zio / interop-cats   23.0.3

Apache License 2.0 GitHub

ZIO instances for cats-effect type classes

Scala versions: 3.x 2.13 2.12
Scala.js versions: 1.x

ZIO Interop Cats


libraryDependencies += "dev.zio" %% "zio-interop-cats" % "<latest-version>"

ZIO Cats Effect 3 instances

ZIO integrates with Typelevel libraries by providing an instance of Concurrent, Temporal and Async for Task as required, for instance, by fs2, doobie and http4s.

For convenience, the ZIO library defines an alias as follows:

type Task[A] = ZIO[Any, Throwable, A]

Therefore, we provide Cats Effect instances based on this specific datatype.


In order to get a Concurrent[Task] or Concurrent[RIO[R, *]] (note * is kind-projector notation) we need to import zio.interop.catz._:

import cats.effect._
import zio._
import zio.interop.catz._

def ceConcurrentForTaskExample = {
  val F: cats.effect.Concurrent[Task] = implicitly
  F.racePair(F.unit, F.unit)


import cats.effect._
import zio._
import zio.interop.catz._

def ceTemporal = {
  val F: cats.effect.Temporal[Task] = implicitly
  F.sleep(1.second) *> F.unit


import cats.effect._
import zio._
import zio.interop.catz._

def ceAsync = {
  val F: cats.effect.Async[Task] = implicitly
  F.racePair(F.unit, F.sleep(1.second) *> F.unit)

Other typeclasses

There are many other typeclasses and useful conversions that this library provides implementations for:

  • See zio/interop/cats.scala file to see all available typeclass implementations for the Cats Effect 3 typeclasses
  • See zio/stream/interop/cats.scala for ZStream typeclass implementations
  • See zio/stream/interop/FS2StreamSyntax.scala for FS2 <-> ZStream conversions


If you only need instances for cats-core typeclasses, not cats-effect import zio.interop.catz.core._:

import zio.interop.catz.core._

Note that this library only has an Optional dependency on cats-effect – if you or your libraries don't depend on it, this library will not add it to the classpath.


The following example shows how to use ZIO with Doobie (a library for JDBC access) and FS2 (a streaming library), which both rely on Cats Effect instances (cats.effect.Async and cats.effect.Temporal):

import zio.{durationInt as _, *}
import zio.interop.catz.*
import doobie.*
import doobie.implicits.*
import scala.concurrent.duration.*

object Example extends ZIOAppDefault:
  val run = {
    val xa: Transactor[Task] =
      Transactor.fromDriverManager[Task]("org.h2.Driver", "jdbc:h2:mem:test;DB_CLOSE_DELAY=-1", "user", "", None)

    sql"SELECT 42"
      .evalTap(i => Console.printLine(i))


Learn more on the ZIO Interop Cats homepage!


For the general guidelines, see ZIO contributor's guide.

Code of Conduct

See the Code of Conduct


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