AnyGeneratorで植木算。なんとかステートレスにしたいんだけど難しいかなぁ… #CodePiece #cswift

CodePiece.swift

func uekizan<S: SequenceType>(sources: S, insert margin: S.Generator.Element) -> AnyGenerator<S.Generator.Element> {
    var gen = sources.generate()
    var isMargin = false
    var preserved: S.Generator.Element? = gen.next()
    return anyGenerator {
        defer {
            isMargin = !isMargin
        }

        switch (isMargin, preserved) {
        case (true, .Some):
            return margin
        case (false, let value?):
            preserved = gen.next()
            return value
        default:
            return nil
        }
    }
}