@@ -1,151 +1,82 @@
1−{-# LANGUAGE CPP #-}
1+{-# LANGUAGE DeriveFoldable #-}
2+{-# LANGUAGE DeriveFunctor #-}
23{-# LANGUAGE DeriveTraversable #-}
34{-# LANGUAGE FlexibleContexts #-}
4−{-# LANGUAGE FlexibleInstances #-}
5−{-# LANGUAGE GeneralizedNewtypeDeriving #-}
65{-# LANGUAGE LambdaCase #-}
7−{-# LANGUAGE MultiParamTypeClasses #-}
86{-# LANGUAGE PatternGuards #-}
9−{-# LANGUAGE PatternSynonyms #-}
107{-# LANGUAGE ScopedTypeVariables #-}
11−{-# LANGUAGE StandaloneDeriving #-}
12−{-# LANGUAGE TemplateHaskell #-}
13−{-# LANGUAGE TypeApplications #-}
148{-# LANGUAGE TypeFamilies #-}
15−{-# LANGUAGE ViewPatterns #-}
16−
179-- | 'Patch'es on 'Map' that can insert, delete, and move values from one key to
1810-- another
19−module Data.Patch.MapWithMove
20− ( PatchMapWithMove
21− ( PatchMapWithMove
22− , unPatchMapWithMove
23− , ..
24− )
25− , patchMapWithMove
26− , patchMapWithMoveInsertAll
27− , insertMapKey
28− , moveMapKey
29− , swapMapKey
30− , deleteMapKey
31− , unsafePatchMapWithMove
32− , patchMapWithMoveNewElements
33− , patchMapWithMoveNewElementsMap
34− , patchThatSortsMapWith
35− , patchThatChangesAndSortsMapWith
36− , patchThatChangesMap
37−
38− -- * Node Info
39− , NodeInfo
40− ( NodeInfo
41− , _nodeInfo_to
42− , _nodeInfo_from
43− , ..
44− )
45− , bitraverseNodeInfo
46− , nodeInfoMapFrom
47− , nodeInfoMapMFrom
48− , nodeInfoSetTo
49−
50− -- * From
51− , From
52− ( From_Insert
53− , From_Delete
54− , From_Move
55− , ..
56− )
57− , bitraverseFrom
11+module Data.Patch.MapWithMove where
5812
59− -- * To
60− , To
61− ) where
62−
63−import Data.Coerce
64−import Data.Kind (Type)
6513import Data.Patch.Class
66−import Data.Patch.MapWithPatchingMove (PatchMapWithPatchingMove(..), To)
67−import qualified Data.Patch.MapWithPatchingMove as PM -- already a transparent synonym
6814
69−import Control.Lens
15+import Control.Arrow
16+import Control.Monad.Trans.State
17+import Data.Foldable
18+import Data.Function
7019import Data.List
7120import Data.Map (Map)
7221import qualified Data.Map as Map
73−import Data.Proxy
74−#if !MIN_VERSION_base(4,11,0)
75−import Data.Semigroup (Semigroup (..))
76−#endif
77−import Data.Traversable (foldMapDefault)
22+import Data.Maybe
23+import Data.Semigroup (Semigroup (..), (<>))
24+import qualified Data.Set as Set
25+import Data.These (These(..))
26+import Data.Tuple
7827
79−-- | Patch a Map with additions, deletions, and moves. Invariant: If key @k1@
28+-- | Patch a DMap with additions, deletions, and moves. Invariant: If key @k1@
8029-- is coming from @From_Move k2@, then key @k2@ should be going to @Just k1@,
8130-- and vice versa. There should never be any unpaired From/To keys.
