atnos-org / eff-scalaz

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Extensible effects are an alternative to monad transformers for computing with effects in a functional way. This library is based on the "free-er" monad and an "open union" of effects described in Oleg Kiselyov in Freer monads, more extensible effects.

You can learn more in the User Guide:

You can also check out this presentation at flatMap Oslo 2016 (slides).


You add eff-scalaz as an sbt dependency:

libraryDependencies += "org.atnos" %% "eff-scalaz" % "2.0.0"

// to write types like Reader[String, ?]
addCompilerPlugin("org.spire-math" %% "kind-projector" % "0.9.3")

// to get types like Reader[String, ?] (with more than one type parameter) correctly inferred
addCompilerPlugin("com.milessabin" % "si2712fix-plugin_2.11.8" % "1.2.0")

If you want to use the scalaz.concurrent.Future or scalaz.concurrent.Task effects:

libraryDependencies += "org.atnos" %% "eff-scalaz-concurrent" % "2.0.0"


eff-scalaz is a Typelevel project. This means we embrace pure, typeful, functional programming, and provide a safe and friendly environment for teaching, learning, and contributing as described in the Typelevel Code of Conduct.

Feel free to open an issue if you notice a bug, have an idea for a feature, or have a question about the code. Pull requests are also gladly accepted.