create balanced tree from sorted list

balanced_from_sorted.hs

-- GHCi, version 8.8.4
{-# LANGUAGE ScopedTypeVariables #-}
import PrettyT -- https://www.youtube.com/watch?v=Ud-1Z0hBlB8&t=379s
import Data.List
import Data.Maybe
-- data Btree a = Empty | Node a (Btree a) (Btree a) deriving Show


-- build balanced binary search tree from sorted list
-- assume list is sorted
-- nodes must be uniq
-- https://www.youtube.com/watch?v=icRN-f408oE

b :: [a] -> Btree a
b [] = Empty
b l = Node m (b l_) (b r_) where
                              m = l !! mi
                              (l_,r) = splitAt mi l
                              r_ = tail r
                              mi = (length l) `div` 2

https://www.youtube.com/watch?v=icRN-f408oE