I'll go ahead and make this change. Thanks for the suggestion!
I agree that ArithException feels more appropriate here. But I make two observations: (1) It replaces specific error messages with less specific ones. The error message will not include the function/operator name anymore, e.g.: ghci> 1 % 0 *** Exception: Ratio.%: zero denominator would become: ghci> 1 % 0 *** Exception: divide by zero (2) It is a breaking API change, and the complier won't help you to detect it in client code. I'm not saying that this is a bad idea, I just try to understand what the benefits of this breaking change are. If it only gives us less useful error messages, than I'm not convinced**. Cheers, Simon ** If we had stack traces with source locations that are enabled by default, I would be less reluctant to this change.