This document discusses functional programming (FP) as an alternative to object-oriented programming (OOP). It notes issues with OOP like null pointer problems and inheritance issues. It then gives reasons for using FP like the need to write concurrent programs and handle data management problems. FP is described as using recursion instead of loops, higher-order functions, and treating programs as mathematical functions. FP avoids variables and assignments and favors immutability. Examples of FP languages provided are Erlang, Haskell and Clojure. Caution is given around maintainability, advocating for readability over one-liners. Real-world adoptions of FP at companies like Facebook and LinkedIn are also mentioned.

1. FUNCTIONAL
PROGRAMMING (FP)
Prateek Jain
(prateekjainaa@gmail.com)

2. Is OOPs, oops?
• NullPointer problems
• Inheritance issues
• “new” operator issues

3. Is OOPs, oops?
• NullPointer problems
• Inheritance issues
• “new” operator issues

4. Is OOPs, oops?
• NullPointer problems
• Inheritance issues
• “new” operator issues

5. Why FP?
• I Have to Be Good at Writing Concurrent Programs
• Most Programs Are Just Data Management Problems
(why ORM?)
• More Modular
• I Have to Work Faster and Faster
• Code is written once, but read many times

6. Why FP?
• I Have to Be Good at Writing Concurrent Programs
• Most Programs Are Just Data Management Problems
(why ORM?)
• More Modular
• I Have to Work Faster and Faster
• Code is written once, but read many times

7. Why FP?
• I Have to Be Good at Writing Concurrent Programs
• Most Programs Are Just Data Management Problems
(why ORM?)
• More Modular
• I Have to Work Faster and Faster
• Code is written once, but read many times

8. Why FP?
• I Have to Be Good at Writing Concurrent Programs
• Most Programs Are Just Data Management Problems
(why ORM?)
• More Modular
• I Have to Work Faster and Faster
• Code is written once, but read many times

9. Why FP?
• I Have to Be Good at Writing Concurrent Programs
• Most Programs Are Just Data Management Problems
(why ORM?)
• More Modular
• I Have to Work Faster and Faster
• Code is written once, but read many times

10. What is FP?
• RECURSION
• ABSTRACTION
• HIGHER ORDER FUNCTIONS
• IMPACT MOST PROGRAMMING LANGUAGES

11. PROGRAMS AS FUNCTIONS
• PROGRAM = DESCRIPTION OF A SPECIFIC
COMPUTATION
• Y = F(X)
• F: X ->Y
• MATHEMATICS
• VARIABLES = ACTUAL VALUES
• NO MEMEORY ALLOCATION CONCEPT
• IMPERATIVE LANGUAGE
• VARIABLES = MEMORY LOCATIONS + VALUES

12. PROGRAMS AS FUNCTIONS
• NO LOOPS BUT RECURSION
• NO VARIABLE EXCEPT AS A NAME FOR A VALUE
• NO ASSIGNMENT OPERATION (x = x+1 ,
MEANINGLESS)
• ONLY CONSTANTS, PARAMETERS AND VALUES

13. imperative
functional
EXAMPLE
Void GCD (int u, int v, int* x) {
Int y, t, z;
z = u;
y = v;
While (y!=0) {
…
…
}
…
}
Void GCD(int u, int v) {
if(v==0)
return u;
else
return GCD(v, u%v);
}

14. NO VARIABLES, NO ASSIGNMENT
• No notion of the internal state of a function.
• Referential Transparency.
• Value Semantics.

15. FP vs Others
• Recursions instead of loops
• Pattern matching instead of “if”
• Pattern matching instead of state machines
• Information transformation instead of sequence of tasks

16. FP vs Others
• Persistent data structures
• Powerful concurrency constructs : Actors
• Software transactional memory
• Avoid “Null”

17. What it really means?
• Immutability is good

18. What it really means?
• Immutability is good
• No bugs (due to nasty side effects)

19. What it really means?
• Immutability is good
• No bugs (due to nasty side effects)
• Benefits from concurrency

20. What it really means?
• Immutability is good
• No bugs (due to nasty side effects)
• Benefits from concurrency
• No more messy loops

21. What it really means?
• Immutability is good
• No bugs (due to nasty side effects)
• Benefits from concurrency
• No more messy loops
• Lazy evaluation

22. FP Examples
• Erlang, Haskell, Clojure
• F#
• JAVA 8 (prject lambda), Scala, Groovy
• R, Mathematica etc. (specialized languages)

23. CAUTION CAUTION

24. Maintaining, Maintainability
• Use functional style wheretill it makes the intent more
readable.
Sort(extract(filter(having(on(Pet.class).getSpecies(), is(Dog)), pets,
on(Pet.class).getName()), on(String.class));
List<Pet> dogs =
filter(having(on(Pet.class).getSpecies(), is(Dog)), pets);
List<String> dogNames = extract(dogs, on(Pet.class).getName());
List<String> sortedDogNames = sort(dogNames, on(String.class));

25. Maintaining, Maintainability
• One liners are always not better.
Convert(pets, new Convert<Pet, VetStay>() {
@override public VetStay converter(Pet pet) {
return new VetStay(pet, new Date(), “….”);
}});
Private Converter<Pet, VetStay> toVetStay () {
@override public VetStay converter(Pet pet) {
return new VetStay(pet, new Date(), “….”);
}});
Convert(pets, toVetStay());

26. FP - Adoption
• Facebook (tchat), Linkedin uses Erlang
• Twitter, UBS, Credit Suisse uses Scala

27. QUESTIONS?
Questions?

28. FEEDBACK
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