Merge remote-tracking branch 'origin/master' into typescript-mapping

semantic-diff.cabal

@@ -53,6 +53,7 @@ library
                      , Renderer.TOC
                      , SemanticDiff
                      , SES
+                     , SES.Myers
                      , Source
                      , SourceSpan
                      , SplitDiff
@@ -150,6 +151,7 @@ test-suite test
                      , InterpreterSpec
                      , PatchOutputSpec
                      , RangeSpec
+                     , SES.Myers.Spec
                      , SourceSpec
                      , TermSpec
                      , TOCSpec
@@ -183,6 +185,12 @@ test-suite test
   default-language:    Haskell2010
   default-extensions:  DeriveFunctor, DeriveGeneric, FlexibleContexts, FlexibleInstances, OverloadedStrings, NoImplicitPrelude, RecordWildCards
 
+custom-setup
+  setup-depends:  base >= 4.8 && < 5
+                , Cabal
+                , directory
+                , process
+
 source-repository head
   type:     git
   location: https://github.com/github/semantic-diff

src/Data/RandomWalkSimilarity.hs

@@ -33,7 +33,7 @@ import Diff
 import Info
 import Patch
 import Prologue as P
-import qualified SES
+import SES
 import System.Random.Mersenne.Pure64
 import Term (Term, TermF)
 
@@ -47,7 +47,7 @@ type Label f fields label = forall b. TermF f (Record fields) b -> label
 -- This implementation is based on the paper [_RWS-Diff—Flexible and Efficient Change Detection in Hierarchical Data_](https://github.com/github/semantic-diff/files/325837/RWS-Diff.Flexible.and.Efficient.Change.Detection.in.Hierarchical.Data.pdf).
 rws :: forall f fields.
        (GAlign f, Traversable f, Eq1 f, HasField fields Category, HasField fields (Maybe FeatureVector))
-    => SES.Cost (Term f (Record fields)) -- ^ A function computes a constant-time approximation to the edit distance between two terms.
+    => (These (Term f (Record fields)) (Term f (Record fields)) -> Int) -- ^ A function computes a constant-time approximation to the edit distance between two terms.
     -> (Term f (Record fields) -> Term f (Record fields) -> Bool) -- ^ A relation determining whether two terms can be compared.
     -> [Term f (Record fields)] -- ^ The list of old terms.
     -> [Term f (Record fields)] -- ^ The list of new terms.
@@ -69,7 +69,7 @@ rws editDistance canCompare as bs
 
   where
     minimumTermIndex = pred . maybe 0 getMin . getOption . foldMap (Option . Just . Min . termIndex)
-    sesDiffs = SES.ses (gliftEq (==) `on` fmap category) cost as bs
+    sesDiffs = ses (gliftEq (==) `on` fmap category) as bs
 
     (featurizedAs, featurizedBs, _, _, countersAndDiffs, allDiffs) =
       foldl' (\(as, bs, counterA, counterB, diffs, allDiffs) diff -> case diff of
@@ -151,8 +151,6 @@ rws editDistance canCompare as bs
       diffs
       ((termIndex &&& This . term) <$> unmappedA)
 
-    cost = these (const 1) (const 1) (const (const 0))
-
     kdas = KdTree.build (elems . feature) featurizedAs
     kdbs = KdTree.build (elems . feature) featurizedBs
 

src/SES.hs

@@ -1,53 +1,11 @@
 {-# LANGUAGE Strict #-}
-module SES where
+module SES
+( Comparable
+, Myers.ses
+) where
 
-import Data.Array.MArray
-import Data.Array.ST
-import Data.These
 import Prologue
-
+import qualified SES.Myers as Myers
 
