[Haskell-cafe] Is this the "right" way to do polymorphism?

[Henning Thielemann]

On Fri, 7 Jan 2011, Daryoush Mehrtash wrote:

> -- | Performs a signed request with the available token.
> serviceRequest :: (HttpClient c,MonadIO m) => c -> OAuthRequest -> OAuthMonadT m Response
> serviceRequest c req = do { result <- lift $ runClient c (unpackRq req)

I do not see, why different download methods need distinct types at all 
(the instances of HttpClient). I would certainly just pass a dictionary of 
access methods around.