Programming Paradigms

Programming Paradigms ( http://www.directi.com | http://wiki.directi.com | http://careers.directi.com )‏ Licensed under Creative Commons Attribution Sharealike Noncommercial By, Janeve George [email_address] & Nilesh Mevada [email_address]

Creative Commons Sharealike Attributions Noncommercial Few Instruction

It's a workshop not a presentation !!!

Parking Lot

Perks

Creative Commons Sharealike Attributions Noncommercial Aim of the session

Introduction to programming concepts and techniques

Differentiate between various programming paradigms

Q: Why there are so many programming paradigms? A: Q: Isn't there 'one language' that would suffice? A: Q: How can we deal with understanding so many paradigms? A:

Creative Commons Sharealike Attributions Noncommercial Flow of the session

Programming Paradigm Definition

Why bother about 'Programming Paradigms'?

Appreciating 'Programming paradigms'

Programming Concepts

An Overview

Eager and Lazy Evaluation

Procedures

Functions

External and Internal State

Concurrency

Static vs Dynamic Typing

Some Real-Life Problems

Search (Java vs Prolog)‏

Higher Order Functions (Java vs Haskell)‏

Programming Paradigm - Definition

An Overview

Procedures

Functions

Concurrency

Creative Commons Sharealike Attributions Noncommercial Programming Paradigm - Definition

What are Programming Paradigms?

Fundamental style of computer programming. (wikipedia.org)‏

It serves as a pattern or model for a programming‏ language

Function Oriented Object Oriented Logical Programming Java ML Haskell Prolog Mercury Oz Erlang Smalltalk

An Overview

Procedures

Functions

Concurrency

Creative Commons Sharealike Attributions Noncommercial Why bother about 'Programming Paradigms'?

Tools (Programming Languages) may not suffice to deal with the real life problems.

They might not support the solution at all or only partially.

Learning new programming languages becomes easier

To bring innovations in programming technologies

An Overview

Procedures

Functions

Concurrency

Creative Commons Sharealike Attributions Noncommercial Appreciating 'Programming paradigms'

An example of how a trivial concept can affect/support a computation and hence a particular style of programming...

Int X; Int Y = X; Print( Y );

Execution Flow

?

An Overview

Procedures

Functions

Concurrency

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – An Overview Set of Programming Concepts Procedures Functions Higher/1 st Order Evaluation Eager/Lazy Variables Single/Multi store Scope Scope of variables Typing State Internal/External Objects Classes Concurrency & on & on & on.....

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – An Overview Subset of Concepts Programming Model Set of Programming Concepts Programming Language(s)‏ Embraced by Followed by Embraced by Followed by

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – An Overview Subset of Concepts OO Programming Model Set of Programming Concepts OO Programming Language(s)‏ Embraced by Followed by

Java

Ruby

Oz

C++

Scala

Etc...

Objects

Classes

Inheritance

Polymorphism

Explicit State

Etc...

Embraced by Followed by

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – An Overview Subset of Concepts Functional Programming Model Set of Programming Concepts Functional Programming Language(s)‏ Embraced by Followed by

Lazy/Eager Evaluation

Functions

Higher Order Func.

Etc...

Haskell

Erlang

ML

Scheme

Etc...

Embraced by Followed by

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – An Overview

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Few important concepts

Eager Evaluation

Lazy Evaluation

Procedures

Functions

External State

Internal State

Concurrency

Programming Concepts – An Overview

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Eager Evaluation

An expression which is evaluated as soon as it gets bound to a variable

Importance

Simple

Commonly found

Easy implementation for languages

Problems

Expressions are always evaluated

Languages supporting easy evaluation

Almost all including java, c#, c, etc.

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Eager Evaluation .... List Gen ( int N ) { ArrayList list = new ArrayList(); list. add ( N ); list. addAll ( Gen (N+1) ); return list; } void myMethod () { List K = Gen (1); System.out. println ( "Elements: " + K. getElementAt ( 3 ) ); } ....

