implement "url" command

client.rkt

@@ -80,6 +80,16 @@
           (let ([url (gmi:match-link document-object line)])
             (get (combine-url/relative current-url (url->string url))))))
 
+    (define/public (url-cmd (link-id #f))
+      (if (null? document-object)
+          (displayln "you need to 'go' somewhere first!")
+          (if link-id
+              (let ([link (gmi:match-link document-object link-id)])
+                (if link
+                    (displayln (url->string link))
+                    (displayln "no link with that id")))
+              (displayln (url->string current-url)))))
+
     (define/private (handle-gmi url c-in)
       (let-values ([(doc) (gmi:parse (port->lines c-in))]
                    [(db-in db-out) (make-pipe #f)])