Monad transformers

This is a port of Hamsters monad transformers to Scala 2.13.

Example : combine Future and Option types then make it work in a for comprehension. More information on why it's useful here.

FutureOption

import io.github.hamsters.FutureOption
import io.github.hamsters.MonadTransformers._
//import your execution context here too, for example import scala.concurrent.ExecutionContext.Implicits.global

def foa: Future[Option[String]] = Future(Some("a"))
def fob(a: String): Future[Option[String]] = Future(Some(a+"b"))

val composedAB: Future[Option[String]] = for {
  a <- FutureOption(foa)
  ab <- FutureOption(fob(a))
} yield ab

FutureTry

import io.github.hamsters.FutureTry
import io.github.hamsters.MonadTransformers._
//import your execution context here too, for example import scala.concurrent.ExecutionContext.Implicits.global

def foa: Future[Try[String]] = Future(Try("a"))
def fob(a: String): Future[Try[String]] = Future(Try(a+"b"))

val composedAB: Future[Try[String]] = for {
  a <- FutureTry(foa)
  ab <- FutureTry(fob(a))
} yield ab

FutureEither

import io.github.hamsters.FutureEither
import io.github.hamsters.MonadTransformers._
//import your execution context here too, for example import scala.concurrent.ExecutionContext.Implicits.global

def fea: Future[Either[String, Int]] = Future(Right(1))
def feb(a: Int): Future[Either[String, Int]] = Future(Right(a+2))

val composedAB: Future[Either[String, Int]] = for {
  a <- FutureEither(fea)
  ab <- FutureEither(feb(a))
} yield ab

OptionT and EitherT

If you use other combinations of F[Option[A]] or F[Either[L,R]], you can bring your own Monad implicit instance and work with OptionT or EitherT. Future and Option instances are provided by default.

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Install

Add this to you build.sbt :

resolvers += Resolver.bintrayRepo("loicdescotte", "Hamsters") 
libraryDependencies += "io.github.scala-hamsters" %% "monad-transformers" % "1.0.0"