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Lazy Evaluation

An expression is evaluated only when needed

Also known as delayed evaluation or call-by-need.

Importance

To deal with potentially infinite data.

Generally, calculations are not repeated.

Problems

Difficult at glance

Difficult to predict time/space complexity

Languages supporting Lazy Evaluation

Haskell, Oz, Scheme, OCamel

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Lazy Evaluation declare fun lazy { Gen N} N | { Gen N+1} end declare K = { Gen 1} { Browse “Elements: ” + Nth K 3}

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Procedures

A code construct which can

Execute a set of statements in an order

Accept zero or more arguments

Return zero or more results

Produce a side effect

Importance

One of the most basic building block of any programming language

A means of telling the system how to execute some behavior

May be used as to abstract out functions, objects & classes

Languages that support procedures

C, C++, C#, Oz

proc { Max X Y ?Z} if X>=Y then Z=X else Z=Y end end

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Procedures local Default MaxOrDefault in Default=10 proc { MaxOrDefault Arg ?Result} if Arg >= Default then Result = Arg else Result = Default end end local Result in { MaxOrDefault 5 Result} { Browse Result} end end

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Functions

A code construct which can

Execute a set of statements in a given order

Accept zero or more arguments

Returns only one result and no side effect

Pure functions avoid state and mutable data

Importance

A basic building block of many programming language

A means of telling the system how to execute some behavior

Can replicate a pure mathematical model

Languages that support Functions

Haskell, OCamel, ML, Oz

fun { Max X Y} if X>=Y then Z=X else Z=Y end end Z = { Max 10, 20}

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Higher Order Functions

Accepts functions as arguments along with other types

Can return a function as result

Ordering means...

1st order :- having no functions as args

2nd order :- can have 1st order functions as args

nth order :- can have n-1th order functions as args

We can build abstraction using Higher Order Functions

map f [] = [] map f (x:xs) = f x : map f xs numbers = [ 7,9,13 ] inc x = x + 1 more_numbers = map inc numbers

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Functions (Higher Order)‏ listsum [] = 0 listsum (x:xs) = x + listsum xs listprod [] = 1 listprod (x:xs) = x * listprod xs fold op init [] = init fold op init (x:xs) = x `op` fold op init xs listsum = fold (+) 0 listprod = fold (*) 1

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Explicit State

State remembrance across calls

Importance

One of the base concept for Object Orientation

Implicit state

Defined by the function for its internal calculations.

Importance

Storing temporary results which otherwise might require repetitive calls.

Languages that support external state

Object Oriented languages like Java, Smalltalk, etc

Languages that have global variables

Languages that support internal state

All languages that have variables in procedures / functions

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – External and Internal State fun { Sum Numbers} Result = { NewCell 0} Input = { NewCell Numbers} proc { Sum } case @Input of nil then skip [] X | Y then Result := @Result + X Input := Y { Sum } end end in { Sum } @Result end

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Multiple and independent executions

From real-life problems point of view, the definition adds this clause “and communicates only when needed”

Importance

relates more to real-life problems

response time improved due to parallel executions

Problems

race condition

Languages that support concurrent execution

Java, Oz

thread ConcurrentFlow1 = { GenerateNumbers 1 10} end

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Concurrency fun { GenerateNumbers FromArg ToArg} { Delay 100} if FromArg > ToArg then nil else FromArg | { GenerateNumbers FromArg+1 ToArg} end end thread ConcurrentFlow1 = { GenerateNumbers 1 10} end thread ConcurrentFlow2 = { GenerateNumbers 11 20} end { Browse ConcurrentFlow1} { Browse ConcurrentFlow2}

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Concurrency .... public void main(String[] args) throws InterruptedException { Temp temp = new Temp(); createAConcurrentFlow(1, 10); createAConcurrentFlow(11, 20); } .... private void createAConcurrentFlow( int FromArg, int ToArg) { new Runnable() { public void run() { try { new Temp().GenerateNumbers(FromArg, ToArg); } catch (InterruptedException e) { } } }; } ....

