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

[Meta]

On Sunday, 20 September 2026 at 18:03:22 UTC, Paul Backus wrote:
> On Sunday, 20 September 2026 at 17:37:36 UTC, Meta wrote:
>>
>> My point was that `case 42 =>` and `case int n if (n == 42) 
>> =>` are equivalent, so his use case is covered. I decided 
>> against adding full pattern matching in lieu of saving it for 
>> a future DIP.
>
> IMO trying to do a partial implementation of pattern matching 
> like this is a mistake. Better to either do it fully, and smoke 
> out any potential issues with the design, or leave it entirely 
> for later.
>
> Even if you want to split sum types and pattern matching into 
> two DIPs, I think it would be best to finish writing both of 
> them before submitting either one.

I already have a fleshed out version of pattern matching that 
builds on this DIP. And if that future DIP is not accepted, then 
what's here is already very useful in terms of functionality.