foldr and foldl in Swift2.0

fold.swift

extension CollectionType {
    func foldr<B>(accm:B, f: (Self.Generator.Element, B) -> B) -> B {
        var g = self.generate()
        func next() -> B {
            return g.next().flatMap {x in f(x, next())} ?? accm
        }
        return next()
    }
    
    func foldl<B>(accm:B, f: (Self.Generator.Element, B) -> B) -> B {
        var result = accm
        for temp in self {
            result = f(temp, result)
        }
        return result
    }
}

[10, 1, 3, 4, -4].foldr(1) { (acc, x) -> Int in
    return acc + 2 * x
}

[10, 1, 3, 4, -4].foldl(1) { (acc, x) -> Int in
    return acc + 2 * x
}