slight fixes to cte

main.py

@@ -1454,9 +1454,11 @@ class CompileTimeVM:
         label_positions = self._label_positions(nodes)
         loop_pairs = self._for_pairs(nodes)
         begin_pairs = self._begin_pairs(nodes)
+        prev_loop_stack = self.loop_stack
         self.loop_stack = []
         begin_stack: List[Dict[str, int]] = []
         ip = 0
+        try:
             while ip < len(nodes):
                 node = nodes[ip]
                 kind = node.op
@@ -1543,6 +1545,8 @@ class CompileTimeVM:
                     continue
 
                 raise ParseError(f"unsupported compile-time op {node!r}")
+        finally:
+            self.loop_stack = prev_loop_stack
 
     def _label_positions(self, nodes: Sequence[Op]) -> Dict[str, int]:
         positions: Dict[str, int] = {}