Functional Networking Tomás Ruiz López Technical Lead at 47 Degrees @tomasruizlopez 

openapi: "3.0.0" info: title: Blogging platform version: "1.0.0" paths: /articles: get: tags: - Article operationId: getArticlesWithTag parameters: - name: tag in: query required: true schema: type: string responses: '200': description: The list of articles for the specified tag content: application/json: schema: $ref: '#/components/schemas/Articles' 

openapi: "3.0.0" info: title: Blogging platform version: "1.0.0" paths: /articles: get: tags: - Article operationId: getArticlesWithTag parameters: - name: tag in: query required: true schema: type: string responses: '200': description: The list of articles for the specified tag content: application/json: schema: $ref: '#/components/schemas/Articles' 

openapi: "3.0.0" info: title: Blogging platform version: "1.0.0" paths: /articles: get: tags: - Article operationId: getArticlesWithTag parameters: - name: tag in: query required: true schema: type: string responses: '200': description: The list of articles for the specified tag content: application/json: schema: $ref: '#/components/schemas/Articles' 

openapi: "3.0.0" info: title: Blogging platform version: "1.0.0" paths: /articles: get: tags: - Article operationId: getArticlesWithTag parameters: - name: tag in: query required: true schema: type: string responses: '200': description: The list of articles for the specified tag content: application/json: schema: $ref: '#/components/schemas/Articles' 

components: schemas: Articles: type: array items: $ref: '#/components/schemas/Article' Article: type: object required: - id - title properties: id: type: integer name: type: string 

components: schemas: Articles: type: array items: $ref: '#/components/schemas/Article' Article: type: object required: - id - title properties: id: type: integer name: type: string 

components: schemas: Articles: type: array items: $ref: '#/components/schemas/Article' Article: type: object required: - id - title properties: id: type: integer name: type: string 

func getArticles(withTag tag: String, callback: @escaping (Result<[Article], Error>) !-> Void) { let path = basePath + "/articles" var components = URLComponents(string: path) components!?.queryItems = [URLQueryItem(name: "tag", value: tag)] guard let url = components!?.url else { callback(.failure(NetworkError.malformedURL)) return } var request = URLRequest(url: url) request.httpMethod = "GET" headers.forEach { header in request.setValue(header.value, forHTTPHeaderField: header.key) } send(request: request, callback: callback) } 

func getArticles(withTag tag: String, callback: @escaping (Result<[Article], Error>) !-> Void) { let path = basePath + "/articles" var components = URLComponents(string: path) components!?.queryItems = [URLQueryItem(name: "tag", value: tag)] guard let url = components!?.url else { callback(.failure(NetworkError.malformedURL)) return } var request = URLRequest(url: url) request.httpMethod = "GET" headers.forEach { header in request.setValue(header.value, forHTTPHeaderField: header.key) } send(request: request, callback: callback) } 

func getArticles(withTag tag: String, callback: @escaping (Result<[Article], Error>) !-> Void) { let path = basePath + "/articles" var components = URLComponents(string: path) components!?.queryItems = [URLQueryItem(name: "tag", value: tag)] guard let url = components!?.url else { callback(.failure(NetworkError.malformedURL)) return } var request = URLRequest(url: url) request.httpMethod = "GET" headers.forEach { header in request.setValue(header.value, forHTTPHeaderField: header.key) } send(request: request, callback: callback) } 

func getArticles(withTag tag: String, callback: @escaping (Result<[Article], Error>) !-> Void) { let path = basePath + "/articles" var components = URLComponents(string: path) components!?.queryItems = [URLQueryItem(name: "tag", value: tag)] guard let url = components!?.url else { callback(.failure(NetworkError.malformedURL)) return } var request = URLRequest(url: url) request.httpMethod = "GET" headers.forEach { header in request.setValue(header.value, forHTTPHeaderField: header.key) } send(request: request, callback: callback) } 

func send(request: URLRequest, callback: @escaping (Result<[Article], Error>) !-> Void) { URLSession.shared.dataTask(with: request) { data, response, error in if let data = data, let response = response as? HTTPURLResponse { switch response.statusCode { case 200 !!..< 300: if let decoded = try? JSONDecoder().decode([Article].self, from: data) { callback(.success(decoded)) } else { callback(.failure(NetworkError.notDecodable)) } default: callback(.failure(NetworkError.malformedURL)) } } else if let error = error { callback(.failure(error)) } }.resume() } 

