while true {
    let args = input("> "):sep(" ")
    let [head] = args
    match head {
        "send" => {
            let [_, target, msg] = args
            if !some(target) {
                print("expected target")
                continue
            }
            if !some(msg) {
                print("expected message")
                continue
            }
            print("sent %s the message: %q":format(target, msg))
        }
        "exit" => { break }
        cmd if cmd:len() > 0 => {
            print("invalid command: %q":format(cmd))
        }
        cmd => {}
    }
}