ListZipper.swift

  init(from list: [T] = []) {
    cursor = list.first
    rightList = list
  }
  
  /// Convert to a swift array
  func toList() -> [T] {
    if let c = cursor {
      return leftList + [c] + rightList.reversed()
    } else {
      return leftList + rightList.reversed()
    }
  }