Swift enum recursive associated value

Question

I'm trying to create a math expression using an Enumeration in Swift. This enumeration can be a constant, with an associated value of type ComplexNumber (a simple struct). It also can be a square root expression, with a recursive associated value. For example, I want to be able to store sqrt(sqrt(1+2i)) in an enum.

enum Expression {
    case Sqrt(Expression)
    case Constant(ComplexNumber)
}

Xcode (6 beta 2) crashes immediately. What's the problem? From what I read in the Swift guide about associated values, this should work.

Answer 1

Now possible with Swift 2.0 since beta 4. Examples taken from release notes:

 enum List<T> {
   case Nil
   indirect case Cons(head: T, tail: List<T>)
 }

 indirect enum Tree<T> {
   case Leaf(T)
   case Branch(left: Tree<T>, right: Tree<T>)
 }