Merge branch 'master' into markdown

2024-12-25 16:02:43 +03:00 · 2016-09-13 10:35:28 -04:00 · 2016-09-13 10:35:28 -04:00 · b4e6e1dbb8
commit b4e6e1dbb8
parent 4533f13973 ed00e99250
24 changed files with 484 additions and 334 deletions
--- a/semantic-diff.cabal
+++ b/semantic-diff.cabal
@ -1,5 +1,5 @@
 name:                semantic-diff
-version:             0.1.0.0
+version:             0.1.0
 synopsis:            Initial project template from stack
 description:         Please see README.md
 homepage:            http://github.com/github/semantic-diff#readme
@ -15,6 +15,7 @@ library
  hs-source-dirs:      src
  exposed-modules:     Algorithm
                     , Alignment
+                     , Arguments
                     , Category
                     , Data.Align.Generic
                     , Data.Bifunctor.Join.Arbitrary
@ -30,6 +31,8 @@ library
                     , Info
                     , Interpreter
                     , Language
+                     , Language.C
+                     , Language.JavaScript
                     , Parser
                     , Patch
                     , Patch.Arbitrary
@ -49,6 +52,7 @@ library
                     , TreeSitter
                     , DiffSummary
                     , Prologue
+                     , Paths_semantic_diff
  build-depends:       aeson
                     , base >= 4.8 && < 5
                     , bifunctors
--- a/src/Alignment.hs
+++ b/src/Alignment.hs
@ -38,15 +38,15 @@ numberedRows = countUp (both 1 1)
        nextLineNumbers from row = modifyJoin (fromThese identity identity) (succ <$ row) <*> from

 -- | Determine whether a line contains any patches.
-hasChanges :: SplitDiff leaf annotation -> Bool
+hasChanges :: (Prologue.Foldable f, Functor f) => SplitDiff f annotation -> Bool
 hasChanges = or . (True <$)

 -- | Align a Diff into a list of Join These SplitDiffs representing the (possibly blank) lines on either side.
-alignDiff :: HasField fields Range => Both (Source Char) -> Diff leaf (Record fields) -> [Join These (SplitDiff leaf (Record fields))]
+alignDiff :: HasField fields Range => Both (Source Char) -> SyntaxDiff leaf fields -> [Join These (SplitSyntaxDiff leaf fields)]
 alignDiff sources diff = iter (alignSyntax (runBothWith ((Join .) . These)) wrap getRange sources) (alignPatch sources <$> diff)

 -- | Align the contents of a patch into a list of lines on the corresponding side(s) of the diff.
-alignPatch :: forall fields leaf. HasField fields Range => Both (Source Char) -> Patch (Term leaf (Record fields)) -> [Join These (SplitDiff leaf (Record fields))]
+alignPatch :: forall fields leaf. HasField fields Range => Both (Source Char) -> Patch (SyntaxTerm leaf fields) -> [Join These (SplitSyntaxDiff leaf fields)]
 alignPatch sources patch = case patch of
  Delete term -> fmap (pure . SplitDelete) <$> alignSyntax' this (fst sources) term
  Insert term -> fmap (pure . SplitInsert) <$> alignSyntax' that (snd sources) term
@ -54,13 +54,13 @@ alignPatch sources patch = case patch of
    (alignSyntax' this (fst sources) term1)
    (alignSyntax' that (snd sources) term2)
  where getRange = characterRange . extract
-        alignSyntax' :: (forall a. Identity a -> Join These a) -> Source Char -> Term leaf (Record fields) -> [Join These (Term leaf (Record fields))]
+        alignSyntax' :: (forall a. Identity a -> Join These a) -> Source Char -> SyntaxTerm leaf fields -> [Join These (SyntaxTerm leaf fields)]
        alignSyntax' side source term = hylo (alignSyntax side cofree getRange (Identity source)) runCofree (Identity <$> term)
        this = Join . This . runIdentity
        that = Join . That . runIdentity

 -- | The Applicative instance f is either Identity or Both. Identity is for Terms in Patches, Both is for Diffs in unchanged portions of the diff.
-alignSyntax :: (Applicative f, HasField fields Range) => (forall a. f a -> Join These a) -> (CofreeF (Syntax leaf) (Record fields) term -> term) -> (term -> Range) -> f (Source Char) -> CofreeF (Syntax leaf) (f (Record fields)) [Join These term] -> [Join These term]
+alignSyntax :: (Applicative f, HasField fields Range) => (forall a. f a -> Join These a) -> (SyntaxTermF leaf fields term -> term) -> (term -> Range) -> f (Source Char) -> TermF (Syntax leaf) (f (Record fields)) [Join These term] -> [Join These term]
 alignSyntax toJoinThese toNode getRange sources (infos :< syntax) = catMaybes $ case syntax of
  Leaf s -> wrapInBranch (const (Leaf s)) <$> alignBranch getRange [] bothRanges
  Syntax.Comment a -> wrapInBranch (const (Syntax.Comment a)) <$> alignBranch getRange [] bothRanges
--- a/src/Arguments.hs
+++ b/src/Arguments.hs
@ -0,0 +1,23 @@
+module Arguments (Arguments(..), args) where
+
+import Data.Functor.Both
+import qualified Prelude as P
+import Prelude
+import qualified Renderer as R
+
+-- | The command line arguments to the application.
+data Arguments = Arguments {
+  format :: R.Format,
+  maybeShas :: Both (Maybe P.String),
+  maybeTimeout :: Maybe Float,
+  output :: Maybe FilePath,
+  filepaths :: [FilePath] }
+  deriving (Show)
+
+args :: String -> String -> [String] -> R.Format -> Arguments
+args sha1 sha2 filePaths format = Arguments { format = format
+                                            , maybeShas = Just <$> both sha1 sha2
+                                            , filepaths = filePaths
+                                            , maybeTimeout = Just 10.0
+                                            , output = Nothing
+                                            }
--- a/src/Diff.hs
+++ b/src/Diff.hs
@ -6,35 +6,39 @@ import Prologue
 import Data.Functor.Foldable as Foldable
 import Data.Functor.Both as Both
 import Data.Mergeable
+import Data.Record
 import Patch
 import Syntax
 import Term

 -- | An annotated series of patches of terms.
-type DiffF leaf annotation = FreeF (CofreeF (Syntax leaf) (Both annotation)) (Patch (Term leaf annotation))
-type Diff a annotation = Free (CofreeF (Syntax a) (Both annotation)) (Patch (Term a annotation))
+type DiffF f annotation = FreeF (TermF f (Both annotation)) (Patch (Term f annotation))
+type Diff f annotation = Free (TermF f (Both annotation)) (Patch (Term f annotation))
+
+type SyntaxDiff leaf fields = Diff (Syntax leaf) (Record fields)
+

 type instance Base (Free f a) = FreeF f a
 instance Functor f => Foldable.Foldable (Free f a) where project = runFree
 instance Functor f => Foldable.Unfoldable (Free f a) where embed = free

-diffSum :: (Patch (Term a annotation) -> Int) -> Diff a annotation -> Int
+diffSum :: (Prologue.Foldable f, Functor f) => (Patch (Term f annotation) -> Int) -> Diff f annotation -> Int
 diffSum patchCost diff = sum $ fmap patchCost diff

 -- | The sum of the node count of the diff’s patches.
-diffCost :: Diff a annotation -> Int
+diffCost :: (Prologue.Foldable f, Functor f) => Diff f annotation -> Int
 diffCost = diffSum $ patchSum termSize

 -- | Merge a diff using a function to provide the Term (in Maybe, to simplify recovery of the before/after state) for every Patch.
-mergeMaybe :: (Patch (Term leaf annotation) -> Maybe (Term leaf annotation)) -> Diff leaf annotation -> Maybe (Term leaf annotation)
+mergeMaybe :: (Functor f, Mergeable f) => (Patch (Term f annotation) -> Maybe (Term f annotation)) -> Diff f annotation -> Maybe (Term f annotation)
 mergeMaybe transform = iter algebra . fmap transform
-  where algebra :: CofreeF (Syntax leaf) (Both annotation) (Maybe (Term leaf annotation)) -> Maybe (Term leaf annotation)
+  where algebra :: Mergeable f => TermF f (Both annotation) (Maybe (Term f annotation)) -> Maybe (Term f annotation)
        algebra (annotations :< syntax) = cofree . (Both.fst annotations :<) <$> sequenceAlt syntax

 -- | Recover the before state of a diff.
-beforeTerm :: Diff leaf annotation -> Maybe (Term leaf annotation)
+beforeTerm :: (Functor f, Mergeable f) => Diff f annotation -> Maybe (Term f annotation)
 beforeTerm = mergeMaybe before

 -- | Recover the after state of a diff.
-afterTerm :: Diff leaf annotation -> Maybe (Term leaf annotation)
+afterTerm :: (Functor f, Mergeable f) => Diff f annotation -> Maybe (Term f annotation)
 afterTerm = mergeMaybe after
--- a/src/Diff/Arbitrary.hs
+++ b/src/Diff/Arbitrary.hs
@ -3,11 +3,13 @@ module Diff.Arbitrary where
 import Diff
 import Data.Bifunctor.Join
 import Data.Bifunctor.Join.Arbitrary ()
+import Data.Functor.Both
 import Data.Functor.Foldable (unfold)
 import Patch
 import Patch.Arbitrary ()
 import Syntax
 import Prologue
+import Term
 import Term.Arbitrary
 import Test.QuickCheck hiding (Fixed)

@ -16,11 +18,11 @@ data ArbitraryDiff leaf annotation
  | ArbitraryPure (Patch (ArbitraryTerm leaf annotation))
  deriving (Show, Eq, Generic)

-unArbitraryDiff :: ArbitraryDiff leaf annotation -> FreeF (CofreeF (Syntax leaf) (Join (,) annotation)) (Patch (ArbitraryTerm leaf annotation)) (ArbitraryDiff leaf annotation)
+unArbitraryDiff :: ArbitraryDiff leaf annotation -> FreeF (TermF (Syntax leaf) (Both annotation)) (Patch (ArbitraryTerm leaf annotation)) (ArbitraryDiff leaf annotation)
 unArbitraryDiff (ArbitraryFree a s) = Free (a :< s)
 unArbitraryDiff (ArbitraryPure p) = Pure p

