	void f(HEAD head, TAIL... tail) {
		cout << head << endl;
		List<TAIL...> ls;
		ls.f(tail...);
	}
};
template <>
struct List<>
{
	void f() {}
};
 
int main()
{
	List<int, double, char> ls;
	ls.f(1, 3.14, 'a');
	return 0;
}

prog.cpp:14:13: error: wrong number of template arguments (0, should be at least 1)
 struct List<>
             ^
prog.cpp:5:8: note: provided for ‘template<class HEAD, class ... TAIL> struct List’
 struct List
        ^~~~
prog.cpp: In instantiation of ‘void List<HEAD, TAIL>::f(HEAD, TAIL ...) [with HEAD = char; TAIL = {}]’:
prog.cpp:10:3:   recursively required from ‘void List<HEAD, TAIL>::f(HEAD, TAIL ...) [with HEAD = double; TAIL = {char}]’
prog.cpp:10:3:   required from ‘void List<HEAD, TAIL>::f(HEAD, TAIL ...) [with HEAD = int; TAIL = {double, char}]’
prog.cpp:22:19:   required from here
prog.cpp:9:17: error: wrong number of template arguments (0, should be at least 1)
   List<TAIL...> ls;
                 ^~
prog.cpp:5:8: note: provided for ‘template<class HEAD, class ... TAIL> struct List’
 struct List
        ^~~~
prog.cpp:9:17: error: wrong number of template arguments (0, should be at least 1)
   List<TAIL...> ls;
                 ^~
prog.cpp:5:8: note: provided for ‘template<class HEAD, class ... TAIL> struct List’
 struct List
        ^~~~

Standard output is empty