From e32342b363c2454de9d2d9bae5f389b11a3cb1d7 Mon Sep 17 00:00:00 2001
From: Brian Hicks <brian@brianthicks.com>
Date: Fri, 11 Jun 2021 15:28:34 -0500
Subject: [PATCH] add not equals

---
 src/Datalog.elm        |  8 ++++++++
 tests/DatalogTests.elm | 12 ++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/src/Datalog.elm b/src/Datalog.elm
index d51a85c..8c18430 100644
--- a/src/Datalog.elm
+++ b/src/Datalog.elm
@@ -870,6 +870,7 @@ type Token
     | GreaterThan
     | GreaterThanOrEquals
     | Equals
+    | NotEquals
     | OrToken
     | NotToken
     | LineComment
@@ -1012,6 +1013,8 @@ opParser =
             |. Parser.token greaterThanToken
         , Parser.succeed eq
             |. Parser.token equalsToken
+        , Parser.succeed (\lhs rhs -> not_ (eq lhs rhs))
+            |. Parser.token notEqualsToken
         ]
 
 
@@ -1174,6 +1177,11 @@ equalsToken =
     Parser.Token "=" (ExpectedToken Equals)
 
 
+notEqualsToken : Parser.Token ParsingProblem
+notEqualsToken =
+    Parser.Token "!=" (ExpectedToken NotEquals)
+
+
 orToken : Parser.Token ParsingProblem
 orToken =
     Parser.Token "||" (ExpectedToken OrToken)
diff --git a/tests/DatalogTests.elm b/tests/DatalogTests.elm
index cefb34e..44a16af 100644
--- a/tests/DatalogTests.elm
+++ b/tests/DatalogTests.elm
@@ -485,6 +485,18 @@ datalogTests =
                                     |> with "thing" [ var "name", var "legs" ]
                                     |> filter (eq "legs" (int 8))
                                 ]
+                    , test "not equal to" <|
+                        \_ ->
+                            expectParses
+                                """
+                                notASpider(name) :-
+                                  thing(name, legs),
+                                  legs != 8.
+                                """
+                                [ rule "notASpider" [ "name" ]
+                                    |> with "thing" [ var "name", var "legs" ]
+                                    |> filter (not_ (eq "legs" (int 8)))
+                                ]
                     , test "or" <|
                         \_ ->
                             expectParses