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// Copyright Louis Dionne 2013-2022
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
template <typename ...xs>
struct list { };
template <typename T>
struct basic_type { using type = T; };
template <typename T>
constexpr basic_type<T> type{};
template <typename x, typename ...xs>
constexpr auto head(list<x, xs...>)
{ return type<x>; }
template <typename x, typename ...xs>
constexpr auto tail(list<x, xs...>)
{ return list<xs...>{}; }
template <typename F, typename State, typename X, typename ...Xs>
constexpr auto foldl(F f, State s, list<X, Xs...> xs)
{ return foldl(f, f(s, head(xs)), tail(xs)); }
template <typename F, typename State>
constexpr auto foldl(F, State s, list<>)
{ return s; }
//////////////////////////////////////////////////////////////////////////////
struct f {
template <typename ...>
struct result { };
template <typename X, typename Y>
constexpr auto operator()(X, Y) const
{ return result<X, Y>{}; }
};
template <int> struct x { };
struct state { };
int main() {
constexpr auto xs = list<
<%= (1..input_size).map { |i| "x<#{i}>" }.join(', ') %>
>{};
constexpr auto result = foldl(f{}, state{}, xs);
(void)result;
}
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