rec.swift

private func processResponse(response: NSURLResponse!, connection: NSURLConnection, data: NSData!, error: NSError!) {
        let result =
        // Check if there was an error reported back
        testError(error, forRequest: connection.originalRequest) >>- { _ in
            Result(connection.currentRequest.URL, failWith: NSError(domain: RecordingProtocol.errorDomain, code: -670,
                userInfo: [NSLocalizedDescriptionKey: "Unable to extract the request's last path component for file name generation."]))
            .analysis(ifSuccess: { url -> Result<NSURL, NSError> in // Extract the request's url
                let docsResult = try { // Get the `Documents` folder path
                    return NSFileManager.defaultManager().URLForDirectory(.DocumentDirectory, inDomain: .UserDomainMask, appropriateForURL: nil, create: false, error: $0)
                }
                
                return docsResult >>- { docsURL -> Result<NSURL, NSError> in
                    if let lastPathComponent = url.lastPathComponent { // Extract the name of the `URL` request
                        return Result.success(docsURL.URLByAppendingPathComponent(lastPathComponent).URLByAppendingPathExtension("json"))
                    }
                    
                    return Result.failure(NSError(
                        domain: RecordingProtocol.errorDomain,
                        code: -670,
                        userInfo: [NSLocalizedDescriptionKey: "Unable to extract the request's last path component for file name generation."]))
                }
            }, ifFailure: {
                return Result.failure(NSError(
                    domain: RecordingProtocol.errorDomain,
                    code: -669,
                    userInfo: [ NSLocalizedDescriptionKey: "Unable to get the «Document»'s directory path", NSUnderlyingErrorKey: $0]))
            }) >>- { fileUrl -> Result<String, NSError> in
                let finalResult = Result(NSString(data: data, encoding: NSUTF8StringEncoding), failWith: NSError(
                    domain: RecordingProtocol.errorDomain,
                    code: -668,
                    userInfo: [NSLocalizedDescriptionKey: "Unable to correctly parse a `JSON` response for \(connection.originalRequest)"]))
                    >>- { json in // Write the parse `JSON` to disk
                        return try { json.writeToURL(fileUrl, atomically: true, encoding: NSUTF8StringEncoding, error: $0) }
                            >>- { Result.success("Filed saved to \(fileUrl.absoluteString)") }
                    }
                
                // «Cascade up» the success or add our own failure.
                return finalResult ?? Result.failure(NSError(
                        domain: RecordingProtocol.errorDomain,
                        code: -671,
                        userInfo: [
                            NSLocalizedDescriptionKey: "Unable to save file \(fileUrl.lastPathComponent) to here \(fileUrl.absoluteString)",
                            NSUnderlyingErrorKey: finalResult.error!
                        ]))
            }
        }

        if let callback = operationResult {
            callback(result)
        }
    }