en nybegynners introduksjon til scalaz

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scalaz

En nybegynners introduksjon

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Agenda•Bakgrunnen for at jeg har tatt i bruk scalaz

•En vei gjennom rammeverket

•Konklusjoner

•Gjerne spørsmål underveis!

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Trond Marius Øvstetun

•Sjesfkonsulent i Mesan

•Utvikler, arkitekt, teamleder +++

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Mesan... når standardsystemer ikke er nok

•Systemutvikling – skreddersøm

•Løsningsfokus

•Transaksjonssystemer

•Lang levetid – langsiktighet ogvedlikeholdbarhet

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Hvorfor scalaz?

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Hvorfor scalaz?•If you are thinking about using Scalaz, stop now while you still have your sanity! ref

•Don’t listen to anyone telling you to use Scalaz!

•Hva er greia med metodene<:::, :::>, <+>, |@|, ★, ☆, <=< ?

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Mitt triggerpunkt

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unfiltered og json

case req @ POST(Path("/person")) => { val x = Body.string(req) val p: Person = read[Person](x) val id: Int = personer.add(p)

Created ~> Json("id" -> id)}

case class Person(name: String, age: Int)

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json

val json = """{"name": "Petter", "age": 22}"""read[Person](json)

val json = """{"name":"Petter"}"""read[Person](json)

=> Person(Petter, 22)

=> org.json4s.package$MappingException: No usable value for age Did not find value which can be converted into int

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Validering av input

def add(p: Person): Int = { Validate.isTrue(p.age > 18 && p.age < 60) 1}

case req @ POST(Path("/person")) => { val x = Body.string(req) val p: Person = read[Person](x) val id: Int = personer.add(p)

Created ~> Json("id" -> id)}

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Fra en klients perspektiv...

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Fra en utviklers perspektiv

Dette føles ikke bra!

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validering med scalaz

case req @ POST(Path("/personz")) => { val x = Body.string(req) val p = fromJSON[Person](parse(x)) val id = p map personer.add

id match { case Success(i) => Created ~> Json("id"->i) case Failure(errors) => Forbidden ~> Json("errors" -> jsonErrors(errors).toList) }}

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validering med scalaz



implicit val personR: JSONR[Person] = Person.applyJSON(field[String]("name"), validate[Int]("age") >==> min(18) >==> max(60))

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Fra en klients perspektiv...

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Fra en utviklers perspektiv

Mye bedre?! Men?!

>==> fromJSON[Person]

Kleisli[Result, JValue, A]

type EitherNel[+a] = NonEmptyList[Error] \/ a

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scalaz

import scalaz._import Scalaz._

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Hva er scalaz?•Scalaz is a Scala library for functional programming.

•It provides purely functional data structures to complement those from the Scala standard library. It defines a set of foundational type classes (e.g. Functor, Monad) and corresponding instances for a large number of data structures.

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Hva er scalaz?1.Funksjonelle datastrukturer

2.Syntaks for utvidelse av standard klasser

3.Typeklasser og instanser for disse

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Syntaks

utvidelser til standard klasserog til hvordan du skriver kode

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Equal

1 == 1=> true

1 == 1.0=> true

val x: Int = 1val y: Person = new Person("Petter")

x == y warning: comparing values of types Int and Person using `==' will always yield false

=> false

y == x warning: Person and Int are unrelated: they will most likely never compare equal

=> false

1 == 1=> false

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Typesikker Equal

1 === 1=> true

1 === 1.0 error: could not find implicit value for parameter F0: scalaz.Equal[Any]

1 =/= 1=> false

1 =/= 1.0 error: could not find implicit value for parameter F0: scalaz.Equal[Any]

1 === 2=> false

1 =/= 2=> true

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Boolean

true && true=> true

true /\ true=> true

true && false=> false

true /\ false=> false

(if (true) "a" else "b")=> "a"

true ? "a" | "b"=> "a"

true option "a"=> Some("a")

false option "a"=> (None:Option[String])

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Option

Some(42)=> Some[Int] = Some(42)

