Polymorphic length function and test.

polylen.rs

fn length<A>(l: @List<A>) -> uint {
    match *l {
        Empty => 0,
        Cons(_, rest) => 1 + length(rest)
    }
}

fn main() {
    let l = @Cons("3", @Cons("little", @Cons("strings", @Empty)));
    println!("Length of l is {}", length(l));
}