-toDiff :: ArbitraryDiff leaf annotation -> Diff leaf annotation
+toDiff :: ArbitraryDiff leaf annotation -> Diff (Syntax leaf) annotation
 toDiff = fmap (fmap toTerm) . unfold unArbitraryDiff

 diffOfSize :: (Arbitrary leaf, Arbitrary annotation) => Int -> Gen (ArbitraryDiff leaf annotation)
--- a/src/DiffSummary.hs
+++ b/src/DiffSummary.hs
@ -22,6 +22,25 @@ import qualified Text.PrettyPrint.Leijen.Text as P
 import SourceSpan
 import Source

+data Identifiable a = Identifiable a | Unidentifiable a
+
+isIdentifiable :: (HasCategory leaf, HasField fields Category, HasField fields Range) => SyntaxTerm leaf fields -> Bool
+isIdentifiable term =
+  case unwrap term of
+    S.FunctionCall _ _ -> True
+    S.Function{} -> True
+    S.Assignment{} -> True
+    S.MathAssignment{} -> True
+    S.VarAssignment{} -> True
+    S.SubscriptAccess{} -> True
+    S.Class _ _ _ -> True
+    S.Method _ _ _ -> True
+    S.Leaf _ -> True
+    _ -> False
+
+identifiable :: (HasCategory leaf, HasField fields Category, HasField fields Range) => SyntaxTerm leaf fields -> Identifiable (SyntaxTerm leaf fields)
+identifiable term = if isIdentifiable term then Identifiable term else Unidentifiable term
+
 data DiffInfo = LeafInfo { categoryName :: Text, termName :: Text }
 | BranchInfo { branches :: [ DiffInfo ], categoryName :: Text, branchType :: Branch }
 | ErrorInfo { errorSpan :: SourceSpan, termName :: Text }
@ -35,7 +54,7 @@ data DiffSummary a = DiffSummary {
 } deriving (Eq, Functor, Show, Generic)

 -- Returns a list of diff summary texts given two source blobs and a diff.
-diffSummaries :: (HasCategory leaf, HasField fields Category, HasField fields Range) => Both SourceBlob -> Diff leaf (Record fields) -> [Either Text Text]
+diffSummaries :: (HasCategory leaf, HasField fields Category, HasField fields Range) => Both SourceBlob -> SyntaxDiff leaf fields -> [Either Text Text]
 diffSummaries blobs diff = summaryToTexts =<< diffToDiffSummaries (source <$> blobs) diff

 -- Takes a 'DiffSummary' and returns a list of summary texts representing the LeafInfos
@ -44,7 +63,7 @@ summaryToTexts :: DiffSummary DiffInfo -> [Either Text Text]
 summaryToTexts DiffSummary{..} = runJoin . fmap (show . (P.<> maybeParentContext parentAnnotation)) <$> (Join <$> summaries patch)

 -- Returns a list of 'DiffSummary' given two source blobs and a diff.
-diffToDiffSummaries :: (HasCategory leaf, HasField fields Category, HasField fields Range) => Both (Source Char) -> Diff leaf (Record fields) -> [DiffSummary DiffInfo]
+diffToDiffSummaries :: (HasCategory leaf, HasField fields Category, HasField fields Range) => Both (Source Char) -> SyntaxDiff leaf fields -> [DiffSummary DiffInfo]
 diffToDiffSummaries sources = para $ \diff ->
  let diff' = free (Prologue.fst <$> diff)
      annotateWithCategory :: [(Diff leaf (Record fields), [DiffSummary DiffInfo])] -> [DiffSummary DiffInfo]
@ -85,7 +104,7 @@ toLeafInfos BranchInfo{..} = toLeafInfos =<< branches
 toLeafInfos err@ErrorInfo{} = pure (pretty err)

 -- Returns a text representing a specific term given a source and a term.
-toTermName :: (HasCategory leaf, HasField fields Category, HasField fields Range) => Source Char -> Term leaf (Record fields) -> Text
+toTermName :: forall leaf fields. (HasCategory leaf, HasField fields Category, HasField fields Range) => Source Char -> SyntaxTerm leaf fields -> Text
 toTermName source term = case unwrap term of
  S.AnonymousFunction _ _ -> "anonymous"
  S.Fixed children -> fromMaybe "branch" $ (toCategoryName . category) . extract <$> head children
@ -95,13 +114,13 @@ toTermName source term = case unwrap term of
    (S.MemberAccess{}, S.AnonymousFunction{..}) -> toTermName' identifier
    (_, _) -> toTermName' identifier <> toTermName' value
  S.Function identifier _ _ -> toTermName' identifier
-  S.FunctionCall i _ -> toTermName' i
+  S.FunctionCall i args -> toTermName' i <> "(" <> (intercalate ", " (toArgName <$> args)) <> ")"
  S.MemberAccess base property -> case (unwrap base, unwrap property) of
    (S.FunctionCall{}, S.FunctionCall{}) -> toTermName' base <> "()." <> toTermName' property <> "()"
    (S.FunctionCall{}, _) -> toTermName' base <> "()." <> toTermName' property
    (_, S.FunctionCall{}) -> toTermName' base <> "." <> toTermName' property <> "()"
    (_, _) -> toTermName' base <> "." <> toTermName' property
-  S.MethodCall targetId methodId _ -> toTermName' targetId <> sep <> toTermName' methodId <> "()"
+  S.MethodCall targetId methodId methodParams -> toTermName' targetId <> sep <> toTermName' methodId <> "(" <> (intercalate ", " (toArgName <$> methodParams)) <> ")"
    where sep = case unwrap targetId of
            S.FunctionCall{} -> "()."
            _ -> "."
@ -143,6 +162,10 @@ toTermName source term = case unwrap term of
        termNameFromSource term = termNameFromRange (range term)
        termNameFromRange range = toText $ Source.slice range source
        range = characterRange . extract
+        toArgName :: (HasCategory leaf, HasField fields Category, HasField fields Range) => SyntaxTerm leaf fields -> Text
+        toArgName arg = case identifiable arg of
+                          Identifiable arg -> toTermName' arg
+                          Unidentifiable _ -> "..."

 maybeParentContext :: Maybe (Category, Text) -> Doc
 maybeParentContext = maybe "" (\annotation ->
@ -151,13 +174,12 @@ maybeParentContext = maybe "" (\annotation ->
 toDoc :: Text -> Doc
 toDoc = string . toS

-termToDiffInfo :: (HasCategory leaf, HasField fields Category, HasField fields Range) => Source Char -> Term leaf (Record fields) -> DiffInfo
+termToDiffInfo :: (HasCategory leaf, HasField fields Category, HasField fields Range) => Source Char -> SyntaxTerm leaf fields -> DiffInfo
 termToDiffInfo blob term = case unwrap term of
  Leaf _ -> LeafInfo (toCategoryName term) (toTermName' term)
  S.AnonymousFunction _ _ -> LeafInfo (toCategoryName term) ("anonymous")
  S.Indexed children -> BranchInfo (termToDiffInfo' <$> children) (toCategoryName term) BIndexed
  S.Fixed children -> BranchInfo (termToDiffInfo' <$> children) (toCategoryName term) BFixed
-  S.FunctionCall identifier _ -> LeafInfo (toCategoryName term) (toTermName' identifier)
  S.Ternary ternaryCondition _ -> LeafInfo (toCategoryName term) (toTermName' ternaryCondition)
  S.Function identifier _ _ -> LeafInfo (toCategoryName term) (toTermName' identifier)
  S.Assignment identifier _ -> LeafInfo (toCategoryName term) (toTermName' identifier)
@ -171,22 +193,11 @@ termToDiffInfo blob term = case unwrap term of
  where toTermName' = toTermName blob
        termToDiffInfo' = termToDiffInfo blob

-prependSummary :: (HasCategory leaf, HasField fields Range, HasField fields Category) => Source Char -> Term leaf (Record fields) -> DiffSummary DiffInfo -> DiffSummary DiffInfo
-prependSummary source term summary = if (isNothing $ parentAnnotation summary) && hasIdentifier term
-  then summary { parentAnnotation = Just (category $ extract term, toTermName source term) }
-  else summary
-  where hasIdentifier term = case unwrap term of
-          S.FunctionCall{} -> True
-          S.Function _ _ _ -> True
-          S.Assignment{} -> True
-          S.MathAssignment{} -> True
-          S.MemberAccess{} -> True
-          S.MethodCall{} -> True
-          S.VarAssignment{} -> True
-          S.SubscriptAccess{} -> True
-          S.Class{} -> True
-          S.Method{} -> True
-          _ -> False
+prependSummary :: (HasCategory leaf, HasField fields Range, HasField fields Category) => Source Char -> SyntaxTerm leaf fields -> DiffSummary DiffInfo -> DiffSummary DiffInfo
+prependSummary source term summary =
+  case (parentAnnotation summary, identifiable term) of
+    (Nothing, Identifiable term) -> summary { parentAnnotation = Just (category . extract $ term, toTermName source term) }
+    (_, _) -> summary

 isBranchInfo :: DiffInfo -> Bool
 isBranchInfo info = case info of
@ -259,7 +270,7 @@ instance HasCategory Category where
    C.CommaOperator -> "comma operator"
    C.Empty -> "empty statement"

-instance (HasCategory leaf, HasField fields Category) => HasCategory (Term leaf (Record fields)) where
+instance (HasCategory leaf, HasField fields Category) => HasCategory (SyntaxTerm leaf fields) where
  toCategoryName = toCategoryName . category . extract

 instance Arbitrary Branch where
--- a/src/Diffing.hs
+++ b/src/Diffing.hs
@ -119,7 +119,7 @@ parserForFilepath path blob = decorateTerm termCostDecorator <$> do
   pure $! breakDownLeavesByWord (source blob) parsed

 -- | Replace every string leaf with leaves of the words in the string.
-breakDownLeavesByWord :: (HasField fields Category, HasField fields Range) => Source Char -> Term Text (Record fields) -> Term Text (Record fields)
+breakDownLeavesByWord :: (HasField fields Category, HasField fields Range) => Source Char -> Term (Syntax Text) (Record fields) -> Term (Syntax Text) (Record fields)
 breakDownLeavesByWord source = cata replaceIn
  where
    replaceIn (info :< syntax) = cofree $ info :< syntax'
@ -132,7 +132,7 @@ breakDownLeavesByWord source = cata replaceIn
    -- Some Category constructors should retain their original structure, and not be sliced
    -- into words. This Set represents those Category constructors for which we want to
    -- preserve the original Syntax.
-    preserveSyntax = Set.fromList [Regex, Category.Comment]
+    preserveSyntax = Set.fromList [Regex, Category.Comment, Category.TemplateString]

