"enum" type values

[mattgodbolt]

I'd love a way to constrain a positional argument to "one of" a range of values only. For example, one of a selection of strings like "slow", "medium" or "fast" (for a --speed slow type argument). I couldn't see how to do it without just checking the string value afterwards (which is fine, but this seems like a common enough use case!)

[grafikrobot]

Hey neighbor.. Thanks for the idea. I implemented that in my Lyra fork: bfgroup/Lyra@ccdf09f (examples here https://raw.githack.com/bfgroup/Lyra/develop/docs/lyra.html#_option_value_choices).