functional programming

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 computer programs, that treats computation as the evaluation of mathematical functions and avoids state and mutable data.

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", age: 65}, {name: "Lucy", age: 36}]; _.max(people, function(p) { return p.age });

function always(VALUE) { return function() { return VALUE; }; };

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) { 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

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) }

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).

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

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) }

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) } }

Pattern Matching

Functional polymorphism

Versus

OO polymorphism

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 }

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:

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.

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://igstan.ro/posts/2011-05-02-understanding-monads-with-javascript.html

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) ++ “ : ” ++ (show b)

Computation = do push 4 push 5 a <- pop b <- pop return $ (show a) ++ “ : “ ++ (show b)

https://www.coursera.org/course/progfun

Thank You

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