BracketTest.hs

hasMatchingBrackets :: String -> Bool
hasMatchingBrackets = fst . foldr reducingFn (True, mempty)
  where
    reducingFn _    (False, xs)                                = (False, xs) -- short circuit if already false
    reducingFn char (True, tokens) | char `elem` openingTokens = (True, char : tokens)
    reducingFn char (True, [])     | char `elem` closingTokens = (False, [])
    reducingFn char (True, x:xs)   | char `elem` closingTokens = if isClosingToken x char then (True, xs) else (False, x:xs)
    reducingFn _    st                                         = st

tokenPairs :: [(Char, Char)]
tokenPairs = [ ('(', ')'), ('{', '}')]

openingTokens :: String
openingTokens = fst <$> tokenPairs

closingTokens :: String
closingTokens = snd <$> tokenPairs

isClosingToken :: Char -> Char -> Bool
isClosingToken opening closing = undefined