Solutions to Page442 exercise of HPFFP

Page442.hs

module Page442 where

data BinaryTree a =
    Leaf
  | Node (BinaryTree a) a (BinaryTree a)
  deriving (Eq, Ord, Show)

preorder :: BinaryTree a -> [a]
preorder Leaf = []
preorder (Node left val right) = [val] ++ (preorder left) ++ (preorder right)

inorder :: BinaryTree a -> [a]
inorder Leaf = []
inorder (Node left val right) = (inorder left) ++ [val] ++ (inorder right)

postorder :: BinaryTree a -> [a]
postorder Leaf = []
postorder (Node left val right) = (postorder left) ++ (postorder right) ++ [val]

testTree :: BinaryTree Integer
testTree =
  Node (Node (Node Leaf 1 Leaf) 2 (Node Leaf 3 Leaf))
       4
       (Node Leaf 8 (Node Leaf 23 Leaf))

testPreorder :: IO ()
testPreorder =
  if preorder testTree == [4, 2, 1, 3, 8, 23]
  then putStrLn "Preorder fine!"
  else putStrLn "Preorder sad"

testInorder :: IO ()
testInorder =
  if inorder testTree == [1, 2, 3, 4, 8, 23]
  then putStrLn "Inorder fine!"
  else putStrLn "Inorder sad"

testPostorder :: IO ()
testPostorder =
  if postorder testTree == [1, 3, 2, 23, 8, 4]
  then putStrLn "Postorder fine!"
  else putStrLn "Postorder sad"

main :: IO ()
main = do
  testPreorder
  testInorder
  testPostorder