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Functional Programming
Contact me: hadoope@gmail.com
Let’s Rock!
Why FP ???
Single Threading can’t scale,
but multi-ple threading is hard!
Simple is Beautiful!
Beautiful Concurrency ???
Thread Safe
Synchronized
Deadlock
Livelock
Races
Debugging
Mutable shared state!!!
Functional Programming
No Mutable
In computer science, functional programming is a programming paradigm,
a style of building the structure and elements of c...
First Class Function
Higher-Order Function
Purify
Curry
Lazy Evaluation
Monoid
Monad
Tail Recursive
First Class Function
http://jsfiddle.net/hadoope/RAYy7/
Number Versus Function
Higher-Order Function
Functions that take other functions
Functions that return other functions
var people = [{name: "Fred...
Currying
Currying using Lambda calculus
(x, y) -> x * x + y *y
x -> y -> x * x + y *y
=
Currying in JavaScript
function curry3(fun) {
return function(last) {
return function(middle) {
return function(first) {
r...
Recursion and Tail Recursive
def factorial(n)
if (n == 1)
return 1
else
return n* factorial(n-1)
end
end
@tailrec def fact...
Lazy Evaluation
In programming language theory, lazy evaluation, or call-by-need is an evaluation strategy
which delays th...
Lazy Evaluation
 Performance increases by avoiding needless calculations, and error conditions in
evaluating compound exp...
Pattern Matching
• Object Matching
Import scala.util.Random
var randomInt = new Random().nextInt(10)
randomInt match {
cas...
Pattern Matching
• Type Matching
var items = List(1, “foo”, 3.5)
for (item <- items) {
item match {
case i: Int => println...
Pattern Matching
Functionalpolymorphism
Versus
OOpolymorphism
Monoid
Just what is a monoid, then? It is simply an implementation of an interface
governed by some laws. Stated tersely, ...
Monoid will buy us ???
Associativity brings high parallelism
op(a, op(b, op(c,d)))Folding to the right:
After folding in p...
Monad
In functional programming, a monad is a structure that
represents computations defined as sequences of steps. A type...
Functional Javascript
• Collection-Centric Programming
Functional Javascript
• Collection-Centric Programming (map, reduce
and filter)
http://jsfiddle.net/hadoope/xhQ4P/
Monad using Javascript
var stack = [];
stack.push(4);
stack.push(5);
stack.pop(); // 5
stack.pop(); // 4
Normal Style
http...
Monad using Javascript
http://jsfiddle.net/hadoope/FcD5S/
Continuation-Passing Style
Monad using Javascript
• Currying push and pop
http://jsfiddle.net/hadoope/62bfe/2/
Monad using Javascript
• Preparing bind to Handle Intermediate Stacks
http://jsfiddle.net/hadoope/Lsgw5/
Monad Using Haskell
computation = push 4 >>= _ ->
push 5 >>= _ ->
pop >> a ->
pop >>= b->
return $ (show a) ++ “ : ” ++ (s...
https://www.coursera.org/course/progfun
Thank You
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Functional Programming

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Transcript of "Functional Programming"

  1. 1. Functional Programming Contact me: hadoope@gmail.com Let’s Rock!
  2. 2. Why FP ??? Single Threading can’t scale, but multi-ple threading is hard! Simple is Beautiful!
  3. 3. Beautiful Concurrency ??? Thread Safe Synchronized Deadlock Livelock Races Debugging Mutable shared state!!!
  4. 4. Functional Programming No Mutable
  5. 5. In computer science, functional programming is a programming paradigm, a style of building the structure and elements of computer programs, that treats computation as the evaluation of mathematical functions and avoids state and mutable data.