82−newtype PatchMapWithMove k (v :: Type) = PatchMapWithMove'
83− { -- | Extract the underlying 'PatchMapWithPatchingMove k (Proxy v)'
84− unPatchMapWithMove' :: PatchMapWithPatchingMove k (Proxy v)
85− }
86− deriving ( Show, Read, Eq, Ord
87−-- Haddock cannot handle documentation here before GHC 8.6
88− ,
89−#if __GLASGOW_HASKELL__ >= 806
90− -- | Compose patches having the same effect as applying the
91− -- patches in turn: @'applyAlways' (p <> q) == 'applyAlways' p .
92− -- 'applyAlways' q@
93−#endif
94− Semigroup
95− , Monoid
96− )
97−
98−pattern Coerce :: Coercible a b => a -> b
99−pattern Coerce x <- (coerce -> x)
100− where Coerce x = coerce x
31+newtype PatchMapWithMove k v = PatchMapWithMove (Map k (NodeInfo k v)) deriving (Show, Eq, Ord, Functor, Foldable, Traversable)
10132
102−{-# COMPLETE PatchMapWithMove #-}
103−pattern PatchMapWithMove :: Map k (NodeInfo k v) -> PatchMapWithMove k v
104−-- | Extract the representation of the 'PatchMapWithMove' as a map of
105−-- 'NodeInfo'.
106−unPatchMapWithMove :: PatchMapWithMove k v -> Map k (NodeInfo k v)
107−pattern PatchMapWithMove { unPatchMapWithMove } = PatchMapWithMove' (PatchMapWithPatchingMove (Coerce unPatchMapWithMove))
108−
109−_PatchMapWithMove
110− :: Iso
111− (PatchMapWithMove k0 v0)
112− (PatchMapWithMove k1 v1)
113− (Map k0 (NodeInfo k0 v0))
114− (Map k1 (NodeInfo k1 v1))
115−_PatchMapWithMove = iso unPatchMapWithMove PatchMapWithMove
116−
117−instance Functor (PatchMapWithMove k) where
118− fmap f = runIdentity . traverse (Identity . f)
119−
120−instance Foldable (PatchMapWithMove k) where
121− foldMap = foldMapDefault
33+-- | Holds the information about each key: where its new value should come from,
34+-- and where its old value should go to
35+data NodeInfo k v = NodeInfo
36+ { _nodeInfo_from :: !(From k v)
37+ -- ^ Where do we get the new value for this key?
38+ , _nodeInfo_to :: !(To k)
39+ -- ^ If the old value is being kept (i.e. moved rather than deleted or
40+ -- replaced), where is it going?
41+ }
42+ deriving (Show, Read, Eq, Ord, Functor, Foldable, Traversable)
12243
123−instance Traversable (PatchMapWithMove k) where
124− traverse =
125− _PatchMapWithMove .
126− traverse .
127− traverse
44+-- | Describe how a key's new value should be produced
45+data From k v
46+ = From_Insert v -- ^ Insert the given value here
47+ | From_Delete -- ^ Delete the existing value, if any, from here
48+ | From_Move !k -- ^ Move the value here from the given key
49+ deriving (Show, Read, Eq, Ord, Functor, Foldable, Traversable)
12850
129−instance FunctorWithIndex k (PatchMapWithMove k)
130−instance FoldableWithIndex k (PatchMapWithMove k)
131−instance TraversableWithIndex k (PatchMapWithMove k) where
132− itraverse = itraversed . Indexed
133− itraversed =
134− _PatchMapWithMove .>
135− itraversed <.
136− traverse
51+-- | Describe where a key's old value will go. If this is 'Just', that means
52+-- the key's old value will be moved to the given other key; if it is 'Nothing',
53+-- that means it will be deleted.
