First Draft: Nominal Sum Types via `enum union` and `switch` Expressions

[DanielG]

Mostly on-board with this, with some minor quibbles:

- Purely aesthetic, but: why () at the end of cases, even with no 
payload? Required for easier parsing or something?

- I still don't understand the appeal of bare type variants, but 
I guess the D community loves them 🤷‍♂️. Is there some language I 
don't know about that mixes these two concepts so directly? I 
don't mean languages that have sum types AND type unions (eg 
Scala 3) - but some language where they are mixed together, as in 
your DIP here?

I wish we could just start with a very simple, conventional, 
no-frills sumtype (named values + optional tupled arguments) and 
then expand from there in the future. Isn't that what Swift has 
today? That's *all* F# has or will ever have, and it's incredibly 
powerful even in that simple form.

At any rate, your DIP's got the minimal feature set I want, for 
my simple needs. Good luck!