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Scala: An OO Surprise

Apostolos Syropoulos
Apostolos Syropoulos

This document outlines the key features of the Scala programming language. It discusses how Scala is a versatile object-oriented language that runs on the Java Virtual Machine, supports both object-oriented and functional programming paradigms, and is designed to be scalable. Specific features mentioned include generic types, operator overloading, anonymous functions, closures, and support for XML processing, parser combinators, and concurrent programming.

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Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala: An OO Surprise Apostolos Syropoulos Xanthi, Greece 4th European Lisp Symposium March 31st - April 1st, 2011 TUHH, Hamburg University of Technology, Hamburg, Germany . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Outline 1. Introduction What is Scala? Object Orientation Scalability 2. Functional Features 3. Parser Builders 4. XML Processing 5. XML Processing 6. Concurrent Programming
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! Allows concurrent programing. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! Allows concurrent programing. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! Allows concurrent programing. Includes facilities for GUI programming. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! Allows concurrent programing. Includes facilities for GUI programming. Seamless integration of XML. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! Allows concurrent programing. Includes facilities for GUI programming. Seamless integration of XML. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! Allows concurrent programing. Includes facilities for GUI programming. Seamless integration of XML. Provides parser combinators. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Principles of Object Orientation . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Principles of Object Orientation Abstraction (i.e., a software object is an idealization of a real world object). . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Principles of Object Orientation Abstraction (i.e., a software object is an idealization of a real world object). Encapsulation (i.e., a data protection mechanism). . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Principles of Object Orientation Abstraction (i.e., a software object is an idealization of a real world object). Encapsulation (i.e., a data protection mechanism). Inheritance (i.e., an object may extend the functionality of another object). . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Principles of Object Orientation Abstraction (i.e., a software object is an idealization of a real world object). Encapsulation (i.e., a data protection mechanism). Inheritance (i.e., an object may extend the functionality of another object). Polymorphism (i.e., software modules may have different instances with identical behavior). . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming What makes a programming language scalable? . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming What makes a programming language scalable? Any language that can be extended seamlessly is scalable. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming What makes a programming language scalable? Any language that can be extended seamlessly is scalable. Gyu L. Steel Jr.: “[A] language design can no longer be a thing. It must be a pattern–a pattern for growth–a pattern for growing the pattern for defining the patterns that programmers can use for their real work and their main goal.” . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming What makes a programming language scalable? Any language that can be extended seamlessly is scalable. Gyu L. Steel Jr.: “[A] language design can no longer be a thing. It must be a pattern–a pattern for growth–a pattern for growing the pattern for defining the patterns that programmers can use for their real work and their main goal.” . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming What makes a programming language scalable? Any language that can be extended seamlessly is scalable. Gyu L. Steel Jr.: “[A] language design can no longer be a thing. It must be a pattern–a pattern for growth–a pattern for growing the pattern for defining the patterns that programmers can use for their real work and their main goal.” There two forms of growth: variable vocabulary or variable semantics. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming What makes a programming language scalable? Any language that can be extended seamlessly is scalable. Gyu L. Steel Jr.: “[A] language design can no longer be a thing. It must be a pattern–a pattern for growth–a pattern for growing the pattern for defining the patterns that programmers can use for their real work and their main goal.” There two forms of growth: variable vocabulary or variable semantics. Generic types, operator overloading, and user-defined light-weight types form the kernel of every scalable language. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . A Generic Stack
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . A Generic Stack class Stack [γ] (n: Int) { private var S = new Array[γ](n) private var top = 0; def push(elem: γ) { top = top + 1 S(top) = elem } def pop () : γ = { var oldtop = top top = top - 1 S(oldtop) } }
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming User-Defined Light-Weight Complex Numbers . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming User-Defined Light-Weight Complex Numbers class Complex(val re: Double, val im: Double) { def + (x: Complex) = new Complex(re + x.re, im + x.im) def unary_- = new Complex(-Re, -Im) . . . . . . . . . . . . . . . . . . override def toString = if(re == 0 && im == 0) "0" … } object Complex{ def apply(re: Double)(im: Double) = . . . . . . new Complex(re, im) } object i extends Complex(0.0, 1.0) . . . . . . . . . . . . . . . . . . . var a = 5 + 3.0*i // a complex number!!!