 -- | Transcode a file to a unicode source.
 transcode :: B1.ByteString -> IO (Source Char)
@ -159,11 +159,11 @@ termCostDecorator :: (Prologue.Foldable f, Functor f) => TermDecorator f a Cost
 termCostDecorator c = 1 + sum (cost <$> tailF c)

 -- | Determine whether two terms are comparable based on the equality of their categories.
-compareCategoryEq :: HasField fields Category => Term leaf (Record fields) -> Term leaf (Record fields) -> Bool
+compareCategoryEq :: Functor f => HasField fields Category => Term f (Record fields) -> Term f (Record fields) -> Bool
 compareCategoryEq = (==) `on` category . extract

 -- | The sum of the node count of the diff’s patches.
-diffCostWithCachedTermCosts :: HasField fields Cost => Diff leaf (Record fields) -> Int
+diffCostWithCachedTermCosts :: Functor f => HasField fields Cost => Diff f (Record fields) -> Int
 diffCostWithCachedTermCosts diff = unCost $ case runFree diff of
  Free (info :< _) -> sum (cost <$> info)
  Pure patch -> sum (cost . extract <$> patch)
--- a/src/Interpreter.hs
+++ b/src/Interpreter.hs
@ -19,23 +19,23 @@ import Syntax as S
 import Term

 -- | Returns whether two terms are comparable
-type Comparable leaf annotation = Term leaf annotation -> Term leaf annotation -> Bool
+type Comparable f annotation = Term f annotation -> Term f annotation -> Bool

 -- | Constructs a diff from the CofreeF containing its annotation and syntax. This function has the opportunity to, for example, cache properties in the annotation.
-type DiffConstructor leaf annotation = CofreeF (Syntax leaf) (Both annotation) (Diff leaf annotation) -> Diff leaf annotation
+type DiffConstructor f annotation = TermF f (Both annotation) (Diff f annotation) -> Diff f annotation

 -- | Diff two terms recursively, given functions characterizing the diffing.
 diffTerms :: (Eq leaf, Eq (Record fields), HasField fields Category, HasField fields (Vector.Vector Double))
-  => DiffConstructor leaf (Record fields) -- ^ A function to wrap up & possibly annotate every produced diff.
-  -> Comparable leaf (Record fields) -- ^ A function to determine whether or not two terms should even be compared.
-  -> SES.Cost (Diff leaf (Record fields)) -- ^ A function to compute the cost of a given diff node.
-  -> Term leaf (Record fields) -- ^ A term representing the old state.
-  -> Term leaf (Record fields) -- ^ A term representing the new state.
-  -> Diff leaf (Record fields)
+  => DiffConstructor (Syntax leaf) (Record fields) -- ^ A function to wrap up & possibly annotate every produced diff.
+  -> Comparable (Syntax leaf) (Record fields) -- ^ A function to determine whether or not two terms should even be compared.
+  -> SES.Cost (SyntaxDiff leaf fields) -- ^ A function to compute the cost of a given diff node.
+  -> SyntaxTerm leaf fields -- ^ A term representing the old state.
+  -> SyntaxTerm leaf fields -- ^ A term representing the new state.
+  -> SyntaxDiff leaf fields
 diffTerms construct comparable cost a b = fromMaybe (replacing a b) $ diffComparableTerms construct comparable cost a b

 -- | Diff two terms recursively, given functions characterizing the diffing. If the terms are incomparable, returns 'Nothing'.
-diffComparableTerms :: (Eq leaf, Eq (Record fields), HasField fields Category, HasField fields (Vector.Vector Double)) => DiffConstructor leaf (Record fields) -> Comparable leaf (Record fields) -> SES.Cost (Diff leaf (Record fields)) -> Term leaf (Record fields) -> Term leaf (Record fields) -> Maybe (Diff leaf (Record fields))
+diffComparableTerms :: (Eq leaf, Eq (Record fields), HasField fields Category, HasField fields (Vector.Vector Double)) => DiffConstructor (Syntax leaf) (Record fields) -> Comparable (Syntax leaf) (Record fields) -> SES.Cost (SyntaxDiff leaf fields) -> SyntaxTerm leaf fields -> SyntaxTerm leaf fields -> Maybe (SyntaxDiff leaf fields)
 diffComparableTerms construct comparable cost = recur
  where recur a b
          | (category <$> a) == (category <$> b) = hylo construct runCofree <$> zipTerms a b
@ -43,7 +43,7 @@ diffComparableTerms construct comparable cost = recur
          | otherwise = Nothing

 -- | Construct an algorithm to diff a pair of terms.
-algorithmWithTerms :: (TermF leaf (Both a) diff -> diff) -> Term leaf a -> Term leaf a -> Algorithm (Term leaf a) diff diff
+algorithmWithTerms :: (TermF (Syntax leaf) (Both a) diff -> diff) -> Term (Syntax leaf) a -> Term (Syntax leaf) a -> Algorithm (Term (Syntax leaf) a) diff diff
 algorithmWithTerms construct t1 t2 = case (unwrap t1, unwrap t2) of
  (Indexed a, Indexed b) -> branch Indexed a b
  (S.FunctionCall identifierA argsA, S.FunctionCall identifierB argsB) -> do
--- a/src/Language.hs
+++ b/src/Language.hs
@ -1,6 +1,13 @@
+{-# LANGUAGE DataKinds #-}
 module Language where

+import Data.Record
+import Info
 import Prologue
+import Source
+import SourceSpan
+import qualified Syntax as S
+import Term

