I recently gave up trying to use Scala in Eclipse (basic stuff like completion doesn't work). So now I'm trying IntelliJ. I'm not getting very far.

I've been able to edit programs (within syntax highlighting and completion... yay!). But I'm unable to run even the simplest "Hello World". This was the original error:

Scala signature Predef has wrong version
Expected 5.0
found: 4.1 in .... scala-library.jar

But that was yesterday with IDEA 9.0.1. See below...

UPDATE

Today I uninstalled IntelliJ 9.0.1, and installed 9.0.2 Early Availability, with the 4/14 stable version of the Scala plug-in.

Then I setup a project from scratch through the wizards:

• new project from scratch
• JDK is 1.6.u20
• accept the default (project) instead of global / module
• accept the download of Scala 2.8.0beta1 into project's lib folder

Created a new class:

object hello {
  def main(args: Array[String]) {
    println("hello: " + args);
  }
}

For my efforts, I now have a brand-new error :)

Here it is:

Scalac internal error: class java.lang.ClassNotFoundException [java.net.URLClassLoader$1.run(URLClassLoader.java:202), java.security.AccessController.doPrivileged(Native Method), java.net.URLClassLoader.findClass(URLClassLoader.java:190), java.lang.ClassLoader.loadClass(ClassLoader.java:307), sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301), java.lang.ClassLoader.loadClass(ClassLoader.java:248), java.lang.Class.forName0(Native Method), java.lang.Class.forName(Class.java:169), org.jetbrains.plugins.scala.compiler.rt.ScalacRunner.main(ScalacRunner.java:72)]

FINAL UPDATE

I uninstalled 9.0.2 EA and reinstalled 9.0.1, but this time went with the 2.7.3 version of Scala rather than the default 2.7.6, because 2.7.3 is the one shown in the screen-shots at the IntelliJ website (I guess the screen-shots prove that they actually tested this version!). Now everything works!!!