How can I write asynchronous code?

async fn add_three(a: Int, b: Int, c: Int) -> Int:
    return a + b + c

async fn call_it():
    var task = add_three(1, 2, 3)
    print(await task)

test_async.mojo:39:17: error: 'Coroutine[Int, {}]' is not copyable because it has no '__copyinit__'
    print(await task)
                ^~~~

async fn add_three(a: Int, b: Int, c: Int) -> Int:
    return a + b + c

async fn call_it():
    var task = await add_three(1, 2, 3)
    print(task)