In this lesson, we will delve into the key principles of functional programming (FP). Understanding these principles is essential for approaching software design through a functional lens, which can help you solve complex problems with more elegant and maintainable code.

During technical interviews you might encounter questions like:

• What are the key principles of functional programming?
• How does immutability contribute to functional programming?
• Can you provide examples of functional programming features in modern programming languages?

Mastering answers to these questions will enable you to highlight your understanding of functional paradigms and their application in real-world scenarios, effectively showcasing your versatility as a software developer.

To start, let's break down the fundamental principles of functional programming:

1. Immutability:

   • Concept: In functional programming, once a data structure is created, it cannot be changed.
   • Why it matters: Immutability helps prevent side effects, making your code more predictable and easier to debug.

2. First-Class and Higher-Order Functions:

   • Concept: Functions in FP can be treated as first-class citizens, meaning they can be passed as arguments and returned from other functions.
   • Why it matters: This enables more abstract and reusable code, fostering a composition of operations rather than imperative sequences.

3. Pure Functions:

   • Concept: Pure functions always produce the same output for the same inputs and have no side effects.
   • Why it matters: Pure functions make your programs easier to reason about, test, and maintain.

4. Function Composition:

   • Concept: Combining simple functions to build more complex functions.