Functional Validation with Arrow and Bow

Examples of validation of two fields in a mobile application using Arrow (Android) and Bow (iOS) frameworks.
The examples in code show how to perform validation with Option, Either and Validated data types.
Examples are in Swift and Kotlin.

Transcript

1. FUNCTIONAL VALIDATION WITH ARROW AND BOW DANIELE CAMPOGIANI @DCAMPOGIANI GIOVANNI CATANIA @GIOEVI90
2. LEARNING KOTLIN LEARNING ARROW LEARNING SWIFT LEARNING FUNCTIONAL PROGRAMMING IOS DEVELOPER ANDROID DEVELOPER
3. WHY SHOULD I CARE ABOUT FUNCTIONAL PROGRAMMING? Mobile Developer
8. FUNCTIONAL COMPANION TO KOTLIN'S STANDARD LIBRARY ARROW-KT.IO
9. BOW IS A LIBRARY FOR TYPED FUNCTIONAL PROGRAMMING IN SWIFT BOW-SWIFT.IO
10. DATA TYPE ▸Option ▸Either ▸Validated
11. OPTION enum Option<T> { case some(_ value: T) case none() }
12. OPTION - FOLD enum Option<T> { func fold<V>(_ f: () -> V, _ g: (T) -> V) -> V { switch self { case .none(): return f() case let .some(value): return g(value) } } }
13. OPTION - FOLD let option: Option<String> = Option.some("Giovanni") let message = option.fold({ "Hello Stranger" }, { "Hello \($0)” }) //Hello Giovanni
14. OPTION - MAP enum Option<T> { func map<V>(_ f: (T) -> V) -> Option<V> { switch self { case let .some(value): return Option<V>.some(f(value)) case .none: return Option<V>.none() } } }
15. OPTION - MAP let value = Option.some(42).map({ $0 * 2 }) // Option.some(84)
16. OPTION - FLATMAP enum Option<T> { func flatMap<V>(_ f: (T) -> Option<V>) -> Option<V> { switch self { case let .some(value): return f(value) case .none: return Option<V>.none() } } }
17. OPTION - FLATMAP func toInt(_ input: String) -> Option<Int> { guard let value = Int(input) else { return Option.none() } return Option.some(value) } let result = Option.some("42").flatMap(toInt) //Option.some(42)
18. OPTION - MAIL public extension String { public func optionEmail() -> Option<String> { guard isValidEmail() else { return Option.none() } return Option.some(self) } }
19. OPTION - NUMBER public extension String { public func optionPhone() -> Option<String> { guard isValidPhone() else { return Option.none() } return Option.some(self) } }
20. public struct FormData { public let email: String public let phone: String } STRUCT - FORMDATA
