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Version: 2.0.x

Getting Started with ZIO

Include ZIO in your project by adding the following to your build.sbt file:

libraryDependencies += "dev.zio" %% "zio" % "2.1.6"

If you want to use ZIO streams, you should also include the following dependency:

libraryDependencies += "dev.zio" %% "zio-streams" % "2.1.6"


Your application can extend ZIOAppDefault, which provides a complete runtime system and allows you to write your whole program using ZIO:

import zio._
import zio.Console._

object MyApp extends ZIOAppDefault {

def run = myAppLogic

val myAppLogic =
for {
_ <- printLine("Hello! What is your name?")
name <- readLine
_ <- printLine(s"Hello, ${name}, welcome to ZIO!")
} yield ()

The run method should return a ZIO value which has all its errors handled,
which, in ZIO parlance, is an unexceptional ZIO value.

One way to do this is to invoke fold over a ZIO value, to get an unexceptional ZIO value. That requires two handler functions: eh: E => B (the error handler) and ah: A => B (the success handler).

If myAppLogic fails, eh will be used to get from e: E to b: B; if it succeeds, ah will be used to get from a: A to b: B.

myAppLogic, as folded above, produces an unexceptional ZIO value, with B being Int.
If myAppLogic fails, there will be a 1; if it succeeds, there will be a 0.

If you are integrating ZIO into an existing application, using dependency injection, or do not control your main function, then you can create a runtime system in order to execute your ZIO programs:

import zio._

object IntegrationExample {
val runtime = Runtime.default

Unsafe.unsafe { implicit unsafe =>"Hello World!"))).getOrThrowFiberFailure()

Ideally, your application should have a single runtime, because each runtime has its own resources (including thread pool and unhandled error reporter).


ZIO provides a module for interacting with the console. You can import the functions in this module with the following code snippet:

If you need to print text to the console, you can use print and printLine:

import zio._

// Print without trailing line break
Console.print("Hello World")

// Print string and include trailing line break
Console.printLine("Hello World")

If you need to read input from the console, you can use readLine:

import zio._

val echo = Console.readLine.flatMap(line => Console.printLine(line))