func send(request: URLRequest, callback: @escaping (Result<[Article], Error>) !-> Void) { URLSession.shared.dataTask(with: request) { data, response, error in if let data = data, let response = response as? HTTPURLResponse { switch response.statusCode { case 200 !!..< 300: if let decoded = try? JSONDecoder().decode([Article].self, from: data) { callback(.success(decoded)) } else { callback(.failure(NetworkError.notDecodable)) } default: callback(.failure(NetworkError.malformedURL)) } } else if let error = error { callback(.failure(error)) } }.resume() } 

func send(request: URLRequest, callback: @escaping (Result<[Article], Error>) !-> Void) { URLSession.shared.dataTask(with: request) { data, response, error in if let data = data, let response = response as? HTTPURLResponse { switch response.statusCode { case 200 !!..< 300: if let decoded = try? JSONDecoder().decode([Article].self, from: data) { callback(.success(decoded)) } else { callback(.failure(NetworkError.notDecodable)) } default: callback(.failure(NetworkError.malformedURL)) } } else if let error = error { callback(.failure(error)) } }.resume() } 

func send(request: URLRequest, callback: @escaping (Result<[Article], Error>) !-> Void) { URLSession.shared.dataTask(with: request) { data, response, error in if let data = data, let response = response as? HTTPURLResponse { switch response.statusCode { case 200 !!..< 300: if let decoded = try? JSONDecoder().decode([Article].self, from: data) { callback(.success(decoded)) } else { callback(.failure(NetworkError.notDecodable)) } default: callback(.failure(NetworkError.malformedURL)) } } else if let error = error { callback(.failure(error)) } }.resume() } 

func send(request: URLRequest, callback: @escaping (Result<[Article], Error>) !-> Void) { URLSession.shared.dataTask(with: request) { data, response, error in if let data = data, let response = response as? HTTPURLResponse { switch response.statusCode { case 200 !!..< 300: if let decoded = try? JSONDecoder().decode([Article].self, from: data) { callback(.success(decoded)) } else { callback(.failure(NetworkError.notDecodable)) } default: callback(.failure(NetworkError.malformedURL)) } } else if let error = error { callback(.failure(error)) } }.resume() } 

func send(request: URLRequest, callback: @escaping (Result<[Article], Error>) !-> Void) { URLSession.shared.dataTask(with: request) { data, response, error in if let data = data, let response = response as? HTTPURLResponse { switch response.statusCode { case 200 !!..< 300: if let decoded = try? JSONDecoder().decode([Article].self, from: data) { callback(.success(decoded)) } else { callback(.failure(NetworkError.notDecodable)) } default: callback(.failure(NetworkError.malformedURL)) } } else if let error = error { callback(.failure(error)) } }.resume() } 

Bow bow-swift.io 

func send(request: URLRequest, callback: @escaping (Result<[Article], Error>) !-> Void) { URLSession.shared.dataTask(with: request) { data, response, error in if let data = data, let response = response as? HTTPURLResponse { switch response.statusCode { case 200 !!..< 300: if let decoded = try? JSONDecoder().decode([Article].self, from: data) { callback(.success(decoded)) } else { callback(.failure(NetworkError.notDecodable)) } default: callback(.failure(NetworkError.malformedURL)) } } else if let error = error { callback(.failure(error)) } }.resume() } Insufficient abstraction 

func send(request: URLRequest, callback: @escaping (Result) !-> Void) { URLSession.shared.dataTask(with: request) { data, response, error in if let data = data, let response = response as? HTTPURLResponse { switch response.statusCode { case 200 !!..< 300: if let decoded = try? JSONDecoder().decode(T.self, from: data) { callback(.success(decoded)) } else { callback(.failure(NetworkError.notDecodable)) } default: callback(.failure(NetworkError.malformedURL)) } } else if let error = error { callback(.failure(error)) } }.resume() } Insufficient abstraction Parametric polymorphism 

func dataTask(with request: URLRequest, completion: @escaping (Data?, URLResponse?, Error?) !-> Void) Illegal states 

func dataTaskADT(with request: URLRequest, completion: @escaping (Either) !-> Void) Illegal states Algebraic Data Types 

func dataTaskADT(with request: URLRequest, completion: @escaping (Either) !-> Void) Callback-based communication & Side-effects 

func dataTaskIO(with request: URLRequest) !-> IO Callbacks & Side-Effects Suspension 

extension URLSession { func dataTaskIO(with request: URLRequest) !-> IO { IO.async { callback in self.dataTask(with: request) { data, response, error in if let data = data, let response = response { callback(.right((data, response))) } else if let error = error { callback(.left(error)) } }.resume() }^ } } 