21. MERGE OPTION OPTION MAIL OPTION NUMBER OPTION FORM DATA ?
22. APPLICATIVE ▸ A way to put a value in the context: Option.some(value) ▸ Map ▸ FlatMap ▸ For experienced FP programmers: we are taking a shortcut here, just wait few slides :)
23. OPTION - APPLICATIVE public func optionFormData(_ inputEmail: String, _ inputPhone: String) -> Option<FormData> { let email = inputEmail.optionEmail() let phone = inputPhone.optionPhone() return Option<FormData> .applicative() .map(email, phone, FormData.init) .fix() }
24. OPTION - PRESENTER struct OptionPresenter: OptionPresenterProtocol { let validation: Validation weak var view: OptionViewProtocol? init(view: OptionViewProtocol?) { self.validation = Validation() self.view = view } func validateEmailAndPhone(_ email: String, phone: String) { validation .optionFormData(email, phone) .fold(showError, validateField) } func showError() { view?.showError() } func validateField(_ field: FormData) { view?.validationSucceded(field) } }
25. OPTION - VIEWCONTROLLER class OptionViewController: UIViewController { @IBOutlet private weak var emailTextField: UITextField? @IBOutlet private weak var phoneTextField: UITextField? var presenter: OptionPresenterProtocol? @IBAction func proceed(_ sender: UIButton) { presenter?.validateEmailAndPhone(emailTextField?.text ?? "", phone: phoneTextField?.text ?? "") } }
26. OPTION - VIEWCONTROLLER - HANDLE RESULTS extension OptionViewController: OptionViewProtocol { func showError() { UIAlertController.showMessage("Validation error", in: self) } func validationSucceded(_ field: FormData) { UIAlertController.showMessage("Validation succeded: \n email: \(field.email) \n phone: \(field.phone)", in: self) } }
30. EITHER enum Either<Left, Right> { case left(_ value: Left) case right(_ value: Right) }
31. EITHER - MAP enum Either<Left, Right> { func map<V>(_ f: (Right) -> V) -> Either<Left, V> { switch self { case let .left(value): return .left(value) case let .right(value): return Either<Left, V>.right(f(value)) } } }
32. EITHER - MAP let value = Either<String, Int>.right(42) let result = value.map({ $0 * 2 }) //Either<String, Int>.right(84)
33. EITHER - FLATMAP enum Either<Left, Right> { func flatMap<V>(_ f: (Right) -> Either<Left, V>) -> Either<Left, V> { switch self { case let .left(value): return .left(value) case let .right(value): return f(value) } } }
34. EITHER - FLATMAP func toInt(_ input: String) -> Either<String, Int> { guard let value = Int(input) else { return Either.left("string in input is not an integer") } return Either.right(value) } let result = Either.right("42").flatMap(toInt) //Either<String, Int>.right(42)
35. EITHER - MAIL public extension String { public func eitherEmail() -> Either<ValidationError, String> { guard isValidEmail() else { return Either.left(.invalidEmail) } return Either.right(self) } }
36. EITHER - NUMBER public extension String { public func eitherPhone() -> Either<ValidationError, String> { guard isValidPhone() else { return Either.left(.invalidPhone) } return Either.right(self) } }
37. EITHER - APPLICATIVE public func eitherFormData(_ inputEmail: String, _ inputPhone: String) -> Either<ValidationError, FormData> { let email = inputEmail.eitherEmail() let phone = inputPhone.eitherPhone() return Either.fix(Either<ValidationError, FormData> .applicative() .map(email, phone, FormData.init)) }
38. EITHER - PRESENTER struct EitherPresenter: EitherPresenterProtocol { let validation: Validation weak var view: EitherViewProtocol? init(view: EitherViewProtocol?) { self.validation = Validation() self.view = view } func validateEmailAndPhone(_ email: String, phone: String) { validation .eitherFormData(email, phone) .fold(showError, validationSucceeded) } func showError(_ error: ValidationError) { view?.showError(error) } func validationSucceeded(_ field: FormData) { view?.validationSucceded(field) } }
39. EITHER - VIEWCONTROLLER class EitherViewController: UIViewController { @IBOutlet private weak var emailTextField: UITextField? @IBOutlet private weak var phoneTextField: UITextField? var presenter: EitherPresenterProtocol? @IBAction func proceed(_ sender: UIButton) { presenter?.validateEmailAndPhone(emailTextField?.text ?? "", phone: phoneTextField?.text ?? "") } }
