foo.rs

fn get_path_to(target: & str, opt: Option<&str>) -> Path {
    let path: ~str = match target {
      "root" => {
        os::homedir().unwrap().to_str() + "/.rsvm"
      }

      "version" => {
        get_path_to(~"root", None).to_str() + ~"/v" + opt.unwrap()
      }

      "src_archive" => {
        get_path_to("version", opt).to_str() + "/src/rust-" + opt.unwrap() + ".tar.gz"
      }

      _ => {
        os::homedir().unwrap().to_str() + "/.rsvm"
      }
    };

    Path(path)
}

==>

    if get_path_to("src_archive", Some(version)).exists() {
        io::println(~"already done");
    }