pad' :: Token a => Int -> [Tree a] -> String
pad' n s =
  let s' = bracket . map showTree $ s
  in replicate (n - length s') ' ' ++ s'
pad' :: Token a => Int -> [Tree a] -> String
pad' n s =
  let s' = bracket . map showTree $ s
  in replicate (n - length s') ' ' ++ s'
pad' n s =
  let s' = bracket . map showTree $ s
  in replicate (n - length s') ' ' ++ s'