func send(request: URLRequest) !-> IO { URLSession.shared.dataTaskIO(with: request) .flatMap { response, data in guard let response = response as? HTTPURLResponse else { return IO.raiseError(NetworkError.malformedURL) } switch response.statusCode { case 200 !!..< 300: return JSONDecoder().safeDecode(T.self, from: data) default: return IO.raiseError(NetworkError.malformedURL) } }^ } Global dependencies 

func send(request: URLRequest, session: URLSession, decoder: SafeDecoder) !-> IO Global dependencies Explicit dependencies 

func send(request: URLRequest, config: APIConfig) !-> IO Global dependencies Explicit dependencies 

func send(request: URLRequest) !-> (APIConfig) !-> IO Global dependencies Explicit dependencies 

func send(request: URLRequest) !-> EnvIO Global dependencies Environmental Effects 

func send(request: URLRequest) !-> EnvIO { EnvIO { config in config.session.dataTaskIO(with: request) .flatMap { response, data in guard let response = response as? HTTPURLResponse else { return IO.raiseError(NetworkError.malformedURL) } switch response.statusCode { case 200 !!..< 300: return config.decoder.safeDecode(T.self, from: data) default: return IO.raiseError(NetworkError.malformedURL) } }^ } } Global dependencies Environmental Effects 

No content

Bow Open Api openapi.bow-swift.io 

OpenAPI.yaml bow-openapi Swift Package 

brew tap bow-swift/bow brew install bow-openapi bow-openapi "#name MyAPI "#schema Swagger.json "#output ./MyAPI Install Run 

import MyAPI let articlesRequest = API.articles.getArticles() Using generated code 

let config = API.Config(basePath: “https:!//url-to-my-server.com") let articles = try? articlesRequest.provide(config).unsafeRunSync() articlesRequest.provide(config).unsafeRunAsync { either in either.fold({ httpError in !/* !!... !*/ }, { articles in !/* !!... !*/ }) } Running a request 

import MyAPITest func testEmptyResponse() { let successConfig = API.Config(basePath: "https:!//url-to-my-server.com") .stub(json: "[]", code: 200) let expected = [] assert(API.article.getArticles(), withConfig: successConfig, succeeds: expected, "An empty array was expected") } func testContentResponse() { let successConfig = API.Config(basePath: "https:!//url-to-my-server.com") .stub(contentsOfFile: fileURL, code: 200) let expected = [ Article(identifier: 1234, title: "Intro to Bow OpenAPI") ] assert(API.article.getArticles(), withConfig: successConfig, succeeds: expected, "An array with a single element was expected") } Testing a request 

import MyAPITest func testEmptyResponse() { let successConfig = API.Config(basePath: "https:!//url-to-my-server.com") .stub(json: "[]", code: 200) let expected = [] assert(API.article.getArticles(), withConfig: successConfig, succeeds: expected, "An empty array was expected") } func testContentResponse() { let successConfig = API.Config(basePath: "https:!//url-to-my-server.com") .stub(contentsOfFile: fileURL, code: 200) let expected = [ Article(identifier: 1234, title: "Intro to Bow OpenAPI") ] assert(API.article.getArticles(), withConfig: successConfig, succeeds: expected, "An array with a single element was expected") } Testing a request 

import MyAPITest func testEmptyResponse() { let successConfig = API.Config(basePath: "https:!//url-to-my-server.com") .stub(json: "[]", code: 200) let expected = [] assert(API.article.getArticles(), withConfig: successConfig, succeeds: expected, "An empty array was expected") } func testContentResponse() { let successConfig = API.Config(basePath: "https:!//url-to-my-server.com") .stub(contentsOfFile: fileURL, code: 200) let expected = [ Article(identifier: 1234, title: "Intro to Bow OpenAPI") ] assert(API.article.getArticles(), withConfig: successConfig, succeeds: expected, "An array with a single element was expected") } Testing a request 

Bow vs. Combine 

Bow vs. Combine Works in earlier versions of iOS and macOS 

Bow vs. Combine Works in earlier versions of iOS and macOS Lazyness guarantees referential transparency 

Bow vs. Combine io.retry(Schedule.exponential(.milliseconds(250)) .and(Schedule.recurs(10))) publisher.retry(10) Composable and powerful retrial policies 

binding( user !<- API.user.getMyProfile(), articles !<- API.article.getArticles(withTag: "featured"), home !<- makeHome(for: user.get, with: articles.get), yield: home.get) Bow vs. Combine Convenient imperative-style syntax 

Conclusion 

Conclusion Bow bow-swift.io 

Conclusion Bow bow-swift.io Bow Open Api openapi.bow-swift.io 

Conclusion FP Bow bow-swift.io Bow Open Api openapi.bow-swift.io 

Functional Networking Tomás Ruiz López Technical Lead at 47 Degrees @tomasruizlopez