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

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

Answer 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