iter_tools.swift

struct InfRepeater: Sequence {
   // a sequence that loops infinitely over another sequence
   typealias Iterator = InfRepeaterIter
   typealias Element = Int
   
   var arr: Array<Element>
   func makeIterator() -> Iterator  {
     return InfRepeaterIter( i: 0, arr: arr ) 
   }
} 

struct InfRepeaterIter : IteratorProtocol {
  typealias Element = Int
  var i : Int = 0 
  var arr : Array<Element>
  
  mutating func next( ) -> Int? {
    let ret = self.arr[self.i] 
    self.i += 1 
    self.i %= self.arr.count
    return ret 
  }
}