Functional programming (FP) is a programming paradigm where programs are constructed by applying and composing functions. It emphasizes the use of pure functions, immutability, and higher-order functions:

1. Pure Functions: A pure function is a function that, given the same inputs, always returns the same output and has no side effects (i.e., it doesn’t alter any state or interact with the outside world).

2. Immutability: In FP, data is immutable, meaning once a data structure is created, it cannot be changed. Instead of modifying data, new data structures are created by copying and modifying existing ones.

3. First-Class and Higher-Order Functions: Functions are first-class citizens in FP, meaning they can be assigned to variables, passed as arguments, and returned from other functions. Higher-order functions are functions that take other functions as arguments or return them as results.

4. Function Composition: Complex functions can be created by combining simpler ones. This allows for more modular and readable code.

5. Declarative Style: FP emphasizes what to do rather than how to do it. This is in contrast to imperative programming, which focuses on explicit steps to achieve a result.

6. Recursion: FP often relies on recursion as a primary mechanism for iteration, as opposed to looping constructs found in imperative programming.

7. Avoiding Side Effects: FP strives to minimize or avoid side effects (changes in state or interactions with outside systems), which makes reasoning about and debugging programs easier.

Advantages of Functional Programming

• Modularity: Code can be more modular and easier to test.
• Concurrency: Easier to write concurrent and parallel programs because there are no side effects and mutable state to manage.
• Predictability: Pure functions and immutability make the code more predictable and easier to debug.

Examples of Functional Programming Languages

• Haskell: A purely functional programming language with strong static typing.
• Erlang: Designed for concurrent and distributed systems.
• Lisp: One of the oldest programming languages, supporting functional programming.
• Scala: Combines functional and object-oriented programming features.
• F#: A functional-first language on the .NET platform.

Functional Programming in Other Languages

Languages like JavaScript, Python, and Java also support functional programming principles, even though they are not purely functional languages. They provide features like first-class functions, higher-order functions, and libraries or modules that support FP practices.

Cahracteristics of OOP that fit into FP

Functional programming is not at odd with object-oriented-programming. Of the four main pillars of OOP, only inheritance doesn’t fit into functional programming.

Encapsulation, abstraction and polymorphism are all part of FP.

References

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