Implement "cond" expression (from Lisp) in Swift

gistfile1.swift

//
//  AppDelegate.swift
//  testasdfsadf
//
//  Created by Benedikt Terhechte on 10/12/14.
//  Copyright (c) 2014 Benedikt Terhechte. All rights reserved.
//

import Cocoa

func _cond<T> (a1: @autoclosure () -> Bool, b1: @autoclosure () -> T?,
    a2: @autoclosure () -> Bool, b2: @autoclosure () -> T?,
    a3: @autoclosure () -> Bool, b3: @autoclosure () -> T?,
    a4: @autoclosure () -> Bool, b4: @autoclosure () -> T?,
    a5: @autoclosure () -> Bool, b5: @autoclosure () -> T?
    ) -> T? {
        if a1() {
            return b1()
        } else if a2() {
            return b2()
        } else if a3() {
            return b3()
        } else if a4() {
            return b4()
        } else if a5() {
            return b5()
        }
        return nil
}
// two parameter implementation
func cond<T>(a1: @autoclosure () -> Bool, b1: @autoclosure () -> T?,
    a2: @autoclosure () -> Bool, b2: @autoclosure () -> T?,
    bf: @autoclosure () -> T?) -> T {
        if let r = _cond(a1, b1, a2, b2, false, {return nil}(), false, {return nil}(), false, {return nil}()) {
            return r
        }
        return bf()!
}

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {

    @IBOutlet weak var window: NSWindow!


    func applicationDidFinishLaunching(aNotification: NSNotification) {
        // Insert code here to initialize your application
        let value = cond(4 == 5, 8, // if 4 equals 5, return 9
                         3 == 3, 9, // if 3 equels 3, return 9
                         10) // else, return 10
        print ("Value is", value)
    }

    func applicationWillTerminate(aNotification: NSNotification) {
        // Insert code here to tear down your application
    }


}