Continuation Passing Style in Swift

Cps.swift

// Poorman's continuation passing style library
struct Cps {
    static func seqByIdx<E, U>(list: [(U, (E?, U) -> ()) -> ()], idx: UInt, value: U,  next: (U) -> (), fail: (E) -> ()) {
        if idx >= UInt(list.count) {
            next(value)
        } else {
            list[Int(idx)](value, { (errorp: E?, result: U) -> () in
                if let error = errorp {
                    fail(error)
                } else {
                    Cps.seqByIdx(list, idx: idx + 1, value: result, next: next, fail: fail)
                }
            })
        }
    }

    static func seq<E,U>(list: [(U, (E?, U) -> ()) -> ()], value: U, _ next: (E?, U) -> ()) {
        seqByIdx(list, idx: 0, value: value, next: { (u) -> () in
            next(nil, u)
        }, fail: { (e) -> () in
            next(e, value)
        })
    }

    static func seq(list: [((Bool) -> ()) -> ()], _ next: (ok: Bool) -> ()) {
        let adapted_list: [((), (()?, ()) ->()) -> ()]

        adapted_list = list.map { e  in {
            (void, next) -> () in
                e { success in
                    next(success ? nil : (), ())
                }
            }
        }

        seqByIdx(adapted_list, idx: 0, value: (), next: { (u) -> () in
            next(ok: true)
        }, fail: { (e) -> () in
            next(ok: false)
        })
    }
}

Inspired by cps