Compile Scala to .mpy?

Question
1

Has anyone attempted to compile Scala code to .mpy?

(I did find Scalapy, https://scalapy.dev/, but I want to do the inverse . That project looks good but is thwarting my search.)

Thanks,

David

2

I donā€™t know of such a project, but what you could try, is a two-step approach: Use ScalaJS to compile Scala to JavaScript, then convert that to Python, i.e. using Js2Py.

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3

Do you want to access Java from Python or convert Scala code to Python code? The latter seems implausible.

For the first case for standard Python look at py4j.
For your ā€œversionā€ of Python I donā€™t know if it is possible.

I also suspect that because you want to work on embedded systems https://www.jython.org/ will also not work for you. But even if it did you still have to be aware that not all Python libraries may be accessed this way. @ansvonwa proposed solution may also have this problem.

HTHs

4

Interesting ā€“ why? I can see that it might be an infeasible amount of work to do well, but weā€™ve got enough proof-of-concept cross-compiles at this point that it seems possible. And the proposed two-step approach seems like a worthwhile experiment, although limited in what it could accomplish.

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5

@jducoeur The problem is that its not just a question of mapping the simple language constructs like if and while, but you need to:

  • Convert programs constructs that donā€™t exist in the other language;
  • Adapt the data structures that are not available in the ā€œhostā€ language

I addition to this, the OP seems to want to use this on an embedded system. Which means you now have to cater for hardware restriction and most probably donā€™t have OS support.

I would say it would be pretty difficult to get this going. :cold_sweat:

Now that I think of it, if the embedded system uses Linux maybe Native Scala could cut it?

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6

The equivalent of ScalaJS, but for Python, wouldnā€™t be any easier or harder than JS I would imagine? Which is to say that it is not impossible, but just a whole lot of work. Of course, a big part of this work ā€“ namely, rewriting a lot of the Java stdlib in pure scala so it can be compiled, has already been done.

I would absolutely love to see such a project, so that Scala can stay relevant in the machine learning/data science world that increasingly relies on Python. But itā€™s definitely a large project.

7

Thanks all.

Iā€™d hoped to find a project that already did most of the work - because of its value to the data science community. It looks like they mostly work the other way - running a JVM alongside python - with a few people running python within the JVM.

Iā€™m working with students using Lego robots. Python isnā€™t a good first language for 10-year-olds, and they get frustrated with Scratchā€™s lack of abstractions.

The newer system - Spike Prime - runs the micropython OS ( https://micropython.org/ ) which is a lot less to support; some things from the full JDK just wouldnā€™t make sense. I donā€™t think Scala Native would be viable there, but a similar approach could work.

(I originally tried getting Scala Native running on the older EV3 system, but Scala Native baked in 64-bit and the ARM cpu in the EV3 is 32-bit. I have had a lot of success - very good performance - using Scala on ev3dev OSā€™s 32-bit JVM.)

Maybe supporting micropython as an initial - smaller than everything - step would make sense, but I think itā€™s beyond what I can contribute to.

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8

It seems like Scala Native has 32-bit support in the pipe, by judging from:

9

The problem (for me) with waiting for Scala native 32-bit is ā€¦ the waiting. Itā€™ll be great when it is available, but the kids get older every year, and - now that Lego has stopped making the EV3 - the EV3s get older, more broken, and more expensive. I plan to use it when itā€™s available if I still have a working EV3 and kids willing to learn it. Itā€™s a slow train coming.

Spike Prime - and micropython - are contemporary technologies in 2022, even if they are more limited.

For Lego robotics I wouldnā€™t need all of Java supported. The project is nearly pure Scala, with just a little device access via nio. On Spike Prime the device access is available from python; Iā€™d just need some way to generate the right python to access the devices.

10

After a little digging - it looks like I could call compiled C code from the micropython OS. And could (with 32-bit support) compile Scala native code for that.

Has anyone called compiled Scala native (in its current 64-bit form) from python? That could address a broad front of problems.

11

Someone posted about this topic in r/scala (Reddit). I donā€™t know if this person succeeded but it might be worth to look for this thread.

12

I found a few things in progress in Scala Native. Itā€™s not possible yet, but is work in progress.

See Allow to link as dynamic library by WojciechMazur Ā· Pull Request #2145 Ā· scala-native/scala-native Ā· GitHub - for Scala Native to produce .o files that can be called from inside Python.

And Add support for 32-bit platforms through a linker-level switch by shadaj Ā· Pull Request #1571 Ā· scala-native/scala-native Ā· GitHub for 32-bit Scala Native.