Le Jeudi 23 Janvier 2003 06:40, Matthew Donadio a écrit :

Hi all,

I have yet another question. I think I have too much time on my hands.

I have two functions:

...

rf :: (RealFloat a, Integral b) => [a] -> b -> Complex a rf x k = ...

cf :: (RealFloat a, Integral b) => [Complex a] -> b -> Complex a cf x k = ...

I would like to add these to the class system so I can create an overloaded version, f.

From my understanding of the Report, the following should work, but I get an error, which I really don't understand.

...

class (Fractional a) => Floating a where f :: (Integral b) => [a] -> b -> a

instance (RealFloat a) => Floating a where f x k = rf x k

instance (RealFloat a) => Floating (Complex a) where f x k = cf x k

hugs98 spits out

ERROR "f.lhs":59 - Syntax error in instance head (constructor expected)

where line 59 is the first instance declaration. Can anyone give me some guidance, or hints, here?

Thanks a million.

On the first "instance" you're trying to instantiate "any type a that is a instance of RealFloat". AFAIK you can instantiate only "real" data types like "Complex a". (sorry for the "real" that is not the good term, but I'm just waking up :) ) -- Ciao Jo