my 2 cents: I don't see algebraic data types as strictly superiour. It's just the other side of the polymorphic coin: there is open and closed ploymorphism. Ope

my 2 cents: I don't see algebraic data types as strictly superiour. It's just the other side of the polymorphic coin: there is open and closed ploymorphism. Open polymorphism happens with interfaces, inheritance, and typeclasses- the number is unlimited. Closed happens with ADTs - an enumeration of the cases. Open is great for extensibility: libraries can be precompiled, plugins are possible. Changes don't propagate - it is ""forward compatible"" which is great for maintaning the code. Closed on the other hand is great for matching. Finite is predictable & faster. Finite is self-contained and self-describing because it exposes the data types without shame. The purpose of the visitor pattern is now clear: it closes the open polymorphism for a finite set. Great, now we only need one kind and we still get matching. Or is it the worst of two worlds? Slow & incomprehensible and all changes propagate everywhere. So which one is better? Neither. But the reality is that all old imperative languages with polymorphism chose the open kind - the kind that adds more features because it was needed for shared libraries. Leaving you to build any pattern matching yourself and to burn yourself with the unmaintainable code. If people get burned, they learn. First they say don't do that and only then they replace the gas stove by induction.