There is a reason for nominal typing though, because nominal types represent an interface contract that generally goes beyond just having the right type signature, but instead it is also about semantics. It's about the parts not covered by the type system, which the compiler therefore can't check. It depends on the kind of objects you are generally working with, but beyond pure data I find nominal typing preferable, because it makes it explicit that an implementation X conforming to interface contract Y is not just a matter of type signatures.