Data/Diff.hs

module Data.Diff (Diff, Diffable, diff, patch) where

import Data.Flat.Instances ()
import GHC.Generics (Generic)
import Linear (V2(V2))

class Eq a => Diffable a where
    data Diff a
    diff :: a -> a -> Maybe (Diff a)
    patch :: a -> Diff a -> a

instance Diffable a => Diffable (V2 a) where
    newtype Diff (V2 a) = DiffV2 (V2 (Maybe (Diff a)))
        deriving (Generic)

    diff v@(V2 x y) v'@(V2 x' y')
        | v == v' = Nothing
        | otherwise = Just . DiffV2 $ V2 (diff x x') (diff y y')

    patch (V2 x y) (DiffV2 (V2 xd yd)) = V2
        ((maybe <*> patch) x xd)
        ((maybe <*> patch) y yd)

instance Flat (Diff a) => Flat (Diff (V2 a))