#pragma once

#include <type_traits>

template <typename L, typename R>
struct compose_fn {
    template <typename... Ts>
    constexpr decltype(auto) operator()(Ts &&...ts) const &
    {
        return l(r(std::forward<Ts>(ts)...));
    }

    template <typename... Ts>
    constexpr decltype(auto) operator()(Ts &&...ts) &
    {
        return l(r(std::forward<Ts>(ts)...));
    }

    template <typename... Ts>
    constexpr decltype(auto) operator()(Ts &&...ts) &&
    {
        return std::move(l)(std::move(r)(std::forward<Ts>(ts)...));
    }

    L l;
    R r;
};

template <typename L, typename R>
constexpr auto compose(L &&l, R &&r) -> compose_fn<std::decay_t<L>, std::decay_t<R>>
{
    return {std::forward<L>(l), std::forward<R>(r)};
}

template <typename... Ts, typename R>
constexpr auto operator|(compose_fn<Ts...> l, R &&r)
{
    return compose(std::forward<R>(r), std::move(l));
}