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

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.