fix single target as tuple

src/scgenerator/evaluator.py

@@ -367,7 +367,7 @@ class Evaluator:
             errors.append(e, lookup_stack, rules_stack)
             return None
 
-        if not isinstance(values, tuple):
+        if len(rule.targets) == 1:
             values = (values,)
 
         return {k: EvaluatedValue(v, rule.targets[k], rule) for k, v in zip(rule.targets, values)}