forward :: Ant -> Dir -> Ant
forward (a,b) d | d == 0 = (a, b+1)
                | d == 1 = (a+1, b)
                | d == 2 = (a, b-1)
                | d == 3 = (a-1, b)
forward :: Ant -> Dir -> Ant
forward (a,b) d | d == 0 = (a, b+1)
                | d == 1 = (a+1, b)
                | d == 2 = (a, b-1)
                | d == 3 = (a-1, b)
forward (a,b) d | d == 0 = (a, b+1)
                | d == 1 = (a+1, b)
                | d == 2 = (a, b-1)
                | d == 3 = (a-1, b)