:(

import Foundation
import ImageIO

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
        }
    } ?? []
}

This is a bit longer, but almost everything is reusable... lines 36-39 could be pulled out. Also, the two functions are of course reusable across any project.

I love it. Didn't think to capture each step in a closure. I was thinking of breaking everything out into their own functions but didn't like that since each step is really only relevant to this implementation. I really appreciate it!