Multi module Java/Scala example project

[mentorj]

Hi all,
I am struggling with a quite simple Java/Scala project. Do you have any sample of such project ?

In one module I have a scala module with a factorial method living inside one object. Dead easy it compiles and runs fine

In one Java module I have a quite simple code getting the factorial method and memoizing this function.

The problem is that the factorial function from my Scala module is not found at compile time.

Using this function in another Scala module works fine of course.

Is it a mill problem ( possible I am quite new) or a Scala problem (it is the first time I try to invoke Scala code from Java).

Thanks for your help

Jerome

[lihaoyi]

@mentorj can you post your code and build.mill file here? That will make it easier to spot ant issues

[mentorj]

Hi,
of course ....

build.sc

import mill._, scalalib._

object factorialscala extends ScalaModule {
  def scalaVersion = "3.7.1"
}

object factorialjava extends JavaModule {
  def mvnDeps = Seq(
    mvn"io.vavr:vavr:0.10.4"
  )
  def moduleDeps = Seq(factorialscala)

}

object mainscala extends ScalaModule{
   def scalaVersion = "3.7.1"

   def moduleDeps = Seq(factorialscala)
}

The Scala for factorial with TCO in module factorialscala

package factorial;
import annotation.tailrec
object Factorial{
  def factorial(x:Int): BigInt = {
    @tailrec def loop(x: Int, acc: BigInt= 1): BigInt = {
      if (x<=1) acc
      else loop(x-1, x*acc)
    }
    loop(x)
  }
}

Java code wrapping Scala factorial in the factorialjava module

import io.vavr.Function1;
import java.math.BigInteger;

class FactorialMemoized{
  private static Function1<Integer,Long> factorialScala=Function1.of(factorial.Factorial.factorial);
  private static Function1<Integer,Long> factorialMemoized = factorialScala.memoized();

  public static Long runFactorial(Integer n){
	  return factorialMemoized.apply(n);
  }

}

Trying to compile whole project gives:

> mill _.compile    
No mill version specified.
You should provide a version via a '//| mill-version: ' comment or a '.mill-version' file.
Using mill version 1.0.3
[121/121] factorialjava.compile
[121] [info] compiling 1 Java source to /home/deadbrain/IdeaProjects/millFactorialMemoization/out/factorialjava/compile.dest/classes ...
[121] [error] /home/deadbrain/IdeaProjects/millFactorialMemoization/factorialjava/src/FactorialMemoized.java:5:89: cannot find symbol
[121] [error]   symbol:   variable factorial
[121] [error]   location: class factorial.Factorial
[121] [error] factorial.Factorial.factorial
[121] [error]                              ^
[121/121, 1 failed] ======================== _.compile ========================
1 tasks failed
factorialjava.compile javac returned non-zero exit code

factorial Scala code works nice as stated by the third module

> mill mainscala.run
No mill version specified.
You should provide a version via a '//| mill-version: ' comment or a '.mill-version' file.
Using mill version 1.0.3
[119/119] mainscala.run
[119] 30414093201713378043612608166064768844377641568960512000000000000
[119/119] =========================== mainscala.run ===========================

Now you have the complete vision...
Thanks for your help

[lefou]

The error messages clearly indicates an issue finding the "variable" factorial, while we only have a def. So this isn't a Mill issue (the factorial.Factorial class can be found), but an programming issue. I don't know the Vavr API, so can't tell what it is expecting.

[mentorj]

Thanks @lefou for pointing out this problem. You are right Vavr does not support to wrap functions in such way, there was a problem with the method reference syntax too.Finally everything works fine after a little work ( I was obliged to throw the BigInt to get back to Java BigInteger).

Thanks again guys for your help.
And Mill was not a problem at all ( I feared some classpath issues) but no such problem,

Kind regards

[mentorj]

Problem solved, not a Mill problem.I was stupid...