Chapter 2. The core rules

This chapter covers a few topics that every newcomer to Scala needs to know. Not every topic is covered in depth, but we cover enough to allow you to explore the subject. You’ll learn about the Read Eval Print Loop and how you can use this to rapidly prototype software. Next we’ll learn about expression-oriented programming, and how to look at control flow in a different light. From this, we’ll spring into immutability and why it can help to greatly simplify your programs, and help them run better concurrently.

2.1. Learn to use the Read Eval Print Loop (REPL)

Scala provides many materials to learn the core language. You can investigate many tutorials, examples, and projects online. But the single most important thing Scala provides is a Read Eval Print Loop (REPL). The REPL is an interactive shell that compiles Scala code and returns results/type immediately. The Scala REPL is instantiated by running scala on the command line, assuming you have Scala installed on your machine and your path is set correctly. The Scala REPL should output something like the following:

2.2. Think in expressions

2.3. Prefer immutability

2.4. Use None instead of null

2.5. Polymorphic equality

2.6. Summary