Cycle.Swift

public struct CycleGen<C: CollectionType> : GeneratorType, LazySequenceType {
  
  typealias Element = C.Generator.Element
  typealias Generator = CycleGen<C>
  
  private let inner: C
  private var innerGen: C.Generator
  
  private init(col: C) {
    self.inner = col
    self.innerGen = col.generate()
  }
  
  public func generate() -> Generator {
    return self
  }
  
  public mutating func next() -> Element? {
    for ;;innerGen = inner.generate() {
      if let next = innerGen.next() {
        return next
      }
    }
  }
}
 
public extension CollectionType {
  func cycle() -> CycleGen<Self> {
    return CycleGen(col: self)
  }
}