Hello Lit — Or, if you squint, it's Lox

Published April 16, 2025 by Matheus Richard

Almost exactly 5 years ago, I started reading Crafting Interpreters and creating my own programming language. It went for a while, I gave it a new name, changed repos, stopped working on it, and then I eventually came back. I’ve decided to release something, so here’s the v0.1.0 of Lit, a safer scripting language (eventually).

What is Lit?

Lit is a dynamically typed, scripting language that aims to be safer than the usual ones. You can check more details on the main page. But the gist is that it will have a minimalistic type system that, if I do it right, will be basically invisible to you, while providing a safer experience.

What’s in v0.1.0?

Because it was created while reading the book, Lit v0.1.0 is basically the Lox language, with a few changes. Whenever possible, I change the syntax to what I envisioned for the language, or something close to that. Lit will evolve and get more and more different from Lox in the future. Here’s a list of the main differences now.

Features

• Arrays are supported

let a = Array(1, 2, 3);
println a.get(0); # 1
a.set(0, 4);
println a; # [4, 2, 3]
a.push(5);
pritnln a.size(); # 4

• String interpolation

let who = "world";
println "Hello, {who}!";

• Pipeline operator |>

fn double { |x| return x * 2; }
fn difference { |a, b| return a - b; }

# pipes lhs to first argument of rhs
println 10 |> double() |> difference(1); # 19

• The let keyword to create immutable bindings

let x = 1;
x = 2; # error!

• The until keyword for creating loops that run until a condition is met
• The loop keyword for creating infinite loops
• The break and next keywords are supported for loops

var i = 0;
loop {
  if i == 10 { break; }
  println i;
  i = i + 1;
}

• Nested multi-line comments

#= Multi-line comments
  #=
    can be nested
  =# still a comment
=# "not here"

• Numbers can have underscores in them

println 1_234_567; # 1234567
println 1_234.567; # 1234.567
println 1.234_567; # 1.234567
println 1_234.567_890; # 1234.56789
println 1_2_3; # 123

• A few extra native functions (typeof, readln, open)
• Minor syntax differences (if, while, function definitions, class definitions).

Anti-features

No inheritance :)

The future

I’ll keep working on Lit and I’ll try to make regular releases. I haven’t decided the frequency yet. I don’t have a set roadmap, but I have several ideas. I’ll probably tackle them as my interest goes. Not a promise, but I’ll try removing the required semicolons and required returns in the next release! I’ll also try making Lit powerful enough to parse itself, so we can build stuff like linters and formatters in Lit itself.

That’s it for today. Thanks for reading! If you want to try it out, you can find the code on GitHub.