Preserve ListExpression

Mathics3 · Dec 25, 2024 · a9792ff · a9792ff
1 parent bc8a285
commit a9792ff
Showing 1 changed file with 7 additions and 2 deletions.
diff --git a/mathics/core/expression.py b/mathics/core/expression.py
@@ -1410,8 +1410,13 @@ def rules():
                 if not isinstance(result, EvalMixin):
                     return result, False
                 if result.sameQ(new):
-                    new._timestamp_cache(evaluation)
-                    return new, False
+                    # Even though result and new may be the same,
+                    # new can be a Expression[SymbolConstant: System`List...]
+                    # while "result' might be ListExpression!?
+                    # So make sure to use "result", not "new".
+                    if isinstance(result, Expression):
+                        result._timestamp_cache(evaluation)
+                    return result, False
                 else:
                     return result, True