I think the artificial shape example does not adequately show how variant types/pattern matching are actually used in languages like SML/F#/Haskell. It combines

I think the artificial shape example does not adequately show how variant types/pattern matching are actually used in languages like SML/F#/Haskell. It combines two different cases. Suppose you have a type `colour` defined as `RGB(int, int, int) | HSL(int, int, int)` and then you add representation as CIE. Then having to update each match on a colour is absolutely a feature not a bug. If you miss some out then your code will be wrong. On the other hand, suppose you have various ways of serialization (JSON/XML/s-expressions). In this case, it would probably be nice if you could add a way to serialize to e.g. protobufs without having to jump around your codebase and all its clients fixing type errors. But in most languages of the kind we're discussing, you can do! You just have to represent the different serialization methods in some way other than a variant type. For instance, in OCaml you could just use classes and inheritance (although in practice you probably wouldn't because the language provides nicer tools).