Shuffle program for Trill in the iOS app

shuffle.tr

foreign type Array {
  foreign init() -> Array
  foreign func push(_: Any)
  foreign subscript(_: Int) -> Any
  foreign var length: Int
}

foreign type Math {
  foreign static func random() -> Double
  foreign static func floor(_: Double) -> Int
}

extension Array {
  /*
   * A standard Fischer-Yates shuffle,
   * in-place.
   */
  mutating func shuffle() {
    for var i = 0; i < self.length; i += 1 {
      let swap = Math.floor(Math.random() * 
           (self.length - i) as Double) + i
      let tmp = self[swap]
      self[swap] = self[i]
      self[i] = tmp
    }
  }
  func shuffled() -> Array {
    var copy = self.copy()
    copy.shuffle()
    return copy
  }
  func copy() -> Array {
    var new_ = Array()
    for var i = 0; i < self.length; i += 1 {
      new_.push(i)
    }
    return new_
  }
}

func main() {
  var nums = Array()
  for var i = 1; i <= 10; i += 1 {
    nums.push(i)
  }
  print("Numbers: ")
  println(nums)

  print("Shuffled: ")
  nums.shuffle()
  let n = nums.shuffled()
  println(nums)
  println(n)
}