Cats Effect Effect example

EffectDempApp.scala

package cats_effect_typeclass_exericise.effect

import java.time.format.DateTimeFormatter

import cats.data.{Chain, WriterT}
import cats.effect._

import scala.language.higherKinds

object Util {
  val formatter = DateTimeFormatter.ofPattern("mm:ss")

  def putIn(milli: Int, s: Any): String = {
    Thread.sleep(milli)
    val threadId      = Thread.currentThread.getId
    val currentMinSec = java.time.LocalTime.now.format(formatter)
    println(s"in thread($threadId) at $currentMinSec): $s")
    s.toString
  }
  def putLine(s: Any):   String = putIn(1000, s)
  def putIn1Sec(s: Any): String = putIn(1000, s)
  def putNow(s: Any):    String = putIn(0,    s)
  def putRnd(s: Any):    String = putIn((math.random * 1000 + 500).toInt, s)
}
import Util._

object EffectRunAsyncDemoApp extends IOApp {
  def run(args: List[String]): IO[ExitCode] = {
//    val task = IO.raiseError(new RuntimeException("dummy")) // prints "get error: 'dummy'"
    val task = IO { putLine("IO body evaluated"); "Hello!" } // prints "got text: 'Hello!'"

    val ioa: SyncIO[Unit] = Effect[IO].runAsync(task) {
      case Right(text) => IO { putLine(s"got text: '$text'") }
      case Left(th)    => IO { putLine(s"got error: ${th.getMessage}") }
    }
    putLine("main thread")
    ioa.toIO.map(_ => ExitCode.Success)  // SyncIO has `toIO: IO`
  }
//  in thread(1)  at 00:40): main thread
//  in thread(11) at 00:41): IO body evaluated
//  in thread(11) at 00:42): got text: 'Hello!'
//
//  Process finished with exit code 0
}

object EffectWriterTDemoApp extends IOApp {
  type WriterIO[T] = WriterT[IO, Chain[String], T]
  val task = IO { putLine("IO body evaluated"); "Hello, WriterT!" }

  def program(implicit E: Effect[WriterIO]) = for {
    s <- E.liftIO(task)
    _ <- WriterT.tell[IO, Chain[String]](Chain("a log line"))
  } yield s

  def run(args: List[String]): IO[ExitCode] = {
    putLine("main thread")
    program.run map { case (l, v) =>
      putLine(s"value:$v, log: $l")
      ExitCode.Success
    }
  }
//  in thread(1) at 03:28): main thread
//  in thread(11) at 03:30): IO body evaluated
//  in thread(11) at 03:31): value:Hello, WriterT!, log: Chain(a log line)
//
//  Process finished with exit code 0
}