improving clarity in Builtin.contribute

Author: mmatera

mathics/builtin/base.py

@@ -283,15 +283,16 @@ def check_options(options_to_check, evaluation):
             rules.append(
                 BuiltinRule(name, pattern, function, check_options, system=True)
             )
-        for pattern, replace in self.rules.items():
-            if not isinstance(pattern, BaseElement):
-                pattern = pattern % {"name": name}
-                pattern = parse_builtin_rule(pattern, definition_class)
-            replace = replace % {"name": name}
-            # FIXME: Should system=True be system=not is_pymodule ?
-            rules.append(Rule(pattern, parse_builtin_rule(replace), system=True))
+        for pattern_str, replace_str in self.rules.items():
+            pattern_str = pattern_str % {"name": name}
+            pattern = parse_builtin_rule(pattern_str, definition_class)
+            replace_str = replace_str % {"name": name}
+            rules.append(
+                Rule(pattern, parse_builtin_rule(replace_str), system=not is_pymodule)
+            )
 
         box_rules = []
+        # FIXME: Why a special case for System`MakeBoxes? Remove this
         if name != "System`MakeBoxes":
             new_rules = []
             for rule in rules: