Hi,

I'm playing around with typeclasses and trying to a feel on how you implement "inheritance"
(not sure if that's the good word here) in Haskell. I have the following code that doesn't compile:

class (Show a) => IPHost a where

class (Show a) => IPMask a where

class IPAddr a where
host :: (IPHost b) => a -> b
mask :: (IPMask b) => a -> b

showIPAddr :: (IPAddr a) => a -> String
showIPAddr a = (show . host $ a) ++ "/" ++ (show . mask $ a)

ghci says:

Net/IP.hs:23:23:
    Ambiguous type variable `b' in the constraint:
      `IPHost b' arising from a use of `host' at Net/IP.hs:23:23-26
    Probable fix: add a type signature that fixes these type variable(s)

Net/IP.hs:23:51:
    Ambiguous type variable `b1' in the constraint:
      `IPMask b1' arising from a use of `mask' at Net/IP.hs:23:51-54
    Probable fix: add a type signature that fixes these type variable(s)

What exactly does this error mean in this case? It's no tclear to me what needs to be made more specific. Am I approaching the problem in the wrong way?
Any help is appreciated.

Thanks,

Patrick
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Patrick LeBoutillier
Rosemère, Québec, Canada