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ZIO from
Home
Wiem Zine Elabidine
@WiemZin
Stay Safe
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Functional Effects
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Functional Programming
Pure functions
Referential
transparency.
Composability
Combine functions
together to build
new data.
Immutability
Values couldn’t be
changed.
Data & Functionality
Pass data through
functions to
change its
behaviors.
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Stay home safe and
use what you have
No Side effects
Pure Function
Trust your types
Total
Test your functions
Deterministic
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Stay home safe and
use what you have
No Side effects
Pure Function
Trust your types
Total
Test your functions
Deterministic
def toInt(str: String): Try[Int] =
Try(str.toInt)
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Stay home safe and
use what you have
No Side effects
Pure Function
Trust your types
Total
Test your functions
Deterministic
def toInt(str: String): Try[Int] =
Try(str.toInt)
toInt("One")
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Stay home safe and
use what you have
No Side effects
Pure Function
Trust your types
Total
Test your functions
Deterministic
def toInt(str: String): Try[Int] =
Try(str.toInt)
toInt("One")
Failure(java.lang.NumberFormatException: For input string: "One")
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Stay home safe and
use what you have
No Side effects
Pure Function
Trust your types
Total
Test your functions
Deterministic
def nextDay(day: DayOfWeek): String =
day.plus(1) .toString
assert(nextDay(THURSDAY)))(equalTo("FRIDAY"))
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Stay home safe and
use what you have
No Side effects
Pure Function
Trust your types
Total
Test your functions
Deterministic
def nextDay(day: DayOfWeek): String =
day.plus(1) .toString
assert(nextDay(THURSDAY)))(equalTo("FRIDAY"))
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Stay home safe and
use what you have
No Side effects
Pure Function
Trust your types
Total
Test your functions
Deterministic
def add(pasta: Pasta, sauce: Sauce,
water: Water): Cooked[Pasta] = {
val p = water.boil.map(_.put(pasta))
p.addSauce(sauce)
}
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Stay home safe and
use what you have
No Side effects
Pure Function
Trust your types
Total
Test your functions
Deterministic
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Effects are useful
❏ handle events
❏ Send messages
❏ read from the DataBase
❏ persist information
❏ print out the result
❏ retry in event of errors
❏ send result to other
services
❏ ...
Real World Applications
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Abstract your programs!
Describe everything in
immutable data type!
Functional Effects
Effects as values?
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Functional Effects
case class IO[A](unsafeRun: () => A) {
def map[B](f: A => B): IO[B] = ???
def flatMap[B](f: A => IO[B]): IO[B] = ???
}
object IO {
def effect[A](a: => A): IO[A] = new IO[A](() => a)
}
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Functional Program
val program: IO[Unit] = for {
event <- IO.effect(handleEvent)
user <- IO.effect(getUser(event.userId))
_ <- IO.effect(logInfo(user))
...
} yield ()
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Functional Program
val program: IO[Unit] = for {
event <- IO.effect(handleEvent)
user <- IO.effect(getUser(event.userId))
_ <- IO.effect(logInfo(user))
...
} yield ()
program.unsafeRun()
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Execution
Just do it!
Description
Make a plan A - Z
Be prepared!
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● Control over all type of interactions
● Testability
● Refactoring
Why Functional Effects?
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Functional Effects
case class IO[A](unsafeRun: () => A) {
def map[B](f: A => B): IO[B] = ???
def flatMap[B](f: A => IO[B]): IO[B] = ???
}
object IO {
def effect[A](a: => A): IO[A] = new IO[A](() => a)
}
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ZIO
Zero dependency Scala library for asynchronous and concurrent
programming using purely functional code.