 -- | A programming language.
 data Language =
@ -32,3 +39,17 @@ languageForType mediaType = case mediaType of
    ".md" -> Just Markdown
    ".rb" -> Just Ruby
    _ -> Nothing
+
+termConstructor
+  :: Source Char -- ^ The source that the term occurs within.
+  -> IO SourceSpan -- ^ The span that the term occupies. This is passed in 'IO' to guarantee some access constraints & encourage its use only when needed (improving performance).
+  -> Text -- ^ The name of the production for this node.
+  -> Range -- ^ The character range that the term occupies.
+  -> [Term (S.Syntax Text) (Record '[Range, Category])] -- ^ The child nodes of the term.
+  -> IO (Term (S.Syntax Text) (Record '[Range, Category])) -- ^ The resulting term, in IO.
+termConstructor source sourceSpan name range children =
+  withDefaultInfo <$> case (name, children) of
+    ("ERROR", _) -> S.Error <$> sourceSpan <*> pure children
+    (_, []) -> S.Leaf <$> pure (toText $ slice range source)
+    _ -> S.Indexed <$> pure children
+  where withDefaultInfo syntax = cofree ((range .: Other name .: RNil) :< syntax)
--- a/src/Language/C.hs
+++ b/src/Language/C.hs
@ -0,0 +1,29 @@
+{-# LANGUAGE DataKinds #-}
+module Language.C where
+
+import Data.Record
+import Info
+import Prologue
+import Source
+import SourceSpan
+import Syntax
+import qualified Syntax as S
+import Term
+
+termConstructor
+  :: Source Char -- ^ The source that the term occurs within.
+  -> IO SourceSpan -- ^ The span that the term occupies. This is passed in 'IO' to guarantee some access constraints & encourage its use only when needed (improving performance).
+  -> Text -- ^ The name of the production for this node.
+  -> Range -- ^ The character range that the term occupies.
+  -> [Term (Syntax Text) (Record '[Range, Category])] -- ^ The child nodes of the term.
+  -> IO (Term (Syntax Text) (Record '[Range, Category])) -- ^ The resulting term, in IO.
+termConstructor source sourceSpan name range children
+  | name == "ERROR" = sourceSpan >>= withDefaultInfo . (`S.Error` children)
+  | otherwise = withDefaultInfo $ case (name, children) of
+  (_, []) -> S.Leaf . toText $ slice range source
+  _ -> S.Indexed children
+  where withDefaultInfo syntax = pure $! cofree ((range .: categoryForCProductionName name .: RNil) :< syntax)
+
+categoryForCProductionName :: Text -> Category
+categoryForCProductionName name = case name of
+  _ -> Other name
--- a/src/Language/JavaScript.hs
+++ b/src/Language/JavaScript.hs
@ -0,0 +1,151 @@
+{-# LANGUAGE DataKinds #-}
+module Language.JavaScript where
+
+import Data.Record
+import Info
+import Prologue
+import Source
+import SourceSpan
+import qualified Syntax as S
+import Term
+
+operators :: [Text]
+operators = [ "op", "bool_op", "math_op", "delete_op", "type_op", "void_op", "rel_op", "bitwise_op" ]
+
+functions :: [Text]
+functions = [ "arrow_function", "generator_function", "function" ]
+
+forStatements :: [Text]
+forStatements = [ "for_statement", "for_of_statement", "for_in_statement" ]
+
+termConstructor
+  :: Source Char -- ^ The source that the term occurs within.
+  -> IO SourceSpan -- ^ The span that the term occupies. This is passed in 'IO' to guarantee some access constraints & encourage its use only when needed (improving performance).
+  -> Text -- ^ The name of the production for this node.
+  -> Range -- ^ The character range that the term occupies.
+  -> [Term (S.Syntax Text) (Record '[Range, Category])] -- ^ The child nodes of the term.
+  -> IO (Term (S.Syntax Text) (Record '[Range, Category])) -- ^ The resulting term, in IO.
+termConstructor source sourceSpan name range children
+  | name == "ERROR" = sourceSpan >>= withDefaultInfo . (`S.Error` children)
+  | otherwise = withDefaultInfo $ case (name, children) of
+    ("return_statement", _) -> S.Return (listToMaybe children)
+    ("assignment", [ identifier, value ]) -> S.Assignment identifier value
+    ("math_assignment", [ identifier, value ]) -> S.MathAssignment identifier value
+    ("member_access", [ base, property ]) -> S.MemberAccess base property
+    ("subscript_access", [ base, element ]) -> S.SubscriptAccess base element
+    ("comma_op", [ a, b ]) -> case unwrap b of
+      S.Indexed rest -> S.Indexed $ a : rest
+      _ -> S.Indexed children
+    ("function_call", _) -> case runCofree <$> children of
+      [ (_ :< S.MemberAccess{..}), (_ :< S.Args args) ] -> S.MethodCall memberId property args
+      [ (_ :< S.MemberAccess{..}) ] -> S.MethodCall memberId property []
+      [ function, (_ :< S.Args args) ] -> S.FunctionCall (cofree function) args
+      (x:xs) -> S.FunctionCall (cofree x) (cofree <$> xs)
+      _ -> S.Indexed children
+    ("ternary", (condition:cases)) -> S.Ternary condition cases
+    ("arguments", _) -> S.Args children
+    ("var_assignment", [ x, y ]) -> S.VarAssignment x y
+    ("var_declaration", _) -> S.Indexed $ toVarDecl <$> children
+    ("switch_statement", (expr:rest)) -> S.Switch expr rest
+    ("case", [ expr, body ]) -> S.Case expr body
+    ("object", _) -> S.Object $ foldMap toTuple children
+    ("pair", _) -> S.Fixed children
+    ("if_statement", [ expr, clause1, clause2 ]) -> S.If expr clause1 (Just clause2)
+    ("if_statement", [ expr, clause ]) -> S.If expr clause Nothing
+    ("while_statement", [ expr, body ]) -> S.While expr body
+    ("do_statement", [ expr, body ]) -> S.DoWhile expr body
+    ("throw_statement", [ expr ]) -> S.Throw expr
+    ("new_expression", [ expr ]) -> S.Constructor expr
+    ("try_statement", [ body ]) -> S.Try body Nothing Nothing
+    ("try_statement", [ body, catch ]) | Catch <- category (extract catch) -> S.Try body (Just catch) Nothing
+    ("try_statement", [ body, finally ]) | Finally <- category (extract finally) -> S.Try body Nothing (Just finally)
+    ("try_statement", [ body, catch, finally ])
+      | Catch <- category (extract catch)
+      , Finally <- category (extract finally) -> S.Try body (Just catch) (Just finally)
+    ("array", _) -> S.Array children
+    ("method_definition", [ identifier, params, exprs ]) -> S.Method identifier (toList (unwrap params)) (toList (unwrap exprs))
+    ("method_definition", [ identifier, exprs ]) -> S.Method identifier [] (toList (unwrap exprs))
+    ("class", [ identifier, superclass, definitions ]) -> S.Class identifier (Just superclass) (toList (unwrap definitions))
+    ("class", [ identifier, definitions ]) -> S.Class identifier Nothing (toList (unwrap definitions))
+    _ | name `elem` forStatements, Just (exprs, body) <- unsnoc children -> S.For exprs body
+    _ | name `elem` operators -> S.Operator children
+    _ | name `elem` functions -> case children of
+          [ body ] -> S.AnonymousFunction Nothing body
+          [ params, body ] -> S.AnonymousFunction (Just params) body
+          [ id, params, body ] -> S.Function id (Just params) body
+          _ -> S.Indexed children
+    (_, []) -> S.Leaf . toText $ slice range source
+    _ -> S.Indexed children
+  where withDefaultInfo syntax@(S.MethodCall _ _ _) = pure $! cofree ((range .:  MethodCall .: RNil) :< syntax)
+        withDefaultInfo syntax = pure $! cofree ((range .: categoryForJavaScriptProductionName name .: RNil) :< syntax)
+
+categoryForJavaScriptProductionName :: Text -> Category
+categoryForJavaScriptProductionName name = case name of
+  "object" -> Object
+  "expression_statement" -> ExpressionStatements
+  "this_expression" -> Identifier
+  "null" -> Identifier
+  "undefined" -> Identifier
+  "arrow_function" -> Function
+  "generator_function" -> Function
+  "math_op" -> BinaryOperator -- bitwise operator, e.g. +, -, *, /.
+  "bool_op" -> BinaryOperator -- boolean operator, e.g. ||, &&.
+  "comma_op" -> CommaOperator -- comma operator, e.g. expr1, expr2.
+  "delete_op" -> Operator -- delete operator, e.g. delete x[2].
+  "type_op" -> Operator -- type operator, e.g. typeof Object.
+  "void_op" -> Operator -- void operator, e.g. void 2.
+  "for_in_statement" -> For
+  "for_of_statement" -> For
+  "new_expression" -> Constructor
+  "class"  -> Class
+  "catch" -> Catch
+  "finally" -> Finally
+  "if_statement" -> If
+  "empty_statement" -> Empty
+  "program" -> Program
+  "ERROR" -> Error
+  "function_call" -> FunctionCall
+  "pair" -> Pair
+  "string" -> StringLiteral
+  "integer" -> IntegerLiteral
+  "symbol" -> SymbolLiteral
+  "array" -> ArrayLiteral
+  "function" -> Function
+  "identifier" -> Identifier
+  "formal_parameters" -> Params
+  "arguments" -> Args
+  "statement_block" -> ExpressionStatements
+  "assignment" -> Assignment
+  "member_access" -> MemberAccess
+  "op" -> Operator
+  "subscript_access" -> SubscriptAccess
+  "regex" -> Regex
+  "template_string" -> TemplateString
+  "var_assignment" -> VarAssignment
+  "var_declaration" -> VarDecl
+  "switch_statement" -> Switch
+  "math_assignment" -> MathAssignment
+  "case" -> Case
+  "true" -> Boolean
+  "false" -> Boolean
+  "ternary" -> Ternary
+  "for_statement" -> For
+  "while_statement" -> While
+  "do_statement" -> DoWhile
+  "return_statement" -> Return
+  "throw_statement" -> Throw
+  "try_statement" -> Try
+  "method_definition" -> Method
+  "comment" -> Comment
+  "bitwise_op" -> BitwiseOperator
+  "rel_op" -> RelationalOperator
+  _ -> Other name
+
+toVarDecl :: (HasField fields Category) => Term (S.Syntax Text) (Record fields) -> Term (S.Syntax Text) (Record fields)
+toVarDecl child = cofree $ (setCategory (extract child) VarDecl :< S.VarDecl child)
+
+toTuple :: Term (S.Syntax Text) (Record fields) -> [Term (S.Syntax Text) (Record fields)]
+toTuple child | S.Indexed [key,value] <- unwrap child = [cofree (extract child :< S.Pair key value)]
+toTuple child | S.Fixed [key,value] <- unwrap child = [cofree (extract child :< S.Pair key value)]
+toTuple child | S.Leaf c <- unwrap child = [cofree (extract child :< S.Comment c)]
+toTuple child = pure child
--- a/src/Parser.hs
+++ b/src/Parser.hs
@ -1,148 +1,9 @@
-{-# LANGUAGE ScopedTypeVariables #-}
 module Parser where

-import Prologue hiding (Constructor)
-import Data.Record
-import Data.Text (pack)
-import Category as C
-import Info
-import qualified Syntax as S
-import Term
-import qualified Data.Set as Set
-import Source hiding (uncons)
-import SourceSpan
+import Prologue
+import Source

 -- | A function that takes a source blob and returns an annotated AST.
 -- | The return is in the IO monad because some of the parsers are written in C
 -- | and aren't pure.
 type Parser f a = SourceBlob -> IO (Cofree f a)
-
-- | Whether a category is an Operator Category
-isOperator :: Category -> Bool
-isOperator = flip Set.member (Set.fromList [ Operator, BinaryOperator, BitwiseOperator, RelationalOperator ])
-
-- | Construct a term given source, the span covered, the annotation for the term, and its children.
--
-- This is typically called during parsing, building terms up leaf-to-root.
-termConstructor :: forall fields. (Show (Record fields), HasField fields Category, HasField fields Range)
-  => Source Char -- ^ The source that the term occurs within.
-  -> IO SourceSpan -- ^ The span that the term occupies. This is passed in 'IO' to guarantee some access constraints & encourage its use only when needed (improving performance).
-  -> Record fields -- ^ The annotation for the term.
-  -> [Term Text (Record fields)] -- ^ The child nodes of the term.
-  -> IO (Term Text (Record fields)) -- ^ The resulting term, in IO.
-termConstructor source sourceSpan info = fmap cofree . construct
-  where
-    withDefaultInfo syntax = pure (info :< syntax)
-    errorWith children = do
-      sourceSpan' <- sourceSpan
-      withDefaultInfo (S.Error sourceSpan' children)
-    construct :: (Show (Record fields), HasField fields Category, HasField fields Range) => [Term Text (Record fields)] -> IO (CofreeF (S.Syntax Text) (Record fields) (Term Text (Record fields)))
-    construct [] = case category info of
-      Return -> withDefaultInfo $ S.Return Nothing -- Map empty return statements to Return Nothing
-      _ -> withDefaultInfo . S.Leaf . pack . toString $ slice (characterRange info) source
-    construct children | Return == category info =
-      withDefaultInfo $ S.Return (listToMaybe children)
-    construct children | Assignment == category info = case children of
-      (identifier:value:[]) -> withDefaultInfo $ S.Assignment identifier value
-      children -> errorWith children
-    construct children | MathAssignment == category info = case children of
-      (identifier:value:[]) -> withDefaultInfo $ S.MathAssignment identifier value
-      children -> errorWith children
-    construct children | MemberAccess == category info = case children of
-      (base:property:[]) -> withDefaultInfo $ S.MemberAccess base property
-      children -> errorWith children
-    construct children | SubscriptAccess == category info = case children of
-      (base:element:[]) -> withDefaultInfo $ S.SubscriptAccess base element
-      _ -> errorWith children
-    construct children | isOperator (category info) = withDefaultInfo $ S.Operator children
-    construct children | CommaOperator == category info = withDefaultInfo $ case children of
-      [child, rest] | S.Indexed cs <- unwrap rest -> S.Indexed $ child : toList cs
-      _ -> S.Indexed children
-    construct children | Function == category info = case children of
-      (body:[]) -> withDefaultInfo $ S.AnonymousFunction Nothing body
-      (params:body:[]) | (info :< _) <- runCofree params, Params == category info ->
-        withDefaultInfo $ S.AnonymousFunction (Just params) body
-      (id:body:[]) | (info :< _) <- runCofree id, Identifier == category info ->
-        withDefaultInfo $ S.Function id Nothing body
-      (id:params:body:[]) | (info :< _) <- runCofree id, Identifier == category info ->
-        withDefaultInfo $ S.Function id (Just params) body
-      _ -> errorWith children
-
-    construct children | FunctionCall == category info = case runCofree <$> children of
-      [ (_ :< S.MemberAccess{..}), (_ :< S.Args args) ] ->
-        pure $! setCategory info MethodCall :< S.MethodCall memberId property args
-      [ (_ :< S.MemberAccess{..}) ] ->
-        pure $! setCategory info MethodCall :< S.MethodCall memberId property []
-      (x:xs) ->
-        withDefaultInfo $ S.FunctionCall (cofree x) (cofree <$> xs)
-      _ -> errorWith children
-
-    construct children | Ternary == category info = case children of
-      (condition:cases) -> withDefaultInfo $ S.Ternary condition cases
-      _ -> errorWith children
-    construct children | Args == category info = withDefaultInfo $ S.Args children
-    construct children | VarAssignment == category info
-                         , [x, y] <- children = withDefaultInfo $ S.VarAssignment x y
-    construct children | VarDecl == category info = withDefaultInfo . S.Indexed $ toVarDecl <$> children
-      where
-        toVarDecl :: (HasField fields Category) => Term Text (Record fields) -> Term Text (Record fields)
-        toVarDecl child = cofree $ (setCategory (extract child) VarDecl :< S.VarDecl child)
-
-    construct children | Switch == category info, (expr:_) <- children =
-      withDefaultInfo $ S.Switch expr children
-
-    construct children | Case == category info, [expr, body] <- children =
-      withDefaultInfo $ S.Case expr body
-
-    construct children | Object == category info = withDefaultInfo . S.Object $ foldMap toTuple children
-      where
-        toTuple :: Term Text (Record fields) -> [Term Text (Record fields)]
-        toTuple child | S.Indexed [key,value] <- unwrap child = [cofree (extract child :< S.Pair key value)]
-        toTuple child | S.Fixed [key,value] <- unwrap child = [cofree (extract child :< S.Pair key value)]
-        toTuple child | S.Leaf c <- unwrap child = [cofree (extract child :< S.Comment c)]
-        toTuple child = pure child
-
-    construct children | Pair == (category info) = withDefaultInfo $ S.Fixed children
-    construct children | C.Error == category info =
-      errorWith children
-    construct children | If == category info, Just (expr, clauses) <- uncons children =
-      case clauses of
-        [clause1, clause2] -> withDefaultInfo $ S.If expr clause1 (Just clause2)
-        [clause] -> withDefaultInfo $ S.If expr clause Nothing
-        _ -> errorWith children
-    construct children | For == category info, Just (exprs, body) <- unsnoc children =
-      withDefaultInfo $ S.For exprs body
-    construct children | While == category info, [expr, body] <- children =
-      withDefaultInfo $ S.While expr body
-    construct children | DoWhile == category info, [expr, body] <- children =
-      withDefaultInfo $ S.DoWhile expr body
-    construct children | Throw == category info, [expr] <- children =
-      withDefaultInfo $ S.Throw expr
-    construct children | Constructor == category info, [expr] <- children =
-      withDefaultInfo $ S.Constructor expr
-    construct children | Try == category info = case children of
-      [body] -> withDefaultInfo $ S.Try body Nothing Nothing
-      [body, catch] | Catch <- category (extract catch) -> withDefaultInfo $ S.Try body (Just catch) Nothing
-      [body, finally] | Finally <- category (extract finally) -> withDefaultInfo $ S.Try body Nothing (Just finally)
-      [body, catch, finally] | Catch <- category (extract catch),
-                               Finally <- category (extract finally) ->
-        withDefaultInfo $ S.Try body (Just catch) (Just finally)
-      _ -> errorWith children
-    construct children | ArrayLiteral == category info =
-      withDefaultInfo $ S.Array children
-    construct children | Method == category info = case children of
-      [identifier, params, exprs] |
-        Params == category (extract params),
-        S.Indexed params' <- unwrap params ->
-          withDefaultInfo $ S.Method identifier params' (toList (unwrap exprs))
-      [identifier, exprs] ->
-        withDefaultInfo $ S.Method identifier mempty (toList (unwrap exprs))
-      _ -> errorWith children
-    construct children | Class == category info = case children of
-      [identifier, superclass, definitions] ->
-        withDefaultInfo $ S.Class identifier (Just superclass) (toList (unwrap definitions))
-      [identifier, definitions] ->
-        withDefaultInfo $ S.Class identifier Nothing (toList (unwrap definitions))
-      _ -> errorWith children
-    construct children =
-      withDefaultInfo $ S.Indexed children
--- a/src/Renderer.hs
+++ b/src/Renderer.hs
@ -1,16 +1,17 @@
 module Renderer (Renderer, DiffArguments(..), Output(..), concatOutputs, toSummaryKey, Format(..)) where

