Getting Started with ZIO

Installation

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

libraryDependencies += "dev.zio" %% "zio" % "2.1.27"

Main

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 =>
    runtime.unsafe.run(ZIO.attempt(println("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).

Console

ZIO provides a Console service for interacting with the console.

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))

Next Steps

Now that you've got ZIO installed and running, the next step is to learn about the ZIO data type.