haskell binary tree traversal - inorder, postorder, preorder

haskell_binary_tree_traversal .hs

-- see video https://youtu.be/sv9y04GHvmY
data Btree a = Leaf a | Node a (Btree a) (Btree a) deriving Show

tr :: Btree Integer
tr_l = Node 1 (Leaf 2) (Leaf 3)
tr_r = Node 4 (Leaf 5) (Leaf 6)
tr = Node 7 tr_l tr_r

pre_order :: Btree a -> [a]

pre_order (Leaf a) = [a]
pre_order (Node a l r) = [a] ++ pre_order(l) ++ pre_order(r)

in_order (Leaf a) = [a]
in_order (Node a l r) = in_order(l) ++ [a] ++ in_order(r)

post_order (Leaf a) = [a]
post_order (Node a l r) = post_order(l) ++ post_order(r) ++ [a]

video with explanation

Videos:

pretty print tree

Level order traversal with BFS
Level order traversall with all paths
Level order traversall with zipwith
Level order traversall with label tree
Level order traversal of binary tree with fmap