// listo.rs - Owned List

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

type List = Option<~Node> ;

trait Map {
    fn mapr(&self, &fn(int) -> int) -> List;
}

impl Map for List {
    fn mapr(&self, f: &fn(int) -> int) -> List { 
         match(*self) {
            None => None,
            // need the ref here to keep the matched variable type borrowed
            Some(ref node) => { Some(~Node{ head: f(node.head), tail: node.tail.mapr(f) }) },
        }
    }
}

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

fn main() {
    let lst0 : List = Some(~Node{head: 1, tail: Some(~Node{head : 2, tail: Some(~Node{head: 3, tail: None})})});
    println(lst0.to_str());
    let lst1 = lst0.mapr(|x: int| { x + 1 });
    println(lst1.to_str());
    let lst2 = lst1.mapr(|x: int| { x * x });
    println(lst2.to_str());
    let lst3 = lst2.mapr(|x: int| { if x % 2 == 0 { x } else { -x }});
    println(lst3.to_str());
    println(lst0.to_str());
}