2 posts tagged with "lox"

For a long time, I wanted to implement a Racket language module with a non-lispy surface syntax. Lox, from Crafting Interpreters, was an obvious candidate: I didn't want to invent a new syntax nor new semantics and I already ported the project to C#. In this case, my main objective was to leverage Racket language-building facilities while learning Racket, Scheme, and macros.

I attempted this already a few years ago, with little success. This time I dropped yacc and lex libraries and instead followed the approach from the book more closely, along with the C# version I had written earlier. The result is not especially functional in style: the scanner and parser are fairly imperative and rely on mutation, mainly because that made the code easier to port from the earlier implementations. Another big help came from LLMs, I used GitHub Copilot and it helped me fill some gaps in my knowledge and troubleshoot issues that I honestly didn't have enough competencies to solve.

I do not use GitHub Copilot autocomplete because that removes all the fun from coding but I "chatted" extensively and I also asked it to generate parts I was not particularly interested in, such as the colorer[^1].

The code is available on GitHub here. In the post I'll go through the implementation, highlighting all the parts that I consider interesting or helpful.

Given my previous attempt of having a basic scaffolding for creating a new racket language, I thought it was worth a shot at implementing Lox from the Crafting interpreters book as a Racket language module.

Racket has a huge ecosystem and extensive documentation, based on my own research and preferences I decided to use a lex/yacc source generator available in Racket itself and documented here https://docs.racket-lang.org/lex-yacc-example/index.html. There are plenty of resources on how to build languages with Racket, both free and paid.

I used only free resources and my feeling is that the amount of information required to approach this project is A LOT, I needed to get familiar with lisp syntax, libraries for parsing, macros, Racket language modules, a different set of tools for coding/debugging.

Another feeling I have is that the documentation, even if it's extensive, it's not providing all the information required to build new languages for Racket or at very least this information is hard to find. I didn't find it, despite trying multiple times.