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Call-By-Name or how to define new commands . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Call-By-Name or how to define new commands def loop(pre: => Unit)(cond: => Boolean) (post: => Unit): Unit = { . . . . . . pre if (!cond) { post loop(pre)(cond)(post) } else () } var x=6; var y=0 loop { x=x-1; y=y+1 } (x == 0 ) { println(x); println(y) }
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features Functions are software modules (objects in Scala’s parlance). . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features Functions are software modules (objects in Scala’s parlance). Users can define anonymous functions. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features Functions are software modules (objects in Scala’s parlance). Users can define anonymous functions. var inc = (x:Int) => x+1 . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features Functions are software modules (objects in Scala’s parlance). Users can define anonymous functions. var inc = (x:Int) => x+1 . . . . . . Supports closures.
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features Functions are software modules (objects in Scala’s parlance). Users can define anonymous functions. var inc = (x:Int) => x+1 . . . . . . Supports closures. var mul = (x: Int) => (y:Int) => x*y var mul3 = mul(3)
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features Functions are software modules (objects in Scala’s parlance). Users can define anonymous functions. var inc = (x:Int) => x+1 . . . . . . Supports closures. var mul = (x: Int) => (y:Int) => x*y var mul3 = mul(3) Pattern matching.
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Data Structures with Class Hierarchies . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Data Structures with Class Hierarchies . . . . . . Haskell binary tree
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Data Structures with Class Hierarchies . . . . . . Haskell binary tree datatype BinTree = Empty | Node(Int, BinTree, BinTree)
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Data Structures with Class Hierarchies . . . . . . Haskell binary tree datatype BinTree = Empty | Node(Int, BinTree, BinTree) Scala binary tree
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Data Structures with Class Hierarchies . . . . . . Haskell binary tree datatype BinTree = Empty | Node(Int, BinTree, BinTree) Scala binary tree abstract class BinTree case object EmptyTree extends BinTree case class Node(elem : Int, left : BinTree, right: BinTree) extends BinTree
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Pattern Matching in Action . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Pattern Matching in Action . . . . . . Depth of a binary tree
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Pattern Matching in Action . . . . . . Depth of a binary tree def depth(t: BinTree): Int = { t match { case EmptyTree => 0 case Node(_,EmptyTree,r) => 1 + depth(r) case Node(_,l,EmptyTree) => 1 + depth(l) case Node(_,l,r) => Math.max(depth(l), depth(r)) + 1 } }
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Constructing Parsers with Parser Builders . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Constructing Parsers with Parser Builders Tools that can be combined to build real parsers. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Constructing Parsers with Parser Builders Tools that can be combined to build real parsers. A toy parser that accepts binary numerals. . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Constructing Parsers with Parser Builders Tools that can be combined to build real parsers. A toy parser that accepts binary numerals. import scala.util.parsing.combinator._ class BinDigit extends JavaTokenParsers { def D = "0" | "1" def B = D~rep(D) def parse(text : String) = parseAll(B,text) } var P = new BinDigit println("input : "+args(0)) println(P.parse(args(0))) . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Variables can be assigned XML content.
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Variables can be assigned XML content. var poem = <poem> <title> Magic Everywhere </title> <poet realname="yes"> Tom Jones </poet> <stanza> <verse> magic everywhere </verse> </stanza> </poem> println(poem)
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Variables can be assigned XML content. var poem = <poem> <title> Magic Everywhere </title> <poet realname="yes"> Tom Jones </poet> <stanza> <verse> magic everywhere </verse> </stanza> </poem> println(poem) Or they can be assigned XML content stored in files.
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Variables can be assigned XML content. var poem = <poem> <title> Magic Everywhere </title> <poet realname="yes"> Tom Jones </poet> <stanza> <verse> magic everywhere </verse> </stanza> </poem> println(poem) Or they can be assigned XML content stored in files. val x = XML.loadFile("listdir.html")
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Saving XML content.
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Saving XML content. var z = <person> <name>Blaise</name> <surname>Pascal</surname> </person> XML.save("persons.xml",z)
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Saving XML content. var z = <person> <name>Blaise</name> <surname>Pascal</surname> </person> XML.save("persons.xml",z) Example: Find all poems that have been published after 1960 and print the title and the poet of each such poem.