54+type To = Maybe
13755
13856-- | Create a 'PatchMapWithMove', validating it
13957patchMapWithMove :: Ord k => Map k (NodeInfo k v) -> Maybe (PatchMapWithMove k v)
140−patchMapWithMove = fmap PatchMapWithMove' . PM.patchMapWithPatchingMove . coerce
58+patchMapWithMove m = if valid then Just $ PatchMapWithMove m else Nothing
59+ where valid = forwardLinks == backwardLinks
60+ forwardLinks = Map.mapMaybe _nodeInfo_to m
61+ backwardLinks = Map.fromList $ catMaybes $ flip fmap (Map.toList m) $ \(to, v) ->
62+ case _nodeInfo_from v of
63+ From_Move from -> Just (from, to)
64+ _ -> Nothing
14165
14266-- | Create a 'PatchMapWithMove' that inserts everything in the given 'Map'
14367patchMapWithMoveInsertAll :: Map k v -> PatchMapWithMove k v
144−patchMapWithMoveInsertAll = PatchMapWithMove' . PM.patchMapWithPatchingMoveInsertAll
68+patchMapWithMoveInsertAll m = PatchMapWithMove $ flip fmap m $ \v -> NodeInfo
69+ { _nodeInfo_from = From_Insert v
70+ , _nodeInfo_to = Nothing
71+ }
72+
73+-- | Extract the internal representation of the 'PatchMapWithMove'
74+unPatchMapWithMove :: PatchMapWithMove k v -> Map k (NodeInfo k v)
75+unPatchMapWithMove (PatchMapWithMove p) = p
14576
14677-- | Make a @'PatchMapWithMove' k v@ which has the effect of inserting or updating a value @v@ to the given key @k@, like 'Map.insert'.
14778insertMapKey :: k -> v -> PatchMapWithMove k v
148−insertMapKey k v = PatchMapWithMove' $ PM.insertMapKey k v
79+insertMapKey k v = PatchMapWithMove . Map.singleton k $ NodeInfo (From_Insert v) Nothing
14980
15081-- |Make a @'PatchMapWithMove' k v@ which has the effect of moving the value from the first key @k@ to the second key @k@, equivalent to:
15182--
@@ -153,53 +84,84 @@ insertMapKey k v = PatchMapWithMove' $ PM.insertMapKey k v
15384-- 'Map.delete' src (maybe map ('Map.insert' dst) (Map.lookup src map))
15485-- @
15586moveMapKey :: Ord k => k -> k -> PatchMapWithMove k v
156−moveMapKey src dst = PatchMapWithMove' $ PM.moveMapKey src dst
87+moveMapKey src dst
88+ | src == dst = mempty
89+ | otherwise =
90+ PatchMapWithMove $ Map.fromList
91+ [ (dst, NodeInfo (From_Move src) Nothing)
92+ , (src, NodeInfo From_Delete (Just dst))
93+ ]
15794
15895-- |Make a @'PatchMapWithMove' k v@ which has the effect of swapping two keys in the mapping, equivalent to:
15996--
16097-- @
16198-- let aMay = Map.lookup a map
16299-- bMay = Map.lookup b map
163−-- in maybe id (Map.insert a) (bMay <> aMay)
164−-- . maybe id (Map.insert b) (aMay <> bMay)
100+-- in maybe id (Map.insert a) (bMay `mplus` aMay)
101+-- . maybe id (Map.insert b) (aMay `mplus` bMay)
165102-- . Map.delete a . Map.delete b $ map
166103-- @
167104swapMapKey :: Ord k => k -> k -> PatchMapWithMove k v
168−swapMapKey src dst = PatchMapWithMove' $ PM.swapMapKey src dst
105+swapMapKey src dst
106+ | src == dst = mempty
107+ | otherwise =
108+ PatchMapWithMove $ Map.fromList
109+ [ (dst, NodeInfo (From_Move src) (Just src))
110+ , (src, NodeInfo (From_Move dst) (Just dst))
111+ ]
169112
170113-- |Make a @'PatchMapWithMove' k v@ which has the effect of deleting a key in the mapping, equivalent to 'Map.delete'.
171114deleteMapKey :: k -> PatchMapWithMove k v
172−deleteMapKey = PatchMapWithMove' . PM.deleteMapKey
115+deleteMapKey k = PatchMapWithMove . Map.singleton k $ NodeInfo From_Delete Nothing
173116
174117-- | Wrap a @'Map' k (NodeInfo k v)@ representing patch changes into a @'PatchMapWithMove' k v@, without checking any invariants.