 -- | Edit constructor for two terms, if comparable. Otherwise returns Nothing.
 type Comparable term = term -> term -> Bool
-
--- | A function that computes the cost of an edit.
-type Cost term = These term term -> Int
-
--- | Find the shortest edit script (diff) between two terms given a function to compute the cost.
-ses :: Comparable term -> Cost term -> [term] -> [term] -> [These term term]
-ses canCompare cost as bs = runST $ do
-  array <- newArray ((0, 0), (length bs, length as)) Nothing
-  editScript <- diffAt array canCompare cost (0, 0) as bs
-  pure $ fst <$> editScript
-
--- | Find the shortest edit script between two terms at a given vertex in the edit graph.
-diffAt :: STArray s (Int, Int) (Maybe [(These term term, Int)]) -> Comparable term -> Cost term -> (Int, Int) -> [term] -> [term] -> ST s [(These term term, Int)]
-diffAt array canCompare cost (i, j) as bs
-  | (a : as') <- as, (b : bs') <- bs = do
-  maybeDiff <- readArray array (i, j)
-  case maybeDiff of
-    Just diffs -> pure diffs
-    Nothing -> do
-      down <- recur (i, succ j) as' bs
-      right <- recur (succ i, j) as bs'
-      nomination <- best <$> if canCompare a b
-        then do
-          diagonal <- recur (succ i, succ j) as' bs'
-          pure [ delete a down, insert b right, consWithCost cost (These a b) diagonal ]
-        else pure [ delete a down, insert b right ]
-      writeArray array (i, j) (Just nomination)
-      pure nomination
-  | null as = pure $ foldr insert [] bs
-  | null bs = pure $ foldr delete [] as
-  | otherwise = pure []
-  where
-    delete = consWithCost cost . This
-    insert = consWithCost cost . That
-    costOf [] = 0
-    costOf ((_, c) : _) = c
-    best = minimumBy (comparing costOf)
-    recur = diffAt array canCompare cost
-
--- | Prepend an edit script and the cumulative cost onto the edit script.
-consWithCost :: Cost term -> These term term -> [(These term term, Int)] -> [(These term term, Int)]
-consWithCost cost edit rest = (edit, cost edit + maybe 0 snd (fst <$> uncons rest)) : rest

