ResourceIOApp.scala

Launcher.scala

import cats.effect._
import cats.implicits._

object Launcher extends IOApp {

  def run(args: List[String]): IO[ExitCode] = {
    val launchMissiles = IO.raiseError[Unit](new Exception("boom!"))
    val runToBunker = IO(println("To the bunker!!!"))

    val p: IO[Unit] = for {
      fiber <- launchMissiles.start
      _ <- runToBunker.handleErrorWith { error =>
             // Retreat failed, cancel launch (maybe we should
             // have retreated to our bunker before the launch?)

             fiber.cancel *> IO.raiseError[Unit](error)
           }
      aftermath <- fiber.join
    } yield aftermath

    val r: Resource[IO, ExitCode] =
      for {
        _      <- Resource.liftF(p) // Initialize log before the engine is setup
      } yield ExitCode.Success

    r.use(_ => IO.never)

  }

}