gistfile1.swift

func sift<T, S: Sequence where S.GeneratorType.Element == Optional<T>>(xs: S) -> GeneratorOf<T> {
    var gen = xs.generate()
    return GeneratorOf<T> {
        var next: T??
        do {
            next = gen.next()
            if !next { return nil }
        } while !(next!)
        return next!
    }
}

let opts: [Int?] = [1, 3, nil, 4, 7]
[Int](sift(opts)) // [1, 3, 4, 7]