fix: make pull_trunk pull from the trunk, rather than the root

src/state.rs

@@ -136,14 +136,14 @@ impl Tree {
     pub fn pull_root(&mut self) -> u16 {
         match self.root.pop() {
             Some(v) => v,
-            None => panic!("Cannot pop from empty root stack in {}", self.rule_id)
+            None => panic!("Cannot pop from empty root stack in rule #{}", self.rule_id)
         }
     }
 
     pub fn pull_trunk(&mut self) -> u16 {
-        match self.root.pop() {
+        match self.trunk.pop() {
             Some(v) => v,
-            None => panic!("Cannot pop from empty trunk stack in {}", self.rule_id)
+            None => panic!("Cannot pop from empty trunk stack in rule #{}", self.rule_id)
         }
     }