-import Prologue
-import Data.Functor.Both
-import Diff
-import Source (SourceBlob)
-import Data.Text as T (intercalate)
 import Data.Aeson (Value, toEncoding)
 import Data.Aeson.Encoding (encodingToLazyByteString)
+import Data.Functor.Both
 import Data.Map as Map hiding (null)
+import Data.Text as T (intercalate)
+import Diff
+import Prologue
+import Source (SourceBlob)
+import Syntax

 -- | A function that will render a diff, given the two source blobs.
-type Renderer annotation = Both SourceBlob -> Diff Text annotation -> Output
+type Renderer annotation = Both SourceBlob -> Diff (Syntax Text) annotation -> Output

 data DiffArguments = DiffArguments { format :: Format, output :: Maybe FilePath, outputPath :: FilePath }
 deriving (Show)
--- a/src/Renderer/JSON.hs
+++ b/src/Renderer/JSON.hs
@ -32,7 +32,7 @@ json blobs diff = JSONOutput $ Map.fromList [
 -- | A numbered 'a'.
 newtype NumberedLine a = NumberedLine (Int, a)

-instance (HasField fields Category, HasField fields Range) => ToJSON (NumberedLine (SplitDiff leaf (Record fields))) where
+instance (HasField fields Category, HasField fields Range) => ToJSON (NumberedLine (SplitSyntaxDiff leaf fields)) where
  toJSON (NumberedLine (n, a)) = object (lineFields n a (getRange a))
  toEncoding (NumberedLine (n, a)) = pairs $ mconcat (lineFields n a (getRange a))
 instance ToJSON Category where
@ -46,18 +46,18 @@ instance ToJSON a => ToJSON (Join These a) where
  toEncoding = foldable
 instance ToJSON a => ToJSON (Join (,) a) where
  toJSON (Join (a, b)) = A.Array . Vector.fromList $ toJSON <$> [ a, b ]
-instance (HasField fields Category, HasField fields Range) => ToJSON (SplitDiff leaf (Record fields)) where
+instance (HasField fields Category, HasField fields Range) => ToJSON (SplitSyntaxDiff leaf fields) where
  toJSON splitDiff = case runFree splitDiff of
    (Free (info :< syntax)) -> object (termFields info syntax)
    (Pure patch)            -> object (patchFields patch)
  toEncoding splitDiff = case runFree splitDiff of
    (Free (info :< syntax)) -> pairs $ mconcat (termFields info syntax)
    (Pure patch)            -> pairs $ mconcat (patchFields patch)
-instance (HasField fields Category, HasField fields Range) => ToJSON (Term leaf (Record fields)) where
+instance (HasField fields Category, HasField fields Range) => ToJSON (SyntaxTerm leaf fields) where
  toJSON term     | (info :< syntax) <- runCofree term = object (termFields info syntax)
  toEncoding term | (info :< syntax) <- runCofree term = pairs $ mconcat (termFields info syntax)

-lineFields :: (HasField fields Category, HasField fields Range) => KeyValue kv => Int -> SplitDiff leaf (Record fields) -> Range -> [kv]
+lineFields :: (HasField fields Category, HasField fields Range) => KeyValue kv => Int -> SplitSyntaxDiff leaf fields -> Range -> [kv]
 lineFields n term range = [ "number" .= n
                          , "terms" .= [ term ]
                          , "range" .= range
@ -102,7 +102,7 @@ termFields info syntax = "range" .= characterRange info : "category" .= category
  S.Method identifier params definitions -> [ "methodIdentifier" .= identifier ] <> [ "params" .= params ] <> [ "definitions" .= definitions ]
  where childrenFields c = [ "children" .= c ]

-patchFields :: (KeyValue kv, HasField fields Category, HasField fields Range) => SplitPatch (Term leaf (Record fields)) -> [kv]
+patchFields :: (KeyValue kv, HasField fields Category, HasField fields Range) => SplitPatch (SyntaxTerm leaf fields) -> [kv]
 patchFields patch = case patch of
  SplitInsert term -> fields "insert" term
  SplitDelete term -> fields "delete" term
--- a/src/Renderer/Patch.hs
+++ b/src/Renderer/Patch.hs
@ -53,7 +53,7 @@ rowIncrement :: Join These a -> Both (Sum Int)
 rowIncrement = Join . fromThese (Sum 0) (Sum 0) . runJoin . (Sum 1 <$)

 -- | Given the before and after sources, render a hunk to a string.
-showHunk :: HasField fields Range => Both SourceBlob -> Hunk (SplitDiff a (Record fields)) -> String
+showHunk :: Functor f => HasField fields Range => Both SourceBlob -> Hunk (SplitDiff f (Record fields)) -> String
 showHunk blobs hunk = maybeOffsetHeader <>
  concat (showChange sources <$> changes hunk) <>
  showLines (snd sources) ' ' (maybeSnd . runJoin <$> trailingContext hunk)
@ -66,18 +66,18 @@ showHunk blobs hunk = maybeOffsetHeader <>
        (offsetA, offsetB) = runJoin . fmap (show . getSum) $ offset hunk

 -- | Given the before and after sources, render a change to a string.
-showChange :: HasField fields Range => Both (Source Char) -> Change (SplitDiff a (Record fields)) -> String
+showChange :: Functor f => HasField fields Range => Both (Source Char) -> Change (SplitDiff f (Record fields)) -> String
 showChange sources change = showLines (snd sources) ' ' (maybeSnd . runJoin <$> context change) <> deleted <> inserted
  where (deleted, inserted) = runJoin $ pure showLines <*> sources <*> both '-' '+' <*> Join (unzip (fromThese Nothing Nothing . runJoin . fmap Just <$> contents change))

 -- | Given a source, render a set of lines to a string with a prefix.
-showLines :: HasField fields Range => Source Char -> Char -> [Maybe (SplitDiff leaf (Record fields))] -> String
+showLines :: Functor f => HasField fields Range => Source Char -> Char -> [Maybe (SplitDiff f (Record fields))] -> String
 showLines source prefix lines = fromMaybe "" . mconcat $ fmap prepend . showLine source <$> lines
  where prepend "" = ""
        prepend source = prefix : source

 -- | Given a source, render a line to a string.
-showLine :: HasField fields Range => Source Char -> Maybe (SplitDiff leaf (Record fields)) -> Maybe String
+showLine :: Functor f => HasField fields Range => Source Char -> Maybe (SplitDiff f (Record fields)) -> Maybe String
 showLine source line | Just line <- line = Just . toString . (`slice` source) $ getRange line
                     | otherwise = Nothing