  6. 6. First Class Function Higher-Order Function Purify Curry Lazy Evaluation Monoid Monad Tail Recursive
  7. 7. First Class Function http://jsfiddle.net/hadoope/RAYy7/ Number Versus Function
  8. 8. Higher-Order Function Functions that take other functions Functions that return other functions var people = [{name: "Fred", age: 65}, {name: "Lucy", age: 36}]; _.max(people, function(p) { return p.age }); function always(VALUE) { return function() { return VALUE; }; };
  9. 9. Currying
  10. 10. Currying using Lambda calculus (x, y) -> x * x + y *y x -> y -> x * x + y *y =
  11. 11. Currying in JavaScript function curry3(fun) { return function(last) { return function(middle) { return function(first) { return fun(first, middle, last); }; }; }; }; function no_curry(fun, last, middle, first){ return fun(last, middle, first); } Define a Method Define a Method in Currying Way
  12. 12. Recursion and Tail Recursive def factorial(n) if (n == 1) return 1 else return n* factorial(n-1) end end @tailrec def factorial(acc: Int, n:Int ) = { if (n <= 1) acc else factorial( n * acc, n - 1) }
  13. 13. Lazy Evaluation In programming language theory, lazy evaluation, or call-by-need is an evaluation strategy which delays the evaluation of an expression until its value is needed (non-strict evaluation) and which also avoids repeated evaluations (sharing).
  14. 14. Lazy Evaluation  Performance increases by avoiding needless calculations, and error conditions in evaluating compound expressions  The ability to construct potentially infinite data structures.  The ability to define control flow (structures) as abstractions instead of primitives
  15. 15. Pattern Matching • Object Matching Import scala.util.Random var randomInt = new Random().nextInt(10) randomInt match { case 7 => println(“lucky seven”) case otherNumber => println( “get” + otherNumber) }
  16. 16. Pattern Matching • Type Matching var items = List(1, “foo”, 3.5) for (item <- items) { item match { case i: Int => println(“got an Integer: ” + i) case s: String => println(“got a String: ” + s) case d: Double => println(“got a double: ” + d) case other => println(“got others” + other) } }
  17. 17. Pattern Matching Functionalpolymorphism Versus OOpolymorphism
  18. 18. Monoid Just what is a monoid, then? It is simply an implementation of an interface governed by some laws. Stated tersely, a monoid is a type together with an associative binary operation (op) which has an identity element (zero). trait Monoid[A] { def op(a1: A, a2: A): A def zero: A } def listMonoid[A] = new Monoid[List[A]] { def op(a1: List[A], a2: List[A]) = a1 ++ a2 def zero = Nil }
  19. 19. Monoid will buy us ??? Associativity brings high parallelism op(a, op(b, op(c,d)))Folding to the right: After folding in parallel: op( op(a,b), op(c,d)) op(op(op(a, b), c), d)Folding to the right:
  20. 20. Monad In functional programming, a monad is a structure that represents computations defined as sequences of steps. A type with a monad structure defines what it means to chain operations, or nest functions of that type together. This allows the programmer to build pipelines that process data in steps, in which each action is decorated with additional processing rules provided by the monad.
  21. 21. Functional Javascript • Collection-Centric Programming
  22. 22. Functional Javascript • Collection-Centric Programming (map, reduce and filter) http://jsfiddle.net/hadoope/xhQ4P/
  23. 23. Monad using Javascript var stack = []; stack.push(4); stack.push(5); stack.pop(); // 5 stack.pop(); // 4 Normal Style http://igstan.ro/posts/2011-05-02-understanding-monads-with-javascript.html
  24. 24. Monad using Javascript http://jsfiddle.net/hadoope/FcD5S/ Continuation-Passing Style
  25. 25. Monad using Javascript • Currying push and pop http://jsfiddle.net/hadoope/62bfe/2/
  26. 26. Monad using Javascript • Preparing bind to Handle Intermediate Stacks http://jsfiddle.net/hadoope/Lsgw5/
  27. 27. Monad Using Haskell computation = push 4 >>= _ -> push 5 >>= _ -> pop >> a -> pop >>= b-> return $ (show a) ++ “ : ” ++ (show b) Computation = do push 4 push 5 a <- pop b <- pop return $ (show a) ++ “ : “ ++ (show b)
  28. 28. https://www.coursera.org/course/progfun
  29. 29. Thank You 29
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