Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data. It emphasizes the use of pure functions, higher-order functions, and immutability, enabling developers to write concise, declarative, and composable code that is easier to reason about and test.
In this paradigm, functions are first-class citizens, meaning they can be passed as arguments, returned as values, and assigned to variables. Functional programming avoids side effects by not altering the state of data, promoting immutability and the use of immutable data structures. This approach leads to more predictable and reliable code, facilitates easier testing and debugging, and supports higher-order functions and function composition. Languages like Haskell, Erlang, and modern features in languages like Python and JavaScript support functional programming principles.