I've had pretty good luck with LLM agents coding C. In this case a C compiler that supports a subset of C and targets a customizable microcoded state machine/processor. Then I had Gemini code up a simulator/debugger for the target machine in C++ and it did it in short order and quite successfully - lets you single step through the microcode and examine inputs (and set inputs), outputs & current state - did that in an afternoon and the resulting C++ code looks pretty decent.

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HarHarVeryFunny 2 days ago | parent [-]

That's remarkably similar to something I've just started on - I want to create a self-compiling C compiler targeting (and to run on) an 8-bit micro via a custom VM. This a basically a retro-computing hobby project.

I've worked with Gemini Fast on the web to help design the VM ISA, then next steps will be to have some AI (maybe Gemini CLI - currently free) write an assembler, disassembler and interpreter for the ISA, and then the recursive descent compiler (written in C) too.

I already had Gemini 3.0 Fast write me a precedence climbing expression parser as a more efficient drop-in replacement for a recursive descent one, although I had it do that in C++ as a proof-of-concept since I don't know yet what C libraries I want to build and use (arena allocator, etc). This involved a lot of copy-paste between Gemini output and an online C++ dev environment (OnlineGDB), but that was not too bad, although Gemini CLI would have avoided that. Too bad that Gemini web only has "code interpreter" support for Python, not C and/or C++.

Using Gemini to help define the ISA was an interesting process. It had useful input in a "pair-design" process, working on various parts of the ISA, but then failed to bring all the ideas together into a single ISA document, repeatedly missing parts of what had been previously discussed until I gave up and did that manually. The default persona of Gemini seems not very well suited to this type of work flow where you want to direct what to do next, since it seems they've RL'd the heck out of it to want to suggest next step and ask questions rather than do what is asked and wait for further instruction. I eventually had to keep asking it to "please answer then stop", and interestingly quality of the "conversation" seemed to fall apart after that (perhaps because Gemini was now predicting/generating a more adversarial conversation than a collaborative one?).

I'm wondering/hoping that Gemini CLI might be better at working on documentation than Gemini web, since then the doc can be an actual file it is editing, and it can use it's edit tool for that, as opposed to hoping that Gemini web can assemble chunks of context (various parts of the ISA discussion) into a single document.

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HarHarVeryFunny 16 hours ago | parent [-]

Just as a self follow-up here (I hate to do it!), after chatting to Gemini some more more about document creation alternatives, it does seem that Gemini CLI is by far the best way to go, since it's working in similar fashion to Claude Code and making targeted edits (string replacements) to files, rather than regenerating from scratch (unless it has misinterpreted something you said as a request to do that, which would be obvious when it showed you the suggested diff).

Another alternative (not recommended due to potential for "drift") is to use Gemini's Canvas capability where it is working on a document rather than a specification being spread out over Chat, but this document is fully regenerated for every update (unlike Claude's artifacts), so there is potential for it to summarize or drop sections of the document ("drift") rather than just making requested changes. Canvas also doesn't have Artifact's versioning to allow you to go back to undo unwanted drifts/changes.

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mattarm 15 hours ago | parent [-]

Yeah, the online Gemini app is not good for long lived conversations that build up a body of decisions. The context window gets too large and things drop.

What I’ve learned is that once you reach that point you’ve got to break that problem down into smaller pieces that the AI can work productively with.

If you’re about to start with Gemini-cli I recommend you look up https://github.com/github/spec-kit. It’s a project out of Microsoft/Github that encodes a rigorous spec-then-implement multi pass workflow. It gets the AI to produce specs, double check the specs for holes and ambiguity, plan out implementation, translate that into small tasks, then check them off as it goes. I don’t use spec-kit all the time, but it taught me that what explicit multi pass prompting can do when the context is held in files on disk, often markdown that I can go in and change as needed. I think it ask basically comes down to enforcing enough structure in the form of codified processes, self checks and/or tests for your code.

Pro tip, tell spec-kit to do TDD in your constitution and the tests will keep it on the rails as you progress. I suspect “vibe coding” can get a bad rap due to lack of testing. With AI coding I think test coverage gets more important.

	▲	HarHarVeryFunny 13 hours ago \| parent [-]
		Thanks for the spec-kit recommendation - I'll give it a try!