@ -116,7 +116,7 @@ emptyHunk :: Hunk (SplitDiff a annotation)
 emptyHunk = Hunk { offset = mempty, changes = [], trailingContext = [] }

 -- | Render a diff as a series of hunks.
-hunks :: HasField fields Range => Diff a (Record fields) -> Both SourceBlob -> [Hunk (SplitDiff a (Record fields))]
+hunks :: HasField fields Range => SyntaxDiff leaf fields -> Both SourceBlob -> [Hunk (SplitSyntaxDiff leaf fields)]
 hunks _ blobs | sources <- source <$> blobs
              , sourcesEqual <- runBothWith (==) sources
              , sourcesNull <- runBothWith (&&) (null <$> sources)
@ -126,14 +126,14 @@ hunks diff blobs = hunksInRows (pure 1) $ alignDiff (source <$> blobs) diff

 -- | Given beginning line numbers, turn rows in a split diff into hunks in a
 -- | patch.
-hunksInRows :: Both (Sum Int) -> [Join These (SplitDiff a annotation)] -> [Hunk (SplitDiff a annotation)]
+hunksInRows :: (Prologue.Foldable f, Functor f) => Both (Sum Int) -> [Join These (SplitDiff f annotation)] -> [Hunk (SplitDiff f annotation)]
 hunksInRows start rows = case nextHunk start rows of
  Nothing -> []
  Just (hunk, rest) -> hunk : hunksInRows (offset hunk <> hunkLength hunk) rest

 -- | Given beginning line numbers, return the next hunk and the remaining rows
 -- | of the split diff.
-nextHunk :: Both (Sum Int) -> [Join These (SplitDiff a annotation)] -> Maybe (Hunk (SplitDiff a annotation), [Join These (SplitDiff a annotation)])
+nextHunk :: (Prologue.Foldable f, Functor f) => Both (Sum Int) -> [Join These (SplitDiff f annotation)] -> Maybe (Hunk (SplitDiff f annotation), [Join These (SplitDiff f annotation)])
 nextHunk start rows = case nextChange start rows of
  Nothing -> Nothing
  Just (offset, change, rest) -> let (changes, rest') = contiguousChanges rest in Just (Hunk offset (change : changes) $ take 3 rest', drop 3 rest')
@ -145,7 +145,7 @@ nextHunk start rows = case nextChange start rows of

 -- | Given beginning line numbers, return the number of lines to the next
 -- | the next change, and the remaining rows of the split diff.
-nextChange :: Both (Sum Int) -> [Join These (SplitDiff a annotation)] -> Maybe (Both (Sum Int), Change (SplitDiff a annotation), [Join These (SplitDiff a annotation)])
+nextChange :: (Prologue.Foldable f, Functor f) => Both (Sum Int) -> [Join These (SplitDiff f annotation)] -> Maybe (Both (Sum Int), Change (SplitDiff f annotation), [Join These (SplitDiff f annotation)])
 nextChange start rows = case changeIncludingContext leadingContext afterLeadingContext of
  Nothing -> Nothing
  Just (change, afterChanges) -> Just (start <> mconcat (rowIncrement <$> skippedContext), change, afterChanges)
@ -155,12 +155,12 @@ nextChange start rows = case changeIncludingContext leadingContext afterLeadingC
 -- | Return a Change with the given context and the rows from the begginning of
 -- | the given rows that have changes, or Nothing if the first row has no
 -- | changes.
-changeIncludingContext :: [Join These (SplitDiff a annotation)] -> [Join These (SplitDiff a annotation)] -> Maybe (Change (SplitDiff a annotation), [Join These (SplitDiff a annotation)])
+changeIncludingContext :: (Prologue.Foldable f, Functor f) => [Join These (SplitDiff f annotation)] -> [Join These (SplitDiff f annotation)] -> Maybe (Change (SplitDiff f annotation), [Join These (SplitDiff f annotation)])
 changeIncludingContext leadingContext rows = case changes of
  [] -> Nothing
  _ -> Just (Change leadingContext changes, afterChanges)
  where (changes, afterChanges) = span rowHasChanges rows

 -- | Whether a row has changes on either side.
-rowHasChanges :: Join These (SplitDiff a annotation) -> Bool
+rowHasChanges :: (Prologue.Foldable f, Functor f) => Join These (SplitDiff f annotation) -> Bool
 rowHasChanges row = or (hasChanges <$> row)
--- a/src/Renderer/Split.hs
+++ b/src/Renderer/Split.hs
@ -77,6 +77,7 @@ styleName category = "category-" <> case category of
  C.Method -> "method"
  C.If -> "if_statement"
  C.Empty -> "empty_statement"
+  C.CommaOperator -> "comma_operator"
  Other string -> string

 -- | Pick the class name for a split patch.
@ -141,15 +142,15 @@ wrapIn f p = f p

 -- Instances

-instance (ToMarkup f, HasField fields Category, HasField fields Cost, HasField fields Range) => ToMarkup (Renderable (CofreeF (Syntax leaf) (Record fields) (f, Range))) where
+instance (ToMarkup f, HasField fields Category, HasField fields Cost, HasField fields Range) => ToMarkup (Renderable (SyntaxTermF leaf fields (f, Range))) where
  toMarkup (Renderable source (info :< syntax)) = classifyMarkup (category info) $ case syntax of
    Leaf _ -> span . string . toString $ slice (characterRange info) source
    _ -> ul . mconcat $ wrapIn li <$> contentElements source (characterRange info) (toList syntax)

-instance (HasField fields Category, HasField fields Cost, HasField fields Range) => ToMarkup (Renderable (Term leaf (Record fields))) where
+instance (HasField fields Category, HasField fields Cost, HasField fields Range) => ToMarkup (Renderable (SyntaxTerm leaf fields)) where
  toMarkup (Renderable source term) = Prologue.fst $ cata (\ t -> (toMarkup $ Renderable source t, characterRange (headF t))) term

-instance (HasField fields Category, HasField fields Cost, HasField fields Range) => ToMarkup (Renderable (SplitDiff leaf (Record fields))) where
+instance (HasField fields Category, HasField fields Cost, HasField fields Range) => ToMarkup (Renderable (SplitSyntaxDiff leaf fields)) where
  toMarkup (Renderable source diff) = Prologue.fst . iter (\ t -> (toMarkup $ Renderable source t, characterRange (headF t))) $ toMarkupAndRange <$> diff
    where toMarkupAndRange patch = let term@(info :< _) = runCofree $ getSplitTerm patch in
            ((div ! patchAttribute patch `withCostAttribute` cost info) . toMarkup $ Renderable source (cofree term), characterRange info)
--- a/src/SplitDiff.hs
+++ b/src/SplitDiff.hs
@ -4,7 +4,7 @@ import Data.Record
 import Info
 import Prologue
 import Syntax
-import Term (Term)
+import Term (Term, TermF)

 -- | A patch to only one side of a diff.
 data SplitPatch a = SplitInsert a | SplitDelete a | SplitReplace a
@ -17,10 +17,11 @@ getSplitTerm (SplitDelete a) = a
 getSplitTerm (SplitReplace a) = a

 -- | Get the range of a SplitDiff.
-getRange :: HasField fields Range => SplitDiff leaf (Record fields) -> Range
+getRange :: Functor f => HasField fields Range => SplitDiff f (Record fields) -> Range
 getRange diff = characterRange $ case runFree diff of
  Free annotated -> headF annotated
  Pure patch -> extract (getSplitTerm patch)

 -- | A diff with only one side’s annotations.
-type SplitDiff leaf annotation = Free (CofreeF (Syntax leaf) annotation) (SplitPatch (Term leaf annotation))
+type SplitDiff f annotation = Free (TermF f annotation) (SplitPatch (Term f annotation))
+type SplitSyntaxDiff leaf fields = SplitDiff (Syntax leaf) (Record fields)
--- a/src/Term.hs
+++ b/src/Term.hs
@ -6,36 +6,40 @@ import Prologue
 import Data.Align.Generic
 import Data.Functor.Foldable as Foldable
 import Data.Functor.Both
+import Data.Record
 import Data.These
 import Syntax

 -- | An annotated node (Syntax) in an abstract syntax tree.
-type TermF a annotation = CofreeF (Syntax a) annotation
-type Term a annotation = Cofree (Syntax a) annotation
+type TermF = CofreeF
+type Term f = Cofree f

-type instance Base (Cofree f a) = CofreeF f a
-instance Functor f => Foldable.Foldable (Cofree f a) where project = runCofree
-instance Functor f => Foldable.Unfoldable (Cofree f a) where embed = cofree
+type SyntaxTermF leaf fields = TermF (Syntax leaf) (Record fields)
+type SyntaxTerm leaf fields = Term (Syntax leaf) (Record fields)
+
+type instance Base (Term f a) = TermF f a
+instance Functor f => Foldable.Foldable (Term f a) where project = runCofree
+instance Functor f => Foldable.Unfoldable (Term f a) where embed = cofree

 -- | Zip two terms by combining their annotations into a pair of annotations.
 -- | If the structure of the two terms don't match, then Nothing will be returned.

