Functional programming

A programming paradigm that builds software by composing functions, emphasizing immutable data and avoiding changes to shared state. It treats computation primarily as the evaluation and transformation of values.

Pure function: A function whose output depends only on its inputs and that produces no observable side effects. Pure functions make composition predictable and reduce hidden dependencies.
Lambda calculus: A formal system for expressing computation through function abstraction and application. Its function-centered model underlies much of functional language design.
MapReduce: A distributed programming model that maps operations over data and combines their results. Its map and reduce stages use composable transformations suited to immutable data.
Imperative programming: A programming paradigm that describes computation through commands that change program state. It contrasts with functional emphasis on value transformations over explicit state updates.
Alonzo Church: An American mathematician and logician who developed lambda calculus and made foundational contributions to computability theory. Lambda calculus provided a formal basis for function-centered computation.
Immutability: The property of data that cannot be changed after it is created. Immutable values avoid shared-state changes that can make behavior order-dependent.
First-class function: A function that can be stored, passed, and returned like other values. First-class functions make functional composition practical in general-purpose languages.
Reactive programming: A programming paradigm for expressing computations over asynchronous streams of changing values. Functional transformations can describe stream processing without manually coordinating every update.
Object-oriented programming: A programming paradigm that organizes software around objects combining data and behavior. Its encapsulated mutable objects offer a different way to organize state and behavior.
John McCarthy: An American computer scientist who created Lisp and helped establish artificial intelligence as a field. Lisp brought symbolic computation and functional techniques into practical programming.

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