175118--
176119-- __Warning:__ when using this function, you must ensure that the invariants of 'PatchMapWithMove' are preserved; they will not be checked.
177120unsafePatchMapWithMove :: Map k (NodeInfo k v) -> PatchMapWithMove k v
178−unsafePatchMapWithMove = coerce PM.unsafePatchMapWithPatchingMove
121+unsafePatchMapWithMove = PatchMapWithMove
179122
180123-- | Apply the insertions, deletions, and moves to a given 'Map'
181124instance Ord k => Patch (PatchMapWithMove k v) where
182125 type PatchTarget (PatchMapWithMove k v) = Map k v
183− apply (PatchMapWithMove' p) = apply p
126+ apply (PatchMapWithMove p) old = Just $! insertions `Map.union` (old `Map.difference` deletions) --TODO: return Nothing sometimes --Note: the strict application here is critical to ensuring that incremental merges don't hold onto all their prerequisite events forever; can we make this more robust?
127+ where insertions = flip Map.mapMaybeWithKey p $ \_ ni -> case _nodeInfo_from ni of
128+ From_Insert v -> Just v
129+ From_Move k -> Map.lookup k old
130+ From_Delete -> Nothing
131+ deletions = flip Map.mapMaybeWithKey p $ \_ ni -> case _nodeInfo_from ni of
132+ From_Delete -> Just ()
133+ _ -> Nothing
184134
185135-- | Returns all the new elements that will be added to the 'Map'.
186136patchMapWithMoveNewElements :: PatchMapWithMove k v -> [v]
187−patchMapWithMoveNewElements = PM.patchMapWithPatchingMoveNewElements . unPatchMapWithMove'
137+patchMapWithMoveNewElements = Map.elems . patchMapWithMoveNewElementsMap
188138
189139-- | Return a @'Map' k v@ with all the inserts/updates from the given @'PatchMapWithMove' k v@.
190140patchMapWithMoveNewElementsMap :: PatchMapWithMove k v -> Map k v
191−patchMapWithMoveNewElementsMap = PM.patchMapWithPatchingMoveNewElementsMap . unPatchMapWithMove'
141+patchMapWithMoveNewElementsMap (PatchMapWithMove p) = Map.mapMaybe f p
142+ where f ni = case _nodeInfo_from ni of
143+ From_Insert v -> Just v
144+ From_Move _ -> Nothing
145+ From_Delete -> Nothing
192146
193147-- | Create a 'PatchMapWithMove' that, if applied to the given 'Map', will sort
194148-- its values using the given ordering function. The set keys of the 'Map' is
195149-- not changed.
196150patchThatSortsMapWith :: Ord k => (v -> v -> Ordering) -> Map k v -> PatchMapWithMove k v
197−patchThatSortsMapWith cmp = PatchMapWithMove' . PM.patchThatSortsMapWith cmp
151+patchThatSortsMapWith cmp m = PatchMapWithMove $ Map.fromList $ catMaybes $ zipWith g unsorted sorted
152+ where unsorted = Map.toList m
153+ sorted = sortBy (cmp `on` snd) unsorted
154+ f (to, _) (from, _) = if to == from then Nothing else
155+ Just (from, to)
156+ reverseMapping = Map.fromList $ catMaybes $ zipWith f unsorted sorted
157+ g (to, _) (from, _) = if to == from then Nothing else
158+ let Just movingTo = Map.lookup to reverseMapping
159+ in Just (to, NodeInfo (From_Move from) $ Just movingTo)
198160
199161-- | Create a 'PatchMapWithMove' that, if applied to the first 'Map' provided,
200162-- will produce a 'Map' with the same values as the second 'Map' but with the
201163-- values sorted with the given ordering function.
