fs2 example code from underscore ported to fs2 v1.0.5 and cats-effect 1.4.0

Fs2SampleCode.scala

import cats.implicits._
import cats.effect.{ConcurrentEffect, Effect, ExitCode, IO, IOApp, Timer}
import fs2._
import fs2.concurrent.Queue
import scala.concurrent.duration._
import scala.concurrent.duration.MILLISECONDS

//
// fs2 example code from
// https://underscore.io/blog/posts/2018/03/20/fs2.html
// ported to fs2 v1.0.5 and cats-effect 1.4.0
//
object Fs2SampleCode extends IOApp {

  def streamData[F[_] : Effect](implicit timer: Timer[F]) =
    Stream.awakeEvery[F](1.second).evalMap(_ => timer.clock.realTime(MILLISECONDS).map(t => (t % 10000).toString))

  def enqueueData[F[_] : Timer](q: Queue[F, String])(implicit F: Effect[F]) =
    Stream.eval(
      streamData.through(q.enqueue)
        .compile
        .drain
    )

  def dequeueData[F[_]](q: Queue[F, String]) = q.dequeue.take(4)

  def withQueue[F[_] : ConcurrentEffect : Timer]: Stream[F, String] = {
    val queue: Stream[F, Queue[F, String]] = Stream.eval(Queue.circularBuffer[F, String](5))

    queue.flatMap { q =>
      val enqueueStream = enqueueData(q)

      val dequeueStream = dequeueData(q)

      dequeueStream.concurrently(enqueueStream)
    }
  }

  override def run(args: List[String]): IO[ExitCode] = {
    val resultQueue = withQueue[IO].compile.toVector.unsafeRunSync()
    println(s"Queue >> $resultQueue")

    IO(ExitCode.Success)
  }
}