There is added complication because there are two possible extensions
that can derive that instance: either GeneralizedNewtypeDeriving or
DerivingDataTypeable. I think the latter always wins (which makes
sense, it's probably what you want).
-- ryan
On Fri, Sep 24, 2010 at 1:41 PM, Christopher
On 24 September 2010 22:18, Christopher Done wrote:
> Can't make a derived instance of `Typeable (A Maybe)':
> `A' has arguments of kind other than `*'
> In the stand-alone deriving instance for `Typeable (A Maybe)'
Nevermind, I figured it out. The arguments refer to the type
construct
Actually I suppose the newtype one makes sense because it's opaque and
not paramerized so it doesn't inspect the unMaybe. I'll think about
this some more.
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Just for what it's worth, the following does work:
newtype AMaybe = AMaybe { unMaybe :: A Maybe }
deriving instance Typeable AMaybe
Which leads me to be kind of baffled by the above error message.
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