runRouteViewT'.hs

  window <- DOM.currentWindowUnchecked
  history <- Window.getHistory window
  location <- Window.getLocation window
  oldUri <- (decodeFrag . T.pack . uriFragment) <$> getLocationUri location
  backState <- wrapDomEvent window (`DOM.on` DOM.popState) $ do
    e <- DOM.event
    jV <- PopStateEvent.getState e
    oUri <- liftJSM $ fromJSVal jV
    pure $ decodeFrag $ fromMaybe (T.pack "") oUri
  setState <- performEvent $ attachWith (switchRoutingState' history) (current route) changeStateE
  route <- foldDynMaybe switchFrag oldUri $ setState
  (result, changeStateE) <- runSetRouteT $ strictDynWidget_ app route
  pure result