manageHistory.hs

  window <- DOM.currentWindowUnchecked
  location <- Window.getLocation window
  history <- Window.getHistory window
  let getCurrentHistoryItem = HistoryItem
        <$> History.getState history
        <*> getLocationUri location
  item0 <- liftJSM getCurrentHistoryItem
  itemSetInternal <- performEvent $ ffor runCmd $ \cmd -> liftJSM $ do
    runHistoryCommand history cmd
    getCurrentHistoryItem
  itemSetExternal <- wrapDomEvent window (`DOM.on` DOM.popState) $ do
    e <- DOM.event
    HistoryItem
      <$> (SerializedScriptValue <$> PopStateEvent.getState e)
      <*> getLocationUri location
  holdDyn item0 $ leftmost [itemSetInternal, itemSetExternal]