Naive Reader

reader.scala

      case class Fun[A, B](run: A => B) {
        def map[C](f: B => C): Fun[A, C] = Fun(a => f(run(a)))
        def flatMap[C](f: B => Fun[A, C]): Fun[A, C] =
          Fun(a => f(run(a)).run(a))
      }
      case class Config(db: String, logColor: String)

      object Repo {
        def get(id: Int): Fun[Config, Int] = Fun(conf => id)
      }
      object Logger {
        def log(value: Int): Fun[Config, Unit] =
          Fun(conf => println(s"$RESET${conf.logColor}$value$RESET"))
      }

      val r = for {
        a <- Repo.get(123)
        _ <- Logger.log(a)
        b <- Repo.get(123)
        _ <- Logger.log(b)

        s = a + b

        _ <- Logger.log(s)

      } yield s

      val conf = Config("", GREEN)
      r.run(conf) must beEqualTo(246)

    }