Semiring has the following law:
With the instance (Semiring a) => Semiring (Maybe a), neither of these hold for a = Nothing - since mul is defined as liftA2 mul, zero * Nothing = Nothing, but zero = Just zero. Changing the definition of zero to be Nothing could fix this but might break other laws, I'm not sure. Maybe we should just remove this instance.
Semiringhas the following law:zero * a = zeroWith the instance
(Semiring a) => Semiring (Maybe a), neither of these hold fora = Nothing- sincemulis defined asliftA2 mul,zero * Nothing = Nothing, butzero = Just zero. Changing the definition ofzeroto beNothingcould fix this but might break other laws, I'm not sure. Maybe we should just remove this instance.