indicthreads-pune12-polyglot & functional programming on jvm

7/30/2019 IndicThreads-Pune12-Polyglot & Functional Programming on JVM

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Polyglot and Functional Programmingon the Java Virtual Machine

Mohan Kumar MuddanaInfoStretch Pvt. Ltd.


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Some of the languages on JVM


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Why so many languages on JVM

JVM has grown over the years and has become amature platform.

Very wide industry adoption.

Availability of large developer community.

Plethora of Tools and Technologies


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Polyglot Programming on the JVM

Different languages bring in different features.

Wider choice of availability.

Better programming features.

Imperative and Functional

Interoperability between the languages.


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JVM The Polyglot Platform

JVM was initially built for (Java) Classes.

How does it handles so different kind of languageconstructs.

the Da Vinci Machine Project

(http://openjdk.java.net/projects/mlvm/)
http://openjdk.java.net/projects/mlvm/http://openjdk.java.net/projects/mlvm/


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How JVM incorporates and consumes

Java 6 : - JSR 223: Scripting for the Java Platform(Groovy, Jython, JRuby)

Java 7 :- JSR 292: Supporting Dynamically Typed Languages onthe JavaTM Platform

MLVM Multi Language Virtual Machine.


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History of Functional Programming

Alonzo ChurchCreator of-Calculus 1940

-Calculus is the basis of all functional programming languages


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History of Functional Programming

What does it fundamentally say-A function is an action that is applied to one thing (the argument) to

obtain another thing (the value).

Two Fundamental functions in-Calculus(I, the identity function). I is defined as follows: (Ix) is x, whatever

x may be.

(H). H is defined as the function that always returns the identityfunction. That is, (Hx) is I for whatever x may be.


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Functional Programming

Derives from mathematics, Lambda Calculus

Built on the basis of functions

Immutability and Concurrency

Data Structures with strong filtering

Lesser code with fewer language constructs.


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Functional Programming Languages

Lisp One of t he oldest programming language

(Lisp is functional language)

Haskel Pure functional language

Erlang - Massively scalable soft real-time systems withrequirements on high availability and fault tolerant systems.

Scheme, ML, OCAML etc.

And many others


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Scala Language aka Scalable

Why Scala

Ordersky says:"We wanted to make Java more expressive, so peoplecould be more productive" and write at a higher levelof abstraction with fewer lines of code, Odersky says.

How it is scalable

Getting Started

S l Ob W ld


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Scala Object World

Scala is Pure Object Oriented Language

Traits

Case Classes and Pattern Matching

Type safety and Type Erasure

S l Cl d Obj


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Scala Classes and Objects

Everything is objects.

Store objects into a variables.

class HelloWorld() {

val welcome: String = Hello World

def msg(name: String) = println(welcome + name)}

val h = new HelloWorld()

h.msg(Your Name)

S l T i


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Scala Traits

trait PolyglotProgrammer {def polyProg() {

println("Polyglot Programmer")}

}

class Person extends PolyglotProgrammer with

PolyglotSpeaker {}val person = new Personprintln(person.polyProg)println(person.polySpeaker)

It is an kind of an Interface with fields and concrete methods.

Unlike Class inheritance, a class can mix (Mixins) in any number

of traits.

S l C Cl d P tt M t h


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Scala Case Classes and Pattern Match

Case classes provides pattern matching on objectswithout large amount of boilerplate code.

Case classes are normal classes with a case modifier as

prefix.

case Class Rectangle(length: Int, breadth: Int)

S l C Cl d P tt M t h


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Scala Case Classes and Pattern Match

Case Classes comes with additional conventions

- The compiler adds a factory method with the nameof the class, so no need to create an instance withnew operator.

- All arguments in the parameter list gets implicit valprefix, so they are maintained as fields.

- Compiler adds natural implementations of toString,hashCode and equals.

G


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Groovy

Groovy is the closest to Java language.

Supports both static and dynamic type binding.

Powerful XML processing constructs.

Very good support for regular expressions

Gr XML Pr ing


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Groovy XML Processing

def writer = new StringWriter();

def xml = new groovy.xml.MarkupBuilder(writer);xml.person(id:2) {

name 'Gweneth age 1

}

println writer.toString();

Gweneth

1

Groovy Beans Conciseness


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Groovy Beans - Conciseness

class Person {private String name

private int age

}

def p = new Person(name: Ramu, age: 15)

(No syntactic ceremony)

@Immutable annotation to make it immutable


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Groovy DSL


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Groovy DSL

DSL with the help of identity: The Context Method

Trade trade = new Trade()

trade.identity {

setOrderId(1)

setOrderStatus(false)setEquityName("Fictious Inc")

setQuantity(100)

setPrice(17.25)

}

Clojure a Lisp dialect on JVM


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Clojure a Lisp dialect on JVM

Why Clojure

Predominately functional language Stateless

Homoiconicity

(Un)digestive Syntax Which you might fall in love

later

Persistent data structures

STM

Atom and Agents

Clojure Functional


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Clojure Functional

Predominately Functional language

(defn name doc-string? attr-map? [params*] body)

