module Exercise04 where

{-WETT-}
xmlLight :: String -> Bool
f :: Int -> [String] -> String -> Bool
g :: Char -> [String] -> String -> Bool

xmlLight = f 0 []
f 0 s      (c:cs)                                 = c == '<' && f 1 ([] : s) cs || c `notElem` "<>" && f 0 s cs
f 1 s      ('/':cs)                               = f 3 s cs
f q (a:s)  (c:cs)   | q < 4 && c `notElem` "< />" = f q ((a ++ [c]) : s) cs
f 3 (a:b:s)(c:cs)   | c `elem` " >"               = a == b && g c s cs
f _ s      (c:cs)   | c `elem` " >"               = g c s cs
f q s      _                                      = q == 0 && null s
g ' ' = f 4
g _   = f 0
{-TTEW-}