Defining a binary tree and traversing it

In this recipe, we will look at a data type that is recursively defined. We will define a binary tree and then explore functions to traverse it.

Getting ready

Create a new project binary-tree-traverse using the simple Stack template. Change into this directory:

    stack new binary-tree-traverse simple

How to do it...

1. Open src/Main.hs; we will be using this file for our recipe.
2. Define a binary tree data type:

        data BinaryTree a = Leaf
          | BinaryTree { left :: BinaryTree a
                               , val :: a
...