Writing basic functions

In this section, we write our first Haskell functions to get acquainted with Haskell’s syntax and basic elements.

Our first function

Let us start with a simple function for incrementing an integer:

increment :: Int -> Int
increment x = x + 1

This function definition consists of two lines. The first line is the type signature and the second line defines the behavior of the function. The type signature states that the function has the name increment and, given a value of the Int type as input, produces a result of the Int type. Here, Int is of course the type of integers such as -1, 0, and 42.

The second line is an equation that says that increment x (where x is any possible input) is equal to x + 1. We can read such an equation also operationally: given any x input, the increment function returns the result x + 1. Here, x is called a variable; it acts as a placeholder for an actual input to the function. The result x + 1 is called the...