// list.rs - list implementing ToStr trait 

struct Node {
    head : int,
    tail : Option<@Node>
}

type List = Option<@Node> ;

impl ToStr for List {
    fn to_str(&self) -> ~str { 
        fn elements_to_str(n: @Node) -> ~str {
            match (n.tail) {
                None => fmt!("%?", n.head),
                Some(tail) => fmt!("%?, %s", n.head, elements_to_str(tail))
            }
        }
        
        match(*self) {
            None => ~"Null",
            Some(n) => fmt!("[%s]", elements_to_str(n))
        }
    }
}

fn main() {
    let lst : List = Some(@Node{head: 1, tail: Some(@Node{head : 2, tail: Some(@Node{head: 3, tail: None})})});
    println(fmt!("%s", lst.to_str()));
}