None=> None.type = None

some(42)=> Option[Int] = Some(42)

none[Int]=> Option[Int] = None

42.some=> Some(42)

val o = 42.someo getOrElse 1o | 1=> 42

val n = option.none[Int]n getOrElse 1n | 1=> 1

~o=> 42

~n=> 0

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Index

val l = List(1,2,3,4)

l(0)=> 1l(2)=> 3

l(-1)=> IndexOutOfBoundsExceptionl(4)=> IndexOutOfBoundsException

l index 0=> Some(1)l index 2=> Some(3)

l index -1=> Nonel index 4=> None

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Alle instanser - Id

"a" ?? "b"=> "a"

val x: String = nullx ?? "asdf"=> "asdf"

def f(i:Int) = i + 1(1 |> f)=> 2

1 + 2 + 3 |> {_ * 6}=> 36

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Typeklasser

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Hva er en Typeklasse?•En form for et interface som definerer oppførsel til en type

•oppførselen er definert utenfor typen

•alle typer som er medlem i typeklassen har implementasjoner av oppførselen

•ikke et interface som i Java

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Typeklasser i Scala

trait Truthy[A] { def truthy(a: A): Boolean}

implicit val intTruthy: Truthy[Int] = new Truthy[Int] { def truthy(a: Int): Boolean = a match { case 0 => false case _ => true }}

intTruthy.truthy(1)=> trueintTruthy.truthy(0)=> false

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Typeklasser i Scala

object Truthy { def apply[A](implicit A: Truthy[A]): Truthy[A] = A}

> Truthy[Int].truthy(0)=> falseTruthy[Int].truthy(1)=> true

1.truthy=> true

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Typeklasser i Scala

trait TruthyOps[A] { def self: A implicit def F:Truthy[A] def truthy: Boolean = F.truthy(self)}

object ToTruthyOps { implicit def toTOps[A](a: A)(implicit ev: Truthy[A]) = new TruthyOps[A] { def self: A = a implicit def F = ev }}

1.truthy=> true

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Typeklasser i Scala

def iffy[A: Truthy, B](t: A)(ifT: =>B)(ifF: =>B): B = { if (t.truthy) ifT else ifF}

iffy(1)("Ja!")("Neeei!")=> Ja!

iffy(0)("Ja!")("Neeei!")=> Neeei!

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Typeklasser i Scalaz

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Equaltrait Equal[F] { self => def equal(a1: F, a2: F): Boolean}

implicit val intInstance: Monoid[Int] with Enum[Int] with Show[Int] = new Monoid[Int] with Enum[Int] with Show[Int] {....}

trait EqualOps[F] extends Ops[F] { final def ===(other: F): Boolean = ??? final def =/=(other: F): Boolean = ???}

1 === 1=> true

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Equal

case class Car(val model: String)implicit val carEqual = new Equal[Car] { def equal(a1: Car, a2: Car): Boolean = a1.model == a2.model}

Car("Honda") === Car("Toyota")=> false

Car("Honda") === Car("Honda")=> true

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SemiGroup

trait Semigroup[F] { self => def append(f1: F, f2: => F): F}

trait SemigroupOps[F] extends Ops[F] { implicit def F: Semigroup[F]

final def |+|(other: => F): F = ??? final def mappend(other: => F): F = ???}

1 |+| 2=> 3

List(1,2) |+| List(3,4)=> List(1,2,3,4)

(1,2) |+| (3,4)=> (4,6)

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Monoid

trait Monoid[F] extends Semigroup[F] { self => def zero: F}

trait MonoidOps[F] extends Ops[F] { final def multiply(n: Int): F = ??? final def ifEmpty[A](tv: => A)(fv: => A) = ???}

(0.ifEmpty("Empty")("NonEmpty"))=> "Empty"(1.ifEmpty("Empty")("NonEmpty"))=> "NonEmpty"

"a" multiply 3=> "aaa"~o.none[Int]=> 0~3.some=> 3

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Monoid avler Monoid!•Option[A] er Monoid hvis A er Monoid

•Map[K, A] er Monoid hivs A er Monoid

•(A, B) er Monoid hvis A og B er Monoid!

(1,2) |+| (3,4)=> (4,6)

Map(1->1, 2->3) |+| Map(1->4, 3->6)=> Map(1->5, 2->3, 3->6)

(1.some, 2.some) |+| (3.some, o.none[Int])=> (4.some, 2.some)

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Og Monider er overalt..•Tall (Int, Double, BigDecimal....)

•Penger (Din egen klasse)

•Dato / Perioder

•Kun fantasien setter grenser...

