Engineering¶

April 14, 2026
in Engineering
4 min read

Embed You a ponyc for Great Good

The ponyc command you run every day is a main() function with a terminal-width detector glued to it. The actual compiler is a library called libponyc. ponyc is a wrapper around that library, and the wrapper is 149 lines of C.

That’s the setup for this post. The Pony compiler is a library and you can link against it. And because you can link against it, you can build your own tools. And if you want your tool to be one binary instead of a ball of loose dependencies, you want libponyc-standalone.

April 10, 2026
in Engineering
7 min read

Claude You Some Pony for Great Good

Here’s how it is:

Two months ago I wrote about teaching Claude to write Pony. That post was about the process — mentoring an LLM like a junior developer, building up engineering principles, establishing review loops. Today, I’m here to talk about the LLM skills I’ve been working on. They’re in ponylang/llm-skills, and if you’re working on Pony with an LLM, you should try them.

March 18, 2026
in Engineering
9 min read

Persistent Data Structures for Concurrent Programs

In my last post, I mentioned that the new json package uses persistent data structures under the hood. Every JsonObject is backed by a CHAMP Map. Every JsonArray is backed by a HAMT Vec. I glossed over why, and I want to fix that.

February 17, 2026
in Engineering
22 min read

Teaching Claude to Write Pony

I’m not really sure how to tell the story of me teaching Claude to write Pony, so I’m just going to tell it and see how it goes.

A year ago, every LLM I tested on Pony produced the same thing: a weird Python/Pony hybrid that didn’t compile and didn’t understand Pony’s semantics. I’d ask for a program that prompts you for your name and prints “Hello {name}.” Simple stuff. They all failed miserably. So when I sat down two weeks ago to try again with Claude Code, my expectations were modest.