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Saving XML content. var z = <person> <name>Blaise</name> <surname>Pascal</surname> </person> XML.save("persons.xml",z) Example: Find all poems that have been published after 1960 and print the title and the poet of each such poem. for ( val poem <- poems "poem" ) { if ( (poem "year").text.trim.toInt > 1960 ) { var poet = (poem "poet").text var title = (poem "title").text println("""+title+"" by "+poet) }
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Truths
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Truths EETimes Europe (http://www.electronics-eetimes.com): “As Moore’s Law runs out of steam and computing goes mobile, technologists are searching for ways to make the leap to new parallel programming frameworks that can leverage low-power multicore architectures.”
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Truths EETimes Europe (http://www.electronics-eetimes.com): “As Moore’s Law runs out of steam and computing goes mobile, technologists are searching for ways to make the leap to new parallel programming frameworks that can leverage low-power multicore architectures.”
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Truths EETimes Europe (http://www.electronics-eetimes.com): “As Moore’s Law runs out of steam and computing goes mobile, technologists are searching for ways to make the leap to new parallel programming frameworks that can leverage low-power multicore architectures.” Concurrent programming is not only the next logical step in software development, but the next necessary step.
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Truths EETimes Europe (http://www.electronics-eetimes.com): “As Moore’s Law runs out of steam and computing goes mobile, technologists are searching for ways to make the leap to new parallel programming frameworks that can leverage low-power multicore architectures.” Concurrent programming is not only the next logical step in software development, but the next necessary step.
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Truths EETimes Europe (http://www.electronics-eetimes.com): “As Moore’s Law runs out of steam and computing goes mobile, technologists are searching for ways to make the leap to new parallel programming frameworks that can leverage low-power multicore architectures.” Concurrent programming is not only the next logical step in software development, but the next necessary step. All modern programming languages must provide constructs and libraries that will ease the construction of concurrent programs
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Scala and Concurrency Scala programmers can code concurrent structures with…
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Scala and Concurrency Scala programmers can code concurrent structures with… threads (i.e., Java’s legacy to Scala)
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Scala and Concurrency Scala programmers can code concurrent structures with… threads (i.e., Java’s legacy to Scala)
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Scala and Concurrency Scala programmers can code concurrent structures with… threads (i.e., Java’s legacy to Scala) mailboxes (something like actors)
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Scala and Concurrency Scala programmers can code concurrent structures with… threads (i.e., Java’s legacy to Scala) mailboxes (something like actors)
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Scala and Concurrency Scala programmers can code concurrent structures with… threads (i.e., Java’s legacy to Scala) mailboxes (something like actors) actors
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Creating threaded applications by extending class Thread . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Creating threaded applications by extending class Thread class PrintProgressMark(val mark: Char, val delay :Int) extends Thread { . . . . . . private var i = 0 override def run(): Unit = try { while (i <= 100) { print(mark); i += 1; Thread.sleep(delay); } } catch { case ex : InterruptedException => return } } object threadExample { def main(args: Array[String]) { new PrintProgressMark('+', 40).start new PrintProgressMark('*', 100).start } }
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Creating threaded applications by using trait Runnable . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Creating threaded applications by using trait Runnable class PrintProgressMark2(val mark: Char, val delay :Int) extends Runnable { . . . . . . private var i = 0 override def run(): Unit = try { while (i <= 100) { print(mark); i += 1; Thread.sleep(delay_) } } catch { case ex : InterruptedException => return } } object threadExample2 { def main(args: Array[String]) { var plus = new PrintProgressMark2('+', 40) var ast = new PrintProgressMark2('*', 100) new Thread(plus).start(); new Thread(ast).start() } }
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of…
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors;
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors;
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and,
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and,
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created.
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created.
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created. Thus,
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created. Thus, behaviors are history sensitive;
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created. Thus, behaviors are history sensitive;
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created. Thus, behaviors are history sensitive; there is no presumed sequentiality in the actions an actor performs; and,
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created. Thus, behaviors are history sensitive; there is no presumed sequentiality in the actions an actor performs; and,
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created. Thus, behaviors are history sensitive; there is no presumed sequentiality in the actions an actor performs; and, actor creation is an integral of the computational model.