-zipTerms :: (Eq a, Eq annotation) => Term a annotation -> Term a annotation -> Maybe (Term a (Both annotation))
+zipTerms :: (Eq annotation, Traversable f, GAlign f) => Term f annotation -> Term f annotation -> Maybe (Term f (Both annotation))
 zipTerms t1 t2 = iter go (alignCofreeWith galign (const Nothing) both (These t1 t2))
  where go (a :< s) = cofree . (a :<) <$> sequenceA s

 -- | Return the node count of a term.
-termSize :: (Prologue.Foldable f, Functor f) => Cofree f annotation -> Int
+termSize :: (Prologue.Foldable f, Functor f) => Term f annotation -> Int
 termSize = cata size where
  size (_ :< syntax) = 1 + sum syntax

 -- | Aligns (zips, retaining non-overlapping portions of the structure) a pair of terms.
 alignCofreeWith :: Functor f
  => (forall a b. f a -> f b -> Maybe (f (These a b))) -- ^ A function comparing a pair of structures, returning `Just` the combined structure if they are comparable (e.g. if they have the same constructor), and `Nothing` otherwise. The 'Data.Align.Generic.galign' function is usually what you want here.
-  -> (These (Cofree f a) (Cofree f b) -> contrasted) -- ^ A function mapping a 'These' of incomparable terms into 'Pure' values in the resulting tree.
+  -> (These (Term f a) (Term f b) -> contrasted) -- ^ A function mapping a 'These' of incomparable terms into 'Pure' values in the resulting tree.
  -> (a -> b -> combined) -- ^ A function mapping the input terms’ annotations into annotations in the 'Free' values in the resulting tree.
-  -> These (Cofree f a) (Cofree f b) -- ^ The input terms.
-  -> Free (CofreeF f combined) contrasted
+  -> These (Term f a) (Term f b) -- ^ The input terms.
+  -> Free (TermF f combined) contrasted
 alignCofreeWith compare contrast combine = go
  where go terms = fromMaybe (pure (contrast terms)) $ case terms of
          These t1 t2 -> wrap . (combine (extract t1) (extract t2) :<) . fmap go <$> compare (unwrap t1) (unwrap t2)
--- a/src/Term/Arbitrary.hs
+++ b/src/Term/Arbitrary.hs
@ -11,10 +11,10 @@ import Test.QuickCheck hiding (Fixed)
 data ArbitraryTerm leaf annotation = ArbitraryTerm { annotation :: annotation, syntax :: Syntax leaf (ArbitraryTerm leaf annotation)}
  deriving (Show, Eq, Generic)

-unArbitraryTerm :: ArbitraryTerm leaf annotation -> TermF leaf annotation (ArbitraryTerm leaf annotation)
+unArbitraryTerm :: ArbitraryTerm leaf annotation -> TermF (Syntax leaf) annotation (ArbitraryTerm leaf annotation)
 unArbitraryTerm (ArbitraryTerm a s) = a :< s

-toTerm :: ArbitraryTerm leaf annotation -> Term leaf annotation
+toTerm :: ArbitraryTerm leaf annotation -> Term (Syntax leaf) annotation
 toTerm = unfold unArbitraryTerm

 termOfSize :: (Arbitrary leaf, Arbitrary annotation) => Int -> Gen (ArbitraryTerm leaf annotation)
@ -26,7 +26,7 @@ arbitraryTermSize = cata (succ . sum) . toTerm

 -- Instances

-type instance Base (ArbitraryTerm leaf annotation) = TermF leaf annotation
+type instance Base (ArbitraryTerm leaf annotation) = TermF (Syntax leaf) annotation
 instance Unfoldable (ArbitraryTerm leaf annotation) where embed (a :< s) = ArbitraryTerm a s

 instance (Eq leaf, Eq annotation, Arbitrary leaf, Arbitrary annotation) => Arbitrary (ArbitraryTerm leaf annotation) where
--- a/src/TreeSitter.hs
+++ b/src/TreeSitter.hs
@ -1,11 +1,13 @@
 {-# LANGUAGE DataKinds #-}
-module TreeSitter where
+module TreeSitter (treeSitterParser) where

 import Prologue hiding (Constructor)
 import Control.Monad
 import Category
 import Data.Record
 import Language
+import qualified Language.JavaScript as JS
+import qualified Language.C as C
 import Parser
 import Range
 import Source
@ -29,97 +31,32 @@ treeSitterParser language grammar blob = do
    ts_document_free document
    pure term)

-- Given a language and a node name, return the correct categories.
-categoriesForLanguage :: Language -> Text -> Category
-categoriesForLanguage language name = case (language, name) of
-  (JavaScript, "object") -> Object
-  (JavaScript, "expression_statement") -> ExpressionStatements
-  (JavaScript, "this_expression") -> Identifier
-  (JavaScript, "null") -> Identifier
-  (JavaScript, "undefined") -> Identifier
-  (JavaScript, "arrow_function") -> Function
-  (JavaScript, "generator_function") -> Function
-  (JavaScript, "math_op") -> BinaryOperator -- bitwise operator, e.g. +, -, *, /.
-  (JavaScript, "bool_op") -> BinaryOperator -- boolean operator, e.g. ||, &&.
-  (JavaScript, "comma_op") -> CommaOperator -- comma operator, e.g. expr1, expr2.
-  (JavaScript, "delete_op") -> Operator -- delete operator, e.g. delete x[2].
-  (JavaScript, "type_op") -> Operator -- type operator, e.g. typeof Object.
-  (JavaScript, "void_op") -> Operator -- void operator, e.g. void 2.
-  (JavaScript, "for_in_statement") -> For
-  (JavaScript, "for_of_statement") -> For
-  (JavaScript, "new_expression") -> Constructor
-  (JavaScript, "class")  -> Class
-  (JavaScript, "catch") -> Catch
-  (JavaScript, "finally") -> Finally
-  (JavaScript, "if_statement") -> If
-  (JavaScript, "empty_statement") -> Empty
-
-  (Ruby, "hash") -> Object
-  _ -> defaultCategoryForNodeName name
-{-# INLINE categoriesForLanguage #-}
-
-- | Given a node name from TreeSitter, return the correct categories.
-defaultCategoryForNodeName :: Text -> Category
-defaultCategoryForNodeName name = case name of
-  "program" -> Program
-  "ERROR" -> Error
-  "function_call" -> FunctionCall
-  "pair" -> Pair
-  "string" -> StringLiteral
-  "integer" -> IntegerLiteral
-  "symbol" -> SymbolLiteral
-  "array" -> ArrayLiteral
-  "function" -> Function
-  "identifier" -> Identifier
-  "formal_parameters" -> Params
-  "arguments" -> Args
-  "statement_block" -> ExpressionStatements
-  "assignment" -> Assignment
-  "member_access" -> MemberAccess
-  "op" -> Operator
-  "subscript_access" -> SubscriptAccess
-  "regex" -> Regex
-  "template_string" -> TemplateString
-  "var_assignment" -> VarAssignment
-  "var_declaration" -> VarDecl
-  "switch_statement" -> Switch
-  "math_assignment" -> MathAssignment
-  "case" -> Case
-  "true" -> Boolean
-  "false" -> Boolean
-  "ternary" -> Ternary
-  "for_statement" -> For
-  "while_statement" -> While
-  "do_statement" -> DoWhile
-  "return_statement" -> Return
-  "throw_statement" -> Throw
-  "try_statement" -> Try
-  "method_definition" -> Method
-  "comment" -> Comment
-  "bitwise_op" -> BitwiseOperator
-  "rel_op" -> RelationalOperator
-  _ -> Other name
-{-# INLINE defaultCategoryForNodeName #-}
-
 -- | Return a parser for a tree sitter language & document.
 documentToTerm :: Language -> Ptr Document -> Parser (Syntax.Syntax Text) (Record '[Range, Category])
-documentToTerm language document blob = alloca $ \ root -> do
+documentToTerm language document SourceBlob{..} = alloca $ \ root -> do
  ts_document_root_node_p document root
  toTerm root
  where toTerm node = do
          name <- ts_node_p_name node document
          name <- peekCString name
          count <- ts_node_p_named_child_count node
-          children <- traverse (alloca . getChild node) $ take (fromIntegral count) [0..]
+          children <- filter isNonEmpty <$> traverse (alloca . getChild node) (take (fromIntegral count) [0..])

          let range = Range { start = fromIntegral $ ts_node_p_start_char node, end = fromIntegral $ ts_node_p_end_char node }

-          let sourceSpan = SourceSpan { spanName = toS (path blob)
+          let sourceSpan = SourceSpan { spanName = toS path
            , spanStart = SourcePos (fromIntegral $! ts_node_p_start_point_row node) (fromIntegral $! ts_node_p_start_point_column node)
            , spanEnd = SourcePos (fromIntegral $! ts_node_p_end_point_row node) (fromIntegral $! ts_node_p_end_point_column node) }

-          -- Note: The strict application here is semantically important. Without it, we may not evaluate the range until after we’ve exited the scope that `node` was allocated within, meaning `alloca` will free it & other stack data may overwrite it.
-          let info = range `seq` range .: categoriesForLanguage language (toS name) .: RNil
-          termConstructor (source blob) (sourceSpan `seq` pure sourceSpan) info (filter (\child -> category (extract child) /= Empty) children)
+          -- Note: The strict application here is semantically important.
+          -- Without it, we may not evaluate the range until after we’ve exited
+          -- the scope that `node` was allocated within, meaning `alloca` will
+          -- free it & other stack data may overwrite it.
+          range `seq` termConstructor source (pure $! sourceSpan) (toS name) range children
        getChild node n out = ts_node_p_named_child node n out >> toTerm out
        {-# INLINE getChild #-}
+        termConstructor = case language of
+          JavaScript -> JS.termConstructor
+          C -> C.termConstructor
+          _ -> Language.termConstructor
+        isNonEmpty child = category (extract child) /= Empty
--- a/test/AlignmentSpec.hs
+++ b/test/AlignmentSpec.hs
@ -32,7 +32,7 @@ spec :: Spec
 spec = parallel $ do
  describe "alignBranch" $ do
    it "produces symmetrical context" $
-      alignBranch getRange ([] :: [Join These (SplitDiff String (Record '[Range]))]) (both [Range 0 2, Range 2 4] [Range 0 2, Range 2 4]) `shouldBe`
+      alignBranch getRange ([] :: [Join These (SplitDiff (Syntax String) (Record '[Range]))]) (both [Range 0 2, Range 2 4] [Range 0 2, Range 2 4]) `shouldBe`
        [ Join (These (Range 0 2, [])
                      (Range 0 2, []))
        , Join (These (Range 2 4, [])
@ -40,7 +40,7 @@ spec = parallel $ do
        ]

    it "produces asymmetrical context" $
-      alignBranch getRange ([] :: [Join These (SplitDiff String (Record '[Range]))]) (both [Range 0 2, Range 2 4] [Range 0 1]) `shouldBe`
+      alignBranch getRange ([] :: [Join These (SplitDiff (Syntax String) (Record '[Range]))]) (both [Range 0 2, Range 2 4] [Range 0 1]) `shouldBe`
        [ Join (These (Range 0 2, [])
                      (Range 0 1, []))
        , Join (This  (Range 2 4, []))
@ -231,7 +231,7 @@ toAlignBranchInputs elements = (sources, join . (`evalState` both 0 0) . travers
        branchElementContents (Margin contents) = contents

 keysOfAlignedChildren :: [Join These (Range, [(String, Range)])] -> [String]
-keysOfAlignedChildren lines = lines >>= these identity identity (++) . runJoin . fmap (fmap Prologue.fst . Prologue.snd)
+keysOfAlignedChildren lines = lines >>= these identity identity (<>) . runJoin . fmap (fmap Prologue.fst . Prologue.snd)

 joinCrosswalk :: Bicrosswalk p => Align f => (a -> f b) -> Join p a -> f (Join p b)
 joinCrosswalk f = fmap Join . bicrosswalk f f . runJoin
@ -257,13 +257,13 @@ instance Arbitrary BranchElement where
 counts :: [Join These (Int, a)] -> Both Int
 counts numbered = fromMaybe 0 . getLast . mconcat . fmap Last <$> Join (unalign (runJoin . fmap Prologue.fst <$> numbered))