100.NOK |+| 250.NOK=> Money(350, NOK)

1.day |+| 1.week=> Period(1, 1)

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Functor

trait Functor[F[_]] { self => def map[A, B](fa: F[A])(f: A => B): F[B]}

List(1, 2, 3) map {_ + 1}=> List(2,3,4)

trait FunctorOps[F[_],A] extends Ops[F[A]] { final def map[B](f: A => B): F[B] = ??? final def fpair: F[(A, A)] = ??? final def fproduct[B](f: A => B): F[(A, B)] = ??? final def >|[B](b: => B): F[B] = ???}

List(1,2,3) >| "a"=> List("a","a","a")

(List(1,2,3) fpair)=> List((1,1),(2,2),(3,3))

List(1,2,3) fproduct {_*2}=> List((1,2), (2,4), (3,6))

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Applicative

trait Applicative[F[_]] extends Apply[F] { self => def point[A](a: => A): F[A]}

trait Apply[F[_]] extends Functor[F] { self => def ap[A,B](fa: => F[A])(f: => F[A => B]): F[B]}

trait ApplyOps[F[_],A] extends Ops[F[A]] { final def <*>[B](f: F[A => B]): F[B] = ??? final def |@|[B](fb: F[B]):ApplicativeBuilder = ???}

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Applicative

val f = (_:Int) * 32.some <*> f.some=> 6.some

9.some <*> { (_: Int) + 3 }.some=> 12.some

^(1.some, 2.some) {_ + _}=> 3.some

(1.some |@| 2.some) {_ + _}=> 3.some

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Applicative

val f: (Int, Int) => Int = (x:Int, y:Int) => x + y

f(1,2)=> 3

f(1.some, 2.some)=> 3.some

f(1.some, o.none[Int])=> o.none[Int]

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Monadtrait BindOps[F[_],A] extends Ops[F[A]] { def flatMap[B](f: A => F[B]) = ??? def >>=[B](f: A => F[B]) = ??? def >>[B](b: => F[B]): F[B] = ???}

val f: Int => Option[Int] = (x:Int) => (x * 10).some(9.some >>= f)

(9.some flatMap f)

(for { x <- 9.some y <- f(x)} yield y)=> 90.some

(9.some >> 4.some)=> 4.some

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Validation

sealed trait Validation[+E, +A]

case class Success[E, A](a: A)extends Validation[E, A]

case class Failure[E, A](e: E)extends Validation[E, A]

type ValidationNel[+E, +X] =Validation[NonEmptyList[E], X]

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Validation

1.success[String]=> scalaz.Validation[String,Int] = Success(1)

1.successNel[String]=> scalaz.ValidationNel[String,Int] = Success(1)

1.successNel=> scalaz.ValidationNel[Nothing,Int] = Success(1)

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Validation

"Too young!".failNel[Int]=> Failure(NonEmptyList("Too young!"))

"Too young!".fail[Int]=> Failure("Too young!")

"Too young!".fail=> Failure("Too young!")

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Validationcase class User(username:String)

def addUser(username: String): ValidationNel[String, User] = { findUser(username) match { case Some(_) => s"Username '${username}' taken!".failNel case _ => User(username).success }}

def findUser(username: String): Option[User] = { (username === "ovstetun") ? User("ovstetun").some | none}

addUser("per")=> Success(User("per"))

addUser("ovstetun")=> Failure(NonEmptyList("Username 'ovstetun' taken!"))

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Validation

val e: Equal[Validation[String, Int]] = Equal[Validation[String, Int]]

val sg: Semigroup[Validation[String, Int]] = Semigroup[Validation[String, Int]]

val m: Monoid[Validation[String, Int]] = Monoid[Validation[String, Int]]

val a: Applicative[({type l[a] = Validation[String, a]})#l] = Validation.ValidationApplicative[String]

val t: Traverse[({type l[a] = Validation[String, a]})#l] = Traverse[({type l[a] = Validation[String, a]})#l]

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Konklusjoner•Scalaz er ikke farlig

•Gir en felles måte å løse like problemer

•Man trenger ikke skjønne hvordan et konsept er implementert for å bruke det

•Validation er killer feature for meg

•Gjenbrukbar, komponerbar og vedlikeholdbar kode

en nybegynners introduksjon til scalaz

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