202−patchThatChangesAndSortsMapWith :: (Ord k, Ord v) => (v -> v -> Ordering) -> Map k v -> Map k v -> PatchMapWithMove k v
164+patchThatChangesAndSortsMapWith :: forall k v. (Ord k, Ord v) => (v -> v -> Ordering) -> Map k v -> Map k v -> PatchMapWithMove k v
203165patchThatChangesAndSortsMapWith cmp oldByIndex newByIndexUnsorted = patchThatChangesMap oldByIndex newByIndex
204166 where newList = Map.toList newByIndexUnsorted
205167 newByIndex = Map.fromList $ zip (fst <$> newList) $ sortBy cmp $ snd <$> newList
@@ -207,106 +169,102 @@ patchThatChangesAndSortsMapWith cmp oldByIndex newByIndexUnsorted = patchThatCha
207169-- | Create a 'PatchMapWithMove' that, if applied to the first 'Map' provided,
208170-- will produce the second 'Map'.
209171patchThatChangesMap :: (Ord k, Ord v) => Map k v -> Map k v -> PatchMapWithMove k v
210−patchThatChangesMap oldByIndex newByIndex = PatchMapWithMove' $
211− PM.patchThatChangesMap oldByIndex newByIndex
212−
213−--
214−-- NodeInfo
215−--
216−
217−-- | Holds the information about each key: where its new value should come from,
218−-- and where its old value should go to
219−newtype NodeInfo k (v :: Type) = NodeInfo' { unNodeInfo' :: PM.NodeInfo k (Proxy v) }
220−
221−deriving instance (Show k, Show p) => Show (NodeInfo k p)
222−deriving instance (Read k, Read p) => Read (NodeInfo k p)
223−deriving instance (Eq k, Eq p) => Eq (NodeInfo k p)
224−deriving instance (Ord k, Ord p) => Ord (NodeInfo k p)
225−
226−{-# COMPLETE NodeInfo #-}
227−pattern NodeInfo :: To k -> From k v -> NodeInfo k v
228−_nodeInfo_to :: NodeInfo k v -> To k
229−_nodeInfo_from :: NodeInfo k v -> From k v
230−pattern NodeInfo { _nodeInfo_to, _nodeInfo_from } = NodeInfo'
231− PM.NodeInfo
232− { PM._nodeInfo_to = _nodeInfo_to
233− , PM._nodeInfo_from = Coerce _nodeInfo_from
234− }
235−
236−_NodeInfo
237− :: Iso
238− (NodeInfo k0 v0)
239− (NodeInfo k1 v1)
240− (PM.NodeInfo k0 (Proxy v0))
241− (PM.NodeInfo k1 (Proxy v1))
242−_NodeInfo = iso unNodeInfo' NodeInfo'
243−
244−instance Functor (NodeInfo k) where
245− fmap f = runIdentity . traverse (Identity . f)
246−
247−instance Foldable (NodeInfo k) where
248− foldMap = foldMapDefault
249−
250−instance Traversable (NodeInfo k) where
251− traverse = bitraverseNodeInfo pure
252−
253−bitraverseNodeInfo
254− :: Applicative f
255− => (k0 -> f k1)
256− -> (v0 -> f v1)
257− -> NodeInfo k0 v0 -> f (NodeInfo k1 v1)
258−bitraverseNodeInfo fk fv = fmap NodeInfo'
259− . PM.bitraverseNodeInfo fk (\ ~Proxy -> pure Proxy) fv
260− . coerce
172+patchThatChangesMap oldByIndex newByIndex = patch
173+ where oldByValue = Map.fromListWith Set.union $ swap . first Set.singleton <$> Map.toList oldByIndex
174+ (insertsAndMoves, unusedValuesByValue) = flip runState oldByValue $ do
175+ let f k v = do
176+ remainingValues <- get
177+ let putRemainingKeys remainingKeys = put $ if Set.null remainingKeys
178+ then Map.delete v remainingValues
179+ else Map.insert v remainingKeys remainingValues
180+ case Map.lookup v remainingValues of
181+ Nothing -> return $ NodeInfo (From_Insert v) $ Just undefined -- There's no existing value we can take
182+ Just fromKs ->
183+ if k `Set.member` fromKs
