[nyanpasu64]

Tagged unions of free-floating types (polymorphic variants, C++ std::variant) and enum holding cases namespaced within themselves (Rust/Haskell) are two alternative designs. I personally prefer having both in a language. But if only one is available in a language, I prefer free-floating types, since it's more flexible and allows using the same type in multiple tagged unions, and you can somewhat emulate enums using tagged unions and namespaces (like I've done in C++ at https://gitlab.com/exotracker/exotracker-cpp/-/blob/eb8458b2...). If you take that approach, to prevent collapsing in the generic case when two type parameters are the same, you'd have to define newtypes for each type stored in a union.