onBackend :: (Block ty -> a)
          -> (FinalPtr ty -> Ptr ty -> ST s a)
          -> UArray ty
          -> a
onBackend onBa _      (UArray _ _ (UArrayBA ba))     = onBa ba
onBackend :: (Block ty -> a)
          -> (FinalPtr ty -> Ptr ty -> ST s a)
          -> UArray ty
          -> a
onBackend onBa _      (UArray _ _ (UArrayBA ba))     = onBa ba
onBackend onBa _      (UArray _ _ (UArrayBA ba))     = onBa ba