Show HN: I built a minimal Forth-like stack interpreter library in C
8 comments
·September 11, 2025gabrielsroka
1. You should add a URL when you you create a post on HN. You can indent code two spaces on HN, eg:
Stack s;
stack_init(&s);
dict_init();
exec(&s, "10 20 + ."); // Prints "30"
exec(&s, "1 2 3 4 .s"); // Shows stack contents
3. I'm not an expert in C but I thought header files shouldn't have code in them. The code should be in a .c file
4. Maybe move the code from USAGE into its own .c file.
#include "stacklib.h"
int main() {
Stack s;
stack_init(&s);
dict_init();
exec(&s, "10 20 + .");
printf("\n");
return 0;
}zoezoezoezoe
technically, "header only libraries" can be exceptions to C code not being in header files. See STB as an example https://github.com/nothings/stb. The advantage theoretically is that you can #include this library and use its code and types from just one file, its a decent model IMHO, but it can be jarring to someone unfamiliar with header only libraries.
tdeck
If you're interested in learning more about how FORTH works I, I can recommend two very old books.
Starting FORTH https://archive.org/details/LeoBrodieStartingFORTHIntroducti...
Threaded Interpretive Languages https://archive.org/details/R.G.LoeligerThreadedInterpretive...
The latter doesn't even mention FORTH, and describes some very archaic CPU architectures, but I found it fascinating because it builds things from the ground up.
elcritch
In particular learning about threaded interpreters, sub-routine interpreters, etc is very eye opening. That and really internalizing that everything, even code, is really just numbers.
fjfaase
Interesting. I am currently in the process of writing an interpreter for a similar stack based language. I already wrote a compiler for this language to x86 assembly that can be compiled to an ELF. The language is used as an intermediate language for a C compiler that I am writing. It is maybe less Forth-like than your language. For more information see: https://github.com/FransFaase/MES-replacement For the interpreter have a look at: stack_c_interpreter.c
At WHY2025, I gave a talk about the reasons why am working on this. See: https://www.youtube.com/watch?v=akzyyO5wvm0
bertili
Another thread on small forth interpreters from just 15 days ago:
https://news.ycombinator.com/item?id=45039301
Forth can be beautifully and efficiently implemented in portable c++ using the using continuation passing style via the clang musttail attribute.
Have a look at Tails (not my project):
acidx
I recently wrote one, in C, using tail calls to implement dispatch with CPS: https://tia.mat.br/posts/2025/08/30/forth-haiku.html
It's already pretty efficient but I'm working on it to make it even more efficient so I can use it as some sort of primitive fragment shader for an art project. This Forth variant is intended to execute Forth Haikus, as defined by the Forth Salon website.
vdupras
Your experiment is certainly a good tool to grok stack mechanics, but that is only one element of what makes a Forth what it is. You're missing out on other crucial ingredients: colon definition and immediateness.
I wrote a series of articles that can help in that kind of discovery: http://tumbleforth.hardcoded.net/
This weekend I created stacklib.h - a single-header library that brings Forth-style stack operations to C. It implements a basic interpreter with:
- Stack operations (push/pop/dup/swap/over/drop) - Arithmetic (+, -, *, /) - Output (., emit, cr) - Stack inspection (.s, depth)
Example usage: Stack s; stack_init(&s); dict_init(); exec(&s, "10 20 + ."); // Prints "30" exec(&s, "1 2 3 4 .s"); // Shows stack contents
The library is self-contained, requires no dependencies, and handles basic error checking. It was inspired by wanting to understand how Forth works at a fundamental level while keeping the simplicity of C.
I'm curious what other stack-based or concatenative programming enthusiasts think about this approach. Has anyone else built something similar? What features would you add to make it more useful?
GitHub: https://github.com/Ferki-git-creator/stacklib