let aa = [1,2,3,4,5]
let aatree = treeFromList aa
split 3 aatree


*Main> let aa = [1,2,3,4,5]
*Main> let aatree = treeFromList aa
*Main> split 3 aatree
(Node 1 Empty (Node 2 Empty *** Exception: a.hs:(13,1)-(18,30): Non-exhaustive patterns in function split



a.hs

import Data.List

data BinTree a = Empty
| Node a (BinTree a) (BinTree a)
deriving (Show)
treeFromList :: (Ord a) => [a] -> BinTree a
treeFromList [] = Empty
treeFromList (x:xs) = Node x (treeFromList (filter (<x) xs))
(treeFromList (filter (>x) xs))


split :: Ord a => a -> BinTree a -> (BinTree a, BinTree a)
split _ Empty = (Empty, Empty)
split s (Node x lst rst)
| s < x = let (nlt, nrt) = split s lst in
(nlt, Node x nrt rst)
| s > x = let (nlt, nrt) = split s rst in
(Node x lst nlt, nrt)

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