diff --git a/haskell-experiments/src/Datalog/NaiveDatabase.hs b/haskell-experiments/src/Datalog/NaiveDatabase.hs
index 0a7948d..51da4be 100644
--- a/haskell-experiments/src/Datalog/NaiveDatabase.hs
+++ b/haskell-experiments/src/Datalog/NaiveDatabase.hs
@@ -30,7 +30,7 @@ data NaiveDatabase = NaiveDatabase
 
 instance DatalogDB NaiveDatabase where
   emptyDB :: NaiveDatabase
-  emptyDB =   NaiveDatabase
+  emptyDB = NaiveDatabase
     { relations = Map.empty
     , constants = Set.empty -- the Herbrand universe
     }
@@ -118,15 +118,15 @@ withFacts =
     newRelationMap = Map.insert relationName newRelation relationMap
     newConstantSet = Set.union constantSet $ Set.fromList terms
 
-data RuleContext = RuleContext
+data (DatalogDB db) => RuleContext db = RuleContext
   { __relation :: Relation
   , _variableNames :: [Text]
   , _headEntries :: [RuleElement]
   , _bodyConstraints :: [BodyConstraint]
-  , _db :: NaiveDatabase
+  , _db :: db
   }
 
-digestHead :: NaiveDatabase -> Relation -> Literal -> RuleContext
+digestHead :: forall db . (DatalogDB db) => db -> Relation -> Literal -> RuleContext db
 digestHead db relation (Literal neg relationName terms) =
   RuleContext
     { __relation = relation
@@ -147,7 +147,7 @@ digestHead db relation (Literal neg relationName terms) =
     extractConstant :: RuleElement -> Maybe Constant
     extractConstant (RuleElementConstant constant) = Just constant
     extractConstant _ = Nothing
-digestBody :: Literal -> RuleContext -> RuleContext
+digestBody :: Literal -> RuleContext NaiveDatabase -> RuleContext NaiveDatabase
 digestBody (Literal neg subRelationName subTerms) context =
   context { 
     _variableNames = variableNames