README.md

ZIO Cheat Sheet

• This is based on ZIO 2.0.X (in particular 2.0.10).
• For simplicity, ZIO environment has been omitted but all the functions also work with the form ZIO[R, E, A].
• Function arguments are usually by name, but that has (mostly) been ignored for simplicity. Also, functions are often "more generic" in their parameter types than shown below.
• For many functions there are several (unmentioned) related functions that are conceptually similar but differ in some detail. They are usually easy to learn due to consistent naming.
• Important ZIO types other than the functional effect type ZIO[R, E, A] have been left out. For example: ZStream[R, E, A], ZLayer[RIn, E, ROut], Fiber[E, A] and Ref[A].
• In the remainder of this cheat sheet, E1 >: E, but E2 can be any error type. Also A1 >: A.

Aliases

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
ZIO.succeed	=> A	IO[Nothing, A]
ZIO.fail	=> E	IO[E, Nothing]
ZIO.interrupt		IO[Nothing, Nothing]
ZIO.die	Throwable	IO[Nothing, Nothing]
ZIO.attempt	=> A	IO[Throwable, A]
ZIO.async	((IO[E, A] => Unit) => Unit) FiberId	IO[E, A]
ZIO.fromEither	Either[E, A]	IO[E, A]
ZIO.left	A	IO[Nothing, Either[A, Nothing]]
ZIO.right	B	IO[Nothing, Either[Nothing, B]]
ZIO.fromFiber	Fiber[E, A]	IO[E, A]
ZIO.fromFuture	ExecutionContext => Future[A]	IO[Throwable, A]
ZIO.fromOption	Option[A]	IO[Option[Nothing], A]
ZIO.none		IO[Nothing, Option[Nothing]]
ZIO.some	A	IO[Nothing, Option[A]]
ZIO.fromTry	Try[A]	IO[Throwable, A]
ZIO.acquireReleaseWith	IO[E, A] (acquire) A => IO[Nothing, Any] (release) A => IO[E, B] (use)	IO[E, B]
ZIO.when	Boolean IO[E, A]	IO[E, Option[A]]
ZIO.whenZIO	IO[E, Boolean] IO[E, A]	IO[E, Option[A]]
ZIO.whenCase	A PartialFunction[A, IO[E, B]]	IO[E, Option[B]]
ZIO.whenCaseZIO	IO[E, A] PartialFunction[A, IO[E, B]]	IO[E, Option[B]]
ZIO.filter	Iterable[A] A => IO[E, Boolean]	IO[E, List[A]]
ZIO.cond	Boolean A E	IO[E, A]

Transforming effects

Name	From	Given	To
map	IO[E, A]	A => B	IO[E, B]
mapAttempt	IO[Throwable, A]	A => B	IO[Throwable, B]
as	IO[E, A]	B	IO[E, B]
asSome	IO[E, A]		IO[E, Option[A]]
asSomeError	IO[E, A]		IO[Option[E], A]
orElseFail	IO[E, A]	E2	IO[E2, A]
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]
mapBoth	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]	E => IO[Nothing, E2]	IO[E2, A]
collect	IO[E, A]	E1 PartialFunction[A, B]	IO[E1, B]
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]	E => IO[E1, _] A => IO[E1, _]	IO[E1, A]
tapError	IO[E, A]	E => IO[E1, _]	IO[E1, A]
absolve	IO[E, Either[E, A]]		IO[E, A]
some	IO[E, Option[A]]		IO[Option[E], A]
head	IO[E, List[A]]		IO[Option[E], A]
toFuture	IO[Throwable, A]		IO[Nothing, Future[A]]
filterOrDie	IO[E, A]	A => Boolean Throwable	IO[E, A]
filterOrDieMessage	IO[E, A]	A => Boolean String	IO[E, A]
filterOrElse	IO[E, A]	A => Boolean A => IO[E, A]	IO[E, A]
filterOrFail	IO[E, A]	A => Boolean E	IO[E, A]
when	IO[E, A]	Boolean	IO[E, Option[A]]
unless	IO[E, A]	Boolean	IO[E, Option[A]]

Declaring and providing the environment

Name	From	Given	To
ZIO.service		given Tag[A]	ZIO[A, Nothing, A]
provideEnvironment	ZIO[R, E, A]	ZEnvironment[R]	IO[E, A]
provideLayer	ZIO[R, E, A]	ZLayer[R0, E, R]	ZIO[R0, E, A]

Configuration

Name	From	Given	To
ZIO.config		Config[A]	IO[Config.Error, 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]
exit	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]
foldZIO	IO[E, A]	E => IO[E2, B] A => IO[E2, B]	IO[E2, B]
foldCauseZIO	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[E, S]	IO[E, A]
eventually	IO[E, A]		IO[Nothing, A]

Terminate fiber with errors

Name	From	Given	To
orDie	IO[Throwable, A]		IO[Nothing, A]
orDieWith	IO[E, A]	E => Throwable	IO[Nothing, A]
refineOrDie	IO[Throwable, A]	PartialFunction[Throwable, E2]	IO[E2, A]
refineOrDieWith	IO[E, A]	PartialFunction[E, E2] E => Throwable	IO[E2, A]

Combining effects + parallelism

Name	From	Given	To
ZIO.foldLeft		Iterable[A] S (S, A) => IO[E, S]	IO[E, S]
ZIO.foreach		Iterable[A] A => IO[E, B]	IO[E, List[B]]
ZIO.foreachPar		Iterable[A] A => IO[E, B]	IO[E, List[B]]
ZIO.collectAll		Iterable[IO[E, A]]	IO[E, List[A]]
ZIO.collectAllPar		Iterable[IO[E, A]]	IO[E, List[A]]
ZIO.forkAll		Iterable[IO[E, A]]	IO[Nothing, Fiber[E, List[A]]]
fork	IO[E, A]		IO[Nothing, Runtime[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]]

Finalizers

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]

Timing and repetition

Name	From	Given	To
ZIO.never			IO[Nothing, Nothing]
ZIO.sleep		Duration	IO[Nothing, Unit]
delay	IO[E, A]	Duration	IO[E, A]
timeout	IO[E, A]	Duration	IO[E, Option[A]]
timed	IO[E, A]		IO[E, (Duration, A)]
forever	IO[E, A]		IO[E, Nothing]
repeat	IO[E, A]	Schedule[A, B]	IO[E, B]
repeatUntil	IO[E, A]	A => Boolean	IO[E, A]
repeatWhile	IO[E, A]	A => Boolean	IO[E, A]

Logging

Name	From	Given	To
ZIO.log		String	IO[Nothing, Unit]
ZIO.logFatal		String	IO[Nothing, Unit]
ZIO.logError		String	IO[Nothing, Unit]
ZIO.logWarning		String	IO[Nothing, Unit]
ZIO.logInfo		String	IO[Nothing, Unit]
ZIO.logDebug		String	IO[Nothing, Unit]
ZIO.logTrace		String	IO[Nothing, Unit]