I enjoyed reading this. Thank you for sharing.

I learned Common Lisp years ago while working in the AI lab at the University of Toronto, and parts of this article resonated strongly with me.

However, if you abandon the idea of REPL-driven development, then the frontier models from Anthropic and OpenAI are actually very capable of writing Lisp code. They struggle sometimes editing it (messing up parens)), but usually the first pass is pretty good.

I've been on an LLM kick the past few months, and two of my favorite AI-coded (mostly) projects are, interestingly, REPL-focused. icl (https://github.com/atgreen/icl) is a TUI and browser-based front end for your CL REPL designed to make REPL programming for humans more fun, whether you use it stand-alone, or as an Emacs companion. Even more fun is whistler (https://github.com/atgreen/whistler), which allows you to write/compile/load eBPF code in lisp right from your REPL. In this case, the AI wrote the highly optimizing SSA-based compiler from scratch, and it is competitive against (and sometimes beating) clang -O2. I mean... I say the AI wrote it... but I had to tell it what I wanted in some detail. I start every project by generating a PRD, and then having multiple AIs review that until we all agree that it makes sense, is complete enough, and is the right approach to whatever I'm doing.

Thank you!

The whistler code you inline with your common lisp is an s-expression based DSL. So you can use common lisp macros, but those macros are generating something that will look familiar to CL devs but is restricted based on the eBPF archictecture and validator requirements. eg. it only supports bounded `dotimes`, some basic progn/let/when/if/cond/eq/setf/incf/decf and math, and a simple array iterator. No lists, loops, tagbody/go, conditions, etc, etc. There's a manual in the docs directory.

They are much better these days.

Besides, one can easily code a skill+script for detecting the problem and suggesting fixes. In my anecdotal experience it cuts down the number of times dumber models walk in circle trying to balance parens.

256k is just's just a placeholder for now. The default will get reduced as we get more experience with the draft implementation. The proposal isn't complete yet.

This very website that you are using right now, Hacker News, runs on sbcl.

It runs on Arc, which itself is implemented with SBCL.

It switched from Racket in late 2024. Context and discussion: https://news.ycombinator.com/item?id=44099006 (9 months ago, 435 comments)

I'm the author. https://atgreen.github.io/repl-yell/posts/sbcl-fibers/

This is fantastic! Godspeed.

Incredible! Is this ready for at scale production use?

No. I have yet to propose the patches formally. The SBCL maintainers are reviewing the high-level proposal (on my blog) first. You can try the implementation, however. There's a pointer to the repo/branch on my blog. I need to build a proper benchmarking framework and publish some real numbers that people can reproduce before I am confident enough to submit the patches for review.

Let me know if you try it out. I would love some feedback (via github)

Would it work with the parallel GC feature?

I haven't really looked into it, but I'm hopeful it can be made to work.

I set out to create a better text repl experience for Common Lisp couple of months ago, but was inspired by the pharo interface and built something much larger: https://atgreen.github.io/icl/ I use it all the time.

The browser inspector stuff looks very interesting, gotta check this out!

this is great! i was on a common lisp exploration a few months ago and mostly got stuck wishing i had smalltalk style tooling

Very cool!

Just saw your post to the Common Lisp reddit.

Consider also posting to the larger Lisp reddit.

Have you looked at the tooling in Genera or other lisp machines?

It's like Dr Ian Malcolm says.. "Your developers were so preoccupied with whether or not they could, they didn't stop to think if they should" - Jurrasic Park (almost)

Here's something I wrote about this work: https://atgreen.github.io/repl-yell/posts/cl-kawa/