MangoMesh/koka-shokki.scala

A very dangerous and experimental effect library for Scala 3.

koka-shokki

This library is in a WORK IN PROGRESS state, it could potentially contain horrible bugs.

Usage

This library is currently available for Scala binary versions 2.13 and 3.1.

To use the latest version, include the following in your build.sbt:

libraryDependencies ++= Seq(
  "io.mangomesh" %% "koka-shokki" % "@VERSION@"
)

to execute this library, you also require the following JVM argument:

--add-exports","java.base/jdk.internal.vm=ALL-UNNAMED"

Code

An example could be this:

def divide(
      x: With[Optional, Int],
      y: With[Optional, Int]
  ): Int <~ Optional :| Lefted[String] =
    WithCapability[Optional :| Lefted[String], Int] {
      val result: With[Lefted[String], Int] =
        if (y.? == 0) asLeft("division by zero") else ok(x.? / y.?)
      result.?
    }

which could be use like this:

def runDivEffect(
      x: With[Optional :| Lefted[String], Int]
  ): Either[String, Int] = {
    runEffect(x) {
      case Left(channel) =>
        channel match {
          case _: Optional[Int] => Left("The value is not present")
          case error: Lefted[String][Int] =>
            Left(error.err)
        }
      case Right(value) => Right(value)
    }
  }

val x = divide(Some(1), Some(0))
val result = runDivEffect(x)

note that we require to provide an evaluator for the channels.