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tel/gist:c0efcea739f2d549df0a

Last active August 29, 2015 14:05
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Diff impl for Either and (,)
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gistfile1.hs
data Zipper t a = Zipper { diff :: D t a, here :: a }
deriving instance Diff t => Functor (Zipper t)
class (Functor t, Functor (D t)) => Diff t where
data D t :: * -> *
inTo :: t a -> t (Zipper t a)
outOf :: Zipper t a -> t a
instance Diff ((,) x) where
data D ((,) x) a = DReader x deriving Functor
inTo (x, a) = (x, Zipper (DReader x) a)
outOf (Zipper (DReader x) a) = (x, a)
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