The answer is type-safety. LLMs produce errors, as do humans. A language with carefully designed semantics and a well-implemented safety checker (or maybe even a proof assistant) will help express much more correct code.

I've had the most success running Claude iteratively with mypy and pytest. But it regularly wants to just delete the tests or get rid of static typing. A language like Haskell augmented with contracts over tests wouldn't allow that. (Except for diverging into a trivial ad-hoc dynamic solution, of course.)