$ program --port 8080 --config some/path Options {port = 8080, daemonize = False, config = Just "some/path"} $ program --port 8080 --daemonize Options {port = 8080, daemonize = True, config = Nothing} $ program --port foo cannot parse as INTEGER: foo # exit-code 1 $ program missing option: --port=INTEGER # exit-code 1 $ program --help program [OPTIONS] --port=INTEGER --daemonize --config=STRING (optional) -h --help show help and exit