Attaching reflex to a particular node

Main.hs

{-# LANGUAGE ConstraintKinds     #-}
{-# LANGUAGE FlexibleContexts    #-}
{-# LANGUAGE RecursiveDo         #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeFamilies        #-}

------------------------------------------------------------------------------
import           Control.Concurrent
import           Control.Monad
import           Control.Monad.Trans
import           Control.Monad.Trans.Reader
import           GHCJS.DOM
import           GHCJS.DOM.Document
import           GHCJS.DOM.Element
import           GHCJS.DOM.EventM (preventDefault, eventTarget)
import           GHCJS.DOM.HTMLDocument
import           GHCJS.DOM.Types hiding (Event, Text)
import           Reflex.Dom hiding (getKeyEvent)
------------------------------------------------------------------------------


------------------------------------------------------------------------------
waitUntilJust :: IO (Maybe a) -> IO a
waitUntilJust a = do
    mx <- a
    case mx of
      Just x -> return x
      Nothing -> do
        threadDelay 10000
        waitUntilJust a


------------------------------------------------------------------------------
main :: IO ()
main = runWebGUI $ \webView -> do
    doc <- waitUntilJust $ liftM (fmap castToHTMLDocument) $
      webViewGetDomDocument webView
    root <- waitUntilJust $ liftM (fmap castToHTMLElement) $
      documentGetElementById doc "app-tag-id"
    attachWidget root webView $ do
      yourApp

Get the following traceback

Main.hs:40:23:
    Couldn't match type ‘DOMWindow’
                   with ‘Widget
                           Reflex.Spider.Internal.Spider
                           (Gui
                              Reflex.Spider.Internal.Spider
                              Reflex.Spider.Internal.SpiderHost
                              (Reflex.Host.Class.HostFrame Reflex.Spider.Internal.Spider))
                           ()’
    Expected type: Widget
                     Reflex.Spider.Internal.Spider
                     (Gui
                        Reflex.Spider.Internal.Spider
                        Reflex.Spider.Internal.SpiderHost
                        (Reflex.Host.Class.HostFrame Reflex.Spider.Internal.Spider))
                     ()
      Actual type: WebView
    In the second argument of ‘attachWidget’, namely ‘webView’
    In a stmt of a 'do' block: attachWidget root webView

Not exactly sure what to put after the do block. I tried "el "div" $ text "Welcome to Reflex"", which yielded similar complaints about webView.