Most of the programming you have done so far has been in the functional style. Although this has enabled you to write succinct, powerful programs, you never quite used the functional style to its full potential. Functional programming means more than just treating functions as values. Embracing the functional programming paradigm and having it help shape your thought process will enable you to write programs that would otherwise be prohibitively difficult in an imperative style.

In this chapter, we build on what you learned about functional programming back in Chapter 3, and introduce new language features that help you to be more productive in the functional style. For example, using active patterns allows you to increase the power of your pattern matching and eliminate the need for when guards, and by creating auto-opened modules, you can extend common F# modules.