Introducing the Klassbook

An easy way to experiment with a programming language is to use a REPL.

REPL is an acronym, describing a tool that will Read typed-in source code, Evaluate it, Print the results of that evaluation in the tool, and Loop back to process more input. Frequently, a REPL resembles an operating system shell or terminal, such as Windows’ Command Prompt or a bash shell in macOS or Linux.

Using a REPL gives you rapid feedback in a low-effort environment. You do not need a full IDE or a full application project to experiment with bits of language syntax and see how they work.

Klassbook is a REPL set up for use with this book. Most of the code examples shown in this book have corresponding Klassbook pages, where you can see the code, run the code to see the results, and even edit the code to try your own experiments. We will see how to use the Klassbook more in the next chapter.