Create your custom Scala REPL

If you ever need to create an interactive console/REPL that let’s users use play with your code in a simple terminal you might (still) find that there’s hardly any documentation. I fixed the console for Gremlin-Scala (a graph DSL) and thought that other people might want a very basic version of a custom shell to have a quick start.
It doesn’t do much more than importing java.lang.Math so that you can type things like `abs(-4.2)` directly in the shell without having to import java.lang.Math._ first. The important part is that your import statements and any initialisation belongs into `addThunk` – those are executed after the shell is fully initialised – otherwise you get all sorts of AST errors that don’t really help much.

This is obviously only a starting point, you can further customise it to automatically do stuff with the executed command like we do in Gremlin-Scala’s Console.

import scala.tools.nsc.Settings
import scala.tools.nsc.interpreter.ILoop

object TestConsole extends App {
  val settings = new Settings
  settings.usejavacp.value = true
  settings.deprecation.value = true

  new SampleILoop().process(settings)
}

class SampleILoop extends ILoop {
  override def prompt = "==> "

  addThunk {
    intp.beQuietDuring {
      intp.addImports("java.lang.Math._")
    }
  }

  override def printWelcome() {
    echo("\n" +
      "         \\,,,/\n" +
      "         (o o)\n" +
      "-----oOOo-(_)-oOOo-----")
  }

}