40. EITHER - VIEWCONTROLLER - HANDLE RESULTS extension EitherViewController: EitherViewProtocol { func showError(_ error: ValidationError) { UIAlertController.showMessage(error.localizedDescription, in: self) } func validationSucceded(_ field: FormData) { UIAlertController.showMessage("Validation succeded: \n email: \(field.email) \n phone: \(field.phone)", in: self) } }
45. VALIDATED sealed class Validated<out A, out B> data class Invalid<out A>(val value: A) : Validated<A, Nothing>() data class Valid<out B>(val value: B) : Validated<Nothing, B>()
46. VALIDATED - MAP sealed class Validated<out A, out B> { fun <C> map(f: (B) -> C): Validated<A, C> = when (this) { is Invalid -> Invalid(value) is Valid -> Valid(f(value)) } }
47. VALIDATED - MAP val input: Validated<List<String>, Int> = Valid(42) val result = input.map { it * 2 } //Valid(value=84)
48. SEMIGROUP interface Semigroup<A> { fun combine(x: A, y: A): A } object StringSemigroup : Semigroup<String> { fun combine(x: String, y: String) = "$x $y" } class ListSemigroup<T> : Semigroup<List<T>> { fun combine(x: List<T>, y: List<T>) = x + y }
49. VALIDATED - APPLY fun Validated<A, B>.ap( SE: Semigroup<A>, f: Validated<A, (B) -> C>): Validated<A, C> = fold( { e -> f.fold({ Invalid(SE.combine(it, e)) },{ Invalid(e) })}, { a -> f.fold(::Invalid, { Valid(it(a)) }) })
50. APPLICATIVE ▸ A way to put a value in the context: ▸ Map ▸ FlatMap ▸ Apply ▸ FlatMap is more powerful than Apply: if a class has FlatMap, Apply can be written using FlatMap
51. VALIDATION ERROR sealed class ValidationError { object InvalidMail : ValidationError() object InvalidPhoneNumber : ValidationError() }
52. VALIDATED - MAIL fun String.validatedMail(): Validated<Nel<ValidationError>, String> = when { validMail(this) -> Valid(this) else -> Invalid(Nel(ValidationError.InvalidMail)) }
53. VALIDATED - NUMBER private fun String.validatedPhoneNumber(): Validated<Nel<ValidationError>, String> = when { validNumber(this) -> Valid(this) else -> Invalid(Nel(ValidationError.InvalidPhoneNumber)) }
54. VALIDATED - APPLICATIVE fun validateData(inputMail: String, inputNumber: String): Validated<Nel<ValidationError>, FormData> { val mail = inputMail.validatedMail() val phoneNumber = inputNumber.validatedPhoneNumber() val SE = Nel.semigroup<ValidationError>() return Validated.applicative(SE).map(mail, phoneNumber) { FormData(it.a, it.b) } }
55. VALIDATED - VIEWMODEL class ValidatedNelValidationErrorViewModel : ViewModel() { private val mutableValidation: MutableLiveData<Validated<Nel<ValidationError>, FormData>> = MutableLiveData() val validation: LiveData<Validated<Nel<ValidationError>, FormData>> get() = mutableValidation fun validate(mail: String, phoneNumber: String) { mutableValidation.value = validateData(mail, phoneNumber) } }
56. VALIDATED - ACTIVITY class ValidatedNelValidationErrorActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_input) val viewModel = ViewModelProviders.of(this)[ValidatedNelValidationErrorViewModel::class.java] signup_button.setOnClickListener { viewModel.validate(email.text.toString(), number.text.toString()) } viewModel.validation.observe(this, Observer { it?.fold(this::handleInvalid, this::handleValid) }) } }
57. VALIDATED - ACTIVITY - HANDLE RESULTS fun handleInvalid(errors: Nel<ValidationError>) = errors.map { getInvalidField(it) }.forEach { it.second.error = it.first } fun getInvalidField(validationError: ValidationError): Pair<String, TextInputLayout> = when (validationError) { ValidationError.InvalidMail -> Pair(getString(R.string.invalid_mail), emailWrapper) ValidationError.InvalidPhoneNumber -> Pair(getString(R.string.invalid_phone_number), numberWrapper) }
62. RECAP ▸ Each data type has his own logic ▸ We can write less code combining existing methods ▸ This is just the beginning :)
63. THANKS https://github.com/DanielaSfregola/data-validation https://github.com/arrow-kt/arrow https://github.com/bow-swift/bow