Creating a Programming Language for the JVM: the Turin Programming Language

Because you know, in the end everyone wants to create his own programming language.

I have been interested in parsers and languages for a while. I worked with Xtext, Jetbrains MPS, created a few DSLs etc. etc. I also wrote my PhD thesis on this topic but so far I did not get started creating a complete programming language from scratch.

Why Creating a New Language?

Well, there are many wrong answers to this question.

My (hopefully right) answer is divided in two parts:

1. first, I think it can be a great experience to learn a few things more
2. second, a programming language is for me a tool to look at reality, describe it and reason about it to understand it better

Laugh if you wish, but for me it is mainly a tool for thinking. Often it is a clunky tool, because I get distracted. Either by technical workarounds or details which are hardly relevent or important for what I am trying to do. For example, I am getting tired of clicking here and there to generate equals and hashCode methods (yes, I know about Lombok and some other tricks).

Ok Kid… But to Make a Language Usable You Need a Lot of Stuff

I think now the barriers to create a programming language and make it usable by sane persons are significantly lower than they used to be. I think that a language needs a great syntax & semantics, sure, but also a large amount of libraries and decent tool support.

To get libraries just make it run on the JVM. Really. If it runs on the JVM you can reuse a gazillion of libraries. Your programming language get batteries included. Consider also deployment: I am fascinated by many languages, but every time I try to deploy something outside the JVM I end up regretting it. Ask my co-maintainer of WorldEngine (a python program) how much fun is to support libraries on Linux, Mac, Windows, across Python versions. A lot of fun.

Of course you need also tool support: it means to me mainly a nice editor and good integration with the platform of reference. I have an advantage here because I have experience developing IDE plugins and I just ended writing a type solver for Java. In addition to that I contribute to JavaParser. So I know a thing or two about tools that I could use down the road for the integration with Java.

In practice I plan to:

1. Create a plugin for IntelliJ which is aware of references to file in my language and to Java files. The nice thing is that basically I wrote the libraries for doing that already.
2. Create a Maven plugin because Maven is awful, but life without Maven is even more awful
3. Write a parser with ANTLR (that’s the easy part)
4. Write a bytecode generator with ASM (what a great library!)

Ok Tell Me More About This Language

I just started working on it but… I have a basic compiler working and supporting a few constructs.

The language is named Turin like my hometown and it is available on GitHub.

It is a static language with type inference and this is an example of a piece of valid code that can be already compiled and run:

namespace manga

// now print is an alias for call to all the overload variants of println on System.out
import java.lang.System.out.println as print

// we define this property in generale: a name is a String
property String : name

// this is our new datatype
type MangaCharacter {
    // we refer to the property defined above
    has name
    // we define a new property, UInt is an unsigned int
    has UInt : age

    // we overload toString. For short methods it can make sense to use 
    // this shorthand. And we have string interpolation
    String toString() = "#{name}, #{age}"
}

// this define a class with a main method
program MangaExample(String[] args) {
    // type inference at work: we are instantiating the class defined above
    // note that the constructor is generated for us
    val ranma = MangaCharacter("Ranma", 16)
    // let's call a java method ( System.out.println(String) ) and use more
    // string interpolation
    print("The protagonist is #{ranma}")
}

So I have a plan, I have something working already and I am having a lot of fun.
Could be idiotic, perhaps, to write yet another language but damn… it is so much fun!