fix: nested return

fix/src/runtime/vm.rs

@@ -1166,11 +1166,11 @@ impl Runtime {
 
     pub(super) fn force_tos(&mut self) -> Action {
         loop {
-            let run = self.arena.mutate_root(|_mc, root| {
+            let (run, target_depth) = self.arena.mutate_root(|_mc, root| {
                 let thunk = root.stack.tos_mut().expect("stack underflow");
 
                 let Some(thunk_state) = thunk.as_gc::<Thunk>() else {
-                    return false;
+                    return (false, 0);
                 };
                 match *thunk_state.borrow() {
                     ThunkState::Pending { ip, env } => {
@@ -1182,12 +1182,12 @@ impl Runtime {
                             .expect("call stack overflow");
                         self.pc = ip;
                         root.current_env = Some(env);
-                        true
+                        (true, root.frames.len())
                     }
                     ThunkState::Apply { .. } => todo!("force_tos"),
                     ThunkState::Evaluated(val) => {
                         *thunk = val;
-                        false
+                        (false, 0)
                     }
                     ThunkState::Blackhole => todo!("force_tos"),
                 }
@@ -1199,7 +1199,12 @@ impl Runtime {
                 self.check_gc();
                 match self.execute_one() {
                     Action::Continue => (),
-                    Action::Return => break,
+                    Action::Return => {
+                        let current_depth = self.arena.mutate_root(|_, root| root.frames.len());
+                        if current_depth < target_depth {
+                            break;
+                        }
+                    }
                     // FIXME: poison thunk
                     Action::Done(err @ Err(_)) => return Action::Done(err),
                     Action::Done(Ok(_)) => unreachable!(),