Hello World

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Source Code

trait AlgInterp[F[_]] {
  val state: F[Int]
  def log(msg: String): F[Unit]
  def query[A](c: ConnectionIO[A]): F[A]
}

type Alg[F[_], A] = ReaderT[F, AlgInterp[F], A]

def state[F[_]]: Alg[F, Int] = Kleisli(_.state)
def log[F[_]](msg: String): Alg[F, Unit] = Kleisli(_.log(msg))

def doobieQuery[F[_], A](query: ConnectionIO[A]): Alg[F, A]

def program[F[_]]: Alg[F, Int] = for {
  env <- state
  _ <- log(s"initState is: $state")
  valueInDatabase <- doobieQuery(sql"select 320032003200".query[Int].unique).handleError{ _ => 0 }
} yield initState + valueInDatabase

val interp = new AlgInterp[IO]{
  val state = IO(1)
  def log(msg: String) = IO(getLogger.log(msg))
  def query[A](c: ConnectionIO[A]) = c.transact(xa)
}
program[IO].run(interp).unsafeRunSync()