import Data.List(notElem)
import Data.Function(on)

data MLABCD = A | B | C | D | MLABCD :# MLABCD
  deriving Show

removeParenteses :: String -> String
removeParenteses = filter (\char -> notElem char "()")

instance Eq MLABCD where
  m0 == m1 = removeParenteses (show m0) == removeParenteses (show m1)
-- poderíamos ter usado
-- on :: (b -> b -> c) -> (a -> b) -> a -> a -> c
-- com b = String, c = Bool, a = MLABCD
-- seria:
-- (==) = (==) `on` (removeParenteses . show)

x = (A :# B) :# C
y = A :# (B :# C)