tada?

app :: MonadWidget t m => m ()
app = mdo
  curRoute <- menu initialRoute
  tool curRoute

modeMenu :: MonadWidget t m => Dynamic t Route -> Mode -> m (Dynamic t Mode)
modeMenu dRoute initial = do
  eMode <- elClass "div" "Mode" $ do
    toV <- menuItem View dCur dRoute
    text " | "
    toE <- menuItem Edit dCur dRoute
    text " | "
    toI <- menuItem Input dCur dRoute
    pure $ leftmost [toV, toE, toI]
  holdDyn initial eMode

levelMenu :: MonadWidget t m => Dynamic t Route -> Level -> m (Dynamic t Level)
levelMenu dRoute initial = do
  eLevel <- elClass "div" "Level" $ do
    toC <- menuItem Content dCur dRoute
    text " | "
    toU <- menuItem User dCur dRoute
    pure $ leftmost [toC, toU]
  holdDyn initial eLevel

menu :: MonadWidget t m => Route -> m (Dynamic t Route)
menu (Route mode level) =
  elClass "div" "Menu" $ mdo
    dMode <- modeMeny dRoute mode
    dLevel <- levelMenu dRoute level
    dRoute <- Route <$> dMode <*> dLevel
    pure dRoute

menuItem :: (Eq a, Show a, MonadWidget t m)
         => a -> Dynamic t a -> Dynamic t Route -> m (Event t a)
menuItem option dCur dRoute = do
...