diff --git a/networks.rkt b/networks.rkt
index 0dda5cb..7f8850f 100644
--- a/networks.rkt
+++ b/networks.rkt
@@ -181,10 +181,9 @@
 
 ;;; Given a state s updates all the variables from xs.
 (define (update network s xs)
-  (for/fold ([new-s s])
-            ([x xs])
-    (let ([f (hash-ref network x)])
-      (hash-set new-s x (f s)))))
+  (define funcs (network-functions network))
+  (for/hash ([x xs])
+    (x ((hash-ref funcs x) s))))
 
 (module+ test
   (test-case "basic definitions"