3 Aug
2007
3 Aug
'07
9:13 p.m.
On 8/3/07, Chris Smith
Yes, unless of course you did:
instance (Monad m, Num n) => Num (m n)
or some such nonsense. :)
I decided to take this as a dare - at first I thought it would be easy to declare (Monad m, Num n) => m n to be an instance of Num (just lift or return the operators as necessary), but I ran into trouble once I realized I needed two things I wasn't going to get: An instance of Eq (m n), and an instance of Show (m n) for all monads m. Eq would need a function of the form: (==) :: Monad m => m a -> m a -> Bool and Show would need a function of type m a -> String There's no way I'm getting a function of those types using return and join to operate on the monad. So, there went that idea. -Antoine