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Functional Effects in ZIO
ZIO[R, E, A]
Description of a program
R
E A
Dependencies
Error Success
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Functional Effects in ZIO
RIO[R, A]
Description of a program
R
Throwable
A
Dependencies
Error Success
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Functional Effects in ZIO
URIO[R, A]
Description of a program
R
A
Dependencies
Success
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Functional Effects in ZIO
Task[A]
Description of a program
Throwable
A
Error Success
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Functional Effects in ZIO
IO[E, A]
Description of a program
E
A
Error Success
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Functional Effects in ZIO
UIO[A]
Description of a program
A
Success
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Run Effects
object Main extends zio.App {
override def run(args: List[String]): IO[Nothing, Int] =
program.fold(_ => 1, _ => 0)
}
OR
object Main {
Runtime.default.unsafeRun(program)
}
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Error
Management
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Error Management
Throwable
def divideM(a: Int, b: Int): Task[Int] =
Task(divide(a, b))
Task[Int]
Throwable Int
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Error Management
Throwable
val throwException: Task[Nothing] =
Task(throw new Exception("sorry"))
Task[Nothing]
Throwable
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Error Management
String
val failedIO: IO[String, Nothing] = IO.fail("sorry again")
IO[String, Nothing]
String
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Error Management
Customized Errors
sealed trait Error
object Error {
case class UserNotFound(id: UserId) extends Error
case class InternalServer(t: Throwable) extends Error
...
}
val program: IO[Error, Unit] = ???
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Error Management
Customized Errors
val program: IO[Error, Unit] =
for {
userId <- requestListener // IO[InternalServer, UserId]
user <- getUser(userId) // IO[UserNotFound, User]
_ <- logInfo(user) // IO[ Nothing, Unit]
_ <- sendResponse(user) // IO[InternalServer, Unit]
} yield ()
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Error Management
The state of the program
val program: IO[Error, Unit] = ???
val programState: IO[Nothing, Exit[Error, Unit]] = program.run
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Error Management
Exit[E, A]
Success[A]
Failure[E]
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Error Management
Exit[E, A]
Success[A]
Failure[E]
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Error Management
Exit[E, A]
Success[A]
Failure[E]
Cause[E]
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Cause[E]
Die
Expected Error
Unexpected Error, Exception
Fail[E]
Interrupted effect
Interrupt
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Many causes?
Both(left, right)
Both(Fail(e1),
Then(Both(Fail(e2), Die(t)), Interrupt)
Then(left, right)
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Example: Cause.Both
IO.fail("error1")
.zipPar(
IO.succeed(throw new Exception(" surprise!"))
)
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Example: Cause.Both
IO.fail("error1") // Cause.Fail("error1")
.zipPar(
IO.succeed(throw new Exception(" surprise!"))
)
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Example: Cause.Both
IO.fail("error1") // Cause.Fail("error1")
.zipPar(
IO.succeed(throw new Exception(" surprise!")) // Cause.Die(...)
)
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Example: Cause.Both
IO.fail("error1") // Cause.Fail("error1")
.zipPar(
IO.succeed(throw new Exception(" surprise!")) // Cause.Die(...)
)
⇒ Both(Cause.Fail("error1"), Cause.Die(java.lang.Exception: surprise!)))
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Example: Cause.Then
IO.fail("error").ensuring(IO.die(new Exception("Don't try this at Home")))
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Example: Cause.Then
IO.fail("error").ensuring(IO.die(new Exception("Don't try this at Home")))
Fail("error")
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Example: Cause.Then
IO.fail("error").ensuring(IO.die(new Exception("Don't try this at Home")))
Fail("error") Die(java.lang.Exception Don’t try this at Home)
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Example: Cause.Then
IO.fail("error").ensuring(IO.die(new Exception("Don't try this at Home")))
Fail("error") Die(java.lang.Exception Don’t try this at Home)
⇒ Then(Cause.Fail("error"), Cause.Die(java.lang.Exception: Don’t try this at Home))
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Error Management
Expose all causes:
def divide(a: Int, b: Int): IO[Cause[Throwable], Int] =
Task(a / b).sandbox
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Error Management
Catch Errors:
def divide(a: Int, b: Int): Task[Int] =
Task(a / b)
.catchSome{
case _: ArithmeticException => UIO(0)
}
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Error Management
Peek at the errors:
def divide(a: Int, b: Int): Task[Int] =
Task(a / b)
.tapError{
error => UIO(println(s"failed with: $e"))
}
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Error Management
Fallback:
val io1: IO[Error, Int] = ???
