GADT map stuff

GEither.hs

data Side = LeftSide | RightSide

data GEither c a b  where
  GLeft :: a -> GEither 'LeftSide a b
  GRight :: b -> GEither 'RightSide a b

data LVal = LVal Int
data RVal = RVal Int

data LeftRightMap where
    MkMap :: IntMap (GEither LeftSide LVal RVal) -> IntMap (GEither RightSide  LVal RVal) -> LeftRightMap

mapBoth :: LeftRightMap -> (forall side. (GEither side LVal RVal) -> (GEither side LVal RVal)) -> LeftRightMap
mapBoth (MkMap lmap rmap) f =
  MkMap (fmap f lmap) (fmap f rmap)

mapLeft :: LeftRightMap -> (forall side. (GEither LeftSide LVal RVal) -> (GEither LeftSide LVal RVal)) -> LeftRightMap
mapLeft (MkMap lmap rmap) f =
  MkMap (fmap f lmap) rmap

fleft :: (GEither LeftSide LVal RVal) -> (GEither LeftSide LVal RVal)
fleft (GLeft (LVal x)) = GLeft $ LVal $ x + 1