Why OptionT doesn't work for Try?
I'm looking at this question from Scala and Scalaz views. OptionT
works for Future
but not Try
. What is the reason for the absence OptionT
for Try
, where there is a usecase function, i.e. def foo(i: Int): Try[Option[Int]] = ...
may or may not return a value, and sometimes a network exception happens? Thanks to
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1 answer
Cause Try is not a valid functor .
You will need to use skazus-out-auls or write your own Try instances. Here's a working example with scalaz-outlaws' Try instances :
import scala.util.{Try,Success,Failure}
import scalaz._
import Scalaz._
implicit val tryOutlawInstances = new Traverse[Try] with Monad[Try] with Plus[Try]{
def point[A](a: ⇒ A): Try[A] = Success(a)
override def map[A,B](fa: Try[A])(f: A ⇒ B) = fa map f
def bind[A,B](fa: Try[A])(f: A ⇒ Try[B]) = fa flatMap f
def traverseImpl[F[_], A, B](fa: Try[A])(f: A ⇒ F[B])(implicit F: Applicative[F]) : F[Try[B]] = fa match {
case Success(a) ⇒ F.map(f(a))(Success.apply)
case Failure(f) ⇒ F.point(Failure(f))
}
def plus[A](a: Try[A], b: ⇒ Try[A]) = a orElse b
}
val foo = Try("foo".some)
val result = OptionT(foo).map(x => x.toUpperCase).run
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