tree.rs

use std::fmt::Show;
use std::fmt::Formatter;
use std::fmt::FormatError;

enum Tree<T> {
    Node(T, Box<Tree<T>>, Box<Tree<T>>),
    Nil,
}

impl<T: Ord + Show> Tree<T> {
    fn add(&mut self, val: T) {
        match *self {
            /*
            Node(ref v, box Nil, box Nil) => {
                if val >= *v {
                    *self = Node(v, box Nil, box Node(val, box Nil, box Nil));
                } else {
                    *self = Node(v, box Node(val, box Nil, box Nil), box Nil);
                }
            },
*/
           format Node(ref v, ref mut l, ref mut r) => {
                if val >= *v {
                    r.add(val);
                } else {
                    l.add(val);
                }
            },

            Nil => {
                *self = Node(val, box Nil, box Nil);
            }
        }
    }
}

impl<T: Ord + Show> Show for Tree<T> {
    fn fmt(&self, f: &mut Formatter) -> Result<(), FormatError> {
        match *self {
            Node(ref v, ref l, ref r) => write!(f, "{} -> ( {} {} )", v, l, r),
            Nil => write!(f, "Nil")
        }
    }
}

fn main() {
    let mut t: Tree<int> = Node(2, box Nil, box Nil);
    t.add(3);
    println!("{}", t);
}
                                                               

thanks a lot steve :) remove format in line 22 though.