introduce typeclass

haskell-experiments/src/Datalog/NaiveDatabase.hs

@@ -3,6 +3,7 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# OPTIONS_GHC -Wno-unrecognised-pragmas #-}
+{-# LANGUAGE InstanceSigs #-}
 
 module Datalog.NaiveDatabase where
 
@@ -25,13 +26,18 @@ data NaiveDatabase = NaiveDatabase
   } deriving (Show, Eq)
 
 
-emptyDB :: NaiveDatabase
+instance DatalogDB NaiveDatabase where
-emptyDB =
+  emptyDB :: NaiveDatabase
-  NaiveDatabase
+  emptyDB =   NaiveDatabase
     { relations = Map.empty
     , constants = Set.empty -- the Herbrand universe
     }
 
+  -- lookupRelation :: NaiveDatabase -> Text -> Maybe Relation -> NaiveDatabase
+  -- lookupRelation = _
+  -- insertRelation :: NaiveDatabase -> Text -> Relation -> NaiveDatabase
+  -- insertRelation = _
+
 lookupRelation :: RelationId -> Map RelationId Relation -> Int -> Set [Term] -> Relation
 lookupRelation relationName relationMap newArity tuples =
   case Map.lookup relationName relationMap of

haskell-experiments/src/Datalog/Rules.hs

@@ -46,3 +46,8 @@ data Relation = Relation
 -- Our constants will be the terms of the Datalog grammar - ints/variables/symbols
 type Constant = Term
 type RelationId = Text
+
+class DatalogDB db where
+  emptyDB :: db
+  -- lookupRelation :: db -> Text -> Maybe Relation -> db
+  -- insertRelation :: db -> Text -> Relation -> db