184+ then do
185+ putRemainingKeys $ Set.delete k fromKs
186+ return $ NodeInfo (From_Move k) $ Just undefined -- There's an existing value, and it's here, so no patch necessary
187+ else do
188+ (fromK, remainingKeys) <- return . fromJust $ Set.minView fromKs -- There's an existing value, but it's not here; move it here
189+ putRemainingKeys remainingKeys
190+ return $ NodeInfo (From_Move fromK) $ Just undefined
191+ Map.traverseWithKey f newByIndex
192+ unusedOldKeys = fold unusedValuesByValue
193+ pointlessMove k = \case
194+ From_Move k' | k == k' -> True
195+ _ -> False
196+ keyWasMoved k = if k `Map.member` oldByIndex && not (k `Set.member` unusedOldKeys)
197+ then Just undefined
198+ else Nothing
199+ patch = unsafePatchMapWithMove $ Map.filterWithKey (\k -> not . pointlessMove k . _nodeInfo_from) $ Map.mergeWithKey (\k a _ -> Just $ nodeInfoSetTo (keyWasMoved k) a) (Map.mapWithKey $ \k -> nodeInfoSetTo $ keyWasMoved k) (Map.mapWithKey $ \k _ -> NodeInfo From_Delete $ keyWasMoved k) insertsAndMoves oldByIndex
261200
262201-- | Change the 'From' value of a 'NodeInfo'
263202nodeInfoMapFrom :: (From k v -> From k v) -> NodeInfo k v -> NodeInfo k v
264−nodeInfoMapFrom f = coerce $ PM.nodeInfoMapFrom (unFrom' . f . From')
203+nodeInfoMapFrom f ni = ni { _nodeInfo_from = f $ _nodeInfo_from ni }
265204
266205-- | Change the 'From' value of a 'NodeInfo', using a 'Functor' (or
267206-- 'Applicative', 'Monad', etc.) action to get the new value
268−nodeInfoMapMFrom
269− :: Functor f
270− => (From k v -> f (From k v))
271− -> NodeInfo k v -> f (NodeInfo k v)
272−nodeInfoMapMFrom f = fmap NodeInfo'
273− . PM.nodeInfoMapMFrom (fmap unFrom' . f . From')
274− . coerce
207+nodeInfoMapMFrom :: Functor f => (From k v -> f (From k v)) -> NodeInfo k v -> f (NodeInfo k v)
208+nodeInfoMapMFrom f ni = fmap (\result -> ni { _nodeInfo_from = result }) $ f $ _nodeInfo_from ni
275209
276210-- | Set the 'To' field of a 'NodeInfo'
277211nodeInfoSetTo :: To k -> NodeInfo k v -> NodeInfo k v
278−nodeInfoSetTo = coerce . PM.nodeInfoSetTo
279−
280−--
281−-- From
282−--
283−
284−-- | Describe how a key's new value should be produced
285−newtype From k (v :: Type) = From' { unFrom' :: PM.From k (Proxy v) }
286−
287−{-# COMPLETE From_Insert, From_Delete, From_Move #-}
288−
289−-- | Insert the given value here
290−pattern From_Insert :: v -> From k v
291−pattern From_Insert v = From' (PM.From_Insert v)
292−
293−-- | Delete the existing value, if any, from here
294−pattern From_Delete :: From k v
295−pattern From_Delete = From' PM.From_Delete
296−
297−-- | Move the value here from the given key
298−pattern From_Move :: k -> From k v
299−pattern From_Move k = From' (PM.From_Move k Proxy)
300−
301−bitraverseFrom
302− :: Applicative f
303− => (k0 -> f k1)
304− -> (v0 -> f v1)
305− -> From k0 v0 -> f (From k1 v1)
306−bitraverseFrom fk fv = fmap From'
307− . PM.bitraverseFrom fk (\ ~Proxy -> pure Proxy) fv
308− . coerce
309−
310−makeWrapped ''PatchMapWithMove
311−makeWrapped ''NodeInfo
312−makeWrapped ''From
212+nodeInfoSetTo to ni = ni { _nodeInfo_to = to }
213+
214+-- |Helper data structure used for composing patches using the monoid instance.
