diff --git a/src/Category.hs b/src/Category.hs
index bbf5456b9..88298819a 100644
--- a/src/Category.hs
+++ b/src/Category.hs
@@ -17,6 +17,8 @@ data Category
   | Pair
   -- | A call to a function.
   | FunctionCall
+  -- | A function declaration
+  | Function
   -- | A string literal.
   | StringLiteral
   -- | An integer literal.
diff --git a/src/DiffSummary.hs b/src/DiffSummary.hs
index ffbbff986..b2d2511e7 100644
--- a/src/DiffSummary.hs
+++ b/src/DiffSummary.hs
@@ -23,6 +23,7 @@ toTermName term = case runCofree term of
   (_ :< Indexed children) -> fromMaybe "EmptyIndexedNode" $ (toCategoryName . category) . extract <$> head children
   (_ :< Fixed children) -> fromMaybe "EmptyFixedNode" $ (toCategoryName . category) . extract <$> head children
   (_ :< Syntax.FunctionCall i _) -> toTermName i
+  (_ :< Syntax.Function _) -> "anonymous function"
 
 class HasCategory a where
   toCategoryName :: a -> Text
diff --git a/src/Parser.hs b/src/Parser.hs
index d9a1cd490..921bec288 100644
--- a/src/Parser.hs
+++ b/src/Parser.hs
@@ -30,6 +30,10 @@ fixedCategories = Set.fromList [ BinaryOperator, Pair ]
 functionCallCategories :: Set.Set Category
 functionCallCategories = Set.singleton Category.FunctionCall
 
+-- | Categories that are treated as functionCall nodes.
+functionCategories :: Set.Set Category
+functionCategories = Set.singleton Category.Function
+
 -- | Should these categories be treated as keyed nodes?
 isKeyed :: Category -> Bool
 isKeyed = flip Set.member keyedCategories
@@ -41,6 +45,9 @@ isFixed = flip Set.member fixedCategories
 isFunctionCall :: Category -> Bool
 isFunctionCall = flip Set.member functionCallCategories
 
+isFunction :: Category -> Bool
+isFunction = flip Set.member functionCategories
+
 -- | Given a function that maps production names to sets of categories, produce
 -- | a Constructor.
 termConstructor :: Constructor
@@ -50,6 +57,7 @@ termConstructor source info children = cofree (info :< syntax)
     construct :: [Term Text Info] -> Syntax Text (Term Text Info)
     construct [] = Leaf . pack . toString $ slice (characterRange info) source
     construct children | isFunctionCall (category info), (x:xs) <- children = Syntax.FunctionCall x xs
+    construct children | isFunction (category info) = Syntax.Function children
     construct children | isFixed (category info) = Fixed children
     construct children | isKeyed (category info) = Keyed . Map.fromList $ assignKey <$> children
     construct children = Indexed children
diff --git a/src/Syntax.hs b/src/Syntax.hs
index e767637f7..22feaa6b7 100644
--- a/src/Syntax.hs
+++ b/src/Syntax.hs
@@ -19,4 +19,6 @@ data Syntax
   | Keyed (OrderedMap T.Text f)
   -- | A function call has an identifier where f is a (Leaf a) and a list of arguments.
   | FunctionCall f [f]
+  -- | A function has a list of expressions.
+  | Function [f]
   deriving (Functor, Show, Eq, Foldable, Traversable)