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A first example in actor programming . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A first example in actor programming import scala.actors.Actor._ object actorsExample { def main(args: Array[String]) { var PrintProgressPlus = actor { var i = 0 while (i <= max) { print('+'); i += 1; Thread.sleep(40) } } var PrintProgressTimes = actor { var i = 0 while (i <= max) { print('*'); i += 1; Thread.sleep(100) } } 1 // <--- block must end in result expression, } } // not in definition . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Defining a class that subclasses trait Actor . . . . . .
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Defining a class that subclasses trait Actor import scala.actors._ class PrintProgressMark(val mark: Char, val delay :Int) extends Actor { . . . . . . private var i = 0 def act: Unit = { while (i <= 100) { print(mark); i += 1; Thread.sleep(delay_) } } } object actorsExample { def main(args: Array[String]) { new PrintProgressMark('+', 40).start new PrintProgressMark('*', 100).start } }
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Carl Hewitt in “Viewing Cotrol Structures as Patterns of Passing Messages” (Artificial Intelligence 8, 3 (1977), 323–364)
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Carl Hewitt in “Viewing Cotrol Structures as Patterns of Passing Messages” (Artificial Intelligence 8, 3 (1977), 323–364) “present[s] an approach to modelling intelligence in terms of a society of communicating knowledge-based problem solving experts”;
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Carl Hewitt in “Viewing Cotrol Structures as Patterns of Passing Messages” (Artificial Intelligence 8, 3 (1977), 323–364) “present[s] an approach to modelling intelligence in terms of a society of communicating knowledge-based problem solving experts”;
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Carl Hewitt in “Viewing Cotrol Structures as Patterns of Passing Messages” (Artificial Intelligence 8, 3 (1977), 323–364) “present[s] an approach to modelling intelligence in terms of a society of communicating knowledge-based problem solving experts”; “each of the experts can be viewed as a society that can be further decomposed in the same way until the primitive actors of the system are reached”;
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Carl Hewitt in “Viewing Cotrol Structures as Patterns of Passing Messages” (Artificial Intelligence 8, 3 (1977), 323–364) “present[s] an approach to modelling intelligence in terms of a society of communicating knowledge-based problem solving experts”; “each of the experts can be viewed as a society that can be further decomposed in the same way until the primitive actors of the system are reached”;
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Carl Hewitt in “Viewing Cotrol Structures as Patterns of Passing Messages” (Artificial Intelligence 8, 3 (1977), 323–364) “present[s] an approach to modelling intelligence in terms of a society of communicating knowledge-based problem solving experts”; “each of the experts can be viewed as a society that can be further decomposed in the same way until the primitive actors of the system are reached”; he was “investigating the nature of the communication mechanisms needed for effective problem-solving by a society of experts and the conventions of civilized discourse that make this possible.”
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Hewitt demonstrates these “principles” by showing how to compute the factorial function with actors:
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Hewitt demonstrates these “principles” by showing how to compute the factorial function with actors:
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Hewitt demonstrates these “principles” by showing how to compute the factorial function with actors: 1. using a resursive procedure, that is, a procedure that uses replication and
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Hewitt demonstrates these “principles” by showing how to compute the factorial function with actors: 1. using a resursive procedure, that is, a procedure that uses replication and
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Hewitt demonstrates these “principles” by showing how to compute the factorial function with actors: 1. using a resursive procedure, that is, a procedure that uses replication and 2. an iterative procudure, that is, a procedure that relies on message passing to deliver a result.
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Actor Replication
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Actor Replication case class Val(a: Actor, n: Int) case class Res(n: Int) class Fact extends Actor { def act = react { case Val(a,0) => a ! Res(1) case Val(a,n) => var p = new Fact p.start p ! Val(self,n-1) react { case Val(_, m) => a ! Val(a, n*m) case Res(m) => a ! Val(a, n*m)} } }
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Using Class Fact
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Using Class Fact object actorsExample { def main(args: Array[String]) { var factorial = actor { react { case Val(a,n) => var q = new Fact q.start q ! Val(self,n) react { case Val(_,f) => a ! Val(a,f) } } } factorial ! Val(self,6) react { case Val(_, n) => println(n) } } }
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Iterative Actor
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Iterative Actor case class InitVal(a: Actor, n: Int) case class Val(a: Actor, n: Int, m: Int) object actorsExample { def main(args: Array[String]) { val loopActor = actor { var ResActor : Actor = null loop{ react { case Val(_,acc,1) => ResActor ! acc; exit("done") case Val(a,1,count) => ResActor = a self ! Val(self,count,count-1) case Val(a,acc,count) => self ! Val(self,acc*count,count-1) } } }
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Using Class Fact
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Using Class Fact var factorial = actor { react { case InitVal(a,0) => a ! InitVal(a, 1) case InitVal(a,1) => a ! InitVal(a, 1) case InitVal(a,n) => loopActor ! Val(self,1,n) react { case f: Int => a ! InitVal(a,f) } } } factorial ! InitVal(self,6) receive { case InitVal(_, n) => println(n) } } }
Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . The end! Thank you so much for your attention!

