visitor visit a b =
  visit
  (fromJust ((getCellKey <$> a) <|> (getCellKey <$> b)))
  (getCellValue <$> a)
  (getCellValue <$> b)
visitor visit a b =
  visit
  (fromJust ((getCellKey <$> a) <|> (getCellKey <$> b)))
  (getCellValue <$> a)
  (getCellValue <$> b)
visitor visit a b =
  visit
  (fromJust ((getCellKey <$> a) <|> (getCellKey <$> b)))
  (getCellValue <$> a)
  (getCellValue <$> b)