How to remove a fold from within a for-comprehension?

Question

I have the following snippet in Scala using Scalaz and Task/EitherT:

def myMethod(request: MyRequest) : EitherT[Task, Failure, Success] =
    EitherT[Task, Failure, Success](
      for {
        aamOpt <- async.findUser(request)
        aamEith <- Task.now(aamOpt.\/>(NoUserFound()))
        result <- aamEith.fold(err => Task.now(-\/(err)), aam => process(aam)).run)
      } yield result)

Where async.findUser returns a Task[Option[MyUser]] and process(aam) returns EitherT[Task, Failure, Success]. These return types are needed as these methods interact (down the line) with external services.

Is there any way to simplify the last line of the for comprehension into something nicer? I mean this one:

result <- aamEith.fold(err => Task.now(-\/(err)), aam => process(aam)).run)

Answer 1

I would probably immediately lift the result from async.findUser into the relevant EitherT monad and then just flatMap:

def myMethod(request: MyRequest): EitherT[Task, Failure, Success] =
  EitherT.eitherT[Task, Failure, MyUser](
    async.findUser(request).map(_.\/>(NoUserFound()))
  ).flatMap(process)

This is untested but something like it should more or less work.