Implement the structure to the check_fail_matcher function.

src/parser/list.rs

@@ -25,7 +25,17 @@ impl<T> List<T> {
         }
     }
 
+    pub fn without_front(&self) -> List<T> {
+        List {
+            head: self.head.as_ref().map(|node| node.parent.clone()).flatten()
+        }
+    }
+
     pub fn get_data(&self) -> Option<&T> {
         self.head.as_ref().map(|rc_node| &rc_node.data)
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.head.is_none()
+    }
 }