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#if defined(__cpp_coroutines) && defined(__has_include)
#if __has_include(<coroutine>)
#include <coroutine>
namespace std_coro = std;
#elif __has_include(<experimental/coroutine>)
#include <experimental/coroutine>
namespace std_coro = std::experimental;
#else
#error Either the compiler or the library lacks support for coroutines
#endif
#else
#error Either the compiler or the library lacks support for coroutines
#endif
struct present
{
struct promise_type
{
int result;
present get_return_object() { return {*this}; }
std_coro::suspend_never initial_suspend() { return {}; }
std_coro::suspend_never final_suspend() noexcept { return {}; }
void return_value(int i) { result = i; }
void unhandled_exception() {}
};
promise_type& promise;
bool await_ready() const { return true; }
void await_suspend(std_coro::coroutine_handle<>) const {}
int await_resume() const { return promise.result; }
};
present f(int n)
{
if (n < 2)
co_return 1;
else
co_return n * co_await f(n - 1);
}
int main()
{
return f(5).promise.result != 120;
}
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