In this chapter you will learn
- how to deal with lists of lists using
flatten - how to write sequential programs using
flatMapinstead offorloops - how to write sequential programs in a readable way using for comprehensions
- how to use conditions inside for comprehensions
- how to get to know more types that have
flatMap
—Tony Hoare, “Efficient Production of Large Programs”
One of the most popular patterns in modern programming languages is pipelining. We can write many computations as a sequence of operations—a pipeline—that together make a bigger, more involved operation. It’s a different take on creating sequential programs. *
* In this chapter we will talk about sequential algorithms or sequential programs. A sequential program is a piece of code representing logic that takes a value, transforms it in a step-by-step manner (sequentially), and returns a final value.
Let’s look at an example. We have a list of three interesting books:
case class Book(title: String, authors: List[String])
val books = List(
Book("FP in Scala", List("Chiusano", "Bjarnason")),
Book("The Hobbit", List("Tolkien")),
Book("Modern Java in Action", List("Urma", "Fusco", "Mycroft"))
)
Our task is to count how many of them have the word “Scala” in the title. Having already met map and filter we can write the solution.
