Sample code from this blog post: http://thepurecoder.com/more-on-fold/

more_fold.swift

func foldl1<A>(list: Array<A>, f: (A, A) -> A) -> A {
    return foldl(list.head!, list: list.tail!, f: f)
}

extension Array {
    var initial: Array<Element>? {
        get {
            if self.empty() { return nil }
            return Array(dropLast(self))
        }
    }
}

func foldr<A,B>(acc: A, list: Array<B>, f: (B, A) -> A) -> A {
    if list.empty() { return acc }
    return foldr(f(list.last!, acc), list: list.initial!, f: f);
}

func foldr1<A>(list: Array<A>, f: (A, A) -> A) -> A {
    return foldr(list.last!, list: list.initial!, f: f)
}