In a binary tree, each node has at most two children. We will define a data structure to encompass the left and right subtrees of each node.
The code in the recipe will represent the following tree. The root node is labeled n3 with a value of 3. It has a left node n1 of value 1, and a right node n2 of value 2.
This code requires no imports. We can jump in and define the data structure recursively. A tree can either be a node with values or null/empty:
data Tree a = Node { value :: a , left :: (Tree a) , right:: (Tree a) } | Leaf deriving ShowIn
main, create the tree shown in the preceding diagram and print it out:main = do let n1 = Node { value = 1, left = Leaf, right = Leaf } let n2 = Node { value = 2, left = Leaf, right = Leaf } let n3 = Node { value = 3, left = n1, right = n2 } print n3The full tree is printed out as follows:
$ runhaskell Main.hs Node {...