Scala 3 — Book



A worksheet is a Scala file that is evaluated on save, and the result of each expression is shown in a column to the right of your program. Worksheets are like a REPL session on steroids, and enjoy 1st class editor support: completion, hyperlinking, interactive errors-as-you-type, etc. Worksheets use the extension

In the following, we show how to use worksheets in IntelliJ, and in VS Code (with the Metals extension).

  1. Open a Scala project, or create one.
    • To create a project in IntelliJ, select “File” -> “New” -> “Project…”, select “Scala” in the left column, and click “Next” to set the project name and location.
    • To create a project in VS Code, run the command “Metals: New Scala project”, select the seed scala/scala3.g8, set the project location, open it in a new VS Code window, and import its build.
  2. Create a file named in the directory src/main/scala/.
    • In IntelliJ, right-click on the directory src/main/scala/, and select “New”, and then “File”.
    • In VS Code, right-click on the directory src/main/scala/, and select “New File”.
  3. Paste the following content in the editor:
    println("Hello, world!")
    val x = 1
    x + x
  4. Evaluate the worksheet.
    • In IntelliJ, click on the green arrow at the top of the editor to evaluate the worksheet.
    • In VS Code, save the file.

    You should see the result of the evaluation of every line on the right panel (IntelliJ), or as comments (VS Code).

A worksheet evaluated in IntelliJ.

A worksheet evaluated in VS Code (with the Metals extension).

Note that the worksheet will use the Scala version defined by your project (set by the key scalaVersion, in your file build.sbt, typically).

Also note that worksheets don’t have a program entry point. Instead, top-level statements and expressions are evaluated from top to bottom.

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