I vibe code extremely extensively with Lean 4, enough to run out 2 claude code $200 accounts api limits every day for a week.

I added LSP support for images to get better feedback loops and opus was able to debug https://github.com/alok/LeanPlot. The entire library was vibe coded by older ai.

It also wrote https://github.com/alok/hexluthor (a hex color syntax highlighting extension that uses lean’s metaprogramming and lsp to show you what color a hex literal is) by using feedback and me saying “keep goign” (yes i misspelled it).

It has serious issues with slop and the limitations of small data, but the rate of progress is really really fast. Opus 4.5 and Gemini were a huge step change.

The language is also improving very fast. not as fast as AI.

The feedback loop is very real even for ordinary programming. The model really resists it though because it’s super hard, but again this is rapidly improving.

I started vibe coding Lean about 3 years ago and I’ve used Lean 3 (which was far worse). It’s my favorite language after churning through idk 30?

A big aspect of being successful with them is not being all or nothing with proofs. It’s very useful to write down properties as executable code and then just not prove them because they still have to type check and fit together and make sense. github.com/lecopivo/scilean is a good example (search “sorry_proof”).

There’s property testing with “plausible” as a nice 80/20 that can be upgraded to full proof at some point.

When the model gets to another jump in capacity, I predict it will emergently design better systems from the feedback needed to prove that they are correct in the first place. Formal Verification has a tendency like optimization to flow through the system in an anti-modular way and if you want to claw modularity back, you have to design it really really well. But ai gives a huge intellectual overhang. Why not let them put their capacity towards making better systems?

Even the documentation system for lean (verso) is (dependently!) typed.

Check out my Lean vibe codes at https://github.com/alok?tab=repositories&q=Lean&type=&langua...