poor soln h99 problemss: p56 - symmetrical binary trees

p56.hs

main = print $ demo
demo = isSym tree1

-- test data
tree1 = (Branch 'x' (Branch 'x' Empty Empty) (Branch 'x' Empty Empty))
tree2 = (Branch 'x' (Branch 'x' Empty Empty) Empty)

data Tree = Branch Char Tree Tree | Empty

isSym :: Tree -> Bool
isSym Empty = True
isSym (Branch _ left right) = isMirror left right

isMirror :: Tree -> Tree -> Bool
isMirror Empty            Empty             = True
isMirror (Branch _ _ _)   Empty             = False
isMirror Empty            (Branch _ _ _)    = False
isMirror (Branch _ al ar) (Branch _ bl br)  = isMirror al br && isMirror ar bl