- if (!ly_is_procedure (cb))
- warning (_ ("not setting modification callback: not a procedure"));
- else
- modification_callback = cb;
- return SCM_EOL;
+
+ SCM_ASSERT_TYPE(ly_is_procedure (cb), cb, SCM_ARG1, __FUNCTION__,
+ "procedure");
+
+ modification_callback = cb;
+ return SCM_UNSPECIFIED;