What Functional Programming Is

Functional programming is a way of writing software by building solutions out of functions and composing them cleanly. In this lesson, Professor Christina Ross introduces the core idea: focus on what should happen, not on step-by-step mutation of shared state. You will see how functional programming emphasizes pure functions, immutable data, and predictable behavior, while also understanding that real-world programs still interact with the outside world.

This lesson is foundational. It defines the mindset of functional programming, explains why it is useful, and contrasts it with common imperative habits without going too deep into language-specific syntax or advanced patterns.