The conditions you’ve set here are very strict, but I have something that may almost fit. I’ve used Grok 3 to create a decompiler and then a compiler for a made up scripting language (for scripts extracted from Final Fantasy VII data files). I’ve fed it an example of how the low-level “assembly/opcodes” look like and then how I would like the higher level scripting language to look. With minimal guiding (I was telling it what I want, but not how I want it) it implemented a working decompiler and compiler that worked exactly to my specifications, written in Typescript. Created a custom tokenizer, parser to a custom AST structure and everything else that was needed. It took a few prompts to get right (and to add features I didn’t think about initially), but the resulting 1400+ lines of code I found to be very impressive for what a “fancy autocomplete” as many people say could generate.

Here’s the initial conversation if you’re interested: https://grok.com/share/bGVnYWN5_9ce1bed4-7136-4761-b45e-0ab0...