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minimal cake + tagless final + free monad
import cats.~>
// domain layer -----------------------------------------------------------
case class Movie(id: Int, title: String)
sealed trait Query[A]
case class GetMovie(id: Int) extends Query[Option[Movie]]
type QueryF[T] = Free[Query, T]
trait MovieRepo[F[_]] {
def getMovie(id: Int): F[Option[Movie]]
trait UsesMovieRepo[F[_]] {
val movieRepo: MovieRepo[F]
trait MovieService[F[_]] extends UsesMovieRepo[F] {
def getMovie(id: Int): F[Option[Movie]] = movieRepo.getMovie(id)
object MovieRepoImpl extends MovieRepo[QueryF] {
def getMovie(id: Int): QueryF[Option[Movie]] = liftF(GetMovie(id))
trait MixInMovieRepo {
val movieRepo: MovieRepo[QueryF] = MovieRepoImpl
object MovieServiceImpl extends MovieService[QueryF] with MixInMovieRepo
// application layer -------------------------------------------------
import monix.eval.Task
val db = Map[Int, Movie](42 -> Movie(42, "A Movie"))
def taskInterpreter: Query ~> Task = new (Query ~> Task) {
def apply[A](fa: Query[A]): Task[A] = fa match {
case GetMovie(id) => Task(db.get(id))
val program = MovieServiceImpl.getMovie(42).foldMap(taskInterpreter)
// runtime ------------------------------------------------------
import scala.concurrent.Await
import scala.concurrent.duration._
Await.result(program.runToFuture, 1.second)
//res0: Option[Movie] = Some(Movie(42,A Movie))
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