I've not heard this called sub- or pattern types before. Perhaps the rfc syntax is complicating the discussion.
We have struct and tuple in Rust where tuple is an ad-hoc/anonymous struct where only the number and order of member types matter. We have enum which are nominal types. We don't have the ad-hoc/anonymous version of them where only the set of possible types matter.
In TypeScript, F#/OCaml they would be like x: TypeA|TypeB
Thanks for the reference. I can see how values of type A could be considered as a subset of values of type A|B, but I think the 'any value of type A' subset of type A|B is more related to types and less about restricting the range/set of values for a type.
We have struct and tuple in Rust where tuple is an ad-hoc/anonymous struct where only the number and order of member types matter. We have enum which are nominal types. We don't have the ad-hoc/anonymous version of them where only the set of possible types matter.
In TypeScript, F#/OCaml they would be like x: TypeA|TypeB