[Haskell-cafe] Re: Unwrapping newtypes

Tony Morris tonymorris at gmail.com
Wed Sep 8 08:24:01 EDT 2010

On 08/09/10 22:19, Kevin Jardine wrote:
> Hi Tony,
> I stared at that specific section for at least half an hour earlier
> today but could not figure out how it applied in my specific case. The
> only examples I have see are for deriving Num. Do you have any more
> detail on how I could use that extension?
Here is an example:

{-# LANGUAGE GeneralizedNewtypeDeriving #-}

class C a where
  c :: a -> Int

data G = G

instance C G where
  c _ = 7

newtype H = H G deriving C

Tony Morris

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