diff --git a/goldfish/liii/lang.scm b/goldfish/liii/lang.scm
index e39affba3a1d20a88ad788b4f070dd0e26f04bf9..41ba263835109a20d5fb6c3bf091a0ec08542c60 100644
--- a/goldfish/liii/lang.scm
+++ b/goldfish/liii/lang.scm
@@ -90,9 +90,10 @@
 
 )
 
+;; 自动生成to-string方法，格式为 "(rich-rational<值>)"
 (define-case-class rich-rational ((data rational?))
+  (define (%get) data) ;; 选择器方法
 
-(define (%get) data)
 
 (define (%abs) 
   (if (< data 0)
diff --git a/tests/goldfish/liii/lang-test.scm b/tests/goldfish/liii/lang-test.scm
index 3ccc129c75a57513c05130cfed17e31488fa9159..99ddf168ba0ab632949cb1a19c9b7be7b8261f13 100644
--- a/tests/goldfish/liii/lang-test.scm
+++ b/tests/goldfish/liii/lang-test.scm
@@ -383,6 +383,10 @@
 (check ($ 0 :get) => 0)
 (check ($ -1/3 :get) => -1/3)
 
+(check ($ 1/3 :to-string) => "(rich-rational 1/3)")
+(check ($ 0 :to-string) => "(rich-rational 0)")
+(check ($ -1/3 :to-string) => "(rich-rational -1/3)")
+
 (check ($ 1/3 :abs) => 1/3)
 (check ($ 0.0 :abs) => 0.0)
 (check ($ -1/3 :abs) => 1/3)