Ruma, a Matrix homeserver written in Rust(ruma.io)

    fn run() -> Result<(), Error> {
        let config = try!(Config::from_file());
        let server = try!(Server::new(&config));
        server.run()
    }

    fn secret() -> Result<(), Error> {
        let key = try!(generate_macaroon_secret_key());
        println!("{}", key);
        Ok(())
    }

    fn main() {
        ...
        let result = match matches.subcommand() {
            ("run", Some(_)) => run(),
            ("secret", Some(_)) => secret(),
            _ => Err(SomeErrorType::new("no such subcommand")),
        };
        if let Err(e) = result {
            println!("error: {}", e);
            // or to stderr via the ugly:
            // writeln!(&mut stderr, "error: {}", e).unwrap();
            process::exit(1);
        }
    }