module Exercise04 where

import Data.List

{-WETT-}

xmlLight :: String -> Bool
xmlLight text = groupBy is_b text `tagCheck` []
  where
    is_b x y = notElem x "<>/" && notElem y "<>/"
    dr = dropWhile (== ' ') . reverse
    tagCheck ("<" : t : ">" : ts) ttc = tagCheck ts $ t : ttc
    tagCheck ("<" : "/" : t : ">" : ts) (tc : ttc) = dr tc == dr t && ' ' `notElem` dr t && tagCheck ts ttc
    tagCheck (t : ts) ttc = null (t `intersect` "<>") && tagCheck ts ttc
    tagCheck _ x = null x

{-TTEW-}