[Haskell-cafe] Why no Monoid, Num, Integral, or Floating RVarT instances?

[Barend Venter]

It seems like you should be able to get instances for:

(Monoid m) => Monoid (RVarT n m)
(Num m) => Num (RVarT n m)

and so forth for integral and floating

Just wondering if I am missing something here or if there is any
particular thing I'm missing. I am aware you would probably not be
able to do an Eq or Show instance but me understanding was that in the
case of the (Num b) => Num (a -> b) instance the solution was simply
to leave those things undefined.