Functional Vs Imperative language paradigms

These days, i am in deep love with Microsoft’s F# language and Apple’s Swift language.F# on one side has picked the good parts from Functional languages like ML and oCaml + Imperative languages / Object-Oriented language like C#.

Swift on the other end is a multi-paradigm languages picking language ideas from Objective-C, Rust, Haskell, Ruby, Python, C#, CLU, and far too many others to list.

While learning these languages,one question (in fact multiple questions) always comes to my mind-

“What is a functional language and what is imperative language? and how are they different ?”

Here are few answers which i read/ got from books and web,

Introduction:

The functional programming paradigm was explicitly created to support a pure functional approach to problem solving. Functional programming is a form of declarative programming. In contrast, most mainstream languages, including object-oriented programming (OOP) languages such as C#, Visual Basic, C++, and Java –, were designed to primarily support imperative (procedural) programming.

With an imperative approach, a developer writes code that describes in exacting detail the steps that the computer must take to accomplish the goal. This is sometimes referred to as algorithmic programming. In contrast, a functional approach involves composing the problem as a set of functions to be executed. You define carefully the input to each function, and what each function returns. The following table describes some of the general differences between these two approaches.

 Differences:

Characteristic	Imperative approach	Functional approach
Programmer focus	How to perform tasks (algorithms) and how to track changes in state.	What information 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 (method) calls.	Function calls, including recursion.
Primary manipulation unit	Instances of structures or classes.	Functions as first-class objects and data collections.

Although most languages were designed to support a specific programming paradigm, many general languages are flexible enough to support multiple paradigms. For example, most languages that contain function pointers can be used to credibly support functional programming. Furthermore, in C# 3.0 and Visual Basic 9.0, explicit language extensions have been added to support functional programming, including lambda expressions and type inference. LINQ technology is a form of declarative, functional programming.

Summarize :

Let’s generalize and say that there are two ways in which we can write code: imperative and declarative.

We could define the difference as follows:

• Imperative programming: telling the “machine” how to do something, and as a result what you want to happen will happen.
• Declarative programming: telling the “machine”¹ what you would like to happen, and let the computer figure out how to do it.

¹ Computer/database/programming language/etc

Courtesy : MSDN
CodeProject