bound.swift

## bound.swift
enum State {
    case Success(value:String)
    case Error(error:NSError)
}

class Bound:Printable {
    let pointer:NSErrorPointer
    var state:State
    var step:Int = 0

    init(initial:String, pointer:NSErrorPointer) {
        self.pointer = pointer
        self.state = .Success(value: initial)
    }

    var description:String {
        var stateDescription:String!
        switch state {
            case .Error(let error): stateDescription = "Error(\(error))"
            case .Success(let value): stateDescription = "Success(\(value))"
        }
        return "Step \(step++): " + stateDescription
    }

    func swiftStyle(op:(String) -> State) -> Bound {
        println(self)
        switch state {
            case .Success(let value):
                state = op(value)
            default: break;
        }

        switch state {
        case .Error(let error):
            if pointer {
                pointer.memory = error // wrapped if you like
            }
        default: break
        }
        return self
    }

    func objCStyle(op2:(String, NSErrorPointer) -> String?) -> Bound {
        swiftStyle { (incoming:String) in
            let localPointer =  UnsafePointer<NSError>.alloc(1)
            if let newValue = op2(incoming, NSErrorPointer(localPointer)) {
                return State.Success(value: newValue)
            }
            var localError = localPointer.move()
            return State.Error (error: localError)
        }
        return self
    }

    func cantFail(op:(inout x:String) -> ()) -> Bound {
        swiftStyle { (x:String) in
            var y:String = x
            op(x: &y)
            return State.Success(value: y)
        }
        return self
    }

    func debugErrors(op:(NSError) -> ()) -> Bound {
        switch state {
            case .Error(let error): op(error)
            default: break
        }
        return self
    }

    func value() -> String? {
        switch state {
            case .Success(let value): return value
            default: return nil
        }
    }
}

class SomeError:NSError {  }

func load(website:String, errorPointer:NSErrorPointer = nil) -> String?
{ return Bound(initial:website, pointer: errorPointer)

    .swiftStyle {
        $0.isEmpty ? .Error(error:SomeError())
                   : .Success(value: "http://www." + $0 + ".com")
    }

    .objCStyle { (incoming, pointer) in
        let url = NSURL(string: incoming)
        return NSString(contentsOfURL:url, encoding:NSUTF8StringEncoding, error:pointer)
    }

    .debugErrors { (error:NSError) in
        println(error) // or set breakpoint here
    }

    .cantFail { (inout value:String) in
        value += ""
    }

    .value()
}

load("google")