The scala command demonstrated in the preceding section starts the Scala interactive shell, also known as Scala's Read-Eval-Print-Loop (REPL) environment. You enter a line and the REPL program evaluates it and prints a response (if applicable). It does this in an infinite loop until you quit the program.
In the Scala shell, you can write Scala code interactively. Because Scala is a compiled language, not an interpreted language, you can dynamically enter and execute Scala code in this program. Under the hood, Scala compiles your code and runs the compiled version. The Scala interactive shell is meant for trying Scala expressions, not for writing full programs. It is ideal for trying out the snippets in this chapter. The shell has commands of its own. Enter the :help command and press Enter to see all the shell commands.
In this chapter, we will only use the scala command to run Scala code. In the next chapter, we will cover the scalac compiler. To run code...