Setting up gears

Running Examples in this Book

The book contains some examples in the src/scala directory. For example, this is the hello example, located in src/scala/hello.scala:

//> using scala 3.4.0
//> using dep "ch.epfl.lamp::gears::0.2.0"
//> using nativeVersion "0.5.1"

import gears.async.*
import gears.async.default.given

@main def main() =
  Async.blocking:
    val hello = Future:
      print("Hello")
    val world = Future:
      hello.await
      println(", world!")
    world.await

All such examples can be run with scala-cli provided the following dependencies:

• A locally published version of gears.
• Additional platform dependencies, as described below.

Compiling gears

To compile gears from source, clone gears from the GitHub repository:

git clone https://github.com/lampepfl/gears --recursive

And run rootJVM/publishLocal.

For Scala Native

Make sure to prepare additional dependencies for Scala Native. You would also need to locally publish a custom version of munit for Scala Native 0.5.0, which is available as a git submodule from the gears repository.

To locally publish munit, from the root directory of gears repository:

git submodule update            # Create and update submodules
dependencies/publish_deps.sh # Locally publish pinned dependencies

Finally, gears artifacts for Scala Native can be locally published by

sbt rootNative/publishLocal

Trying out examples

On JVM

As mentioned in the introduction, we require a JVM version that supports virtual threads. With that provided, examples can be run simply with

scala-cli run "path-to-example"

For the hello example:

scala-cli run src/scala/hello.scala

On Scala Native

The current Scala Native version required by Gears is 0.5.1. Therefore examples in this book hardcodes 0.5.1 as the Scala Native version, which is also the version gears is currently compiled against.

Examples can be run with

scala-cli --platform scala-native run "path-to-example"

For the hello example:

scala-cli --platform scala-native run src/scala/hello.scala