dnaumenko

val program: Env[Any, Unit] = for {
  _ <- EnvCtx(println("Starting"))
  _ <- EnvCtx(println("Finished"))
} yield ()
program.unsafeRunSync(())

dnaumenko

trait Context[Ctx] {
  def ctx: Context.Service[Ctx]
}

dnaumenko

object Context {
  trait Service[Ctx] {
    val read: UIO[Ctx]
    def set[R, E, A](value: Ctx): UIO[Unit]
    def update[R, E, A](f: Ctx => Ctx): UIO[Ctx]
  }
}

dnaumenko

def init[Ctx](value: Ctx): UIO[Context[Ctx]] = {
  makeService(value).map {service =>
    new Context[Ctx] {
      override def ctx: Service[Ctx] = service
    }
  }
}

def makeService[Ctx](value: Ctx): UIO[Context.Service[Ctx]] =
  FiberRef.make(value).map { fiberRef =>

dnaumenko

// helper methods
def read[Ctx]: ZIO[Context[Ctx], Nothing, Ctx] = 
  ZIO.accessM[Context[Ctx]](_.ctx.read)
def update[Ctx, R <: Context[Ctx], E, A](f: Ctx => Ctx): ZIO[R, Nothing, Ctx] =
  ZIO.accessM[R](_.ctx.update(f))
def set[Ctx, R <: Context[Ctx]](value: Ctx): ZIO[R, Nothing, Unit] = 
  ZIO.accessM[R](_.ctx.set(value))

dnaumenko

trait Context[Ctx] {
  def ctx: Context.Service[Ctx]
}

object Context {
  trait Service[Ctx] {
    val read: UIO[Ctx]
    def set[R, E, A](value: Ctx): UIO[Unit]
    def update[R, E, A](f: Ctx => Ctx): UIO[Ctx]
  }

dnaumenko

object EnvCtx {
  def apply[R, A](body: => A): Env[R, A] = ofZIO(ZIO(body))
  def pure[R, A](x: A): Env[R, A] = ofZIO(ZIO.succeed(x))
  def delay[R, A](x: A): Env[R, A] = ofZIO(ZIO.effect(x))
  def context[R]: Env[R, R] = ofZIO(Context.read[R])
  def updateContext[Ctx, A](f: Ctx => Ctx): Env[Ctx, Ctx] = ofZIO(Context.update(f))
  def setContext[Ctx, A](value: Ctx): Env[Ctx, Unit] = ofZIO(Context.set(value))
  
  private def ofZIO[R, A](zio: RIO[Context[R], A]): Env[R, A] = new EnvCtx(zio)
}

dnaumenko

object EnvTest extends App {
  val program: Env[ExampleEnv, Unit] = for {
    _ <- EnvCtx(println("Starting"))
    _ <- EnvCtx.setContext(ExampleEnv("request B"))
    newCtx <- EnvCtx.context
    _ <- EnvCtx(println(s"Read $newCtx"))
    _ <- EnvCtx(println("Finished"))
  } yield ()
  
  program.unsafeRunSync(ExampleEnv("request A"))

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implicit def concurrentEffect[Ctx](implicit runtime: Runtime[Context[Ctx]]): effect.ConcurrentEffect[Env[Ctx, ?]] =
    new EnvConcurrentEffect[Ctx]

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object EnvFinalTaglessTest extends App {
  import com.example.functional.env.catz._
  
  def buildProgram[F[_] : Sync]: F[Unit] = {
    import cats.implicits._
    for {
      _ <- Sync[F].delay(println("Starting"))
      _ <- Sync[F].delay(println("Finished"))
    } yield ()
  }