val io2: IO[String, Int] = ???
val result: IO[String, Int] = io1.orElse(io2)
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Error Management
Fallback:
val loginUser: IO[Error, Profile] = ???
val loginAnonymous: IO[Throwable, LimitedProfile] = ???
val result: IO[Throwable, Either[Profile, LimitedProfile]] =
loginUser.orElseEither(loginAnonymous)
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Error Management
Recover:
def divide(a: Int, b: Int): UIO[Int] =
Task(a / b).foldM(_ => UIO(0), n => UIO(n))
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Error Management
Crash it:
def divide(a: Int, b: Int): UIO[Int] =
Task(a / b).orDie
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Error Management
Make defects as expected errors:
val io: IO[String, Nothing] =
IO.succeed(throw new Exception(""))
.unrefine(e => s"The error is: $e")
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Error Management
What about fatal Errors?
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Error Management
def simpleName[A](c: Class[A]) = c.getSimpleName
object Example
Task(simpleName(Example.getClass))
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Error Management
def simpleName[A](c: Class[A]) = c.getSimpleName
object Example
Task(simpleName(Example.getClass))
[error] java.lang.InternalError: Malformed class name
[error] at java.lang.Class.getSimpleName(Class.java:1330)
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Error Management
object Main extends zio.App {
override val platform: Platform =
Platform.default.withFatal (_ => false)
override def run(args: List[String]): ZIO[zio.ZEnv, Nothing, Int] = {
Task(simpleName(Example.getClass)).fold(_ =>1, _ => 0)
}
}
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Error Management
override val platform: Platform = new Platform {
val executor = Executor.makeDefault(2)
val tracing = Tracing.disabled
def fatal(t: Throwable): Boolean =
!t.isInstanceOf[InternalError] && t.isInstanceOf[VirtualMachineError]
def reportFatal(t: Throwable): Nothing = {
t.printStackTrace()
throw t
}
def reportFailure(cause: Cause[Any]): Unit = {
if (cause.died)
System.err.println(cause.prettyPrint)
}
...
}
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Build concurrent
programs
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ZIO Fibers
Fibers are lightweight mechanism of concurrency.
OS Thread
ZIO Fiber
Task1 Task2 Task3 ... ..
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How ZIO runs Effects?
ZIO[R, E, A]
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How ZIO runs Effects?
ZIO[R, E, A]
R => IO[E, A]
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How ZIO runs Effects?
ZIO[R, E, A]
R => IO[E, A]
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How ZIO runs Effects?
ZIO[R, E, A]
R => IO[E, A]
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How ZIO runs Effects?
IO[E, A]
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How ZIO runs Effects?
IO[E, A]
Fiber[E, A]
unsafeRun
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How ZIO runs Effects?
IO[E, A]
Fiber[E, A]
unsafeRun
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How ZIO runs Effects?
IO[E, A]
Fiber[E, A]
unsafeRun
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How ZIO runs concurrent Effects?
IO[E, A]
Fiber[E, A]
unsafeRun
IO[Nothing,Fiber[E, A]]
fork
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How ZIO runs concurrent Effects?
IO[E, A]
Fiber[E, A]
unsafeRun
IO[Nothing,Fiber[E, A]]
fork
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How ZIO runs concurrent Effects?
IO[E, A]
Fiber[E, A]
unsafeRun
IO[Nothing,Fiber[E, A]]
fork
Fiber[E, A]
unsafeRun
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How ZIO runs concurrent Effects?
