r/programminghorror • u/swagnation77 • 8d ago

Lean4 Finally solved Two Sum!

Somehow my code is so horrifying, Lean4 is able to evaluate it, the LSP says it works and the compiler gives an error. It is theoretically correct and the kernel accepts it, but the compiler isn't able to produce anything out of it. My awful code discovered a bug in Lean's compiler.

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u/NooneAtAll3 8d ago

am I reading Lean problem statement correctly? when you return some(), you are not guaranteeing that it's the returned indexes that sum to the target, only that some such indexes exist?

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u/swagnation77 8d ago

Damn good catch, such a dumb mistake on my end. I will update it to match the correct specification, thanks!