negative index

Author: rayokota

.gitignore

@@ -17,3 +17,5 @@ venv/
 .idea
 .venv
 tests/gen
+
+.claude

src/jsonata/jsonata.py

@@ -519,7 +519,7 @@ def evaluate_filter(self, predicate: Optional[Any], input: Optional[Any], enviro
             if index < 0:
                 # count in from end of array
                 index = len(input) + index
-            item = input[index] if index < len(input) else None
+            item = input[index] if 0 <= index < len(input) else None
             if item is not None:
                 if isinstance(item, list):
                     results = item

tests/array_test.py

@@ -3,6 +3,12 @@
 
 class TestArray:
 
+    def test_negative_index(self):
+        expr = jsonata.Jsonata("item[-1]")
+        assert expr.evaluate({"item": []}) is None
+        expr = jsonata.Jsonata("$[-1]")
+        assert expr.evaluate([]) is None
+
     def test_array(self):
         assert jsonata.Jsonata("$.[{ }] ~> $reduce($append)").evaluate([True, True]) == [{}, {}]