listZipFromFwd :: Fwd a -> Maybe (ListZip a)
listZipFromFwd (a :> as) = Just (ListZip B0 a as)
listZipFromFwd :: Fwd a -> Maybe (ListZip a)
listZipFromFwd (a :> as) = Just (ListZip B0 a as)
listZipFromFwd (a :> as) = Just (ListZip B0 a as)