BracketMatch.hs

data Bracket = Open | Close
data Nat = Ze | Su Nat

isZero :: Nat -> Bool
isZero Ze = True
isZero (Su _) = False

match :: [Bracket] -> Bool
match = go Ze
  where
  go :: Nat -> [Bracket] -> Bool
  go l [] = isZero l
  go l (Open : w) = go (Su l) w
  go Ze (Close : w) = False
  go (Su l) (Close : w) = go l w