haskell - Haskell: レンズを使用して状態を変更しているときに TChannel のラッピングが複製される

Question

次のコード (およびエラー) を検討してください。

import Control.Lens
import Control.Monad.STM
import Control.Monad.IO.Class
import Control.Monad.State.Lazy
import Control.Concurrent.STM.TChan

data Broadcast = Broadcast Int

data ImmutableState = ImmutableState
    { _broadcastChan :: TChan Broadcast
    , _encryption    :: Int
    }

makeLenses ''ImmutableState

helper :: MonadIO m => StateT ImmutableState m a
helper = do
    broadcastChan <~ (liftIO . atomically $ dupTChan $ use broadcastChan)
    {- ^
        Test.hs:
            Couldn't match expected type `Broadcast'
                        with actual type `TChan Broadcast'
            Expected type: StateT ImmutableState m (TChan Broadcast)
              Actual type: StateT ImmutableState m (TChan (TChan Broadcast))
            In the second argument of `(<~)', namely
              `(liftIO . atomically $ dupTChan $ use broadcastChan)'
            In a stmt of a 'do' block:
              broadcastChan
              <~ (liftIO . atomically $ dupTChan $ use broadcastChan)
    -}

forkImmState :: MonadIO m => ImmutableState -> m ImmutableState
forkImmState s = evalStateT helper s

誰かがどのよう(TChan (TChan Broadcast))になるのか説明できますか?