Clean Architecture: A Craftsman's Guide to Software Structure and Design

6FUNCTIONAL PROGRAMMING

In many ways, the concepts of functional programming predate programming itself. This paradigm is strongly based on the l-calculus invented by Alonzo Church in the 1930s.

SQUARES OF INTEGERS

To explain what functional programming is, it’s best to examine some examples. Let’s investigate a simple problem: printing the squares of the first 25 integers.

In a language like Java, we might write the following:

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public class Squint {   public static void main(String args[]) {     for (int i=0; i<25; i++)       System.out.println(i*i);   } }

In a language like Clojure, which is a derivative of Lisp, ...