#[derive(Debug)]
enum List<T> {
    Nil,
    Node(T, Box<List<T>>)
}

impl List<T> {
    fn prepend(self, item: T) -> Self {
        Node(item, Box::new(self))
    }

    fn head(&self) -> Option<T> {
        match self {
            Node(t, _) => Some(t),
            Nil => None
        }
    }
}

use List::*;

fn main() {
    let list = Node(2, Box::new(Node(3, Box::new(Nil))));
    println!("{:?}", list);
}