Sure, I can use a Maybe variant, but the consequence would be that I wrap the whole program in a layer of maybes for cases that I "know" shouldn't happen but happened -- because I do make mistakes.

Or in other words, an "AssertionMonad". No thanks, I'm perfectly fine with assertion errors (i.e. "Index out of bounds"). I just need help with finding my own errors. Stacktraces are a good thing.