title: Change gtk window state from callback
body: <p>I have a simple GTK window with menu bar which has <code>Open</code> item. It gets filename inside callback of <code>menuItemActivate</code>:</p>
  
  <pre><code>openPressed = do
      chooser &lt;- fileChooserDialogNew
  
  ...
      filename &lt;- performResponse res chooser
          widgetHide chooser
          where
              performResponse ResponseCancel _ = return ("")
              performResponse ResponseOk chooser = do
                  Just fname &lt;- fileChooserGetFilename chooser
                  putStrLn fname 
                  --how can i put filename in label inside MainForm from here?
                  return fname
  </code></pre>
  
  <p>How can I put filename to label located in my main window if <code>openPressed</code> is not nested in the main function which initialize main window?</p>