Kevin Jardine <[email protected]> wrote:
> My goal was to find a way to define all that was needed using
> Haskell's automatic instance deriving mechanism. Haskell can
> automatically derive Foldable, which is why I was looking at that.
>
> However, that requires writing two lines for each wrapper newtype to
> get around the kind problem.
>
> I wanted one line.
There:
newtype Blog = Blog { getBlogObj :: Obj }
newtype Comment = Comment { getCommentObj :: Obj }
newtype User = User { getUserObj :: Obj }
class GetObject a where getObject :: a -> Obj
instance GetObject Blog where getObject = getBlogObject
instance GetObject Comment where getObject = getCommentObject
instance GetObject User where getObject = getUserObject
You shouldn't abuse Foldable for this purpose, unless you really mean
it.
> I agree that the Foldable solution was a bit of a kludge.
And not necessary either.
Greets,
Ertugrul
--
nightmare = unsafePerformIO (getWrongWife >>= sex)
http://ertes.de/
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