+def _negation_expression_parser(index, tokens):
+ failure = (False, index, None)
+
+ if tokens[index].match != '-':
+ return failure
+
+ success, index, value = _literal_level_expression_parser(index + 1, tokens)
+
+ if not success:
+ return failure
+
+ return (True, index, FurNegationExpression(value=value))
+