adjusting types, developing addFact

haskell-experiments/src/Datalog/NaiveDatabase.hs

@@ -24,24 +24,28 @@ data Value =
 
 data NaiveDatabase = NaiveDatabase {
   relations :: Map RelationId Relation,
-  constants :: Set ConstantId
+  constants :: Set Constant
 }
 
 data Relation = Relation {
   arity :: Int,
-  tuples :: Set [ConstantId]
+  tuples :: Set [Constant]
 }
 
-newtype RelationId = RelationId Text
+-- newtype RelationId = RelationId Text
-  deriving (Eq, Ord, Show)
+--   deriving (Eq, Ord, Show)
 
-newtype ConstantId = ConstantId Text
+-- Our constants will be the terms of the Datalog grammar - ints/variables/symbols
-  deriving (Eq, Ord, Show)
+type Constant = Term
+type RelationId = Text
+
+-- newtype Constant = Constant Text
+--   deriving (Eq, Ord, Show)
 
 emptyDB :: NaiveDatabase
 emptyDB = NaiveDatabase {
   relations = Map.empty,
-  constants = Set.empty
+  constants = Set.empty   -- the Herbrand universe
 }
 
 withFacts :: [Text] -> NaiveDatabase
@@ -54,8 +58,13 @@ withFacts facts =
         Right otherStatement -> throw $ NonFactException factText otherStatement
         Left ex -> throw $ CannotParseStatementException factText ex
     addFact :: NaiveDatabase -> Literal -> NaiveDatabase
-    addFact db lit =
+    addFact (NaiveDatabase relations constants) (Literal neg relationName terms) =
-      db
+      NaiveDatabase newRelations newConstants where
+        newRelations =
+          case Map.lookup relationName relations of
+            Nothing -> relations
+            Just relation -> relations
+        newConstants = Set.union constants $ Set.fromList terms
 
 query :: NaiveDatabase -> Text -> Text
 query db qText =