Custom Scala REPL Issues

问题

I'm trying to write a basic Scala REPL using some information I found on various sites. My most basic REPL implementation looks like this,

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

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

  new ILoop().process(settings)
}

With the following build settings,

import sbt._
import sbt.Keys._

object BillyREPLBuild extends Build {

  lazy val billyrepl = Project(
    id = "billyrepl",
    base = file("."),
    settings = Project.defaultSettings ++ Seq(
      name := "BillyREPL",
      organization := "tv.yobriefcasts",
      version := "0.1-SNAPSHOT",
      scalaVersion := "2.10.1",
      libraryDependencies ++= Seq(
        "org.scala-lang" % "scala-compiler" % "2.10.1",
        "org.scala-lang" % "scala-library" % "2.10.1"
      )
    )
  )
}

Attempting to run this however leads to some warnings and eventual error (which I presume are caused by the initial warning),

Welcome to Scala version 2.10.1 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_12-ea).
Type in expressions to have them evaluated.
Type :help for more information.

scala>
Failed to initialize compiler: object scala.annotation.Annotation in compiler mirror not found.
** Note that as of 2.8 scala does not assume use of the java classpath.
** For the old behavior pass -usejavacp to scala, or if using a Settings
** object programatically, settings.usejavacp.value = true.

And the error when trying to read/evaluate ANYTHING is below. I'm not sure if this is due to some extra missing dependency and I do realise what the error message says suggests this is not common but I wondered if before I open an issue if anyone has dealt with this before?

2

Failed to initialize the REPL due to an unexpected error.
This is a bug, please, report it along with the error diagnostics printed below.
java.lang.NullPointerException
    at scala.tools.nsc.interpreter.ExprTyper$codeParser$.applyRule(ExprTyper.scala:24)
    at scala.tools.nsc.interpreter.ExprTyper$codeParser$.stmts(ExprTyper.scala:35)
    at scala.tools.nsc.interpreter.ExprTyper$$anonfun$parse$2.apply(ExprTyper.scala:43)
    at scala.tools.nsc.interpreter.ExprTyper$$anonfun$parse$2.apply(ExprTyper.scala:42)
    at scala.tools.nsc.reporters.Reporter.withIncompleteHandler(Reporter.scala:51)
    at scala.tools.nsc.interpreter.ExprTyper$class.parse(ExprTyper.scala:42)
    at scala.tools.nsc.interpreter.IMain$exprTyper$.parse(IMain.scala:1074)
    at scala.tools.nsc.interpreter.IMain.parse(IMain.scala:1078)
    at scala.tools.nsc.interpreter.IMain$$anonfun$showCodeIfDebugging$1.apply(IMain.scala:1168)
    at scala.tools.nsc.interpreter.IMain$$anonfun$showCodeIfDebugging$1.apply(IMain.scala:1168)
    at scala.tools.nsc.interpreter.IMain.beSilentDuring(IMain.scala:238)
    at scala.tools.nsc.interpreter.IMain.showCodeIfDebugging(IMain.scala:1168)
    at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.compileAndSaveRun(IMain.scala:800)
    at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.compile(IMain.scala:761)
    at scala.tools.nsc.interpreter.IMain.bind(IMain.scala:618)
    at scala.tools.nsc.interpreter.IMain.bind(IMain.scala:661)
    at scala.tools.nsc.interpreter.IMain$$anonfun$quietBind$1.apply(IMain.scala:660)
    at scala.tools.nsc.interpreter.IMain$$anonfun$quietBind$1.apply(IMain.scala:660)
    at scala.tools.nsc.interpreter.IMain.beQuietDuring(IMain.scala:232)
    at scala.tools.nsc.interpreter.IMain.quietBind(IMain.scala:660)
    at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1$$anonfun$apply$mcZ$sp$2.apply$mcV$sp(ILoop.scala:838)
    at scala.tools.nsc.interpreter.ILoopInit$class.runThunks(ILoopInit.scala:122)
    at scala.tools.nsc.interpreter.ILoop.runThunks(ILoop.scala:42)
    at scala.tools.nsc.interpreter.ILoopInit$class.postInitialization(ILoopInit.scala:95)
    at scala.tools.nsc.interpreter.ILoop.postInitialization(ILoop.scala:42)
    at scala.tools.nsc.interpreter.ILoopInit$$anonfun$createAsyncListener$1.apply$mcV$sp(ILoopInit.scala:63)
    at scala.tools.nsc.interpreter.ILoopInit$$anonfun$createAsyncListener$1.apply(ILoopInit.scala:60)
    at scala.tools.nsc.interpreter.ILoopInit$$anonfun$createAsyncListener$1.apply(ILoopInit.scala:60)
    at scala.tools.nsc.io.package$$anon$3.call(package.scala:40)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
    at java.util.concurrent.FutureTask.run(FutureTask.java:166)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)
.

回答1:

A problem occurs when you embed a REPL and the project is run with sbt. Because of class loader issues (?), launching a custom interpreter from sbt does not work.

You can try building a standalone with sbt-assembly and see if that starts up correctly.

回答2:

Maybe you can get it to work with this hint:

How do I use the Scala interpreter in my code?