-align :: Both (Source.Source Char) -> ConstructibleFree (Patch (Term String (Record '[Range]))) (Both (Record '[Range])) -> PrettyDiff (SplitDiff String (Record '[Range]))
+align :: Both (Source.Source Char) -> ConstructibleFree (Patch (Term (Syntax String) (Record '[Range]))) (Both (Record '[Range])) -> PrettyDiff (SplitDiff (Syntax String) (Record '[Range]))
 align sources = PrettyDiff sources . fmap (fmap (getRange &&& identity)) . alignDiff sources . deconstruct

 info :: Int -> Int -> Record '[Range]
 info start end = Range start end .: RNil

-prettyDiff :: Both (Source.Source Char) -> [Join These (ConstructibleFree (SplitPatch (Term String (Record '[Range]))) (Record '[Range]))] -> PrettyDiff (SplitDiff String (Record '[Range]))
+prettyDiff :: Both (Source.Source Char) -> [Join These (ConstructibleFree (SplitPatch (Term (Syntax String) (Record '[Range]))) (Record '[Range]))] -> PrettyDiff (SplitDiff (Syntax String) (Record '[Range]))
 prettyDiff sources = PrettyDiff sources . fmap (fmap ((getRange &&& identity) . deconstruct))

 data PrettyDiff a = PrettyDiff { unPrettySources :: Both (Source.Source Char), unPrettyLines :: [Join These (Range, a)] }
@ -273,23 +273,23 @@ instance Show a => Show (PrettyDiff a) where
  showsPrec _ (PrettyDiff sources lines) = (prettyPrinted ++) -- . (("\n" ++ show lines) ++)
    where prettyPrinted = showLine (maximum (0 : (maximum . fmap length <$> shownLines))) <$> shownLines >>= ('\n':)
          shownLines = catMaybes $ toBoth <$> lines
-          showLine n line = uncurry ((++) . (++ " | ")) (fromThese (replicate n ' ') (replicate n ' ') (runJoin (pad n <$> line)))
+          showLine n line = uncurry ((<>) . (++ " | ")) (fromThese (replicate n ' ') (replicate n ' ') (runJoin (pad n <$> line)))
          showDiff (range, _) = filter (/= '\n') . toList . Source.slice range
-          pad n string = (++) (take n string) (replicate (max 0 (n - length string)) ' ')
+          pad n string = (<>) (take n string) (replicate (max 0 (n - length string)) ' ')
          toBoth them = showDiff <$> them `applyThese` modifyJoin (uncurry These) sources

 newtype ConstructibleFree patch annotation = ConstructibleFree { deconstruct :: Free (CofreeF (Syntax String) annotation) patch }


 class PatchConstructible p where
-  insert :: Term String (Record '[Range]) -> p
-  delete :: Term String (Record '[Range]) -> p
+  insert :: Term (Syntax String) (Record '[Range]) -> p
+  delete :: Term (Syntax String) (Record '[Range]) -> p

-instance PatchConstructible (Patch (Term String (Record '[Range]))) where
+instance PatchConstructible (Patch (Term (Syntax String) (Record '[Range]))) where
  insert = Insert
  delete = Delete

-instance PatchConstructible (SplitPatch (Term String (Record '[Range]))) where
+instance PatchConstructible (SplitPatch (Term (Syntax String) (Record '[Range]))) where
  insert = SplitInsert
  delete = SplitDelete

--- a/test/Data/RandomWalkSimilarity/Spec.hs
+++ b/test/Data/RandomWalkSimilarity/Spec.hs
@ -21,14 +21,14 @@ spec = parallel $ do
  let positively = succ . abs
  describe "pqGramDecorator" $ do
    prop "produces grams with stems of the specified length" $
-      \ (term, p, q) -> pqGramDecorator (rhead . headF) (positively p) (positively q) (toTerm term :: Term Text (Record '[Text])) `shouldSatisfy` all ((== (positively p)) . length . stem . rhead)
+      \ (term, p, q) -> pqGramDecorator (rhead . headF) (positively p) (positively q) (toTerm term :: Term (Syntax Text) (Record '[Text])) `shouldSatisfy` all ((== (positively p)) . length . stem . rhead)

    prop "produces grams with bases of the specified width" $
-      \ (term, p, q) -> pqGramDecorator (rhead . headF) (positively p) (positively q) (toTerm term :: Term Text (Record '[Text])) `shouldSatisfy` all ((== (positively q)) . length . base . rhead)
+      \ (term, p, q) -> pqGramDecorator (rhead . headF) (positively p) (positively q) (toTerm term :: Term (Syntax Text) (Record '[Text])) `shouldSatisfy` all ((== (positively q)) . length . base . rhead)

  describe "featureVectorDecorator" $ do
    prop "produces a vector of the specified dimension" $
-      \ (term, p, q, d) -> featureVectorDecorator (rhead . headF) (positively p) (positively q) (positively d) (toTerm term :: Term Text (Record '[Text])) `shouldSatisfy` all ((== (positively d)) . length . rhead)
+      \ (term, p, q, d) -> featureVectorDecorator (rhead . headF) (positively p) (positively q) (positively d) (toTerm term :: Term (Syntax Text) (Record '[Text])) `shouldSatisfy` all ((== (positively d)) . length . rhead)

  describe "rws" $ do
    let decorate = defaultFeatureVectorDecorator (category . headF)
--- a/test/DiffSummarySpec.hs
+++ b/test/DiffSummarySpec.hs
@ -26,7 +26,7 @@ arrayInfo = ArrayLiteral .: Range 0 3 .: RNil
 literalInfo :: Record '[Category, Range]
 literalInfo = StringLiteral .: Range 1 2 .: RNil

-testDiff :: Diff Text (Record '[Category, Range])
+testDiff :: Diff (Syntax Text) (Record '[Category, Range])
 testDiff = free $ Free (pure arrayInfo :< Indexed [ free $ Pure (Insert (cofree $ literalInfo :< Leaf "a")) ])

 testSummary :: DiffSummary DiffInfo
@ -67,7 +67,7 @@ spec = parallel $ do
        extractLeaves (BranchInfo children _ _) = join $ extractLeaves <$> children
        extractLeaves leaf = [ leaf ]

-        extractDiffLeaves :: Term Text (Record '[Category, Range]) -> [ Term Text (Record '[Category, Range]) ]
+        extractDiffLeaves :: Term (Syntax Text) (Record '[Category, Range]) -> [ Term (Syntax Text) (Record '[Category, Range]) ]
        extractDiffLeaves term = case unwrap term of
          (Indexed children) -> join $ extractDiffLeaves <$> children
          (Fixed children) -> join $ extractDiffLeaves <$> children
@ -81,7 +81,7 @@ spec = parallel $ do
               in
                length listOfLeaves `shouldBe` length listOfDiffLeaves

-isIndexedOrFixed :: Patch (Term a annotation) -> Bool
+isIndexedOrFixed :: Patch (Term (Syntax a) annotation) -> Bool
 isIndexedOrFixed = any (isIndexedOrFixed' . unwrap)

 isIndexedOrFixed' :: Syntax a f -> Bool
--- a/weekly/2016-09-09.md
+++ b/weekly/2016-09-09.md
@ -0,0 +1,100 @@
+# September 9th, 2016
+
+- Hack week was last week and we skipped the weekly.
+- We moved the weekly to the end of the week to try to cut down on the “wait, what _did_ happen last week?” thing.
+- This ended up being @tclem’s first weekly 👋
+
+
+#### What went well?
+
+@joshvera:
+
+Hack week:
+
+- Made a lot of progress on the TypeScript parser.
+- May be able to use that as the basis for a more rigorous JavaScript parser as well.
+
+This week:
+
+- Understand RWS & some other diffing algos a lot better than before.
+
+
+@rewinfrey:
+
+- Pairing w/ @tclem.
+- Updating test cases is much more efficient.
+- Modelling effects in Free.
+
+
+@tclem:
+
+- Little fixes.
+- Static linking of ICU in dev.
+- statsd client.
+
+
+@robrix:
+
+- semantic-diffd
+- Docker
+- kubes
+- Markdown
+
+
+#### What were the challenges?
+
+@joshvera:
+
+- Integrating a pass before RWS. Using constant-time (per-subtree)SES before RWS to match up equal things. There are some ordering problems with the result.
+- Ambiguities in the TypeScript grammar. Possibly due to JS actually being context-sensitive. @maxbrunsfeld advises parsing a superset of the language… but which superset?
+
+
+@rewinfrey:
+
+- Trying to get an effect system in Free. Got it, but tricky.
+- Also picked up an issue with template strings which defies debugging.
+
+
+@tclem:
+
+- > My head hurts by the end of the day.
+- Being challenged by some of the new concepts, the vernacular &c.
+- Hard to know when to jump down the rabbit hole and learn a thing or when to gloss over it.
+- Have a queue of things to read.
+
+
+@robrix:
+
+- Converting between line/column ranges and character ranges.
+
+
+#### What did you learn?
+
+@joshvera:
+
+- > I became one with the TypeScript grammar.
+- > Maybe we should find a way to have the grammars write themselves.
+- Working on this `effects` package (formerly called `freer`) & its `Eff` type. It uses an open union data structure, which `Data.Record` is sort of an approximation of. `Eff` has this detail where it’s list of function types are “type-aligned.” Every item in the list is a function type where they all chain together, a -> b, b -> c, etc. Adding, removing, & replacing effects is constant-time.
+
+@rewinfrey:
+
+- Free, and how to model effects in Free.
+- Straight-up category theory stuff. Compositions of natural transformations &c.
+
+@tclem:
+
+- Post about functors, applicatives, and monads shown in pictures.
+- How this manages to be a bridge between pure & stateful functions.
+- Helped explain the optparse-applicative syntax.
+
+@robrix:
+
+- CMark exists, which is cool.
+- Parsing/term ingestion had been producing errors for weirdly-formatted for loops &c. Not only were we hitting this on a regular basis, it was also causing confusing/poor change summaries.
+
+
+#### Meta
+
+“What were the challenges?” can be a bit redundant with “what did you learn?” Should we focus this on challenges that we need help with? Gonna give that a try.
+
+Next week: @joshvera, @rewinfrey, & @robrix are off to ICFP. @tclem may or may not hold weekly solo at his discretion.