[Haskell-beginners] monad transformer show help

[Tobias Brandt]

On 29 May 2012 14:35, rickmurphy <rick at rickmurphy.org> wrote:
> w' :: Num (I a) => O I a
> w' = (OC (IC 0)) >>= return . id

w' requires a Num instance for 'I a', but there is none.

You need to define:

instance Num a => Num (I a) where
   ...

by lifting all operations into I.