My hobbyist coding updates and releases as the mysterious "Mr. Tines"

Saturday, 23 August 2008

Scaling the tower of Babel

A few months ago, I was playing around with seeing how I could adapt an existing Java code base so that I could finish doing the work in better languages -- and have the code work on both the JVM and the CLR.

It seems that frustration will inevitably follow any attempt to incorporate any J# into the .Net versions of the stack (both IKVM and the Scala-net compilers bork when they see another Java in the stack) -- even though you can call Jython into Scala into Java on the JVM, this Tower of Babel cannot stand on the CLR with the J# runtime in the picture -- Java e.g. a Swing-based GUI using the J# extensions, has to stand off to one side.

That said, the Scala on .Net "hello world" with Scala 2.7.1 is comparatively painless.

  1. Install the scala-msil package (sbaz install scala-msil)
  2. Create file Hello.scala as
    import System.Console
    object test extends Application {
      Console.WriteLine("Hello world!")
  3. In a Visual Studio command prompt, issue %SCALA_HOME%\bin\scalac-net.bat hello.scala
  4. Copy %SCALA_HOME%\lib\*.dll to the current directory
  5. Run the resulting test.exe

This uses the 1.0 version of mscorlib.dll; as a post-processing step you may wish to re-base against the .Net 2.0 version -- for this, you need to rebuild predef.dll and scalaruntime.dll using the same technique as needed to strong-name them after the fact; only this time you want to reset the mscorlib reference from

.assembly extern mscorlib
  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )                         // .z\V.4..
  .ver 1:0:5000:0
.assembly extern mscorlib
  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )                         // .z\V.4..
  .ver 2:0:0:0

as well as doing any strong-naming you may desire.

To set the assembly name, add -Xassem [assembly name] to the compile command, to generate hello.exe.

To control the type of the generated assembly (.dll rather than .exe), I've not found a way other than taking the generated [assembly name].msil and ilasming it manually. In particular trying to skip generating the unwanted .exe will mean figuring why using scalac.bat -target:msil always gives

error: fatal error: class scala.runtime.BoxedBooleanArray not found.

whatever I do with -Xassem-path or tweaking environment variables.

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