Embedded Scala REPL Interpreter example for 2.10

Question

Please give a code example of how to create an embedded Scala REPL interpreter programmatically, that works in Scala 2.10. (I added this Q&A after spending hours combing various code scraps to get a working interpreter)

Ben Hutchison · Accepted Answer · 2013-09-23T03:58:57.647

23

Example Repl.scala:

import scala.tools.nsc.interpreter._
import scala.tools.nsc.Settings


object Repl extends App {
  def repl = new ILoop {
    override def loop(): Unit = {
      intp.bind("e", "Double", 2.71828)
      super.loop()
    }
  }

  val settings = new Settings
  settings.Yreplsync.value = true


  //use when launching normally outside SBT
  settings.usejavacp.value = true      

  //an alternative to 'usejavacp' setting, when launching from within SBT
  //settings.embeddedDefaults[Repl.type]

  repl.process(settings)
}

Some notes

I choose to show the JLineReader (default) rather than SimpleReader because it works much better, correctly handling arrow keys, delete etc. JLine does add an jar dependency.
The example shows how to bind values into the repl (variable e above).
When I omit settings.Yreplsync.value = true, the REPL hangs and is useless.
From my testing, if both usejavacp and embeddedDefaults settings are combined together, an error results

I find this easiest to test via SBT; a sample build.sbt:

name := "Repl"

organization := "ExamplesRUs"

scalaVersion := "2.10.2"

libraryDependencies ++= Seq(
 "org.scala-lang" % "scala-compiler" % "2.10.2",
 "org.scala-lang" % "jline" % "2.10.2"
)

Sample SBT session:

> run-main Repl
[info] Running Repl
Welcome to Scala version 2.10.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_37).
Type in expressions to have them evaluated.
Type :help for more information.
e: Double = 2.71828

scala> 2 * e
res1: Double = 5.43656

scala>

edited Sep 23 '13 at 03:58

answered Sep 05 '13 at 05:35

Ben Hutchison

2,433
2
21
25

I answered this one http://stackoverflow.com/a/18418634/1296806 but I don't think I tried 2.10, and I always forget that -Yrepl-sync option. Also haven't been using sbt console. Thanks! – som-snytt Sep 05 '13 at 05:48
1

There was also this question about binding values and class loaders http://stackoverflow.com/a/18503457/1296806 I can't tell if it's good info because it was ignored. Where is crowd think when you need it? – som-snytt Sep 05 '13 at 05:49
@som-snytt Yes, your answer was the single most useful source for this example – Ben Hutchison Sep 05 '13 at 05:51
5

doesnt work with scala 2.11 as "method loop cannot override final method" – simbo1905 Mar 14 '15 at 21:41
2

@simbo1905 For 2.11, instead override createInterpreter and just call super().createInterpreter() before calling the intp.bind. – Clark Updike Feb 26 '16 at 20:24
How can bind all local scope to the REPL? (In latest version) – HappyFace Apr 30 '19 at 15:12

score 4 · Answer 2 · answered Feb 26 '14 at 10:51

Based on Ben's excellent answer, below is a helper class to ease starting the interpreter. Usage:

Repl.run(("e", "Double", 2.71828), ("pi", "Double", 3.1415))

It automatically detects when you're running from SBT and accommodates.

Repl.scala:

import scala.tools.nsc.interpreter.ILoop
import scala.tools.nsc.Settings
import java.io.CharArrayWriter
import java.io.PrintWriter

object Repl {

  def run(params: (String, String, Any)*) {

    def repl = new ILoop {
      override def loop(): Unit = {
        params.foreach(p => intp.bind(p._1, p._2, p._3))
        super.loop()
      }
    }

    val settings = new Settings
    settings.Yreplsync.value = true

    // Different settings needed when running from SBT or normally
    if (isRunFromSBT) {
      settings.embeddedDefaults[Repl.type]
    } else {
      settings.usejavacp.value = true
    }

    repl.process(settings)
  }

  def isRunFromSBT = {
    val c = new CharArrayWriter()
    new Exception().printStackTrace(new PrintWriter(c))
    c.toString().contains("at sbt.")
  }

}

Embedded Scala REPL Interpreter example for 2.10

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