Unless I'm misinterpreting the example, it seems rather unfortunate that you need to create a sentential value before a `read` call to update some `&n` location

Unless I'm misinterpreting the example, it seems rather unfortunate that you need to create a sentential value before a `read` call to update some `&n` location. The `twice` function really could be just `return read() * 2` no? I guess I should look into how this is actually compiled to sh. I agree the README would benefit from adding some examples of this.