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

I don't know if a generator itself can be recursive. Will M proved me wrong!

Here is a possible implementation for a pre-order traversal, using a stack for the child nodes which still have to be enumerated:

extension XMLNode : SequenceType {
    public func generate() -> AnyGenerator {
        var stack : [XMLNode] = [self]
        return anyGenerator {
            if let next = stack.first {
                stack.removeAtIndex(0)
                stack.insertContentsOf(next.childNodes, at: 0)
                return next
            }
            return nil
        }
    }
}

For a level-order traversal, replace

stack.insertContentsOf(next.childNodes, at: 0)

by

stack.appendContentsOf(next.childNodes)