Programming Paradigms

Programming Paradigms

Object-oriented programming is one of several programming paradigms. Other programming paradigms include the imperative programming paradigm (as exemplified by languages such as Pascal or C), the logic programming paradigm (Prolog), and the functional programming paradigm (exemplified by languages such as ML, Haskell or Lisp). Logic and functional languages are said to be declarative languages. We use the word paradigm to mean “any example or model”. This usage of the word was popularized by the science historian Thomas Kuhn.He used the term to describe a set of theories, standards and methods that together represent a way of organising knowledge—a way of viewing the world. Thus a programming paradigm is a "way of conceptualizing what it means to perform computation and how tasks to be carried out on a computer should be structured and organized".
We can distinguish between two types of programming languages: Imperative languages and declarative languages. Imperative knowledge describes how-to knowledge while declarative knowledge is what-is knowledge. A program is ”declarative” if it describes what something is like, rather than how to create it. This is a different approach from traditional imperative programming languages such as Fortran, and C, which require the programmer to specify an algorithm to be run. In short, imperative programs make the algorithm explicit and leave the goal implicit, while declarative programs make the goal explicit and leave the algorithm implicit.
Imperative languages require you to write down a step-by-step recipe specifing how something is to be done. For example to calculate the factorial function in an imperative language we would write something like:
public int factorial(int n) {
int ans=1;
for (int i = 2; i <= n; i++){
ans = ans i;
}
return ans;
}
Here, we give a procedure (a set of steps) that when followed will produce the answer.
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Functional programming
Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions. Functional programming emphasizes the definition of functions, in contrast to procedural programming, which emphasizes the execution of sequential commands. The following is the factorial function written in a functional language called Lisp:
(defun factorial (n)
(if (<= n 1) 1 ( n (factorial (− n 1))))
)
Notice that it defines the factorial function rather than give the steps to calculate it.
The factorial of n is defined as 1 if n <= 1 else it is n factorial(n − 1)

Logic Programming
Prolog (PROgramming in LOGic) 2 is the most widely available language in the logic programming paradigm. It is based on the mathematical ideas of relations and logical inference. Prolog is a declarative language meaning that rather than describing how to compute a solution, a program consists of a data base of facts and logical relationships (rules) which describe the relationships which hold for the given application.
Rather then running a program to obtain a solution, the user asks a question. When asked a question, the run time system searches through the data base of facts and rules to determine (by logical deduction) the answer.
Logic programming was an attempt to make a programming language that enabled the expression of logic instead of carefully specified instructions on the computer. In the logic programming language Prolog you supply a database of facts and rules; you can then perform queries on the database.
The factorial function is written in prolog as two rules. Again, notice the declarative nature of the program.
fac(0,1).
fac(N,F) :− N > 0,
M is N − 1,
fac(M,Fm),
F is N * Fm.
To summarize:
• In procedural languages, everything is a procedure.
• In functional languages, everything is a function.
• In logic programming languages, everything is a logical expression (predicate).
• In object-oriented languages, everything is an object.