parse negatable atoms

src/Datalog.elm

@@ -871,6 +871,7 @@ type Token
     | GreaterThanOrEquals
     | Equals
     | OrToken
+    | NotToken
 
 
 type alias Parser a =
@@ -936,7 +937,16 @@ ruleBodyParser =
 
 bodyAtomParser : Parser (Rule -> Rule)
 bodyAtomParser =
-    Parser.succeed with
+    Parser.succeed
+        (\negative name body ->
+            if negative then
+                without name body
+
+            else
+                with name body
+        )
+        |= notParser
+        |. Parser.spaces
         |= nameParser
         |. Parser.spaces
         |= Parser.sequence
@@ -949,6 +959,15 @@ bodyAtomParser =
             }
 
 
+notParser : Parser Bool
+notParser =
+    Parser.oneOf
+        [ Parser.succeed True
+            |. Parser.token notToken
+        , Parser.succeed False
+        ]
+
+
 filterParser : Parser (Rule -> Rule)
 filterParser =
     Parser.andThen
@@ -1143,6 +1162,11 @@ orToken =
     Parser.Token "||" (ExpectedToken OrToken)
 
 
+notToken : Parser.Token ParsingProblem
+notToken =
+    Parser.Token "not" (ExpectedToken NotToken)
+
+
 {-| This is down here because my editor's highlighting is busted and it
 thinks everything after '"' is a string.
 -}

tests/DatalogTests.elm

@@ -534,7 +534,20 @@ datalogTests =
                                         )
                                 ]
                     ]
-                , todo "rule with negation"
+                , test "rule with negation" <|
+                    \_ ->
+                        expectParses
+                            """
+                            unreachable(a, b) :-
+                              node(a),
+                              node(b),
+                              not reachable(a, b).
+                            """
+                            [ rule "unreachable" [ "a", "b" ]
+                                |> with "node" [ var "a" ]
+                                |> with "node" [ var "b" ]
+                                |> without "reachable" [ var "a", var "b" ]
+                            ]
                 ]
             , describe "errors"
                 [ todo "errors!" ]