Problem 56 Solution

type Tree a
    = Empty
    | Node a (Tree a) (Tree a)


mirror : Tree a -> Tree a -> Bool
mirror left right =
    case left of
        Empty ->
            case right of 
                Empty ->
                    True
                _ ->
                    False
        Node ln ll lr ->
            case right of 
                Empty ->
                    False
                Node rn rl rr -> 
                    (mirror ll rr) && (mirror lr rl)



isSymmetric : Tree a -> Bool
isSymmetric tree = 
    case tree of 
        Empty ->
            True

        Node n left right ->
            mirror left right