src/SES/Myers.hs

@@ -0,0 +1,415 @@
+{-# LANGUAGE GADTs, ImplicitParams, MultiParamTypeClasses, ScopedTypeVariables #-}
+module SES.Myers
+( MyersF(..)
+, EditScript
+, Step(..)
+, Myers
+, EditGraph(..)
+, Distance(..)
+, Diagonal(..)
+, Endpoint(..)
+, ses
+, runMyers
+, runMyersSteps
+, lcs
+, editDistance
+, MyersState(..)
+) where
+
+import Control.Exception
+import Control.Monad.Free.Freer
+import qualified Data.Array as Array
+import Data.Ix
+import Data.Functor.Classes
+import Data.String
+import Data.These
+import GHC.Show hiding (show)
+import GHC.Stack
+import Prologue hiding (for, State, error)
+import qualified Prologue
+import Text.Show (showListWith)
+
+-- | Operations in Myers’ algorithm.
+data MyersF a b result where
+  SES :: MyersF a b (EditScript a b)
+  LCS :: MyersF a b [(a, b)]
+  EditDistance :: MyersF a b Int
+  SearchUpToD :: Distance -> MyersF a b (Maybe (EditScript a b, Distance))
+  SearchAlongK :: Distance -> Diagonal -> MyersF a b (Maybe (EditScript a b, Distance))
+  MoveFromAdjacent :: Distance -> Diagonal -> MyersF a b (Endpoint a b)
+  MoveDownFrom :: Endpoint a b -> MyersF a b (Endpoint a b)
+  MoveRightFrom :: Endpoint a b -> MyersF a b (Endpoint a b)
+  SlideFrom :: Endpoint a b -> MyersF a b (Endpoint a b)
+
+  GetK :: Diagonal -> MyersF a b (Endpoint a b)
+  SetK :: Diagonal -> Endpoint a b -> MyersF a b ()
+
+
+-- | An edit script, i.e. a sequence of changes/copies of elements.
+type EditScript a b = [These a b]
+
+-- | Steps in the execution of Myers’ algorithm, i.e. the sum of MyersF and State.
+data Step a b result where
+  M :: HasCallStack => MyersF a b c -> Step a b c
+  S :: State (MyersState a b) c -> Step a b c
+
+type Myers a b = Freer (Step a b)
+
+-- | Notionally the cartesian product of two sequences, represented as a simple wrapper around those arrays holding those sequences’ elements for O(1) lookups.
+data EditGraph a b = EditGraph { as :: !(Array.Array Int a), bs :: !(Array.Array Int b) }
+  deriving (Eq, Show)
+
+-- | Construct an edit graph from Foldable sequences.
+makeEditGraph :: (Foldable t, Foldable u) => t a -> u b -> EditGraph a b
+makeEditGraph as bs = EditGraph (Array.listArray (0, pred (length as)) (toList as)) (Array.listArray (0, pred (length bs)) (toList bs))
+
+-- | An edit distance, i.e. a cardinal number of changes.
+newtype Distance = Distance { unDistance :: Int }
+  deriving (Eq, Show)
+
+-- | A diagonal in the edit graph of lists of lengths n and m, numbered from -m to n.
+newtype Diagonal = Diagonal { unDiagonal :: Int }
+  deriving (Eq, Ix, Ord, Show)
+
+-- | The endpoint of a path through the edit graph, represented as the x/y indices and the script of edits made to get to that point.
+data Endpoint a b = Endpoint { x :: !Int, y :: !Int, script :: !(EditScript a b) }
+  deriving (Eq, Show)
+
+
+-- API
+
+-- | Compute the shortest edit script using Myers’ algorithm.
+ses :: (HasCallStack, Foldable t, Foldable u) => (a -> b -> Bool) -> t a -> u b -> EditScript a b
+ses eq as bs = runMyers eq (makeEditGraph as bs) (M SES `Then` return)
+
+
+-- Evaluation
+
+-- | Fully evaluate an operation in Myers’ algorithm given a comparator function and an edit graph.
+runMyers :: forall a b c. HasCallStack => (a -> b -> Bool) -> EditGraph a b -> Myers a b c -> c
+runMyers eq graph step = evalState (go step) (emptyStateForGraph graph)
+  where go :: forall c. Myers a b c -> Prologue.State (MyersState a b) c
+        go = iterFreerA algebra
+        algebra :: forall c x. Step a b x -> (x -> Prologue.State (MyersState a b) c) -> Prologue.State (MyersState a b) c
+        algebra step cont = case step of
+          M m -> go (decompose' m) >>= cont
+          S Get -> get >>= cont
+          S (Put s) -> put s >>= cont
+        decompose' :: forall c. MyersF a b c -> Myers a b c
+        decompose' = decompose eq graph
+
+-- | Fully evaluate an operation in Myers’ algorithm given a comparator function and an edit graph, returning a list of states and next steps.
