Implementing recursive generator for simple tree structure in Swift

Question

I have a simple tree structure in memory based on an XML document and I am trying to write a recursive generator to support SequenceType, but I am stuck on how

Answer 1

While Martin's answer is certainly more concise, it has the downside of making a lot of using a lot of array/insert operations and is not particularly usable in lazy sequence operations. This alternative should work in those environments, I've used something similar for UIView hierarchies.

public typealias Generator = AnyGenerator

public func generate() -> AnyGenerator {
    var childGenerator = childNodes.generate()
    var subGenerator : AnyGenerator?
    var returnedSelf = false

    return anyGenerator {
        if !returnedSelf {
            returnedSelf = true
            return self
        }

        if let subGenerator = subGenerator,
            let next = subGenerator.next() {
                return next
        }

        if let child = childGenerator.next() {
            subGenerator = child.generate()
            return subGenerator!.next()
        }

        return nil
    }
}

Note that this is preorder iteration, you can move the if !returnedSelf block around for post order.