test.rs

mod config {
    pub enum Node<T> {
        Directory(~str, ~[Node<T>]),
        Entry(~str, ~T)
    }

    pub fn add_entry<T>(node: &Node<T>, entry: &Node<T>) -> ::std::option::Option<&Node<T>> {
        match node {
            Directory(name, list) => { ::std::vec::append_one(list, entry); Some(node) }
            _ => { None }
        }
    }
}

fn main() {
    let entry = config::Entry(~"test", ~0.0);
    let dir = config::Directory(~"dir", ~[]);

    let dir2 = config::add_entry(dir, entry);
}