+runMyersSteps :: HasCallStack => (a -> b -> Bool) -> EditGraph a b -> Myers a b c -> [(MyersState a b, Myers a b c)]
+runMyersSteps eq graph = go (emptyStateForGraph graph)
+  where go state step = let ?callStack = popCallStack callStack in prefix state step $ case runMyersStep eq graph state step of
+          Left result -> [ (state, return result) ]
+          Right next -> uncurry go next
+        prefix state step = case step of
+          Then (M _) _ -> ((state, step) :)
+          _ -> identity
+
+-- | Evaluate one step in Myers’ algorithm given a comparator function and an edit graph, returning Either the final result, or the next state and step.
+runMyersStep :: HasCallStack => (a -> b -> Bool) -> EditGraph a b -> MyersState a b -> Myers a b c -> Either c (MyersState a b, Myers a b c)
+runMyersStep eq graph state step = let ?callStack = popCallStack callStack in case step of
+  Return a -> Left a
+  Then step cont -> case step of
+    M myers -> Right (state, decompose eq graph myers >>= cont)
+
+    S Get -> Right (state, cont state)
+    S (Put state') -> Right (state', cont ())
+
+
+-- | Decompose an operation in Myers’ algorithm into its continuation.
+--
+--   Dispatches to the per-operation run… functions which implement the meat of the algorithm.
+decompose :: HasCallStack => (a -> b -> Bool) -> EditGraph a b -> MyersF a b c -> Myers a b c
+decompose eq graph myers = let ?callStack = popCallStack callStack in case myers of
+  SES -> runSES graph
+  LCS -> runLCS graph
+  EditDistance -> runEditDistance graph
+  SearchUpToD d -> runSearchUpToD graph d
+  SearchAlongK d k -> runSearchAlongK graph d k
+  MoveFromAdjacent d k -> runMoveFromAdjacent graph d k
+  MoveDownFrom e -> runMoveDownFrom graph e
+  MoveRightFrom e -> runMoveRightFrom graph e
+
+  GetK k -> runGetK graph k
+  SetK k x -> runSetK graph k x
+
+  SlideFrom from -> runSlideFrom eq graph from
+{-# INLINE decompose #-}
+
+
+-- | Compute the shortest edit script (diff) of an edit graph.
+runSES :: HasCallStack => EditGraph a b -> Myers a b (EditScript a b)
+runSES (EditGraph as bs)
+  | null bs = return (This <$> toList as)
+  | null as = return (That <$> toList bs)
+  | otherwise = let ?callStack = popCallStack callStack in do
+    result <- for [0..(length as + length bs)] (searchUpToD . Distance)
+    case result of
+      Just (script, _) -> return (reverse script)
+      _ -> fail "no shortest edit script found in edit graph (this is a bug in SES.Myers)."
+
+-- | Compute the longest common subsequence of an edit graph.
+runLCS :: HasCallStack => EditGraph a b -> Myers a b [(a, b)]
+runLCS (EditGraph as bs)
+  | null as || null bs = return []
+  | otherwise = let ?callStack = popCallStack callStack in do
+    result <- M SES `Then` return
+    return (catMaybes (these (const Nothing) (const Nothing) ((Just .) . (,)) <$> result))
+
+-- | Compute the edit distance of an edit graph.
+runEditDistance :: HasCallStack => EditGraph a b -> Myers a b Int
+runEditDistance _ = let ?callStack = popCallStack callStack in length . filter (these (const True) (const True) (const (const False))) <$> (M SES `Then` return)
+
+
+-- | Search an edit graph for the shortest edit script up to a given proposed edit distance, building on the results of previous searches.
+runSearchUpToD :: HasCallStack => EditGraph a b -> Distance -> Myers a b (Maybe (EditScript a b, Distance))
+runSearchUpToD (EditGraph as bs) (Distance d) = let ?callStack = popCallStack callStack in
+  for [ k | k <- [negate d, negate d + 2 .. d], inRange (negate m, n) k ] (searchAlongK (Distance d) . Diagonal)
+  where (n, m) = (length as, length bs)
+
+-- | Search an edit graph for the shortest edit script along a specific diagonal.
+runSearchAlongK :: HasCallStack => EditGraph a b -> Distance -> Diagonal -> Myers a b (Maybe (EditScript a b, Distance))
+runSearchAlongK (EditGraph as bs) d k = let ?callStack = popCallStack callStack in do
+  Endpoint x y script <- moveFromAdjacent d k
+  if x >= length as && y >= length bs then
