BST :)

data Tree a = EmptyTree | Node a (Tree a) (Tree a) deriving (Show)

{- constructors -}
treeByList :: (Ord a) => [a] -> Tree a
treeByList x = foldr treeInsert EmptyTree x
{--}


printTreeHelper :: (Show t) => Tree t -> Int -> [Char]
printTreeHelper EmptyTree margin                    = ""
printTreeHelper (Node a EmptyTree EmptyTree) margin = (replicate margin ' ') ++ (show a)
printTreeHelper (Node a left right) margin          = (replicate margin ' ') ++ (show a) ++ "\n" ++ (printTreeHelper left (margin + 3)) ++ "\n" ++  (printTreeHelper right (margin + 3))

printTree :: (Show t) => Tree t -> [Char]
printTree a = printTreeHelper a 0

{- methods -}
inTree :: (Ord a) => a -> Tree a -> Bool
inTree _ EmptyTree = False
inTree x (Node a left right)
    | x == a  = True
    | x < a   = inTree x left
    | x > a   = inTree x right

treeInsert :: (Ord a) => a -> Tree a -> Tree a
treeInsert x EmptyTree = (Node x EmptyTree EmptyTree)
treeInsert x (Node a left right)
    | x == a = Node a left right
    | x > a  = Node a left (treeInsert x right)
    | x < a  = Node a (treeInsert x left) right

treeGetMin :: (Ord a) => Tree a -> a
treeGetMin (Node a EmptyTree right) = a
treeGetMin (Node a left right) = treeGetMin left

treeErase :: (Ord a) => a -> Tree a -> Tree a
treeErase x EmptyTree = EmptyTree
treeErase x (Node a left right)
    | x > a = (Node a left (treeErase x right))
    | x < a = (Node a (treeErase x left) right)
treeErase x (Node a EmptyTree right)     = right
treeErase x (Node a left EmptyTree)      = left
treeErase x (Node a left right)          = Node (treeGetMin right) left (treeErase (treeGetMin right) right)
{--}


elems = [7, 5, 3, 1, 6, 2, 4]

mytree = treeByList elems

main = putStrLn $ printTree (foldr treeErase mytree [4, 3, 2])