[randomdata]

You can't have closed enums without value constraints. Yes, some languages have been lazy and provided value constraints only for enum types.

Which is an interesting choice: Give a noose for developers to hang themselves with for every single other type other than enums – the types they are going to use most often – and not think twice, but then go full on helicopter parent when using enums – the one type that isn't particularly interesting.

It's a neat parlour trick, don't get me wrong, but I guess that's why almost all of the popular statically typed languages since Pascal (C, C++[1], Typescript[2], etc.) didn't bother with closed enums. They put their time into features that actually mattered to developers instead.

[1] Added later in life, granted.

[2] Ironically, does support value constraints except in the case of using enum.

[grumpyprole]

> You can't have closed enums without value constraints

Sum types and closed enums don't need to constrain existing sets of values, they define the set of values. Again, I think you might be confusing the type system with runtime representation.

> It's a neat parlour trick, don't get me wrong,

It's a step towards sum types which are the mathematical dual of product types. Not a parlour trick at all, every modern language should have algebraic data types.