> I have defined:
>
> > class Aggregate a where
> > toList::(Num b)=>a->[b]
> > fromList::(Num b)=>[b]->a
>
> > data MyAgg =Agg Int Int
> > instance Aggregate MyAgg where
> > toList (Agg x y) = [x,y]
> > fromList [x,y] = (Agg x y)
>
> Hugs won't compile this because it says the declared type is too general.
> Any function that requires an Aggregate can use MyAgg. Why am I
> getting an error?
The type of toList in the class declaration claims that it can
produce a list of any type in Num, but with MyAgg you can only get
a list of Int. So the type of toList in the class is more general
than the one you have given.
fromList has a similar problem.
-- Lennart
