Functional Programming

• the main unit of functional programming is a function
• the aim is to abstract control flows and operations on data with functions
  • by doing so we could avoid side effects and reduce mutation of state

Imperative programming paradigm

• it is one of the oldest programming paradigms
• It has a close connection to machine architecture
• By changing the state through assignment statements we are achieving results
• The state is changing by performing step-by-step tasks
• The main concept is how to achieve our goal
• If you are following the imperative programming paradigm you have several statements and the result is stored after execution of all of them

pro	cons
Very simple to implement	Less efficient and less productive
	Parallel programming is not possible

• example

  • creation of new empty array doubled
  • going through array with for loop
  • double each element
  • push the doubled element into doubled array
  • return doubled array

  const doubleMap = (numbers) => {
    const doubled = [];
  
    for (let i = 0; i < numbers.length; i++) {
      doubled.push(numbers[i] * 2);
    }
  
    return doubled;
  };
  
  console.log(doubleMap([2, 3, 4])); // [4, 6, 8]

Declarative programming paradigm

• The main idea is to define what needs to be accomplished by the program, but not how it needs to be implemented

• instead of instructing how to achieve the desired results we focus only on the result itself

• It is different from imperative programming which focuses on a set of commands which need to be executed in order to achieve the required solution

• it describes a particular class of problems that have to be solved and a language implementation takes care of finding the solution

• With this approach, the resulting program is simpler to read

• example

  • all routine work is done by map
  • we only pass the callback in which we provide the condition which is important to us in this case

  const doubleMap = (numbers) => numbers.map((n) => n * 2);
  
  console.log(doubleMap([2, 3, 4])); // [4, 6, 8]

Is FP imperative or declarative

• FP implements most of the declarative rules
  • such as programmers focus on what to do, composition, recursion, immutability, functions as first-class objects, etc.

Characteristic	Imperative Approach	Functional Approach
Description	The program directly changes computed state	The program avoids mutating state and computation data
Key points	Direct assignments, global variables, common data structures	Compositional, recursion, no side effects
Programmer focus	How to perform tasks and how to track state changing	What is desired and what transformations are required
State changes	Important	Non-existent
Order of execution	Important	Low importance
Primary flow control	Loops, conditionals and function calls	Function calls, recursion
Primary manipulation unit	Instances of structures or classes	Functions as first-class objects and data collections