IO[E, A]
Fiber[E, A]
unsafeRun
IO[Nothing,Fiber[E, A]]
fork
Fiber[E, A]
unsafeRun
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Concurrent Tasks
trait ZIO[R, E, A] {
def race(that: ZIO[R, E, A]): ZIO[R, E, A]
def raceAll(ios: Iterable[ZIO[R, E, A]]): ZIO[R, E, A]
def zipPar(that: ZIO[R, E, B]): ZIO[R, E, (A, B)]
def on(ec: ExecutionContext): ZIO[R, E, A]
...
}
object ZIO {
def foreachPar(as: Iterable[A])(fn: A => ZIO[R, E, B]): ZIO[R, E, List[B]]
...
}
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Concurrent Tasks
def getUserInfo(id: Id): Task[(User, Profile)] =
fetchUser(id).zipPar(fetchProfile(id))
Task 1 Task 2
(User, Profile)
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Example
case class IlForno(queue: Queue[Request], currentIngredients: Ref[Ingredients]) {
def handleRequests(p: Promise[Nothing, Unit]): ZIO[Clock, MissingIngredient, Unit] =
(for {
request <- queue.take
rest <- currentIngredients.update(preparePizza(request, _))
_ <- evaluate(rest)
} yield ())
.tapError(_ => p.succeed(()))
.repeat(Schedule.duration(8.hours) && Schedule.spaced(10.minutes))
.unit
val listenRequests: IO[Error, Unit] = ???
}
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val program: ZIO[Clock, Error, Unit] = for {
ilForno <- IlForno(initialIngredient)
f1 <- ilForno.listenRequests.fork
p <- Promise.make[Nothing, Unit]
f2 <- ilForno.handleRequests(p).fork
_ <- p.await
_ <- f1.interrupt.zipPar(f2.interrupt)
} yield ()
Example
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Example
val program: ZIO[Clock, Error, Unit] = for {
ilForno <- IlForno(initialIngredient)
f1 <- ilForno.listenRequests.fork
p <- Promise.make[Nothing, Unit]
f2 <- ilForno.handleRequests(p).fork
_ <- p.await
_ <- f1.interrupt.zipPar(f2.interrupt)
} yield ()
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Example
val program: ZIO[Clock, Error, Unit] = for {
ilForno <- IlForno(initialIngredient)
f1 <- ilForno.listenRequests.fork
p <- Promise.make[Nothing, Unit]
f2 <- ilForno.handleRequests(p).fork
_ <- p.await
_ <- f1.interrupt.zipPar(f2.interrupt)
} yield ()
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Example
val program: ZIO[Clock, Error, Unit] = for {
ilForno <- IlForno(initialIngredient)
f1 <- ilForno.listenRequests.fork
p <- Promise.make[Nothing, Unit]
f2 <- ilForno.handleRequests(p).fork
_ <- p.await
_ <- f1.interrupt.zipPar(f2.interrupt)
} yield ()
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Resource
Management
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Resource Management
File Connection
Open / close / use = Acquire / release / use
Database Clients
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Resource Management
IO.effect(startApp)
.ensuring(
console.putStr("Shutdown ..."))
ensuring
01
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Resource Management
IO.effect(startApp)
.ensuring(
console.putStr("Shutdown ..."))
createClient(config)
.bracket(_.close)(c =>
processEvents(c))
ensuring bracket
01 02
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Resource Management
IO.effect(startApp)
.ensuring(
console.putStr("Shutdown ..."))
ensuring
val resource =
Managed.make(openFile(file))(_.close)
...
resource.use(computeLines)
Management
bracket
01 03
02
createClient(config)
.bracket(_.close)(c =>
processEvents(c))
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Resource Management
● You can use the methods provided by the dependencies in your
program.
● once you provide a layer or an environment, the implementation
will be acquired and used then released at the end.
ZIO Environment & ZLayer[R, E, A]
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ZIO
is Awesome
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WrapUp
documentation
https://github.com/zio/zio
zio.dev
ZIO projects
Blog post
https://medium.com/@wiemzin
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THANKS
Follow me: @WiemZin
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