unsafeMapIncrementalWithOldValue.hs

-- | Like `unsafeMapIncremental` but the patch function also takes the old
-- target.
unsafeMapIncrementalWithOldValue ::
  (Reflex t, Patch p, Patch p') =>
  (PatchTarget p -> PatchTarget p') ->
  (PatchTarget p -> p -> p') ->
  Incremental t p ->
  Incremental t p'
unsafeMapIncrementalWithOldValue f g x =
  let x0 = currentIncremental x
      xE = updatedIncremental x
   in unsafeBuildIncremental (f <$> sample x0) $ uncurry g <$> attach x0 xE