Added NULL description and added :when option for attribute active

[clinton/lisp-on-lines.git] / src / attribute.lisp

diff --git a/src/attribute.lisp b/src/attribute.lisp
index 210b36d..d332f60 100644 (file)
--- a/src/attribute.lisp
+++ b/src/attribute.lisp
@@ -134,6 +134,12 @@
                       :layered t
                       :special t)))
 
+(define-layered-method attribute-active-p :around (attribute)                 
+ (let ((active? (call-next-method)))
+   (if (eq :when active?)
+       (not (null (attribute-value attribute)))
+       active?)))
+                      
 (define-layered-method attribute-label-formatter :around (attribute)
    (or (slot-value attribute 'label-formatter) 
        (attribute-value (find-attribute (attribute-description attribute) 'label-formatter))