+    return (Just (script, d))
+  else
+    return Nothing
+
+-- | Move onto a given diagonal from one of its in-bounds adjacent diagonals (if any), and slide down any diagonal edges eagerly.
+runMoveFromAdjacent :: HasCallStack => EditGraph a b -> Distance -> Diagonal -> Myers a b (Endpoint a b)
+runMoveFromAdjacent (EditGraph as bs) (Distance d) (Diagonal k) = let ?callStack = popCallStack callStack in do
+  let (n, m) = (length as, length bs)
+  from <- if d == 0 || k < negate m || k > n then
+    -- The top-left corner, or otherwise out-of-bounds.
+    return (Endpoint 0 0 [])
+  else if k == negate d || k == negate m then
+    -- The lower/left extent of the search region or edit graph, whichever is smaller.
+    getK (Diagonal (succ k)) >>= moveDownFrom
+  else if k /= d && k /= n then do
+    -- Somewhere in the interior of the search region and edit graph.
+    prev <- getK (Diagonal (pred k))
+    next <- getK (Diagonal (succ k))
+    if x prev < x next then
+      moveDownFrom next
+    else
+      moveRightFrom prev
+  else
+    -- The upper/right extent of the search region or edit graph, whichever is smaller.
+    getK (Diagonal (pred k)) >>= moveRightFrom
+  endpoint <- slideFrom from
+  setK (Diagonal k) endpoint
+  return endpoint
+
+-- | Move downward from a given vertex, inserting the element for the corresponding row.
+runMoveDownFrom :: HasCallStack => EditGraph a b -> Endpoint a b -> Myers a b (Endpoint a b)
+runMoveDownFrom (EditGraph _ bs) (Endpoint x y script) = return (Endpoint x (succ y) (if y < length bs then That (bs ! y) : script else script))
+
+-- | Move rightward from a given vertex, deleting the element for the corresponding column.
+runMoveRightFrom :: HasCallStack => EditGraph a b -> Endpoint a b -> Myers a b (Endpoint a b)
+runMoveRightFrom (EditGraph as _) (Endpoint x y script) = return (Endpoint (succ x) y (if x < length as then This (as ! x) : script else script))
+
+-- | Return the maximum extent reached and path taken along a given diagonal.
+runGetK :: HasCallStack => EditGraph a b -> Diagonal -> Myers a b (Endpoint a b)
+runGetK graph k = let ?callStack = popCallStack callStack in do
+  v <- checkK graph k
+  let (x, script) = v ! k in return (Endpoint x (x - unDiagonal k) script)
+
+-- | Update the maximum extent reached and path taken along a given diagonal.
+runSetK :: HasCallStack => EditGraph a b -> Diagonal -> Endpoint a b -> Myers a b ()
+runSetK graph k (Endpoint x _ script) = let ?callStack = popCallStack callStack in do
+  v <- checkK graph k
+  put (MyersState (v Array.// [(k, (x, script))]))
+
+-- | Slide down any diagonal edges from a given vertex.
+runSlideFrom :: HasCallStack => (a -> b -> Bool) -> EditGraph a b -> Endpoint a b -> Myers a b (Endpoint a b)
+runSlideFrom eq (EditGraph as bs) (Endpoint x y script)
+  | x >= 0, x < length as
+  , y >= 0, y < length bs
+  , a <- as ! x
+  , b <- bs ! y
+  , a `eq` b  = slideFrom  (Endpoint (succ x) (succ y) (These a b : script))
+  | otherwise = return (Endpoint       x        y               script)
+
+
+-- Smart constructors
+
+-- | Compute the longest common subsequence.
+lcs :: HasCallStack => Myers a b [(a, b)]
+lcs = M LCS `Then` return
+
+-- | Compute the edit distance.
+editDistance :: HasCallStack => Myers a b Int
+editDistance = M EditDistance `Then` return
+
+-- | Search an edit graph for the shortest edit script up to a given proposed edit distance, building on the results of previous searches.
+searchUpToD :: HasCallStack => Distance -> Myers a b (Maybe (EditScript a b, Distance))
+searchUpToD distance = M (SearchUpToD distance) `Then` return
+
+-- | Search an edit graph for the shortest edit script along a specific diagonal.
+searchAlongK :: HasCallStack => Distance -> Diagonal -> Myers a b (Maybe (EditScript a b, Distance))
+searchAlongK d k = M (SearchAlongK d k) `Then` return
+
+-- | Move onto a given diagonal from one of its in-bounds adjacent diagonals (if any), and slide down any diagonal edges eagerly.
