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Free Monads example
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| package com.softwaremill.freemonads | |
| import cats.free.Free | |
| import cats.~> | |
| import cats._, cats.std.all._ | |
| import scala.concurrent.ExecutionContext.Implicits.global | |
| import scala.concurrent.Future | |
| sealed trait External[A] | |
| case class Tickets(count: Int) extends AnyVal | |
| case class InvokeTicketingService(count: Int) extends External[Tickets] | |
| case class UserTicketsRequest(ticketCount: Int) | |
| object GetTicketsExample { | |
| def purchaseTickets(input: UserTicketsRequest): Free[External, Option[Tickets]] = { | |
| if (input.ticketCount > 0) { | |
| // creates a "Suspend" node | |
| Free.liftF(InvokeTicketingService(input.ticketCount)).map(Some(_)) | |
| } else { | |
| Free.pure(None) | |
| } | |
| } | |
| def bonusTickets(purchased: Option[Tickets]): Free[External, Option[Tickets]] = { | |
| if (purchased.exists(_.count > 10)) { | |
| Free.liftF(InvokeTicketingService(1)).map(Some(_)) | |
| } else { | |
| Free.pure(None) | |
| } | |
| } | |
| def formatResponse(purchased: Option[Tickets], bonus: Option[Tickets]): String = | |
| s"Purchased tickets: $purchased, bonus: $bonus" | |
| val input = UserTicketsRequest(11) | |
| val logic: Free[External, String] = for { | |
| purchased <- purchaseTickets(input) | |
| bonus <- bonusTickets(purchased) | |
| } yield formatResponse(purchased, bonus) | |
| val externalToServiceInvoker = new (External ~> Future) { | |
| override def apply[A](e: External[A]): Future[A] = e match { | |
| case InvokeTicketingService(c) => serviceInvoker.run(s"/tkts?count=$c") | |
| } | |
| } | |
| val result = logic.foldMap(externalToServiceInvoker) | |
| result.foreach(println) | |
| object serviceInvoker { | |
| def run(path: String) = { | |
| Future { | |
| Tickets(11) | |
| } | |
| } | |
| } | |
| } |
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hi @kciesielski can you please mention the cat dependencies required for above code snippet as well?
I could not find
cats.std.all._in following dependencies,I found
alleycats.std.all._but not sure if thats correct. I get following compilation error[error] /Users/prayagupd/buybest/learnyouascala.fm/9_error_handling/src/test/scala/FreeMonad.scala:103:29: could not find implicit value for parameter M: cats.Monad[scala.concurrent.Future] [error] val result = logic.foldMap(externalToServiceInvoker) [error] ^ [error] three errors found [error] (test:compileIncremental) Compilation failed [error] Total time: 6 s, completed Jun 18, 2018 10:18:56 PM