tree.hs

data Tree a = EmptyTree | Node a (Tree a) (Tree a) deriving (Show)
singleton :: a -> Tree a
singleton x = Node x EmptyTree EmptyTree
 
treeInsert :: (Ord a) => a -> Tree a -> Tree a
treeInsert x EmptyTree = singleton x
treeInsert x (Node a left right)
  | x == a = Node a left right
  | x < a  = Node a (treeInsert x left) right
  | x > a  = Node a left (treeInsert x right)
 
treeElem :: (Ord a) => a -> Tree a -> Bool  
treeElem x EmptyTree = False
treeElem x (Node a left right)
  | x == a = True
  | x < a  = treeElem x left
  | x > a  = treeElem x right
 
main = do
--  let nums = []
  let numsTree = foldr treeInsert EmptyTree nums
  print $ numsTree