Build an experimental language compiler with an LLM coder
The author has Claude write the compiler and runtime for an experimental language called 5emel (about 15,000 lines of TypeScript/JavaScript and 3,000 of C), reading little of the code himself. ·
Done withClaude
- What they did
- Over a few weeks the author elicited the compiler and runtime for an experimental language, 5emel, from Claude Opus 5.5. The result is about 15,000 lines of TypeScript/JavaScript and 3,000 of C. He has read almost none of it, not even all of the roughly 1,600-line compiler, and relies on his background in programming books to steer.
- How it went
- A working compiler and runtime exist. As a test, an incognito Claude session was shown one function snippet and explained most of the language, though it was unsure about some parts.
- Worth knowing
- He says anyone recreating it from the snippet will have to fight through many of the same problems he did.
Try it yourself with Claude
I want to build a small experimental programming language called [language name] with these core ideas: [2-3 syntax or semantic features]. Write the compiler or interpreter in [TypeScript/Python/other], plus a few example programs and a test suite that runs them. Work in small steps, run the tests after each one, and stop when all the example programs compile and run correctly. Then give me a short summary of the architecture.
Want help getting this working? Join the Vibe Coding Academy ↗ Run by Alex Finn, who also runs this site.
Source: HN · Nov 8, 2026
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