Skip to content
ZIO Cheat Sheet
Branch: master
Clone or download
Latest commit 504566d Aug 6, 2019
Type Name Latest commit message Commit time
Failed to load latest commit information. Update Aug 6, 2019

ZIO Cheat Sheet

  • This is based on ZIO 1.0.0-RC11.
  • For simplicity, ZIO environment has been omitted but all the functions also work with the form ZIO[R, E, A].


Alias Full Form
UIO[A] ZIO[Any, Nothing, A]
IO[E, A] ZIO[Any, E, A]
Task[A] ZIO[Any, Throwable, A]
RIO[R, A] ZIO[R, Throwable, A]
URIO[R, A] ZIO[R, Nothing, A]

Creating effects

Name Given To
IO.succeed A IO[Nothing, A]
IO.succeedLazy => A IO[Nothing, A] E IO[E, Nothing]
IO.interrupt IO[Nothing, Nothing]
IO.die Throwable IO[Nothing, Nothing]
=> A IO[Throwable, A]
=> A IO[Nothing, A]
IO.effectAsync ((IO[E, A] => Unit) => Unit) IO[E, A]
IO.fromEither Either[E, A] IO[E, A]
IO.left A IO[Nothing, Either[A, Nothing]]
IO.right A IO[Nothing, Either[Nothing, A]]
IO.fromFiber Fiber[E, A] IO[E, A]
IO.fromFuture ExecutionContext => Future[A] IO[Throwable, A]
IO.fromOption Option[A] IO[Unit, A]
IO.none IO[Nothing, Option[Nothing]]
IO.some A IO[Nothing, Option[A]
IO.fromTry Try[A] IO[Throwable, A]
IO.bracket IO[E, A] (acquire)
A => IO[Nothing, Unit] (release)
A => IO[E, B] (use)
IO[E, B]
IO.when Boolean
IO[E, _]
IO[E, Unit]
IO.whenM IO[E, Boolean]
IO[E, _]
IO[E, Unit]
IO.whenCase A
PartialFunction[A, IO[E, _]]
IO[E, Unit]
IO.whenCaseM IO[E, A]
PartialFunction[A, IO[E, _]]
IO[E, Unit]

Transforming effects

Name From Given To
map IO[E, A] A => B IO[E, B]
const IO[E, A] B IO[E, B]
unit IO[E, A] IO[E, Unit]
>>= (flatmap) IO[E, A] A => IO[E1, B] IO[E1, B]
flatten IO[E, IO[E1, A]] IO[E1, A]
bimap IO[E, A] E => E2
A => B
IO[E2, B]
mapError IO[E, A] E => E2 IO[E2, A]
mapErrorCause IO[E, A] Cause[E] => Cause[E2] IO[E2, A]
flatmapError IO[E, A] IO[Nothing, E2] IO[E2, A]
sandbox IO[E, A] IO[Cause[E], A]
flip IO[E, A] IO[A, E]
tap IO[E, A] A => IO[E1, _] IO[E1, A]
tapBoth IO[E, A] A => IO[E1, _]
E => IO[E1, _]
IO[E1, A]
tapError IO[E, A] E => IO[E1, _] IO[E1, A]
absolve IO[E, Either[E, A]] IO[E, A]
get IO[Nothing, Option[A]] IO[Unit, A]
head IO[E, List[A]] IO[Option[E], A]
toFuture IO[Throwable, A] IO[Nothing, Future[A]]

Recover from errors

Name From Given To
either IO[E, A] IO[Nothing, Either[E, A]]
option IO[E, A] IO[Nothing, Option[A]]
ignore IO[E, A] IO[Nothing, Unit]
run IO[E, A] IO[Nothing, Exit[E, A]]
<> (orElse) IO[E, A] IO[E2, A1] IO[E2, A1]
orElseEither IO[E, A] IO[E2, B] IO[E2, Either[A, B]]
fold IO[E, A] E => B
A => B
IO[Nothing, B]
foldM IO[E, A] E => IO[E2, B]
A => IO[E2, B]
IO[E2, B]
foldCauseM IO[E, A] Cause[E] => IO[E2, B]
A => IO[E2, B]
IO[E2, B]
catchAll IO[E, A] E => IO[E2, A1] IO[E2, A1]
catchAllCause IO[E, A] Cause[E] => IO[E2, A1] IO[E2, A1]
catchSome IO[E, A] PartialFunction[E, IO[E1, A1]] IO[E1, A1]
retry IO[E, A] Schedule[E1, S] ZIO[Clock, E1, A]
eventually IO[E, A] IO[Nothing, A]

Combining effects + parallelism

Name From Given To
IO.foldLeft Iterable[A]
(S, A) => IO[E, S]
IO[E, S]
IO.foreach Iterable[A]
A => IO[E, B]
IO[E, List[B]]
IO.foreachPar Iterable[A]
A => IO[E, B]
IO[E, List[B]]
IO.foreachParN Long
A => IO[E, B]
IO[E, List[B]]
IO.forkAll Iterable[IO[E, A]] IO[Nothing, Fiber[E, List[A]]]
fork IO[E, A] IO[Nothing, Fiber[E, A]]
<*> (zip) IO[E, A] IO[E1, B] IO[E1, (A, B)]
*> (zipRight) IO[E, A] IO[E1, B] IO[E1, B]
<* (zipLeft) IO[E, A] IO[E1, B] IO[E1, A]
<&> (zipPar) IO[E, A] IO[E1, B] IO[E1, (A, B)]
&> (zipParRight) IO[E, A] IO[E1, B] IO[E1, B]
<& (zipParLeft) IO[E, A] IO[E1, B] IO[E1, A]
race IO[E, A] IO[E1, A1] IO[E1, A1]
raceAll IO[E, A] Iterable[IO[E1, A1]] IO[E1, A1]
raceEither IO[E, A] IO[E1, B] IO[E1, Either[A, B]]


Name From Given To
ensuring IO[E, A] UIO[_] IO[E, A]
onError IO[E, A] Cause[E] => UIO[_] IO[E, A]
onInterrupt IO[E, A] UIO[_] IO[E, A]
onTermination IO[E, A] Cause[Nothing] => UIO[_] IO[E, A]


Name From Given To
IO.never IO[Nothing, Nothing]
IO.sleep Duration ZIO[Clock, Nothing, Unit]
delay IO[E, A] Duration ZIO[Clock, E, A]
timeout IO[E, A] Duration ZIO[Clock, E, Option[A]]
timed IO[E, A] ZIO[Clock, E, (Duration, A)]
forever IO[E, A] IO[E, Nothing]
repeat IO[E, A] Schedule[A, B] ZIO[Clock, E, B]
You can’t perform that action at this time.