OptionalT fromOptional and liftF in ScalaZ

Question

I´ve been watching some examples of monads transformers with Cats , and I was trying to reproduce those in Scalaz

Here I have a for comprehension where I first receive an optional which I flatMap with OptionalT , and the second function return a Future of Employee.

Here my code

  //Attributes for this example
  sealed trait Employee {
    val id: String
  }

  final case class EmployeeWithoutDetails(id: String) extends Employee

  final case class EmployeeWithDetails(id: String, name: String, city: String, age: Int) extends Employee

  case class Company(companyName: String, employees: List[EmployeeWithoutDetails])

  trait HybridDBOps {
    protected def getDetails(employeeId: String): Future[EmployeeWithDetails]

    protected def getCompany(companyName: String): Option[Company]
  }

  class DbHybrid extends HybridDBOps {
    override def getDetails(employeeId: String): Future[EmployeeWithDetails] = Future {
      EmployeeWithDetails("1", "name", "city", 36)
    }

    override def getCompany(companyName: String): Option[Company] = Some(Company(companyName, List(EmployeeWithoutDetails("1"))))
  }

  def getEmployeeAgeScalaZHybrid(employeeId: String, companyName: String): Future[Option[Int]] = {
    val db = new DbHybrid
    val eventualOption = (for {
      company <- OptionT.fromOption(db.getCompany(companyName)) --> Wont compile
      if company.employees map (_.id) contains employeeId
      details <- OptionT.liftF(db.getDetails(employeeId)) --> Wont compile
    } yield details.age).run
    eventualOption
  }

This code is from cats version, and in scalaz the OptionT.fromOption to wrap a Option does not exist, I notice that I can do OptionT(Some(db.getCompany(companyName)) and then compile but now the signature of the method says that I returning an Optional instead of a future.

Also how can use the OptionT.liftF in ScalaZ

Here the complete example https://github.com/politrons/reactiveScala/blob/master/scala_features/src/main/scala/app/impl/scalaz/MonadTransformer.scala

Regards.

Answer 1

These should work as substitutes:

import scalaz.std.future._
import scalaz.syntax.monad._

// instead of OptionT.fromOption(db.getCompany(companyName))
OptionT(db.getCompany(companyName).pure[Future])

// instead of OptionT.liftF(db.getDetails(employeeId))
db.getDetails(employeeId).liftM[OptionT]

However, it would be good to have both methods also on OptionT . You could add them and open a pull request.