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Scala (Wasm)

Scala is a statically typed language that combines functional and object-oriented programming. Scala 3 programs can target the JVM, JavaScript (via Scala.js) and native platforms.

In LiveCodes, Scala source is compiled and linked in the browser by the Scala 3 compiler and the Scala.js linker, both compiled to WebAssembly. The program then runs in the result page. Nothing is sent to a server.

Note

The toolchain is about 46 MB and is downloaded on the first run, which can take some time. Macros work but download a second compiler and about 23 MB of additional compiler IR the first time they are used.

Usage​

Demo:

show code
import { createPlayground } from 'livecodes';

const options = {
  "config": {
    "activeEditor": "script",
    "script": {
      "language": "scala-wasm",
      "content": "@main def hello(): Unit =\n  val squares = (1 to 5).map(n => n * n)\n  println(\"squares: \" + squares.mkString(\", \"))\n  println(\"sum: \" + squares.sum)\n"
    },
    "mode": "simple",
    "editor": "auto",
    "tools": {
      "status": "full"
    }
  }
};
createPlayground('#container', options);

Standard I/O​

Scala code runs in the context of the result page. Standard output (e.g. println) is captured and displayed in the console. Standard input is passed by setting the livecodes.scala.input property in JavaScript.

The input is a one-shot buffer: once it is exhausted, readLine() returns null and the typed StdIn readers throw EOFException. It is not an interactive terminal. The following read from the supplied buffer:

  • scala.io.StdIn.readLine() and the typed readers (readInt, readDouble, ...)
  • scala.Console.in
  • System.in.read() and BufferedReader(new InputStreamReader(System.in))

java.util.Scanner and scala.io.Source.stdin have no working Scala.js implementation, and a parameterized @main method cannot be wrapped (use an object main or a parameterless @main).

Communication with JavaScript​

A few helper properties and methods are available in the browser global livecodes.scala object:

  • livecodes.scala.input: The standard input passed to the Scala program. It can be set before the initial run, or passed to run for subsequent runs.
  • livecodes.scala.loaded: A promise that resolves when the Scala environment is ready (and rejects if it fails to load). Other helpers should be used after this promise resolves.
  • livecodes.scala.ready: A boolean that is true once the environment is loaded and a run has completed.
  • livecodes.scala.output: The standard output of the last run.
  • livecodes.scala.error: The compiler diagnostics or runtime error of the last run, if any.
  • livecodes.scala.exitCode: The exit code of the last run.
  • livecodes.scala.run(input): Runs the code in the editor, optionally passing standard input, and returns a promise that resolves to { output, error, exitCode }.
await livecodes.scala.loaded;
const { output, error, exitCode } = await livecodes.scala.run(livecodes.scala.input);
console.log(output);

Language Info​

Name​

scala-wasm

Aliases / Extensions​

scala, scala-wasm, wasm.scala

Editor​

script

Compiler​

The Scala 3 compiler and the Scala.js linker compiled to WebAssembly, provided by scala-toolchain-wasm and packaged for LiveCodes by @live-codes/scala-wasm.

Version​

Scala 3.8.3, Scala.js 1.20.2

Code Formatting​

Not supported.

Limitations​

  • java.util.Scanner and scala.io.Source.stdin are not available.
  • A parameterized @main method cannot read the supplied standard input.

Example Usage​

This example passes standard input and runs the code again on each click, using the browser global livecodes.scala (also check the code in the HTML editor):

show code
import { createPlayground } from 'livecodes';

const options = {
  "template": "scala"
};
createPlayground('#container', options);

Live Reload​

By default, new code changes are sent to the result page for re-evaluation without a full page reload, avoiding the need to reinitialize the Scala WebAssembly environment. This behavior can be disabled by adding the code comment // __livecodes_reload__ to the Scala code, which forces a full page reload.

This comment can be added in the hiddenContent property of the editor for embedded playgrounds.

Starter Template​

https://livecodes.io/?template=scala

Sponsors