panic for undefined variables

renrs/src/parser/event.rs

@@ -34,7 +34,7 @@ fn interpolate_string(input: &str, variables: &HashMap<String, Token>) -> String
         if let Some(value) = variables.get(var_name) {
             value.to_string()
         } else {
-            format!("[{}]", var_name)
+            panic!("undefined variable `{var_name}`");
         }
     });