# Lesson 5 Intro

## Introduction

This lesson builds upon the idea of hierarchical structures—structures made up of parts, which themselves are made up of parts, and so on. We will use these ideas to make a simple calculator in Racket at the end of the lesson.

### Warning

This lesson is substantially more dense and time-consuming than previous lessons. Make sure you pace yourself so as not to fall behind.

## Prerequisites and What to Expect

Material from Lesson 4 is required before working on this lesson.

We will briefly go over cons and list before extending their usage to build more complex structures.

## Readings

Here are the relevant readings for this lesson: