Update style to match @laszlopandy's upcoming recommendations

The idea here is to use a more regular code style, based on 4 space indentations. Can we share the draft with Max, I don't know if it's viewable if you have the link?
I preserved this from the old code, but I'm wondering if it is a bug?

I feel like it should be `Exit code`, not `Exit n` which shadows the `n` argument and is used in the recursive call.