https://DevOpsCloud.io -- Cloud Monk Losang Jinpa, Ph.D., MCSE/MCT, GitOps DevOps Engineer

The Purely Functional Programming Paradigm is a subset of functional programming that emphasizes the use of pure functions exclusively. In purely functional programming, functions have no side effects and their outputs are determined solely by their inputs. This paradigm promotes immutability and avoids mutable state, ensuring that functions do not alter any state or interact with the outside world during their execution. This leads to highly predictable and reliable code.

The core concepts of purely functional programming include immutability, pure functions, and referential transparency. Immutability means that data structures cannot be modified after they are created. Pure functions are those that consistently produce the same output given the same input and do not cause any side effects, such as modifying global variables or performing I/O operations. Referential transparency ensures that expressions can be replaced with their corresponding values without changing the program's behavior, which simplifies reasoning about code and enables powerful optimization techniques.

Purely functional programming offers several advantages, including easier reasoning about code, improved modularity, and enhanced maintainability. Since pure functions have no side effects, understanding and testing them is straightforward; their behavior is predictable and isolated from the rest of the system. This modularity allows for easier composition of functions to build complex operations. The immutability of data structures prevents unexpected state changes, reducing bugs and making the code more robust. Additionally, purely functional code is highly amenable to parallel and concurrent execution, as there are no side effects that could cause race conditions.

The Purely Functional Programming Paradigm is widely used in fields that require high reliability, maintainability, and ease of reasoning, such as financial systems, concurrent and parallel computing, and formal verification. It is particularly well-suited for developing compilers, static analysis tools, and mathematical software, where the predictability of pure functions is crucial. Languages such as Haskell, Elm, and PureScript exemplify purely functional programming, providing robust frameworks and libraries that enforce purity and immutability, thus promoting best practices in functional programming.

• Purely functional programming Wikipedia: https://en.wikipedia.org/wiki/Purely_functional_programming
• Introduction to Haskell: https://www.haskell.org/
• Elm language documentation: https://guide.elm-lang.org/
• PureScript official site: https://www.purescript.org/
• Benefits of immutability: https://www.martinfowler.com/articles/collection-pipeline/immutability.html

Snippet from Wikipedia: Purely functional programming

In computer science, purely functional programming usually designates a programming paradigm—a style of building the structure and elements of computer programs—that treats all computation as the evaluation of mathematical functions.

Program state and mutable objects are usually modeled with temporal logic, as explicit variables that represent the program state at each step of a program execution: a variable state is passed as an input parameter of a state-transforming function, which returns the updated state as part of its return value. This style handles state changes without losing the referential transparency of the program expressions.

Purely functional programming consists of ensuring that functions, inside the functional paradigm, will only depend on their arguments, regardless of any global or local state. A pure functional subroutine only has visibility of changes of state represented by state variables included in its scope.

Creative Commons Attribution-Share Alike 4.0