closeTBMChan :: TBMChan a -> STM ()
closeTBMChan (TBMChan closed _limit _chan) =
    writeTVar closed True
closeTBMChan :: TBMChan a -> STM ()
closeTBMChan (TBMChan closed _limit _chan) =
    writeTVar closed True
closeTBMChan (TBMChan closed _limit _chan) =
    writeTVar closed True