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Scala: An OO Surprise

  • 1. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala: An OO Surprise Apostolos Syropoulos Xanthi, Greece 4th European Lisp Symposium March 31st - April 1st, 2011 TUHH, Hamburg University of Technology, Hamburg, Germany . . . . . .
  • 2. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Outline 1. Introduction What is Scala? Object Orientation Scalability 2. Functional Features 3. Parser Builders 4. XML Processing 5. XML Processing 6. Concurrent Programming
  • 3. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language . . . . . .
  • 4. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. . . . . . .
  • 5. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. . . . . . .
  • 6. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. . . . . . .
  • 7. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. . . . . . .
  • 8. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! . . . . . .
  • 9. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! Allows concurrent programing. . . . . . .
  • 10. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! Allows concurrent programing. . . . . . .
  • 11. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! Allows concurrent programing. Includes facilities for GUI programming. . . . . . .
  • 12. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! Allows concurrent programing. Includes facilities for GUI programming. Seamless integration of XML. . . . . . .
  • 13. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! Allows concurrent programing. Includes facilities for GUI programming. Seamless integration of XML. . . . . . .
  • 14. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A versatile programming language A purely object-oriented language. Runs on the Java Virtual Machine. A scalable language. Has features found in functional programming languages, but it is not a functional langauge! Allows concurrent programing. Includes facilities for GUI programming. Seamless integration of XML. Provides parser combinators. . . . . . .
  • 15. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Principles of Object Orientation . . . . . .
  • 16. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Principles of Object Orientation Abstraction (i.e., a software object is an idealization of a real world object). . . . . . .
  • 17. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Principles of Object Orientation Abstraction (i.e., a software object is an idealization of a real world object). Encapsulation (i.e., a data protection mechanism). . . . . . .
  • 18. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Principles of Object Orientation Abstraction (i.e., a software object is an idealization of a real world object). Encapsulation (i.e., a data protection mechanism). Inheritance (i.e., an object may extend the functionality of another object). . . . . . .
  • 19. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Principles of Object Orientation Abstraction (i.e., a software object is an idealization of a real world object). Encapsulation (i.e., a data protection mechanism). Inheritance (i.e., an object may extend the functionality of another object). Polymorphism (i.e., software modules may have different instances with identical behavior). . . . . . .
  • 20. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming What makes a programming language scalable? . . . . . .
  • 21. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming What makes a programming language scalable? Any language that can be extended seamlessly is scalable. . . . . . .
  • 22. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming What makes a programming language scalable? Any language that can be extended seamlessly is scalable. Gyu L. Steel Jr.: “[A] language design can no longer be a thing. It must be a pattern–a pattern for growth–a pattern for growing the pattern for defining the patterns that programmers can use for their real work and their main goal.” . . . . . .
  • 23. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming What makes a programming language scalable? Any language that can be extended seamlessly is scalable. Gyu L. Steel Jr.: “[A] language design can no longer be a thing. It must be a pattern–a pattern for growth–a pattern for growing the pattern for defining the patterns that programmers can use for their real work and their main goal.” . . . . . .
  • 24. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming What makes a programming language scalable? Any language that can be extended seamlessly is scalable. Gyu L. Steel Jr.: “[A] language design can no longer be a thing. It must be a pattern–a pattern for growth–a pattern for growing the pattern for defining the patterns that programmers can use for their real work and their main goal.” There two forms of growth: variable vocabulary or variable semantics. . . . . . .
  • 25. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming What makes a programming language scalable? Any language that can be extended seamlessly is scalable. Gyu L. Steel Jr.: “[A] language design can no longer be a thing. It must be a pattern–a pattern for growth–a pattern for growing the pattern for defining the patterns that programmers can use for their real work and their main goal.” There two forms of growth: variable vocabulary or variable semantics. Generic types, operator overloading, and user-defined light-weight types form the kernel of every scalable language. . . . . . .
