Generate definitions with labels when translating a PlusCal algorithm

The PlusCal translator could generate a PCOK from the set of possible pc values that is manually added as a conjunct in a user-provided TypeOK, and that is robust against algorithm changes:

\* BEGIN TRANSLATION

... \*

PCOK == pc \in {"lbl1", "lbl2", ..., "Done"}

\* END TRANSLATION 
 
TypeOK ==
   /\ PCOK
   /\ ....

Alternatively, the translator could generate a definition with a set or even sequence of all labels.

\* BEGIN TRANSLATION

... \*

Labels == {"lbl1", "lbl2", ..., "Done"}

\* END TRANSLATION 
 

Related: https://github.com/tlaplus/Examples/issues/34

[Calvin-L]

I’ve never needed this feature in my work, but I can see how it would be useful. Three quick comments:

I agree with @muenchnerkindl; legal PC values should be separated by process ID.

Between Labels and PCOK: Labels seems more generic and useful to me.

Although, rather than Labels, I would use a very long and descriptive name like PossiblePCValuesByProcessID. This is (1) self-documenting and (2) less likely to clash with identifiers in existing PlusCal modules.

[muenchnerkindl]

I think it would be nice to have, but in practice it would rather be something like

pc \in [p \in ProcSet |-> 
              CASE p \in Server -> ServerLabels
              [] p \in Client -> ClientLabels]

(and even more complicated for Distributed PlusCal if we ever get to release it).