b-studios / scala-effekt

Extensible algebraic effects with handlers

Disclaimer

This Scala library is different from the equally named standalone "Effekt language", developed by the same authors. Recent publications only address the latter.

Scala Effekt

The Effekt library allows you to structure your effectful programs in a functional way. It thus represents an alternative to traditional monad transformer based program structuring techniques.

To use Effekt (tested with Scala 2.12 and Scala 2.13), include the following line to your build.sbt file:

resolvers += Opts.resolver.sonatypeSnapshots

libraryDependencies += "de.b-studios" %% "effekt" % "0.4-SNAPSHOT"

To learn how to use the library, see Your First Effect.

scala-effekt's Issues

Not able to pull for scala 2.13

I modified my build.sbt according to the instruction and it looks like there is no library distribution for scala 2.13 in the repository.

sbt output

[error] (core / ssExtractDependencies) sbt.librarymanagement.ResolveException: Error downloading de.b-studios:effekt_2.13:0.4-SNAPSHOT
[error]   Not found
[error]   Not found
[error]   not found: /Users/sitiritis/.ivy2/localde.b-studios/effekt_2.13/0.4-SNAPSHOT/ivys/ivy.xml
[error]   not found: https://repo1.maven.org/maven2/de/b-studios/effekt_2.13/0.4-SNAPSHOT/effekt_2.13-0.4-SNAPSHOT.pom
[error]   not found: https://oss.sonatype.org/content/repositories/snapshots/de/b-studios/effekt_2.13/0.4-SNAPSHOT/effekt_2.13-0.4-SNAPSHOT.pom

Is there a way to fix this? I would be happy to get some help 🙏

Lazy handler for Amb

Is there a way to implement a handler similar to ambList that returns a stream, lazily returning the results?
My naive attempt did not work, but will result in an infinite loop:

def ambStream[R](prog: Amb => Control[R]): Control[Stream[R]] =
  new Handler[Stream[R]] with Amb {
    def flip() = use { resume =>
      for {
        x <- resume(true)
        y <- resume(false)
      } yield x ++ y
    }
  } handle { amb => prog(amb).map(Stream(_)) }

def flip(implicit amb: Amb): Control[Boolean] = amb.flip()

def from(n: Int)(implicit amb: Amb): Control[Int] = for {
  x <- flip
  y <- if (x) pure(n) else from(n + 1)
} yield y

First Effect link dead

For some reason the link to Your first effect is dead. 😢

All other links seem to work though.

Can not import the library with sbt

Hello,

libraryDependencies += "de.b-studios" %% "effekt" % "0.3-SNAPSHOT" does not work.

The modul wasn't found, so maybe the repo
https://repo1.maven.org/maven2/de/b-studios/scala-effekt_2.12/0.3-SNAPSHOT/scala-effekt_2.12-0.3-SNAPSHOT.pom
is down?