adjust the DatalogDB API, give access to relation names

haskell-experiments/src/Datalog/DatalogDB.hs

@@ -57,6 +57,7 @@ type RelationId = Text
 
 class DatalogDB db where
   emptyDB :: db
+  relationNames :: db -> [Text]
   lookupRelation :: db -> Text -> Maybe Relation
   insertRelation :: db -> Relation -> db
   addConstants :: db -> Set Constant -> db
@@ -79,7 +80,7 @@ addFact (Literal neg relationName terms) db =
   newRelation = lookupRelationArity relationName db newArity (Set.singleton terms)
   extraConstants = Set.fromList terms
 
--- the world isn't quite ready for these, as the 'update relation' pattern doesn't fir - maybe use a lens?
+-- the world isn't quite ready for these, as the 'update relation' pattern doesn't fit - maybe use a lens?
 -- lookupRelation00 :: DatalogDB db => 
 --   Text -> db -> Int -> (Relation -> Relation) -> db
 -- lookupRelation00 relationName db newArity update =

haskell-experiments/src/Datalog/InMemoryDB.hs

@@ -8,7 +8,7 @@
 module Datalog.InMemoryDB where
 
 import Control.Exception.Base
-import Data.Map (Map)
+import Data.Map (Map, keys)
 import Data.Map qualified as Map
 import Data.Set (Set)
 import Data.Set qualified as Set
@@ -45,7 +45,10 @@ instance DatalogDB InMemoryDB where
       _constants = Set.union newConstants (_constants db)
     }
 
-withFacts :: DatalogDB db => [Text] -> db
+  relationNames :: InMemoryDB -> [Text]
+  relationNames db = keys (_relations db)
+
+withFacts :: [Text] -> InMemoryDB
 withFacts =
   foldr (addFact . extractFact) emptyDB
  where

haskell-experiments/test/Test/Datalog/InMemoryDBSpec.hs

@@ -40,6 +40,7 @@ spec = do
             , Relation "parent" 2 (Set.fromList $ Sym <<$>> [["alice", "bob"], ["bob", "carol"]]) []
             )
           ]
+      relationNames db `shouldBe` [ "parent" ]
     it "can ingest facts and rules" do
       let db =
             InMemoryDB.withFactsAndRules
@@ -86,6 +87,7 @@ spec = do
           [ ("ancestor", ancestorRelation)
           , ("parent", parentRelation)
           ]
+      Set.fromList (relationNames db) `shouldBe` Set.fromList [ "parent", "ancestor" ]
 
     it "can ingest facts and rules with constants" do
       let db =
@@ -109,6 +111,7 @@ spec = do
 
       _constants db
         `shouldBe` Set.fromList (Sym <$> ["patriarch"])
+      Set.fromList (relationNames db) `shouldBe` Set.fromList [ "ancestor" ]
 
     it "can ingest facts and rules with duplicate head entries" do
       let db =
@@ -132,6 +135,7 @@ spec = do
 
       _constants db
         `shouldBe` Set.empty
+      relationNames db `shouldBe` [ "equivalent" ]
 
     it "can ingest a theory of equivalence relations" do
       let db =
@@ -172,6 +176,7 @@ spec = do
 
       _constants db
         `shouldBe` Set.empty
+      Set.fromList (relationNames db) `shouldBe` Set.fromList [ "equivalent" ]
 
     it "can do basic queries" do
       let db :: InMemoryDB =