+moveFromAdjacent :: HasCallStack => Distance -> Diagonal -> Myers a b (Endpoint a b)
+moveFromAdjacent d k = M (MoveFromAdjacent d k) `Then` return
+
+-- | Move downward from a given vertex, inserting the element for the corresponding row.
+moveDownFrom :: HasCallStack => Endpoint a b -> Myers a b (Endpoint a b)
+moveDownFrom e = M (MoveDownFrom e) `Then` return
+
+-- | Move rightward from a given vertex, deleting the element for the corresponding column.
+moveRightFrom :: HasCallStack => Endpoint a b -> Myers a b (Endpoint a b)
+moveRightFrom e = M (MoveRightFrom e) `Then` return
+
+-- | Return the maximum extent reached and path taken along a given diagonal.
+getK :: HasCallStack => Diagonal -> Myers a b (Endpoint a b)
+getK diagonal = M (GetK diagonal) `Then` return
+
+-- | Update the maximum extent reached and path taken along a given diagonal.
+setK :: HasCallStack => Diagonal -> Endpoint a b -> Myers a b ()
+setK diagonal x = M (SetK diagonal x) `Then` return
+
+-- | Slide down any diagonal edges from a given vertex.
+slideFrom :: HasCallStack => Endpoint a b -> Myers a b (Endpoint a b)
+slideFrom from = M (SlideFrom from) `Then` return
+
+
+-- Implementation details
+
+-- | The state stored by Myers’ algorithm; an array of m + n + 1 values indicating the maximum x-index reached and path taken along each diagonal.
+newtype MyersState a b = MyersState { unMyersState :: Array.Array Diagonal (Int, EditScript a b) }
+  deriving (Eq, Show)
+
+-- | State effect used in Myers.
+data State s a where
+  Get :: State s s
+  Put :: s -> State s ()
+
+-- | Compute the empty state of length m + n + 1 for a given edit graph.
+emptyStateForGraph :: EditGraph a b -> MyersState a b
+emptyStateForGraph (EditGraph as bs) = let (n, m) = (length as, length bs) in
+  MyersState (Array.listArray (Diagonal (negate m), Diagonal n) (repeat (0, [])))
+
+-- | Evaluate some function for each value in a list until one returns a value or the list is exhausted.
+for :: [a] -> (a -> Myers c d (Maybe b)) -> Myers c d (Maybe b)
+for all run = foldr (\ a b -> (<|>) <$> run a <*> b) (return Nothing) all
+
+
+-- | Throw a failure. Used to indicate an error in the implementation of Myers’ algorithm.
+fail :: (HasCallStack, Monad m) => String -> m a
+fail s = let ?callStack = fromCallSiteList (filter ((/= "M") . fst) (getCallStack callStack)) in
+  throw (MyersException s callStack)
+
+-- | Bounds-checked indexing of arrays, preserving the call stack.
+(!) :: (HasCallStack, Ix i, Show i) => Array.Array i a -> i -> a
+v ! i | inRange (Array.bounds v) i = v Array.! i
+      | otherwise = let ?callStack = fromCallSiteList (filter ((/= "M") . fst) (getCallStack callStack)) in
+          throw (MyersException ("index " <> show i <> " out of bounds") callStack)
+
+-- | Check that a given diagonal is in-bounds for the edit graph, returning the actual index to use and the state array.
+checkK :: HasCallStack => EditGraph a b -> Diagonal -> Myers a b (Array.Array Diagonal (Int, EditScript a b))
+checkK _ k = let ?callStack = popCallStack callStack in do
+  v <- gets unMyersState
+  unless (inRange (Array.bounds v) k) $ fail ("diagonal " <> show k <> " outside state bounds " <> show (Array.bounds v))
+  return v
+
+
+-- | Lifted showing of arrays.
+liftShowsVector :: Show i => (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> Array.Array i a -> ShowS
+liftShowsVector sp sl d = liftShowsPrec sp sl d . toList
+
+-- | Lifted showing of operations in Myers’ algorithm.
+liftShowsMyersF :: (Int -> a -> ShowS) -> (Int -> b -> ShowS) -> Int -> MyersF a b c -> ShowS
+liftShowsMyersF sp1 sp2 d m = case m of
+  SES -> showString "SES"
+  LCS -> showString "LCS"
+  EditDistance -> showString "EditDistance"
+  SearchUpToD distance -> showsUnaryWith showsPrec "SearchUpToD" d distance
+  SearchAlongK distance diagonal -> showsBinaryWith showsPrec showsPrec "SearchAlongK" d distance diagonal
+  MoveFromAdjacent distance diagonal -> showsBinaryWith showsPrec showsPrec "MoveFromAdjacent" d distance diagonal
