Application wide errors with Either

appError.scala

// Start writing your ScalaFiddle code here
import cats.implicits._

trait UseCase[Parameters, Error, Result] {
  def execute(p: Parameters): Either[Error, Result]
}


import CreateLoanApplication._
trait CreateLoanApplication extends UseCase[CreateLoanApplicationRequest, CreateLoanApplicationError, CreateLoanApplicationResult] {
  override def execute(r: CreateLoanApplicationRequest): Either[CreateLoanApplicationError, CreateLoanApplicationResult] = ???
}

object CreateLoanApplication {
  
  case class CreateLoanApplicationRequest()
  
  sealed trait CreateLoanApplicationError
  object DbError extends CreateLoanApplicationError
  object ExternalServiceError extends CreateLoanApplicationError
  
  case class CreateLoanApplicationResult()
  
}

import CompletePersonalInformation._
trait CompletePersonalInformation extends UseCase[CompletePersonalInformationRequest, CompletePersonalInformationError, CompletePersonalInformationResult] {
  override def execute(r: CompletePersonalInformationRequest): Either[CompletePersonalInformationError, CompletePersonalInformationResult] = ???
}

object CompletePersonalInformation {
  case class CompletePersonalInformationRequest()
  
  sealed trait CompletePersonalInformationError
  object DbError extends CompletePersonalInformationError
  object ExternalServiceError extends CompletePersonalInformationError
  
  case class CompletePersonalInformationResult()
}

trait AppError
object AppError { 
	case class CreateLoanApplicationError(err: CreateLoanApplication.CreateLoanApplicationError) extends AppError
  case class CompletePersonalInformationError(err: CompletePersonalInformation.CompletePersonalInformationError) extends AppError
}

val main: (CreateLoanApplication, CompletePersonalInformation) => Unit = (createLoanApplication, completePersonalInformation) => {
  val result: Either[AppError, Unit] = for {
    _ <- createLoanApplication.execute(CreateLoanApplicationRequest())
          .leftMap(AppError.CreateLoanApplicationError(_))
    _ <- completePersonalInformation.execute(CompletePersonalInformationRequest())
          .leftMap(AppError.CompletePersonalInformationError(_))
  } yield ()
}