that's true, you can recreate it in some sense but you can't get to what F# can guarantee. A big promise of discriminated unions is the ability to make invalid state unrepresentable. Matching on the different type constructors is a fantastic way to only express coherent states.
Terminology nitpick: Pattern matching is done on value constructors (or just "constructors", but at the intersection of FP and OOP that could be confusing).
"type constructor" means something like `List` (as opposed to `List[Int]`) – a generic type that hasn't been applied to any type argument(s) yet, and will "construct" a type (like `List[int]`) when you apply it.
