Troubles with Rust

strtest.rs

extern mod std;

fn main() {
    let s = @"foo bar baz";
    // similar results with ~"foo bar baz"

    // These work
    s.substr(1, 5);
    s.slice(1,5);

    // These don't
    s.split_str(s, @" ");
    s.split_str(s, ~" ");
    s.is_empty();
    s.to_lower();
    s.lines();
    s.words();
}