What are Higher-Order Functions?

In this chapter, we will see the actual power of functional programming and how functions in a functional programming language differ from functions in a non-functional programming language.

Higher-Order Functions

Functional programming languages treat functions as first-class values. What this means is that, like any other value, such as Integers or Strings, a function can be passed as a parameter to another function and can also be returned as a result.

Functions that take other functions as parameters or that return functions as results are called higher-order functions.

Syntax

As we already know, the syntax for defining a function which takes a simple variable as a parameter is:

When we want to define a function which takes another function as a parameter, the syntax of the parameter would be the following:

We have taken the function name to be f. f is the function to be passed as a parameter. It is followed by a : which is further followed by the data type of f's argument. We then insert an arrow => which is followed by the data type of f's result.

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In the next lesson, we will be looking at an example which will be carried forward for the next several lessons.