How can I run a Scala 3 `.scala` script?

Question

How can I run a *.scala script in interpreting mode? For example I have simple.scala:

// simple.scala
println("a simple program")

If use scala simple.scala, I got

error: Compile server encountered fatal condition: javax/tools/DiagnosticListener
java.lang.ClassNotFoundException: javax.tools.DiagnosticListener
        at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:433)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:586)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:519)
        at scala.tools.util.PathResolverBase$Calculated$.javaBootClasspath(PathResolver.scala:277)
        at scala.tools.util.PathResolverBase$Calculated$.basis(PathResolver.scala:283)
        at scala.tools.util.PathResolverBase$Calculated$.containers$lzycompute(PathResolver.scala:293)
        at scala.tools.util.PathResolverBase$Calculated$.containers(PathResolver.scala:293)
        at scala.tools.util.PathResolverBase.containers(PathResolver.scala:309)
        at scala.tools.util.PathResolver.computeResult(PathResolver.scala:341)
        at scala.tools.util.PathResolver.computeResult(PathResolver.scala:332)
        at scala.tools.util.PathResolverBase.result(PathResolver.scala:314)
        at scala.tools.nsc.backend.JavaPlatform$class.classPath(JavaPlatform.scala:28)
        at scala.tools.nsc.Global$GlobalPlatform.classPath(Global.scala:115)
        at scala.tools.nsc.Global.scala$tools$nsc$Global$$recursiveClassPath(Global.scala:131)
        at scala.tools.nsc.Global$GlobalMirror.rootLoader(Global.scala:64)
        at scala.reflect.internal.Mirrors$Roots$RootClass.<init>(Mirrors.scala:307)
        at scala.reflect.internal.Mirrors$Roots.RootClass$lzycompute(Mirrors.scala:321)
        at scala.reflect.internal.Mirrors$Roots.RootClass(Mirrors.scala:321)
        at scala.reflect.internal.Mirrors$Roots$EmptyPackageClass.<init>(Mirrors.scala:330)
        at scala.reflect.internal.Mirrors$Roots.EmptyPackageClass$lzycompute(Mirrors.scala:336)
        at scala.reflect.internal.Mirrors$Roots.EmptyPackageClass(Mirrors.scala:336)
        at scala.reflect.internal.Mirrors$Roots.EmptyPackageClass(Mirrors.scala:276)
        at scala.reflect.internal.Mirrors$RootsBase.init(Mirrors.scala:250)
        at scala.tools.nsc.Global.rootMirror$lzycompute(Global.scala:73)
        at scala.tools.nsc.Global.rootMirror(Global.scala:71)
        at scala.tools.nsc.Global.rootMirror(Global.scala:39)
        at scala.reflect.internal.Definitions$DefinitionsClass.ObjectClass$lzycompute(Definitions.scala:257)
        at scala.reflect.internal.Definitions$DefinitionsClass.ObjectClass(Definitions.scala:257)
        at scala.reflect.internal.Definitions$DefinitionsClass.init(Definitions.scala:1390)
        at scala.tools.nsc.Global$Run.<init>(Global.scala:1242)
        at scala.tools.nsc.StandardCompileServer.session(CompileServer.scala:151)
        at scala.tools.util.SocketServer$$anonfun$doSession$1$$anonfun$apply$1.apply(SocketServer.scala:74)
        at scala.tools.util.SocketServer$$anonfun$doSession$1$$anonfun$apply$1.apply(SocketServer.scala:74)
        at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)
        at scala.Console$.withOut(Console.scala:65)
        at scala.tools.util.SocketServer$$anonfun$doSession$1.apply(SocketServer.scala:74)
        at scala.tools.util.SocketServer$$anonfun$doSession$1.apply(SocketServer.scala:69)
        at scala.tools.nsc.io.Socket.applyReaderAndWriter(Socket.scala:49)
        at scala.tools.util.SocketServer.doSession(SocketServer.scala:69)
        at scala.tools.util.SocketServer.loop$1(SocketServer.scala:85)
        at scala.tools.util.SocketServer.run(SocketServer.scala:97)
        at scala.tools.nsc.CompileServer$$anonfun$execute$2$$anonfun$apply$mcZ$sp$1.apply$mcZ$sp(CompileServer.scala:218)
        at scala.tools.nsc.CompileServer$$anonfun$execute$2$$anonfun$apply$mcZ$sp$1.apply(CompileServer.scala:213)
        at scala.tools.nsc.CompileServer$$anonfun$execute$2$$anonfun$apply$mcZ$sp$1.apply(CompileServer.scala:213)
        at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)
        at scala.Console$.withOut(Console.scala:53)
        at scala.tools.nsc.CompileServer$$anonfun$execute$2.apply$mcZ$sp(CompileServer.scala:213)
        at scala.tools.nsc.CompileServer$$anonfun$execute$2.apply(CompileServer.scala:213)
        at scala.tools.nsc.CompileServer$$anonfun$execute$2.apply(CompileServer.scala:213)
        at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)
        at scala.Console$.withErr(Console.scala:80)

But I can open the interpreter by command scala and then > println("a simple program") It works correctly. Also, if I compile a more complete .scala (with an object which contains a main function) by scalac then run it by scala, things goes well.

I wonder if I can run a .scala script in the interpreter. Is there any thing wrong?

Update: After I update scala from 2.11 to 3.20, there is no javax.tools.DiagnosticListener exceptions. But when I run scala -explain simple.scala, the error is:

-- [E103] Syntax Error: ~/simple.scala:2:0
2 |println("a simple program")
  |^^^^^^^
  |Illegal start of toplevel definition
  |-----------------------------------------------------------------------------
  | Explanation (enabled by `-explain`)
  |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  | A statement is an import or export, a definition or an expression.
  | Some statements are only allowed in certain contexts
   -----------------------------------------------------------------------------
1 error found
Error: Errors encountered during compilation

JAVA version: openjdk 16.0.1 2021-04-20

If you want to write and run simple scripts give it a look to scala-cli. If you would rather write bigger programs then use sbt and use either the native packager or assembly plugin to produce the final executables. — Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez, Commented Oct 13, 2022 at 12:12
Try scala -nocompdaemon. But also, what version of Scala are you using? I suspect you're on an ancient version and that might be part of the difficulty. — Seth Tisue
– Seth Tisue, Commented Oct 14, 2022 at 11:59
@SethTisue Thank you. I installed scala directly by apt-get, its version is 2.11. Now I re-installed 3.2. There are no javax.tools.DiagnosticListener exception. However, other error occurs. — Kera
– Kera, Commented Oct 17, 2022 at 2:47
Unlike Scala 2, Scala 3's scala command doesn't include a script runner, as per github.com/lampepfl/dotty-feature-requests/issues/38. You either have to define a @main method, or (my personal recommendation) use scala-cli instead (scala-cli.virtuslab.org/scripting). — Seth Tisue
– Seth Tisue, Commented Oct 19, 2022 at 6:58

philwalk · Accepted Answer · 2023-03-03 19:26:09Z

1

As mentioned by Seth Tisue, the following works:

def main(args: Array[String]): Unit =
    // simple.scala
    println("a simple program")

if you invoke it like this:

scala3 ~/simple.scala

Although by default, there is no script called scala3, if scala3 is installed here: /opt/scala3-3.2.2, then the command line would be:

/opt/scala3-3.2.2/bin/scala ~/simple.scala

edited Mar 3, 2023 at 19:26

answered Dec 1, 2022 at 20:04

philwalk

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