$ 04_01_enum_derive --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: 04_01_enum_derive[EXE] <MODE>
Arguments:
<MODE> What mode to run the program in [possible values: fast, slow]
Options:
-h, --help Print help information
-V, --version Print version information
$ 04_01_enum_derive fast
Hare
$ 04_01_enum_derive slow
Tortoise
$ 04_01_enum_derive medium
? failed
error: "medium" isn't a valid value for '<MODE>'
[possible values: fast, slow]
For more information try '--help'