  • 26. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . A Generic Stack
  • 27. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . A Generic Stack class Stack [γ] (n: Int) { private var S = new Array[γ](n) private var top = 0; def push(elem: γ) { top = top + 1 S(top) = elem } def pop () : γ = { var oldtop = top top = top - 1 S(oldtop) } }
  • 28. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming User-Defined Light-Weight Complex Numbers . . . . . .
  • 29. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming User-Defined Light-Weight Complex Numbers class Complex(val re: Double, val im: Double) { def + (x: Complex) = new Complex(re + x.re, im + x.im) def unary_- = new Complex(-Re, -Im) . . . . . . . . . . . . . . . . . . override def toString = if(re == 0 && im == 0) "0" … } object Complex{ def apply(re: Double)(im: Double) = . . . . . . new Complex(re, im) } object i extends Complex(0.0, 1.0) . . . . . . . . . . . . . . . . . . . var a = 5 + 3.0*i // a complex number!!!
  • 30. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Call-By-Name or how to define new commands . . . . . .
  • 31. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Call-By-Name or how to define new commands def loop(pre: => Unit)(cond: => Boolean) (post: => Unit): Unit = { . . . . . . pre if (!cond) { post loop(pre)(cond)(post) } else () } var x=6; var y=0 loop { x=x-1; y=y+1 } (x == 0 ) { println(x); println(y) }
  • 32. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features . . . . . .
  • 33. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features Functions are software modules (objects in Scala’s parlance). . . . . . .
  • 34. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features Functions are software modules (objects in Scala’s parlance). Users can define anonymous functions. . . . . . .
  • 35. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features Functions are software modules (objects in Scala’s parlance). Users can define anonymous functions. var inc = (x:Int) => x+1 . . . . . .
  • 36. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features Functions are software modules (objects in Scala’s parlance). Users can define anonymous functions. var inc = (x:Int) => x+1 . . . . . . Supports closures.
  • 37. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features Functions are software modules (objects in Scala’s parlance). Users can define anonymous functions. var inc = (x:Int) => x+1 . . . . . . Supports closures. var mul = (x: Int) => (y:Int) => x*y var mul3 = mul(3)
  • 38. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Scala’s Functional Features Functions are software modules (objects in Scala’s parlance). Users can define anonymous functions. var inc = (x:Int) => x+1 . . . . . . Supports closures. var mul = (x: Int) => (y:Int) => x*y var mul3 = mul(3) Pattern matching.
  • 39. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Data Structures with Class Hierarchies . . . . . .
  • 40. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Data Structures with Class Hierarchies . . . . . . Haskell binary tree
  • 41. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Data Structures with Class Hierarchies . . . . . . Haskell binary tree datatype BinTree = Empty | Node(Int, BinTree, BinTree)
  • 42. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Data Structures with Class Hierarchies . . . . . . Haskell binary tree datatype BinTree = Empty | Node(Int, BinTree, BinTree) Scala binary tree
  • 43. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Data Structures with Class Hierarchies . . . . . . Haskell binary tree datatype BinTree = Empty | Node(Int, BinTree, BinTree) Scala binary tree abstract class BinTree case object EmptyTree extends BinTree case class Node(elem : Int, left : BinTree, right: BinTree) extends BinTree
  • 44. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Pattern Matching in Action . . . . . .
  • 45. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Pattern Matching in Action . . . . . . Depth of a binary tree
  • 46. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Pattern Matching in Action . . . . . . Depth of a binary tree def depth(t: BinTree): Int = { t match { case EmptyTree => 0 case Node(_,EmptyTree,r) => 1 + depth(r) case Node(_,l,EmptyTree) => 1 + depth(l) case Node(_,l,r) => Math.max(depth(l), depth(r)) + 1 } }
  • 47. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Constructing Parsers with Parser Builders . . . . . .
  • 48. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Constructing Parsers with Parser Builders Tools that can be combined to build real parsers. . . . . . .
  • 49. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Constructing Parsers with Parser Builders Tools that can be combined to build real parsers. A toy parser that accepts binary numerals. . . . . . .
