viewL :: Sequence a -> FT.ViewL Sequence a
viewL (Sequence s) = case FT.viewL s of
  FT.EmptyL -> FT.EmptyL
  (Element a) FT.:< tree -> a FT.:< Sequence tree
viewL :: Sequence a -> FT.ViewL Sequence a
viewL (Sequence s) = case FT.viewL s of
  FT.EmptyL -> FT.EmptyL
  (Element a) FT.:< tree -> a FT.:< Sequence tree
viewL (Sequence s) = case FT.viewL s of
  FT.EmptyL -> FT.EmptyL
  (Element a) FT.:< tree -> a FT.:< Sequence tree