:(.swift

import Foundation
import ImageIO


//
// before
//

func datesFromImagesInDir(dir: String) -> [NSDate] {
  let fm = NSFileManager.defaultManager()
  var error: NSError?
 
  let df = NSDateFormatter()
  df.dateFormat = "yyyy:MM:dd HH:mm:ss"
 
  typealias rn_CGPropDictionary = Dictionary<String, AnyObject>
 
  var dates = [NSDate]()
 
  let options = [(kCGImageSourceShouldCache as String): false]
 
  if let imageURLs = fm.contentsOfDirectoryAtPath(dir, error: &error) as? [String] {
    for fileName in imageURLs {
      if let url = NSURL(fileURLWithPath: dir)?.URLByAppendingPathComponent(fileName) {
        if let imageSource = CGImageSourceCreateWithURL(url, nil) {
          if let imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, options) as? rn_CGPropDictionary {
            if let exif = imageProperties[kCGImagePropertyExifDictionary] as? rn_CGPropDictionary {
              if let originalDateString = exif[kCGImagePropertyExifDateTimeOriginal] as? String {
                if let date = df.dateFromString(originalDateString) {
                  dates.append(date)
                }
              }
            }
          }
        }
      }
    }
  }
 
  return dates
}

//
// after
//

infix operator >>= { associativity left }

func >>=<A,B>(l: A?, r: A -> B?) -> B? {
    if let x = l {
        return r(x)
    }
    return nil
}

func flatMap<A,B>(list: [A], f: A -> B?) -> [B] {
    var result : [B] = []
    for x in list {
        if let value = f(x) {
            result.append(value)
        }
    }
    return result
}

func datesFromImagesInDir(dir: String) -> [NSDate] {
    let fm = NSFileManager.defaultManager()
    var error: NSError?
    
    let df = NSDateFormatter()
    df.dateFormat = "yyyy:MM:dd HH:mm:ss"
    
    typealias rn_CGPropDictionary = Dictionary<String, AnyObject>
    
    var dates = [NSDate]()
    
    let options = [(kCGImageSourceShouldCache as String): false]
    
    let dateTimeOriginal = { (exif: rn_CGPropDictionary) in (exif[kCGImagePropertyExifDateTimeOriginal] as? String) }
    let exif = { (imageProperties: rn_CGPropDictionary) in imageProperties[kCGImagePropertyExifDictionary] as? rn_CGPropDictionary }
    let imageProperties =  { CGImageSourceCopyPropertiesAtIndex($0, 0, options) as? rn_CGPropDictionary }
    let imageSource = { CGImageSourceCreateWithURL($0, nil) }
    let absoluteURL = { (fileName: String) in NSURL(fileURLWithPath: dir)?.URLByAppendingPathComponent(fileName) }

    let directoryContents = fm.contentsOfDirectoryAtPath(dir, error: &error) as? [String]
    
    return directoryContents.map  {
        return flatMap($0) { fileName in
            absoluteURL(fileName) >>= imageSource >>= imageProperties >>= exif >>= dateTimeOriginal >>= df.dateFromString
        }
    } ?? []
}