Programming Paradigms

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Programming Paradigms
By, Janeve George janeve.g_at_directi.com
Nilesh Mevada nilesh.m_at_directi.com
(http//www.directi.com http//wiki.directi.com
http//careers.directi.com)?
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Few Instruction

• It's a workshop not a presentation !!!
• Parking Lot
• Perks

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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
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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)?

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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)?

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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

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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)?

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Why bother about 'Programming Paradigms'?
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Why bother about 'Programming Paradigms'?
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Why bother about 'Programming Paradigms'?
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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

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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)?

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Appreciating 'Programming paradigms'

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

Execution Flow
Int X Int Y X Print( Y )
?
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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)?

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Programming Concepts An Overview
Set of Programming Concepts Procedures Functions
Higher/1st Order Evaluation Eager/Lazy Variable
s Single/Multi store Scope Scope of
variables Typing State Internal/External Objects
Classes Concurrency on on on.....
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Programming Concepts An Overview
Set of Programming Concepts
Programming Model
Embraced by
Followed by
Programming Language(s)?
Subset of Concepts
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Programming Concepts An Overview
Set of Programming Concepts
OO Programming Model
Embraced by
Followed by
OO Programming Language(s)?
Subset of Concepts

• Java
• Ruby
• Oz
• C
• Scala
• Etc...

• Objects
• Classes
• Inheritance
• Polymorphism
• Explicit State
• Etc...

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Programming Concepts An Overview
Set of Programming Concepts
Functional Programming Model
Followed by
Embraced by
Functional Programming Language(s)?
Subset of Concepts

• Lazy/Eager Evaluation
• Functions
• Higher Order Func.
• Etc...

• Haskell
• Erlang
• ML
• Scheme
• Etc...

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Programming Concepts An Overview
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Programming Concepts An Overview
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Programming Concepts An Overview

• Few important concepts
• Eager Evaluation
• Lazy Evaluation
• Procedures
• Functions
• External State
• Internal State
• Concurrency
• Static vs Dynamic Typing

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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.

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Programming Concepts Eager Evaluation
.... List Gen( int N ) ArrayList list new
ArrayList() list.add( N ) list.addAll(
Gen(N1) ) return list void myMethod ()
List K Gen(1) System.out.println(
"Elements " K.getElementAt( 3 ) ) ....
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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

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Programming Concepts Lazy Evaluation
declare fun lazy Gen N N Gen
N1 end declare K Gen 1 Browse Elements
Nth K 3
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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 XgtY then ZX else ZY
end end
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Programming Concepts Procedures
local Default MaxOrDefault in Default10 proc
MaxOrDefault Arg ?Result if Arg gt Default
then Result Arg else Result
Default end end local Result
in MaxOrDefault 5 Result Browse
Result end end
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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 XgtY then ZX else ZY
end end Z Max 10, 20
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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 (xxs) f x map f
xs numbers 7,9,13 inc x x 1 more_numbers
map inc numbers
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Programming Concepts Functions (Higher Order)?
listsum 0 listsum (xxs) x listsum
xs listprod 1 listprod (xxs) x
listprod xs
fold op init init fold op init (xxs) x
op fold op init xs listsum fold ()
0 listprod fold () 1
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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

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Programming Concepts External and Internal State
fun Sum Numbers Result NewCell 0
Input NewCell Numbers proc Sum
case _at_Input of nil then skip X Y
then Result _at_Result X
Input Y Sum end end
in Sum _at_Result end
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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
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Programming Concepts Concurrency
fun GenerateNumbers FromArg ToArg Delay
100 if FromArg gt ToArg then nil else FromA
rg GenerateNumbers FromArg1
ToArg end end thread ConcurrentFlow1
GenerateNumbers 1 10 end thread ConcurrentFlow
2 GenerateNumbers 11 20 end Browse
ConcurrentFlow1 Browse ConcurrentFlow2
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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().GenerateNumbe
rs(FromArg, ToArg) catch
(InterruptedException e) ....
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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

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Programming Concepts Static Typing
int num, sum // explicit declaration num 5 //
now use the variables sum 10 sum sum num
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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

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Programming Concepts Dynamic Typing
foo() x 1 x 'hello'
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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)?

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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). par
ent(hrithik,salman). parent(hrithik,diya). parent(
shahrukh,abhishek). parent(shahrukh,akshay). paren
t(salman,aishwarya). parent(salman,katrina). paren
t(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), \ (XY).
Queries cmd mother(diya,malaika) Outupt
yes/no cmd mother(Mother,Child). Output
lists (mother,child) pair found in facts
according to associations defined
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Some Real-Life Problems Statistics
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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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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.htm
  l

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What we expect post this session

• Experimentation with other programming languages
• Functional language -gt Haskell / ML / Scheme
• Object Oriented language -gt Java, C, C, Scala
• Aspect Oriented language -gt AspectJ, AspectC
• Logic language -gt Prolog / Mercury
• Mixed languages -gt 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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Questions???janeve.g_at_directi.com
nilesh.m_at_directi.comhttp//directi.comhttp//ca
reers.directi.com Download slides
http//wiki.directi.com
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Retrospective!!!janeve.g_at_directi.com
nilesh.m_at_directi.comhttp//directi.comhttp//ca
reers.directi.com Download slides
http//wiki.directi.com
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