Mutable vs Immutable:
Values
You can name the results of expressions with the value keyword. Referencing a value doesn’t re-compute it.
Variable
var keyword is used to define a variable. Variables are immutable. Variables are similar to values, except we can re-assign them.
REPL (Read Evaluate Print Loop)
The REPL is a command line interpreter which is used to test our Scala code. It is simple to start a REPL session, just type Scala on your operating system command line and write a simple equation and the output will be:
When we do not assign the result of our equation to any variable, the REPL automatically creates variable that start with the name res. The output of variable is stored in res0; the next one is stored in res1, and so on.
REPL is also immutable, the reference example can be used as a reference.
