Comment by LightMachine
13 hours ago
Hi, I'm the author.
HN staff: someone posted before me. Could we change the title to "Bend - a language that blocks AI mistakes via proof and runs on GPUs"?
Everyone: feel free to ask any question, but I'd be highly appreciative if you could be a bit civilized and respectful this time. I've worked on this for 1 year, nearly 16h/day, 7 days a week, and I'm giving it for free. You need not to use it. So, I'd be thankful if you could point occasional failures politely rather than throwing me in a lava pit.
Thank you!
Don't know whether this is a common outcome, but I tried the "remove the walls" example, and the result was... scary. It completely changed the game so that movement is now diagonal, and made the arbitrary decision that up/down move you on the positive diagonal, and left/right move you on the negative diagonal.
The problem, of course, is that having only the one single "you can't win" law is severely underspecified, but the solution was too clever by half, and highlights the problem with this approach — every program will be under-specified, because, at some point, writing the laws becomes a bigger problem than writing the code itself.
This becomes a real issue because the combination of underspecified but rigid laws pushes the aI towards this sort of "creative" solution that matches the letter but not spirit of the law. In this case, the issue was obvious, but I seriously worry about what sort of shenanigans will occur in less obvious cases.
Exactly, "you can't win" is grossly under-specified. The goal of the demo is just to show that laws can't be broken. Yet, if that's your only law, the AI can do whatever to protect it - including changing how the character moves, or even removing the flag entirely!
So, yes, that's the issue with laws: they only protect what you remember to write. They're not a silver bullet. But they can still be incredibly useful, because it takes a small law to protect against entire classes of bug, covering your entire codebase. For example:
LAW: "the sum of all balances in this contract must be zero"
This one liner would have prevented Ethereum's infamous "The DAO" hack, where millions were stolen and almost undermined the entire project. But if your laws are under-specifying or ill-specifying your intents, Bend can't do anything to protect you.
Thought about automated discovery of laws in an existing codebase?
If you can find a law which the existing code obeys, and show it to a human, and if they agree, save it. And maybe the AI could make a decent guess as to what kind of laws would appeal to a human versus which wouldn't – a simple law identifying a fundamental constraint the system obeys is good, something really complicated or constraining something coincidentally true isn't
Or some kind of measure of coverage? you'd never want 100% – then your laws would become so complex you couldn't follow or maintain them – but if it is very low, that can be a signal to increase it
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Yeah all of these attempts to try and control AI outputs by using language fail to grasp that language is itself the problem. It is a closed system with no ground truth. Words only point to other words in an endless self-referential chain. There is no "closure" in language, ambiguity cannot be erased.
Imo LLM researchers would benefit a lot by reading what continental philosophers have said on the topic of language. Barthes, Sarte, Deluze, Derrida, et. Al have a lot to say that explains why we're running into the same problems over and over.
Natural language is ambiguous. Specifying exactly what you want in a way that is truly verifiable is the act of coding.
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Bend would make Dijkstra happy even when proof checking can’t verify if the laws are what was actually meant.
I actually think Asimov is more instructive here, while Gödel and Tarski tell us the tool can’t prove itself…
Nonetheless, it is a worthwhile endeavor and I hope more rigorous practices like this catch on.
I think LLM researchers understand how LLMs work and what the limits of using natural language as an interface are. The problem is everyone else thinks they're basically magic, expecting them to be infinitely intuitive but also strictly deterministic, like the computer from Star Trek.
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> writing the laws becomes a bigger problem than writing the code itself.
But that's how it is anyway, no?
Defining clear boundaries and clear goals is the hardest part. If you get those right everything else is rather trivial.
Side thought - I like the idea of this as a game, where you’re essentially fighting a monkeys paw / tricky genie. Not totally sure it’d work but I like the concept of trying not to get caught out.
I got the same result when I tried the "remove the walls" example. I followed up by telling it to reimplement up/down/left/right movement without reinserting the walls and it basically made the square with the flag "unenterable". Like with a force field.
Respectfully I'm not sure if I share your worry though. You would have the same problem if you wrote extremely thorough / exhaustive unit tests or extremely precise types and didn't allow the LLM to amend them. You're basically shrinking the state space of what is considered a "correct" program per your spec. That the LLM has to get extremely creative to break your program is a _feature_; in my experience, an LLM does not have to get creative at all to break a typical program written in an enterprise setting, and that's unfortunate.
Heh, We're writing Asimov in real life after been warned to decades.
> writing the laws becomes a bigger problem than writing the code itself.
Of course because at its limit programming is basically defining desired behaviour under all circumstances and logical conditions.
Well described the problem scope.
I wonder if harness-hooks + Jev (equivalents) could semantically lint for `sloppy_law` etc when ever they are edited
Hey Victor! Been following you since HVM/Kind, partly because I'm moderately unhappy with the state of out of the box automatic parallelism in modern languages!
Do you plan to invest in profile guided optimization or autotuning in Bend2 - using runtime profiles / cost models to make decisions around SIMD vs. multicore vs. GPU parallelization?
