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Comment by simonw | Hacker News Reader

I'm finding that code is the area where hallucinations matter the least... because if it hallucinates an API function that doesn't exist, the mistake becomes apparent the moment you actually try to run it.

It's like having an automated fact checker! I wish I had the same thing for the other kinds of output it produces.

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It will, however from time to time insert lines and variables that do nothing, but could result in bugs or confusion if not removed. I’ve encountered these hallucinations a few times. Overall, I agree with your sentiment, but I think it’s important to note that running isn’t always the indicator or correctness we think it to be.

You're still supposed to read it, like you hopefully wouldn't blindly paste a big code block from SO. A useless/unused line or variable doesn't seem that hard to spot?

Of course, but ease of detection can vary relative to the complexity of the code being returned. GPT-4, correctly prompted, can produce some pretty complicated stuff. But it also hallucinates in ways that are more subtle than one might think. The example I’m thinking of, it created an unused variable in a set of fairly complex ML training set up scripts that I mostly caught because I was familiar with all the proper inputs. But the unused variable was quite plausible if you were not familiar, new to the domain etc.

Compilers automatically detect unused variables. Unused variables are the last of your problems. You should be far, far more worried about all the misused variables.

I've noticed some other funny things, maybe harmless but undesirable.

One example was really really hard to spot. Once I queried GPT 3.5 for a function to do X, and it did pretty well, when I looked closer though, it had wrapped 90% of the code in an unnecessary if statement. I looked at the code an thought something was off until I realized.

My point here is, if that was easy to spot, who knows what else people are missing because even in a simple case, unless you're actually trying to spot issues, you likely won't see them.

Don't IDEs highlight variables that aren't read/written to?

In this case “unused” might mean declaring or initializing a variable and then assigning or reassigning a value to it later. In this case, it is technically used, so most linters won’t pick that up. But it actually does nothing so it’s wasted cycles.

No decent compiler would waste a cycle on that.

If it imagines a function it's fine. You can fix it in one prompt. But when it doesn't see it may move in the wrong way and produce limited solution. And you wouldn't know.

You would know in a similar way to a colleague of yours having done this code the previous day, or you joining a company with legacy code. It either has tests or you can't really trust it anyway regardless. You can ask the AI to also write tests for you, inspecting tests is usually much faster than understanding all the nuances of the code.

> because if it hallucinates an API function that doesn't exist

Yes, absolutely agree.

And also I’m no fanboy but when it does this and I only notice because the code doesn’t run, half the time I’m thinking to myself that the API function really should exist because it’s so logical!

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