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Static Typing

Type checking is performed during compile-time

Variables should be defined before they're used.

Variables can be cast into other types

Variables don't get converted

Importance

Improved error-catching ability, efficiency, security

partial program verification

Problems

reducing expressiveness of the programming language

restrictions for the programmer on the programs he can write

Languages that use static typing

C, C++, C#, Java, ML, Pascal, Haskell

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Static Typing int num, sum; // explicit declaration num = 5; // now use the variables sum = 10; sum = sum + num;

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Dynamic Typing

Type checking is performed during runtime

It's not necessary to define the variable before used

Variables can be converted to other types implicitly

Importance

variables can be bound to any first-class-citizen in the lang. (proc, func, mix of data-types, etc.)‏

independent compilations of the program (since no type checking at compile time)‏

Problems

more type-error-prone code at run-time.

Languages that uses dynamic typing

JavaScript, Lisp, Perl, PHP, Prolog, Python, Ruby

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Dynamic Typing foo() { x = 1; x = 'hello'; }

Programming Paradigm Definition

An Overview

Procedures

Functions

Concurrency

Creative Commons Sharealike Attributions Noncommercial Some Real-Life Problems – Prolog vs Java % % Facts % male(hrithik). male(shahrukh). male(salman). male(abhishek). male(akshay). male(aamir). female(diya). female(aishwarya). female(katrina). female(malaika). parent(hrithik,shahrukh). parent(hrithik,salman). parent(hrithik,diya). parent(shahrukh,abhishek). parent(shahrukh,akshay). parent(salman,aishwarya). parent(salman,katrina). parent(salman,aamir). parent(diya,malaika). % % Rules % father(X,Y) :- parent(X,Y), male(X). mother(X,Y) :- parent(X,Y), female(X). grandparent(X,Y) :- parent(X,Z), parent(Z,Y). paternalgrandfather(X,Y) :- father(X,Z), father(Z,Y). sibling(X,Y) :- parent(Z,X), parent(Z,Y). brothers(X,Y) :- sibling(X,Y),male(X),male(Y), + (X=Y). % % Queries % cmd: mother(diya,malaika) % Outupt: yes/no cmd: mother(Mother,Child). % Output: lists (mother,child) pair found in facts % according to associations defined

Creative Commons Sharealike Attributions Noncommercial Some Real-Life Problems – Statistics

Creative Commons Sharealike Attributions Noncommercial How to approach Programming Paradigm?

Our Way was...

Concepts first, Languages Later.

Other effective ways...

Mastering any one programming model (e.g. Object Oriented) and then comparing it with others (e.g. functional, procedural, etc.)‏

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Books

Concepts, Techniques & Models Of Computer Programming by Peter Van Roy & Seif Haridi

Links On Web

http://wikipedia.org

http://www.infocheese.com/programmingparadigms.html

Creative Commons Sharealike Attributions Noncommercial What we expect post this session

Experimentation with other programming languages

Functional language -> Haskell / ML / Scheme

Object Oriented language -> Java, C++, C#, Scala

Aspect Oriented language -> AspectJ, AspectC++

Logic language -> Prolog / Mercury

Mixed languages -> Scala, Oz

Sharing your experiences with us...

A testimonial

“ I want to thank you and DIRECTI for conducting such a marvelous session and I am very much indebted for that. I fell in love with LISP programming language and found that it was very much ideal for signal processing algos. The approach u have suggested was just great and the book you have suggested was really really great.” - Chinni Krishna, Mukt '08 Session Attendee

Questions??? [email_address] & [email_address] http://directi.com http://careers.directi.com Download slides: http://wiki.directi.com

Retrospective!!! [email_address] & [email_address] http://directi.com http://careers.directi.com Download slides: http://wiki.directi.com