(defn helloworld [username] returns a String hello message

(str Hello, username))

Dynamic Language

Resolves types at runtime

Clojure Homoiconicity


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Representation of its own data structures and atomic

values or more casually code-as-data and data-as-code

(defn average [numbers]

(/ (apply + numbers) (count numbers)))

This definition is a list of data structure containing symbols,

values, vectors and another list consists of function body

(+ 7 3) on REPL yields

=> (+ 7 3)

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Stateless



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Data as Code Consider map

(def names {"Rich" "Hickey" "Martin" "Odersky"})

Now use names as function(names Rich) will result in Hickey

else more verbose get

(get names Rich None)

Any Clojure data structure can be a key in a map(def names {:Lisp Rich :Scala Martin})

Clojure Parenthesis and Prefix Notation


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Clojure Parenthesis and Prefix Notation

A method in general of most of the languages

methodName(arg1, arg2, arg3);

A clojure function has prefix notation

(function-name arg1 arg2 arg3)

Imagine if you want to operate on a large list of values

sum (60+80+90+120)

Whereas in Lisp or Clojure syntax

(apply + [60 80 90 120])

Clojure Functional


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Clojure Functional

First Class Functions

Functions that always return the same result when passed thesame arguments

Functions exist as data (function value).

Higher Order Functions

Take other functions as arguments or return a function as aresult.

Clojure Collections


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Clojure Collections

All of them are immutable, heterogeneous and persistent.

Heterogeneous means that they can hold any kind of

object.

Being persistent means that old versions of them arepreserved when new versions are created.

Very rich data structures as well functions to operate on.

Clojure Sequences


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Clojure Sequences In Clojure, all these data structures can be accessed

through a single abstraction: the sequence (seq)

Every aggregate data structure in Clojure can be viewedas a sequence

(first {"Rich" "Hickey" "Martin" "Odersky"})

(rest {"Rich" "Hickey" "Martin" "Odersky"})

(cons [James" Gosling] {"Rich" "Hickey" "Martin"

"Odersky"})

Clojure STM


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Clojure STM

Software Transactional Manager is the way to handle

concurrency of mutable data in Clojure.STM is very optimistic.

Alternative to lock based synchronization.

Mutual Exclusion

Every read and write that it is performing is in a log.

Onus is on reader which will commit to the shared memory in

case no modifications are done during the time, else wouldre-execute the transaction.

Clojure STM


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jMutable References

ref, deref or @, ref-set, dosync

Need to be explicit when mutable data is required.

(def value (ref 100))

ref wraps and protects access to its internal state.

Even to read, it needs to deref

(deref value) or @value

As the value is in STM

Clojure STM


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j

STM provides similar transaction properties of a Database

But STM handles in memory, so cant guarantee durability.

Updates are atomic. If you update more than one ref in atransaction, the cumulative effect of all the updates willappear as a single instantaneous event to anyone not inside

your transaction.

Updates are consistent. Refs can specify validation functions.If any of these functions fail, the entire transaction will fail.

Updates are isolated. Running transactions cannot seepartially completed results from other transactions.

Stateless

Clojure STM


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jAgents

Agents provide independent, asynchronous change ofindividual locations.

Agents are bound to a single storage location for their

lifetime, and only allow mutation of that location (to a newstate) to occur as a result of an action.

Interop Clojure to Java


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p j J

Clojure is complied and generates Bytecode

Clojure embraces Java and its libraries. Idiomatic

Clojure code can call Java libraries directly

Creating Java instances and accessing its methods.

In REPL:

(def cal (java.util.Calendar/getInstance)

(. cal getTime)

Code:

(import [java.util.Calendar])

(defn cal (.getInstance java.util.Calendar))

Stateless

Interop Java to Clojure


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Clojure is implemented as Java class library.

Embed Clojure using load code and call functions

import clojure.lang.RT;

import clojure.lang.Var;

public class Foo {

public static void main(String[] args) throws Exception {

RT.loadResourceScript("foo.clj"); Var foo = RT.var("user", "foo");

Object result = foo.invoke("Hi", "there");System.out.println(result);

}}

(user being the namespace and foo being the function from Clj)

Stateless

Polylingualism


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y g

Sapir-Whorf Hypothesis

According to the first, linguistic determinism,our thinking is determined by language.

According to the second, linguistic relativity,people who speak different languages

perceive and think about the world quitedifferently.

References


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Programming in Scala (Martin Odersky, Lex Spoon, Bill Venners)

Clojure Programming (Chas Emerick, Brian Carper, ChristopheGrand)

Programming Clojure (Stuart Halloway)

Well Gounded Java Developer (Benjamin Evans, Martin Verburg)

Programming in Groovy (Venkat Subramaniam)

Wikipedia.org


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Thank you !

gmail [email protected]

twitter @mohanjune Stateless

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