UseCase with Function1

useCaseFn.scala

import cats.implicits._

trait UseCase[In, Out, Err] extends Function1[In, Either[Err, Out]]

trait CreateLoanApplication extends UseCase[CreateLoanApplicationIn, CreateLoanApplicationOut, CreateLoanApplicationErr] {
  override def apply(in: CreateLoanApplicationIn): Either[CreateLoanApplicationErr, CreateLoanApplicationOut] = {
    Either.right(CreateLoanApplicationOut())
  }
}
case class CreateLoanApplicationIn()
case class CreateLoanApplicationOut()
sealed trait CreateLoanApplicationErr 
case class DbErr() extends CreateLoanApplicationErr
case class ExternalErr() extends CreateLoanApplicationErr

object CreateLoanApplication extends CreateLoanApplication

trait CompletePersonalInformation extends UseCase[CompletePersonalInformationIn, CompletePersonalInformationOut, CompletePersonalInformationErr] {
  override def apply(in: CompletePersonalInformationIn): Either[CompletePersonalInformationErr, CompletePersonalInformationOut] = {
    Either.right(CompletePersonalInformationOut())
  }
}

case class CompletePersonalInformationIn()
case class CompletePersonalInformationOut()
sealed trait CompletePersonalInformationErr
case class DbError() extends CompletePersonalInformationErr

object CompletePersonalInformation extends CompletePersonalInformation

val main = for {
  _ <- CreateLoanApplication(CreateLoanApplicationIn())
  _ <- CompletePersonalInformation(CompletePersonalInformationIn())
} yield ()