struct WideList<T> {
    hd: T,
    tl: Option<Box<WideList<(T, T)>>>
}

impl<T> Clone for WideList<T>
where
    T: Clone,
    Option<Box<WideList<(T, T)>>>: Clone
{
    fn clone(&self) -> WideList<T> {
        WideList {
            hd: self.hd.clone(),
            tl: self.tl.clone()
        }
    }
}

fn main() {
    let x = WideList { hd: 1i32, tl: Some(Box::new(WideList { hd: (2i32, 3i32), tl: None })) };
    x.clone()
}