The Toy Robot exercise was originally developed by Jon Eaves. He explains why he did it in this blog post.

If you're a new Elixir developer who's gone through some basic Elixir tutorials and you're looking for the next thing to build your skills, this book is a great start. It covers the Toy Robot exercise from start to finish, testing with Elixir features such as ExUnit and Doctests along the way.

The Toy Robot exercise is commonly used in interviews as the ways to solve it in any language are not as simple as they first may seem. This book covers one implementation of this exercise in Elixir. It is not intended to be the most perfect implementation of the Toy Robot exercise possible, but instead is my personal take on it.

In this book, I demonstrate best practices for developing a small Mix application that can solve the Toy Robot exercise. Along the way, you'll learn about:

• How to break a complex problem down into small, approachable chunks
• When to use Doctests or regular ExUnit tests
• Tradeoffs between different ways of pattern matching
• How to work with Elixir processes using GenServer + DynamicSupervisor

The Toy What Now?

The Toy Robot! It's a very common interview exercise given to new programmers. Here's the variant of the problem's description that we use in the book:

The application is a simulation of a toy robot moving on a square tabletop, of dimensions 5 units x 5 units. There are no other obstructions on the table surface. The robot is free to roam around the surface of the table. Any movement that would result in the robot falling from the table is prevented, however further valid movement commands are still allowed.

The application reads a file using a name passed in the command line, the following commands are valid:

• PLACE X,Y,F
• MOVE
• LEFT
• RIGHT
• REPORT

Here's some rules for these commands:

• PLACE will put the toy robot on the table in position X,Y and facing NORTH, SOUTH, EAST or WEST.
• The origin (0,0) is the SOUTH WEST most corner.
• All commands are ignored until a valid PLACE is made.
• MOVE will move the toy robot one unit forward in the direction it is currently facing.
• LEFT and RIGHT rotates the robot 90 degrees in the specified direction without changing the position of the robot.
• REPORT announces the X,Y and F of the robot.

The file is assumed to have ASCII encoding. It is assumed that the PLACE command has only one space, that is PLACE 1, 2, NORTH is an invalid command. All commands must be in upcase, all lower and mixed case commands will be ignored.

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All of that may seem a little bit overwhelming but if you break it down into little chunks and tackle those chunks one-at-a-time (like this book does!) it becomes much easier.