A demonstration of Swift sequences

gistfile1.swift

// a demonstration of Swift sequences

// a sequence that lazily creates a Fibonacci sequence
class Fibonacci : Sequence {
  
  let id:String
  init(_ id: String) {
    self.id = id;
  }
  
  func generate() -> GeneratorOf<Int> {
    var current = -1, last = 0
    
    return GeneratorOf<Int> {
      if current == -1 {
        current = 0
      } else if current == 0 {
        current = 1
      } else {
        var next = last + current
        last = current
        current = next
      }
      println("\(self.id) - \(current)")
      return current
    }
  }
}

extension SequenceOf {
  // a skip extension, that skips the first 'n'
  // items in a sequence
  func skip (n:Int) -> SequenceOf<T> {
    var generator =  self.generate();
    for _ in 0..n {
      println("skipped")
      generator.next()
    }
    return SequenceOf(generator)
  }
}

// odd fibonacci numbers
let evenNumbers = filter(Fibonacci("#1")) { $0 % 2 == 0}
// even fibonacci numbers
let oddNumbers = filter(Fibonacci("#2")) { $0 % 2 == 1}
// zipped and skipped!
var zipped = SequenceOf(Zip2(oddNumbers, evenNumbers))
               .skip(2).generate()

// output the first few results
for _ in 1...2 {
  println(zipped.next())
}