Scala delimited continuations error at runtime

Question

Scala newbie here, I just downloaded Eclipse 3.6.2 and Scala IDE 2.0.0-beta4 (with Scala 2.9.0.final). I create a new Scala project to try delimited continuations:

package delimCCTests

import scala.util.continuations._

object Test extends App {
  val result = reset {
    1 + shift { k: (Int => Int) => k(k(5)) } + 1
  }
  println(result)
}

This compiles fine, then I click Run as -> Scala application and get this exception:

Exception in thread "main" java.lang.NoSuchMethodError: scala.util.continuations.package$.shift(Lscala/Function1;)Ljava/lang/Object;
    at delimCCTests.Test$$anonfun$1.apply$mcI$sp(DelimCCTests.scala:7)
    at delimCCTests.Test$$anonfun$1.apply(DelimCCTests.scala:7)
    at delimCCTests.Test$$anonfun$1.apply(DelimCCTests.scala:7)
    at scala.util.continuations.package$.reset(package.scala:20)
    at delimCCTests.Test$delayedInit$body.apply(DelimCCTests.scala:6)
    at scala.Function0$class.apply$mcV$sp(Function0.scala:34)
    at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:12)
    at scala.App$$anonfun$main$1.apply(App.scala:60)
    at scala.App$$anonfun$main$1.apply(App.scala:60)
    at scala.collection.LinearSeqOptimized$class.foreach(LinearSeqOptimized.scala:59)
    at scala.collection.immutable.List.foreach(List.scala:45)
    at scala.collection.generic.TraversableForwarder$class.foreach(TraversableForwarder.scala:30)
    at scala.App$class.main(App.scala:60)
    at delimCCTests.Test$.main(DelimCCTests.scala:5)
    at delimCCTests.Test.main(DelimCCTests.scala)

What am I doing wrong? Am I missing some configuration?

BTW I thought the compiler inferred the type of the continuation? This article uses:

val result = reset {
   1 + shift { k => k(k(5)) } + 1                   
}

but this doesn't compile in my environment...

So what changes between the compile environment and the run-time environment? :-) My first suspect is a conflicting (unexpected and different) Scala run-time library being used. — user166390
@pst: it certainly looks like that, but I've never had Scala in this box before, so it can't be a version mismatch, right? — Mauricio Scheffer
Tried this code on the REPL with identical result (Scala version 2.9.0.final (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_25) on Windows 7 64-bit) — Mauricio Scheffer
Ultimately, I couldn't make this work with Eclipse, but IDEA worked flawlessly. — Mauricio Scheffer

Vasil Remeniuk Vasil Remeniuk · Accepted Answer · 2011-05-20T05:04:53

This error means that you didn't add Scala CPS plugin - it's not a part of a standard assembly (so far). Put the jar on the classpath, and run Scala is follows, in order to have continuations enabled:

$ scala -P:continuations:enable

Scala delimited continuations error at runtime

2 Answers