Real World Haskell

Chapter 4. Functional Programming

Thinking in Haskell

Our early learning of Haskell has two distinct obstacles. The first is coming to terms with the shift in mindset from imperative programming to functional: we have to replace our programming habits from other languages. We do this not because imperative techniques are bad, but because in a functional language other techniques work better.

Our second challenge is learning our way around the standard Haskell libraries. As in any language, the libraries act as a lever, enabling us to multiply our problem-solving ability. Haskell libraries tend to operate at a higher level of abstraction than those in many other languages. We’ll need to work a little harder to learn to use the libraries, but in exchange they offer a lot of power.

In this chapter, we’ll introduce a number of common functional programming techniques. We’ll draw upon examples from imperative languages in order to highlight the shift in thinking that we’ll need to make. As we do so, we’ll walk through some of the fundamentals of Haskell’s standard libraries. We’ll also intermittently cover a few more language features along the way.

A Simple Command-Line Framework

In most of this chapter, we will concern ourselves with code that has no interaction with the outside world. To maintain our focus on practical code, we will begin by developing a gateway between our “pure” code and the outside world. Our framework simply reads the contents of one file, applies a function to the ...