+  MoveDownFrom endpoint -> showsUnaryWith (liftShowsEndpoint sp1 sp2) "MoveDownFrom" d endpoint
+  MoveRightFrom endpoint -> showsUnaryWith (liftShowsEndpoint sp1 sp2) "MoveRightFrom" d endpoint
+  GetK diagonal -> showsUnaryWith showsPrec "GetK" d diagonal
+  SetK diagonal v -> showsBinaryWith showsPrec (liftShowsEndpoint sp1 sp2) "SetK" d diagonal v
+  SlideFrom endpoint -> showsUnaryWith (liftShowsEndpoint sp1 sp2) "SlideFrom" d endpoint
+
+-- | Lifted showing of ternary constructors.
+showsTernaryWith :: (Int -> a -> ShowS) -> (Int -> b -> ShowS) -> (Int -> c -> ShowS) -> String -> Int -> a -> b -> c -> ShowS
+showsTernaryWith sp1 sp2 sp3 name d x y z = showParen (d > 10) $
+  showString name . showChar ' ' . sp1 11 x . showChar ' ' . sp2 11 y . showChar ' ' . sp3 11 z
+
+-- | Lifted showing of State.
+liftShowsState :: (Int -> a -> ShowS) -> Int -> State a b -> ShowS
+liftShowsState sp d state = case state of
+  Get -> showString "Get"
+  Put s -> showsUnaryWith sp "Put" d s
+
+-- | Lift value/list showing functions into a showing function for steps in Myers’ algorithm.
+liftShowsStep :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> (Int -> b -> ShowS) -> ([b] -> ShowS) -> Int -> Step a b c -> ShowS
+liftShowsStep sp1 sl1 sp2 sl2 d step = case step of
+  M m -> showsUnaryWith (liftShowsMyersF sp1 sp2) "M" d m
+  S s -> showsUnaryWith (liftShowsState (liftShowsPrec2 sp1 sl1 sp2 sl2)) "S" d s
+
+-- | Lifted showing of These.
+liftShowsThese :: (Int -> a -> ShowS) -> (Int -> b -> ShowS) -> Int -> These a b -> ShowS
+liftShowsThese sa sb d t = case t of
+  This a -> showsUnaryWith sa "This" d a
+  That b -> showsUnaryWith sb "That" d b
+  These a b -> showsBinaryWith sa sb "These" d a b
+
+-- | Lifted showing of edit scripts.
+liftShowsEditScript :: (Int -> a -> ShowS) -> (Int -> b -> ShowS) -> Int -> EditScript a b -> ShowS
+liftShowsEditScript sa sb _ = showListWith (liftShowsThese sa sb 0)
+
+-- | Lifted showing of edit graph endpoints.
+liftShowsEndpoint :: (Int -> a -> ShowS) -> (Int -> b -> ShowS) -> Int -> Endpoint a b -> ShowS
+liftShowsEndpoint sp1 sp2 d (Endpoint x y script) = showsTernaryWith showsPrec showsPrec (liftShowsEditScript sp1 sp2) "Endpoint" d x y script
+
+-- | Exceptions in Myers’ algorithm, along with a description and call stack.
+data MyersException = MyersException String CallStack
+  deriving (Typeable)
+
+
+-- Instances
+
+instance MonadState (MyersState a b) (Myers a b) where
+  get = S Get `Then` return
+  put a = S (Put a) `Then` return
+
+instance Show2 MyersState where
+  liftShowsPrec2 sp1 _ sp2 _ d (MyersState v) = showsUnaryWith showsStateVector "MyersState" d v
+    where showsStateVector = showsWith liftShowsVector (showsWith liftShowsPrec (liftShowsEditScript sp1 sp2))
+          showsWith g f = g f (showListWith (f 0))
+
+instance Show s => Show1 (State s) where
+  liftShowsPrec _ _ = liftShowsState showsPrec
+
+instance Show s => Show (State s a) where
+  showsPrec = liftShowsPrec (const (const identity)) (const identity)
+
+instance Show2 EditGraph where
+  liftShowsPrec2 sp1 sl1 sp2 sl2 d (EditGraph as bs) = showsBinaryWith (liftShowsVector sp1 sl1) (liftShowsVector sp2 sl2) "EditGraph" d as bs
+
+instance Show2 Endpoint where
+  liftShowsPrec2 sp1 _ sp2 _ = liftShowsEndpoint sp1 sp2
+
+instance (Show a, Show b) => Show1 (MyersF a b) where
+  liftShowsPrec _ _ = liftShowsMyersF showsPrec showsPrec
+
+instance (Show a, Show b) => Show (MyersF a b c) where
+  showsPrec = liftShowsMyersF showsPrec showsPrec
+
+instance (Show a, Show b) => Show1 (Step a b) where
+  liftShowsPrec _ _ = liftShowsStep showsPrec showList showsPrec showList
+
+instance (Show a, Show b) => Show (Step a b c) where
+  showsPrec = liftShowsStep showsPrec showList showsPrec showList
+
+instance Exception MyersException
+
+instance Show MyersException where
+  showsPrec _ (MyersException s c) = showString "Exception: " . showString s . showChar '\n' . showString (prettyCallStack c)

