I think moving the error around is a good idea. E.g. integer division would end up with five cases: Int / 0 -> DivisionByZeroError PositiveInt / PositiveI

I think moving the error around is a good idea. E.g. integer division would end up with five cases: Int / 0 -> DivisionByZeroError PositiveInt / PositiveInt -> PositiveFloat PositiveInt / NegativeInt -> NegativeFloat NegativeInt / PositiveInt -> NegativeFloat NegativeInt / NegativeInt -> PositiveFloat And the type signatures of those possible return values can drive validation checks upstream of the calculation, so you're not actually ever going to return DivisionByZeroError. You're making sure through validation checks or case logic that that can never be returned.