Completion for user-defined arguments

[dos4boss]

How hard would it be to extend it to allow completion also for arguments?
Let's say, for example, I have an command, that can only be called in the following way to be valid:
set_state RUNNING, set_state WAITING and set_state TERMINATED.
I want to have completion of set_state R to set_state RUNNING in this case.

[daniele77]

Thank you @dos4boss for the idea: it would be great to have completion on arguments.
Before that, however, the library should be able to manage "enumeration" arguments (i.e., a string argument that can assume only a finite set of values).
In particular, the library should be able to handle "user-defined arguments" in the first place (see issue #69).

[suikabreaker]

Even further, could it be extended to allow this?

select node N<tab>

N1-s N2-s

select node N2-s

in which node list is determined at runtime.

[suikabreaker]

And filepath completion can also be useful.