Bend2's model might give you a really nice view into available parallelization. Heck I can imagine integrating an LLM to profile and optimize in an absurdly expensive `-O7` optimization mode one day!
Hi. Yes and of course, I plan to invest in everything that makes Bend better. The language is, in theory, capable of parallelizing perfectly in any setup. Currently, though, only a very simple scheduler is shipped, and you must still tune it manually. We're a small team, but we're not stopping here, and I hope I can make it grow to the point where that kind of tooling becomes part of the ecosystem.
Amazing work, one question regarding the guide, it states:
> That same file is the CPU program and the GPU kernel: clang builds it for the host, Metal or CUDA builds it for the device, so a `!` runs the exact same code on either chip.
What exactly is this saying? The guide doesn't really explicitly define `!`, and it's unclear from this sentence whether it's saying that, "clang builds it for the host and Metal, and CUDA builds it for the device", or if it's saying, "clang builds it for the host, Metal, and CUDA, and builds it for the device", or something else entirely.
I will improve that phrasing, thanks.
It just means that Bend compiles to a single .c file, and that file compiles to either Metal or CUDA, via macros, depending on your target. This shouldn't be relevant to most users. It is just a way I found to keep the file small and reuse as much code as possible, rather than rewriting the runtime 3 times (once for C, once for Metal, once for CUDA).
Sorry for not knowing, but in the AI world that we are in, I need to learn more about the creator behind a project to trust it. Something that can help me know why the creator is qualified to deliver on the promises being made, that I can trust their judgement and decision, that they know what they are doing and don't need AI to tell them what/how to do it, and that they are committed long term to the project. Do you think you could share a bit about you that would give me some answers on those?
A lot of information here:
https://gist.github.com/VictorTaelin/77fd5a2a8a4a07e1da6157e...
https://github.com/victortaelin
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This is a nice reminder for people.
Cool project!
This is really interesting, I’ve been very interested in the power of checks for code and things like hypothesis (which seem very similar in terms of writing a “for this kind of case, this holds true”, obviously different in terms of statistical checking vs actual proof).
I’ll have to explore and this isn’t my field so this isn’t a substantive comment and this may be bikeshedding but I found the game example a little confusing at first because we’d want winning to be possible. It fits the context of stopping a bad thing happening if it’s “evil actor can’t do X” and if your mind is on CTF but games we want to win.
Potential changes:
Make it a proof that the game can be won.
Make it require something first - so the game can’t be won unless the key is found for example. End result is still roughly the same and the failure case is still the same (walk over side of game) but it’s the kind of thing I’d want encoded in a puzzle game - game is winnable, but not winnable without getting the key first.
Since my other direction normally would be quickcheck style, I’d be interested in cases that are statistically hard to find but easy to prove exist. And in fairness, the other way too I guess. When to use each approach.
In the spirit of your comment, these are not things I see as failings, they are not things I in any way expect to be changed or done, they are intended as just an outsiders perspective if useful.
Thanks for making things, and thanks for releasing them!
I like the idea of a language intended from the start to be proved and it seems very compelling given coding agents. It's a good idea that others don't see coming -- so expect it to be frequently misunderstood and even verbally abused!
Hi author :wave:
I'm confused - could you explain how the board/flag animation relates to Bend's compile time checking? Is it actually a direct demonstration of Bend running a check?
The check is happening in between the animations. When the AI edits the code, Bend will check if all laws still hold, mathematically so. If not, the AI repeats, until that's the case. So, the animations just show what happens to the app with and without Bend's involvement.
Could you recommed literature (preferrably a single book) that does not require prior knowledge and allows to fully understand the logical foundation of it?
(Why it is done the way it is, what problems are solved by affinity, why closure can be called at most once, how a function that never returns can prove anything, and everything else)
There isn't a single book that covers all of it... Bend's theory touches various domains (dependent types, substructural types, termination). And then there's the runtime, compiler, GPU kernels...
If you mean about the type theory specifically, "Type Theory and Formal Proof by Nederpelt and Geuvers" is a good introduction. Not sure what I'd recommend on linear types, no book I know of is very introductory? Perhaps "Idris 2: Quantitative Type Theory in Practice", which is a language with similar foundations to Bend, and the author wrote a book on it (and inspired myself!)
Does Bend have linear types? I didn't see anything on them in a quick skim of the GUIDE file.
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Thank you.
Just wanted to say this is really, really cool, and impressive stuff. Looking forward to reading your papers and playing with it. Thanks for working hard on it and sharing it with us.
Congrats, Victor!
É ótimo ver um brasileiro criando algo tão único!
obrigado amg
Thank you for adding a 5-line AGENTS.md. Other projects force you to install skills or MCP even when they're just doing the same thing.
what happened to your other project? HVM?
Surprise - HVM has been reimplemented in Bend 2.
You can find it on Bend's demo directory in our GitHub.
Don't tell anyone though!
i'm asking you what happened to HVM that it needed to be reimplemented as Bend.
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honestly just Bend is a great HN title, you can describe it more concretely on the homepage
Thank you for being honest.
Speaking of lava, you should do a presentation to the local tech group if you're ever here in Bend, Oregon...
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