mmollaverdi

$ gradle create
Starting a Gradle Daemon (subsequent builds will be faster)

> Task :compileKotlin
w: file:///Users/mmollaverdi/projects/cash-monorepo-builder/src/main/kotlin/commands/create/Main.kt:11:10 Parameter 'args' is never used

> Task :create
/Users/mmollaverdi/projects/monorepo-staging/cash-server git init .
hint: Using 'master' as the name for the initial branch. This default branch name
hint: is subject to change. To configure the initial branch name to use in all

mmollaverdi

// Read on Applicatives here: https://drboolean.gitbooks.io/mostly-adequate-guide/content/ch10.html

function function1(f) {
  return {
    ap: g => function1(x => f(x)(g.apply(x))),
    apply: f
  }
}

Function1 = {

mmollaverdi

import scala.concurrent.Future

def fetchSystem(id: String): Future[System] = ??? // do some magic to get system data from an API in a different galaxy
def fetchSystemStatus(id: String): Future[SystemStatus] = ??? // do some other magic to get system status from another API

mmollaverdi

trait Applicative[F[_]] {
  def ap[A, B](ff: F[A => B])(fa: F[A]): F[B]

  def pure[A](x: A): F[A]

  def map2[A, B, C](fa: F[A], fb: F[B])(f: (A, B) => C): F[C] = {
    val fCurried: A => B => C = f.curried
    val fbc: F[B => C]  = ap[A, (B => C)](pure(fCurried))(fa)
    ap[B, C](fbc)(fb)
  }

mmollaverdi

implicit val TaskApplicative = new Applicative[Task] {
  override def ap[A, B](ff: Task[A => B])(fa: Task[A]): Task[B] = Task.mapBoth(ff, fa)((f, a) => f(a))

  override def pure[A](x: A): Task[A] = Task.now(x)
}

mmollaverdi

implicit val OptionApplicative = new Applicative[Option] {
  def ap[A, B](ff: Option[A => B])(fa: Option[A]): Option[B] = for {
    f <- ff
    a <- fa
  } yield f(a)

  def pure[A](a: A): Option[A] = Option(a)
}

mmollaverdi

trait Applicative[F[_]] {
  def ap[A, B](ff: F[A => B])(fa: F[A]): F[B]

  def pure[A](x: A): F[A]
}

mmollaverdi

getSystemStatusInfo(fetchSystem("consumer_desktop"), fetchSystemStatus("consumer_desktop"))

mmollaverdi

def getSystemStatusInfo[F[_]: Applicative](fetchSystem: F[System], fetchSystemStatus: F[SystemStatus]): F[SystemStatusInfo] = {
  Applicative[F].map2(fetchSystem, fetchSystemStatus)((system, systemStatus) => SystemStatusInfo(system, systemStatus))
}

mmollaverdi

trait Applicative[F[_]] {
  def map2[A, B, C](fa: F[A], fb: F[B])(f: (A, B) => C): F[C] = ??? // ...
}