[Haskell-cafe] Can't make a derived instance of `Typeable (A B)':
`A' has arguments of kind other than `*'
Christopher Done
chrisdone at googlemail.com
Fri Sep 24 16:18:33 EDT 2010
Suppose I have a data type:
data A f = A { a :: f Integer }
why can't I derive a Typeable instance like so?
deriving instance Typeable (A Maybe)
I get:
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)'
I would have expected that the arguments are instantiated by the Maybe
type constructor and thus the type of A would be:
Maybe Integer -> A
What am I missing?
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