Conclusions

Our focus in this chapter was on getting Scala code running in a worksheet, and starting to build a basic model of program evaluation.

We introduced expressions, types, and values:

• expressions are program text;
• values are the result of running programs; and
• types are a property of expressions that indicate the set of values an expression may evaluate to.

We also also discussed evaluation, which connects expressions and values, and compilation, which is a process that happens before evaluation and performs type checking.

Finally, we introduced the concepts of compile-time, which means the time when a program is compiled, and run-time, which refers to the time when a program is evaluated.