test/SES/Myers/Spec.hs

@@ -0,0 +1,25 @@
+module SES.Myers.Spec where
+
+import Data.These
+import Prologue
+import SES.Myers
+import Test.Hspec
+import Test.Hspec.LeanCheck
+
+spec :: Spec
+spec = do
+  describe "ses" $ do
+    prop "returns equal lists in These" $
+      \ as -> (ses (==) as as :: EditScript Char Char) `shouldBe` zipWith These as as
+
+    prop "returns deletions in This" $
+      \ as -> (ses (==) as [] :: EditScript Char Char) `shouldBe` fmap This as
+
+    prop "returns insertions in That" $
+      \ bs -> (ses (==) [] bs :: EditScript Char Char) `shouldBe` fmap That bs
+
+    prop "returns all elements individually for disjoint inputs" $
+      \ as bs -> length (ses (==) ((,) 0 <$> as :: [(Int, Char)]) ((,) 1 <$> bs :: [(Int, Char)])) `shouldBe` length as + length bs
+
+    prop "is lossless w.r.t. both input elements & ordering" $
+      \ as bs -> foldr (\ each (as, bs) -> these (flip (,) bs. (:as)) ((,) as . (:bs)) (\ a b -> (a:as, b:bs)) each) ([], []) (ses (==) as bs :: EditScript Char Char) `shouldBe` (as, bs)

test/Spec.hs

@@ -9,6 +9,7 @@ import qualified SummarySpec
 import qualified InterpreterSpec
 import qualified PatchOutputSpec
 import qualified RangeSpec
+import qualified SES.Myers.Spec
 import qualified SourceSpec
 import qualified TermSpec
 import qualified TOCSpec
@@ -27,6 +28,7 @@ main = hspec . parallel $ do
   describe "Interpreter" InterpreterSpec.spec
   describe "PatchOutput" PatchOutputSpec.spec
   describe "Range" RangeSpec.spec
+  describe "SES.Myers" SES.Myers.Spec.spec
   describe "Source" SourceSpec.spec
   describe "Term" TermSpec.spec
   describe "TOC" TOCSpec.spec

test/fixtures/javascript/class.diffB-A.txt

@@ -2,7 +2,7 @@
   (ExpressionStatements
     (Class
       (Identifier)
-			{+(Assignment(Identifier)(NumberLiteral))+}
+      {+(Assignment(Identifier)(NumberLiteral))+}
       (Method
       { (Identifier)
       ->(Identifier) }

test/fixtures/ruby/math-assignment.diffB-A.txt

@@ -1,8 +1,7 @@
 (Program
-  (OperatorAssignment
+  {-(OperatorAssignment
     (Identifier)
-  { (IntegerLiteral)
+    (IntegerLiteral))-}
-  ->(IntegerLiteral) })
   (OperatorAssignment
     (Identifier)
     (IntegerLiteral))
@@ -14,4 +13,7 @@
     (IntegerLiteral))
   (OperatorAssignment
     (Identifier)
-    (IntegerLiteral)))
+    (IntegerLiteral))
+  {+(OperatorAssignment
+    (Identifier)
+    (IntegerLiteral))+})

vendor/haskell-tree-sitter

@@ -1 +1 @@
-Subproject commit 825bdfaf9488a1be49f8f5d3921cdcd22b7a46cb
+Subproject commit c70bc6dafcbdc572082c46345e6425508ceaf43f