You should have experience with at least one programming language. It doesn't have to be JavaScript or ReasonML, even though we use these languages as examples of dynamic and statically-typed languages in this book.

You should have a macOS, Linux, or Windows computer on which to install ReasonML and the associated software.

You should type in and compile (in some cases, run) the examples shown throughout the chapters. The examples have been designed to show the ideas covered, and deliberately trying out some of the negative examples shown in the chapters will be very instructive.

You can download the example code files for this book from your account at www.packt.com. If you purchased this book elsewhere, you can visit www.packt.com/support and register to have the files emailed directly to you.

You can download the code files by following these steps:

1. Log in or register at www.packt.com.
2. Select the SUPPORT tab.
3. Click on Code Downloads & Errata.
4. Enter the name of the book in the Search box and follow the onscreen instructions.

Once the file is downloaded, please make sure that you unzip or extract the folder using the latest version of:

• WinRAR/7-Zip for Windows
• Zipeg/iZip/UnRarX for Mac
• 7-Zip/PeaZip for Linux

The code bundle for the book is also hosted on GitHub at https://github.com/PacktPublishing/Learn-Type-Driven-Development. We also have other code bundles from our rich catalog of books and videos available at https://github.com/PacktPublishing/. Check them out!

There are a number of text conventions used throughout this book.

CodeInText: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: "Mount the downloaded WebStorm-10*.dmg disk image file as another disk in your system".

A block of code is set as follows:

let sumOfSquares(x: int, y: int) = { /* (1) */
 let xSq = x * x;
 let ySq = y * y;
 xSq + ySq
};

The code is highlighted as follows:

• Types are bolded
• Values are slanted
• Language-reserved words (keywords) are underlined

Also note that numbered comments are added to certain points in the code that need further explanation, for example:

1. This note explains the code marked with the comment /* (1) */

Any command-line input or output is written as follows:

$ mkdir css
$ cd css

Bold: Indicates a new term, an important word, or words that you see on screen. For example, words in menus or dialog boxes appear in the text like this. Here is an example: "Select System info from the Administration panel".