implement an "up" command

client.rkt

@@ -29,6 +29,21 @@
 
     (super-new)
 
+    (define/public (up-cmd)
+      (if (string=?  (path->string
+                      (simplify-path
+                       (url->path current-url)))
+                    "/")
+
+          (displayln "already at root!")
+
+          (let ([parent
+                 (simplify-path
+                  (build-path (url->path current-url) 'up)
+                  #f)])
+            (get (struct-copy url current-url
+                              [path (url-path (path->url parent))])))))
+
     (define/public (go-cmd url-string)
       (if (non-empty-string? url-string)
           (let ()