enum List {
    Cons(u32, Box<List>),
    Nil,
}

impl List {
    fn new() -> List {
        List::Nil
    }

    fn prepend(self, element: u32) -> List {
        List::Cons(element, Box::new(self))
    }

    fn len(&self) -> u32 {
        match *self {
            List::Nil => 0_u32,
            List::Cons(_, ref next) => 1 + next.len(),
        }
    }

    fn stringify(&self) -> String {
        match *self {
            List::Nil => format!("Nil"),
            List::Cons(this, ref next) => format!("{} -> {}", this, next.stringify()),
        }
    }
}

fn main() {
    let mut list = List::new();
    list = list.prepend(1);
    list = list.prepend(2);
    list = list.prepend(3);

    println!("Len: {}", list.len());
    println!("Str: {}", list.stringify());
}