Swift's Optional is just Maybe with some built-in sugar. Sum types are supported, with the caveat that the compiler is sort of broken when it comes to generics.

Swift's Optional is just Maybe with some built-in sugar. Sum types are supported, with the caveat that the compiler is sort of broken when it comes to generics. Personally, I just want higher-kinded types, and for the following code snippets to work as-is: enum Either<A,B> { case Left(A) case Right(B) } enum Tree<A> { case Leaf case Node(Tree<A>, A, Tree<A>) } The first breaks because of the "Unimplemented non-fixed multi-payload enum layout" compiler error, and the second breaks because enums have value semantics. Both can be worked around in full generality by declaring a 'Box<T>' generic wrapper class, but that workaround is inelegant and cumbersome.