add values/call-with-values

piclib/built-in.scm

@@ -212,3 +212,16 @@
 	(if (compare obj (caar list))
 	    (car list)
 	    (assoc obj (cdr list) compare)))))
+
+(define (values . args)
+  (if (and (pair? args)
+	   (null? (cdr args)))
+      (car args)
+      (cons '*values-tag* args)))
+
+(define (call-with-values producer consumer)
+  (let ((res (producer)))
+    (if (and (pair? res)
+	     (eq? '*values-tag* (car res)))
+        (apply consumer (cdr res))
+        (consumer res))))