Mtl Example

MtlExample.scala

import cats.Monad
import cats.data.EitherT
import cats.implicits._
import cats.mtl.implicits._
import cats.mtl.{ApplicativeAsk, FunctorRaise}
import doobie.free.connection.ConnectionIO

object MtlExample {

  case class RequestId(value: String)
  case class PersonId(value: String)
  case class Person(id: PersonId, name: String, siblings: List[PersonId])

  sealed trait PersonError
  case class PersonNotFound(id: Int) extends PersonError
  case class InvalidName(name: String) extends PersonError

  def getPerson(id: PersonId): EitherT[ConnectionIO, PersonError, Person] = ???

    // how to impl in using getPerson ?
  def getPersonMtl[F[_]](id: PersonId)(implicit F: FunctorRaise[F, PersonError]): F[Person] = ???

  def log[F[_]](message: String)(implicit F: ApplicativeAsk[F, RequestId]): F[Unit] =
    F.reader(id => println(s"$id $message"))


  // how to run F in one transaction ?
  def getSiblings[F[_]: Monad: ApplicativeAsk[?[_], RequestId] : FunctorRaise[?[_], PersonError]](id: PersonId): F[List[Person]] =
    for {
      person   <- getPersonMtl[F](id)
      _        <- log[F](s"fetched $person")
      siblings <- person.siblings.traverse(getPersonMtl[F](_))
    } yield siblings

}