Freestyle tagless program example with multiple algebras composed into module

TaglessModulesExample.scala

import cats.Monad
import cats.effect.IO
import freestyle.tagless._

@tagless trait Logger {
  def debug(message: String): FS[Unit]
}

@tagless trait Summer {
  def sum(a: Int, b: Int): FS[Int]
}

@module trait TaglessApp {
  // necessary boilerplate to provide map/flatmap syntax on log/summer for the for comprehension
  implicit val M: Monad[FS]
  import cats.implicits._

  val log: Logger
  val summer: Summer

  def program(a: Int, b: Int): FS[Int] =
    for {
      sum <- summer.sum(a, b)
      _   <- log.debug(s"$a + $b = $sum")
    } yield sum
}

object TaglessModulesExample extends App {

  implicit val loggerHandler = new Logger.Handler[IO] {
    def debug(message: String): IO[Unit] = IO { println(s"Logger debug: $message") }
  }

  implicit val summerHandler = new Summer.Handler[IO] {
    override def sum(a: Int, b: Int): IO[Int] = IO { a + b }
  }

  val result = TaglessApp.to[IO].program(5, 3).unsafeRunSync()
  println(s"Result is: $result")
  
  // Logger debug: 5 + 3 = 8
  // Result is: 8
}