diff --git a/datalog/src/Datalog/Syntax.hs b/datalog/src/Datalog/Syntax.hs
index 9cfb858..5f3bab5 100644
--- a/datalog/src/Datalog/Syntax.hs
+++ b/datalog/src/Datalog/Syntax.hs
@@ -41,8 +41,8 @@ type Rule = Rule' ()
 data Rule' a = Rule a (Atom' a) [Atom' a]
   deriving (Eq, Ord, Show)
 {-# COMPLETE (:-) #-}
-pattern (:-) :: Atom' () -> [Atom' ()] -> Rule' ()
-pattern a :- b = Rule () a b
+pattern (:-) :: Atom' a -> [Atom' a] -> Rule' a
+pattern a :- b <- Rule _ a b
 
 type Program = Program' ()
 data Program' a = Program a [Rule' a]
@@ -63,7 +63,7 @@ instance HasConstants (Atom' a) where
   constants (Atom _ _ ts) = constants ts
 
 instance HasConstants (Rule' a) where
-  constants (Rule _ h b) = Set.union (constants h) (constants b)
+  constants (h :- b) = Set.union (constants h) (constants b)
 
 instance HasConstants (Program' a) where
   constants (Program _ rs) = constants rs