[Haskell-beginners] Typeclasses vs. Data

[David Place]

On Jul 20, 2011, at 5:58 PM, Thomas wrote:

> class Continuation a where
>   resume :: a -> Expression -> Expression
> 
> data BeginCont a = BeginCont a Expression deriving (Show)
> instance (Continuation a) => Continuation (BeginCont a) where
>  resume (BeginCont k es) v = eval_begin es k

I think we need to know the definition of Expression.  if define it with a dummy type

eval_begin a b = a
type Expression = Int

this code fragment compiles.  Would you send a code fragment that will yield the error?
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