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)‏

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)‏

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

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

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

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 ?

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

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...

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...

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – An Overview

Creative Commons Sharealike Attributions Noncommercial Few important concepts Eager Evaluation Lazy Evaluation Procedures Functions External State Internal State Concurrency Static vs Dynamic Typing 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}

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Functions (Higher Order)‏ 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

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – External and Internal State 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

Creative Commons Sharealike Attributions Noncommercial Programming Concepts – Concurrency 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'; }

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.)‏

Creative Commons Sharealike Attributions Noncommercial References 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

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Programming Paradigms

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