215+data Fixup k v
216+ = Fixup_Delete
217+ | Fixup_Update (These (From k v) (To k))
218+
219+-- |Compose patches having the same effect as applying the patches in turn: @'applyAlways' (p <> q) == 'applyAlways' p . 'applyAlways' q@
220+instance Ord k => Semigroup (PatchMapWithMove k v) where
221+ PatchMapWithMove ma <> PatchMapWithMove mb = PatchMapWithMove m
222+ where
223+ connections = Map.toList $ Map.intersectionWithKey (\_ a b -> (_nodeInfo_to a, _nodeInfo_from b)) ma mb
224+ h :: (k, (Maybe k, From k v)) -> [(k, Fixup k v)]
225+ h (_, (mToAfter, editBefore)) = case (mToAfter, editBefore) of
226+ (Just toAfter, From_Move fromBefore)
227+ | fromBefore == toAfter
228+ -> [(toAfter, Fixup_Delete)]
229+ | otherwise
230+ -> [ (toAfter, Fixup_Update (This editBefore))
231+ , (fromBefore, Fixup_Update (That mToAfter))
232+ ]
233+ (Nothing, From_Move fromBefore) -> [(fromBefore, Fixup_Update (That mToAfter))] -- The item is destroyed in the second patch, so indicate that it is destroyed in the source map
234+ (Just toAfter, _) -> [(toAfter, Fixup_Update (This editBefore))]
235+ (Nothing, _) -> []
236+ mergeFixups _ Fixup_Delete Fixup_Delete = Fixup_Delete
237+ mergeFixups _ (Fixup_Update a) (Fixup_Update b)
238+ | This x <- a, That y <- b
239+ = Fixup_Update $ These x y
240+ | That y <- a, This x <- b
241+ = Fixup_Update $ These x y
242+ mergeFixups _ _ _ = error "PatchMapWithMove: incompatible fixups"
243+ fixups = Map.fromListWithKey mergeFixups $ concatMap h connections
244+ combineNodeInfos _ nia nib = NodeInfo
245+ { _nodeInfo_from = _nodeInfo_from nia
246+ , _nodeInfo_to = _nodeInfo_to nib
247+ }
248+ applyFixup _ ni = \case
249+ Fixup_Delete -> Nothing
250+ Fixup_Update u -> Just $ NodeInfo
251+ { _nodeInfo_from = fromMaybe (_nodeInfo_from ni) $ getHere u
252+ , _nodeInfo_to = fromMaybe (_nodeInfo_to ni) $ getThere u
253+ }
254+ m = Map.differenceWithKey applyFixup (Map.unionWithKey combineNodeInfos ma mb) fixups
255+ getHere :: These a b -> Maybe a
256+ getHere = \case
257+ This a -> Just a
258+ These a _ -> Just a
259+ That _ -> Nothing
260+ getThere :: These a b -> Maybe b
261+ getThere = \case
262+ This _ -> Nothing
263+ These _ b -> Just b
264+ That b -> Just b
265+
266+--TODO: Figure out how to implement this in terms of PatchDMapWithMove rather than duplicating it here
267+-- |Compose patches having the same effect as applying the patches in turn: @'applyAlways' (p <> q) == 'applyAlways' p . 'applyAlways' q@
268+instance Ord k => Monoid (PatchMapWithMove k v) where
269+ mempty = PatchMapWithMove mempty
270+ mappend = (<>)