Scala : Is there a more concise way to compose the following higher kind method?

Question

UserRepository trait has two methods isRegistered and insert.

trait UserRepository[F[_]] {
  def insert(user: domain.User): F[Long]
  def isRegistered(user: domain.User): F[Boolean]
}

Boundary class is the boundary of the core application. For this example, it has only one method register which creates a new user only if it does not exist.

class Boundary[F[_]: Monad] private (userrepo: UserRepository[F]) {

  def registerUser(user: User): F[Either[UserAlreadyRegistered, Long]] =
    userrepo.isRegistered(user).flatMap {
      case true  =>
        UserAlreadyRegistered(user).asLeft[Long].pure[F]
      case false =>
        for {
          id <- userrepo.insert(user)
          errorOrId = id.asRight[UserAlreadyRegistered]
        } yield errorOrId
    }
}

My question is there a more concise way to implement registerUser method. I use cats core in the project.

Answer 1

As @Luis Miguel Mejía Suárez suggested, you can use ifM function from the cats.syntax.apply:

import cats.Monad
import cats.syntax.apply._
import cats.syntax.applicativeError._
import cats.syntax.either._
import cats.syntax.functor._

class Boundary[F[_]: Monad] private (userRepo: UserRepository[F]) {

  def registerUser(user: User): F[Either[UserAlreadyRegistered, Long]] =
    userRepo.isRegistered(user).ifM(
      UserAlreadyRegistered(user).raiseError[F, Long Either UserAlreadyRegistered],
      userRepo.insert(user).map(_.asRight[UserAlreadyRegistered])
    )
}