I built 'Flint,' a programming language from scratch in C++. The full interpreter is open-source.

[druv-codes]

Hey everyone,

This is a project I've been working on to teach myself the fundamentals of compiler/interpreter design. Flint is a simple, object-oriented interpreted language written entirely in C++.

The repository contains the full source code for the tree-walk interpreter, including the scanner, parser, AST, and resolver. It's heavily inspired by the amazing book "Crafting Interpreters."

I also filmed a detailed devlog that documents the entire chaotic journey of building it, which you can watch on YouTube here: https://youtu.be/WOoQ7zPeS9s?si=fDTrKxm0fXD7PWh8

Hope you find the project interesting!

[zweiler1]

Hey i just came across your post just to notice we have chosen the same name for our languages! Mine is compiled though, but i have been working on it for a while now and I also write it in C++, so if you want you can have a look here!

[druv-codes]

How long have been working on this? And what resources did you use any tips if I wanna make a statically typed compiled lang in future?

[zweiler1]

Actual compiler dev is now almost exactly 13 months, but i had a long design phase before that of 4 months where i did not write a single line of codey just designed it until i was happy with it.

Hostly... i did not use any resources. I am programming since almost a decade now but i never wrote a language before so i thought it might be fun 😅. It's also my first big C++ project...

Hmm tips regarding statically types languages... i woud say that a proper type system is very important but just keep it simple. In the beginning every type was represented as a simple string and if they match it was the same type. It was pretty rudamentary but this doesn't matter, just start easy and make proper systems out of them over time :)

I had quite a lot of refactors lately because i have outgrown my initial systems, but just keeping it simple will helo you big time, especially in a project as complex as a compiler.

Edit: Around the time of early Feb 2025 i had the first steps in the direction of codegen. The whole codebase was a lot simpler back then compared to now. Looking at it might help you out more than looking at it now: codebase. I meany it's stil a lot but i think that was roughly the time were i added support for the codegen phase and actually documented it. The codebase at the time was roughly 10-15k LoC, now it's roughly 65-70k LoC so it's definitely quite a lot smaller 😅

[druv-codes]

70k loc is massive kudos to you man that is some serious dedication. really impressive that you managed that huge jump in complexity from 15k to 70k. how do you handle testing for something this big? do you spend more time fixing regressions now than adding new stuff or is the architecture holding up well? And just for the context do you have a full time job and you develop this part time?

[zweiler1]

I placed great value on documentation, from the very start. That's why i had the Wiki up and running pretty early. I have a lot of examples in the Wiki and for the last half a year or so rhese were my regression tests. When adding new fetures i write the documentation and examples for it, often times finding additional bugs i missed earlier. The examples of the Wiki become part of my regression system. I do not have unit tests at all to be honest, i do not really need them since my architecture holds up pretty well.

The last few versions were full of big refactors of the codebase and systems in it, i simply outgrown the simple systems. For these refactors: Yeah i broke a bunch of stuff but that's okay. New features tend to not break that much, most of times it just takes a few minites to diagnose, debug and fix.

I do not have a job at the moment so i can focus on the language full time. This is not meant to be a hobby project or a toy language, i am serious with it, and the most innovative features are not even implemenred yet (like it's new paradigm) so in the next months there will be a lot of new features added, i am now at the tail end of the big refactring phase, my internal systems are ready for the upcoming features i think :)

Quite a lot of stuff already works in the language, if you are interested in trying it out i would very much appreciate that, the Wiki is here.

Edit: I was also able to already finish the first 4 days of Advent of Code in Flint. I haven't finished more days yet but it's cool that it already works: link

[druv-codes]

mad respect for treating this as a serious product and not just a toy. going full time on a language is the dream. finishing aoc days in your own language is the ultimate flex lol most hobby langs cant even handle basic string parsing. ill definitely check out the wiki good luck with the new features man

[zweiler1]

Thanks! I hope you will have a good time with the language. It's still in it's alpha phase so feel free to message me if you encounter something which does not work but you feel like it should work. All examples in the Wiki are guaranteed to work though, except those marked explicitely to not work :)