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oop to fp - free monad
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import cats.free.Free.liftF | |
import cats.free.Free | |
import cats.{Id, ~>} | |
// 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] | |
object MovieRepoOps { | |
def getMovie(id: Int): QueryF[Option[Movie]] = liftF(GetMovie(id)) | |
} | |
object MovieService { | |
def getMovie(id: Int): QueryF[Option[Movie]] = for { | |
movie <- MovieRepoOps.getMovie(id) | |
} yield movie | |
} | |
// 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 = MovieService.getMovie(42).foldMap(taskInterpreter) | |
// rumtime layer ------------------------------------------------- | |
import scala.concurrent.Await | |
import monix.execution.Scheduler.Implicits.global | |
import scala.concurrent.duration._ | |
Await.result(program.runToFuture, 1.second) | |
// Some(Movie(42, A Movie)) | |
// test environment ------------------------------------------------------- | |
def testInterpreter: Query ~> Id = new (Query ~> Id) { | |
def apply[A](fa: Query[A]): Id[A] = fa match { | |
case GetMovie(_: Int) => Option(Movie(-1, "Test")) | |
} | |
} | |
val id1 = MovieService.getMovie(42).foldMap(testInterpreter) | |
// Some(Movie(-1,Test)) |
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