diff --git a/core/actor.lisp b/core/actor.lisp
index 3d2fcb5..092635a 100644
--- a/core/actor.lisp
+++ b/core/actor.lisp
@@ -6,7 +6,7 @@
                     (:shape :scopes/shape)
                     (:util :scopes/util))
   (:export #:start #:stop #:create #:send
-           #:message #:content #:customer
+           #:message #:content #:customer #:set-content
            #:*logger* #:*root*
            #:echo #:inc #:lgi
            #:calculator #:plus #:minus #:show #:send-value))
@@ -31,6 +31,11 @@
 (defun message (content &optional customer)
   (make-instance 'message :content content :customer customer))
 
+(defgeneric set-content (msg fn)
+  (:method (msg fn) (funcall fn msg))
+  (:method ((msg message) fn) 
+    (message (funcall fn (content msg)) (customer msg))))
+
 ;;;; actor loop (listener)
 
 (eval-when (:compile-toplevel :load-toplevel :execute)