Re: [Haskell-cafe] convergence of functions of Complex variables

15 Dec 2004

      On Wed, Dec 15, 2004 at 02:07:10AM -0800, William Lee Irwin III wrote:
...
This does not work as expected on Complex numbers due to some odd
typechecking hassles apparently associated with abs. How do I get this
to typecheck for both real (e.g. Double) and Complex arguments?
abs :: Num a => a -> a, whereas you want something that returns a Double.
You could define

class Norm a where
        norm :: a -> Double

instance Norm Float where
        norm = realToFrac . abs

instance Norm Double where
        norm = abs

instance RealFloat a => Norm (Complex a) where
        norm = realToFrac . magnitude

and use norm instead of abs.

Re: [Haskell-cafe] convergence of functions of Complex variables

Ross Paterson