gistfile1.swift

struct OddNumbersTimesFiveGenerator<S : Sequence where S.GeneratorType.Element == Int> : Generator {
    typealias Element = Int
    var elements : S.GeneratorType

    mutating func next() -> Int? {
        while (true) {
            if let x = elements.next() {
                if x % 2 == 0 { continue }
                else          { return x * 5 }
            }
            else { return nil }
        }
    }

    init(_ seq: S) {
        self.elements = seq.generate()
    }
}

let xs = [1, 5, 8, 3]
let gen = OddNumbersTimesFiveGenerator(xs)
let seq = SequenceOf<Int>({ gen })
for x in seq {
    println(String(x))
}