I know nothing about pony, but if it does have an optional type, this would be a much better choice. You lose information by returning 0. Returning "none" would keep the information that you tried to divide by 0. Of course, this means all division would return an optional instead of a value. This is the cost of safe, robust programming.
<rant>
I see a lot of software engineers trying to get rid of the cost of writing robust programs. It's not possible. Stop trying. You are either safe, or you are not. You either handle all cases, or you don't.
</rant>
<rant> I see a lot of software engineers trying to get rid of the cost of writing robust programs. It's not possible. Stop trying. You are either safe, or you are not. You either handle all cases, or you don't. </rant>