  • 50. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Constructing Parsers with Parser Builders Tools that can be combined to build real parsers. A toy parser that accepts binary numerals. import scala.util.parsing.combinator._ class BinDigit extends JavaTokenParsers { def D = "0" | "1" def B = D~rep(D) def parse(text : String) = parseAll(B,text) } var P = new BinDigit println("input : "+args(0)) println(P.parse(args(0))) . . . . . .
  • 51. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing
  • 52. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Variables can be assigned XML content.
  • 53. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Variables can be assigned XML content. var poem = <poem> <title> Magic Everywhere </title> <poet realname="yes"> Tom Jones </poet> <stanza> <verse> magic everywhere </verse> </stanza> </poem> println(poem)
  • 54. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Variables can be assigned XML content. var poem = <poem> <title> Magic Everywhere </title> <poet realname="yes"> Tom Jones </poet> <stanza> <verse> magic everywhere </verse> </stanza> </poem> println(poem) Or they can be assigned XML content stored in files.
  • 55. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Variables can be assigned XML content. var poem = <poem> <title> Magic Everywhere </title> <poet realname="yes"> Tom Jones </poet> <stanza> <verse> magic everywhere </verse> </stanza> </poem> println(poem) Or they can be assigned XML content stored in files. val x = XML.loadFile("listdir.html")
  • 56. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing
  • 57. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Saving XML content.
  • 58. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Saving XML content. var z = <person> <name>Blaise</name> <surname>Pascal</surname> </person> XML.save("persons.xml",z)
  • 59. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Saving XML content. var z = <person> <name>Blaise</name> <surname>Pascal</surname> </person> XML.save("persons.xml",z) Example: Find all poems that have been published after 1960 and print the title and the poet of each such poem.
  • 60. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . XML Processing Saving XML content. var z = <person> <name>Blaise</name> <surname>Pascal</surname> </person> XML.save("persons.xml",z) Example: Find all poems that have been published after 1960 and print the title and the poet of each such poem. for ( val poem <- poems "poem" ) { if ( (poem "year").text.trim.toInt > 1960 ) { var poet = (poem "poet").text var title = (poem "title").text println("""+title+"" by "+poet) }
  • 61. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Truths
  • 62. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Truths EETimes Europe (http://www.electronics-eetimes.com): “As Moore’s Law runs out of steam and computing goes mobile, technologists are searching for ways to make the leap to new parallel programming frameworks that can leverage low-power multicore architectures.”
  • 63. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Truths EETimes Europe (http://www.electronics-eetimes.com): “As Moore’s Law runs out of steam and computing goes mobile, technologists are searching for ways to make the leap to new parallel programming frameworks that can leverage low-power multicore architectures.”
  • 64. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Truths EETimes Europe (http://www.electronics-eetimes.com): “As Moore’s Law runs out of steam and computing goes mobile, technologists are searching for ways to make the leap to new parallel programming frameworks that can leverage low-power multicore architectures.” Concurrent programming is not only the next logical step in software development, but the next necessary step.
  • 65. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Truths EETimes Europe (http://www.electronics-eetimes.com): “As Moore’s Law runs out of steam and computing goes mobile, technologists are searching for ways to make the leap to new parallel programming frameworks that can leverage low-power multicore architectures.” Concurrent programming is not only the next logical step in software development, but the next necessary step.
  • 66. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Truths EETimes Europe (http://www.electronics-eetimes.com): “As Moore’s Law runs out of steam and computing goes mobile, technologists are searching for ways to make the leap to new parallel programming frameworks that can leverage low-power multicore architectures.” Concurrent programming is not only the next logical step in software development, but the next necessary step. All modern programming languages must provide constructs and libraries that will ease the construction of concurrent programs
  • 67. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Scala and Concurrency Scala programmers can code concurrent structures with…
  • 68. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Scala and Concurrency Scala programmers can code concurrent structures with… threads (i.e., Java’s legacy to Scala)
  • 69. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Scala and Concurrency Scala programmers can code concurrent structures with… threads (i.e., Java’s legacy to Scala)
  • 70. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Scala and Concurrency Scala programmers can code concurrent structures with… threads (i.e., Java’s legacy to Scala) mailboxes (something like actors)
  • 71. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Scala and Concurrency Scala programmers can code concurrent structures with… threads (i.e., Java’s legacy to Scala) mailboxes (something like actors)
  • 72. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Scala and Concurrency Scala programmers can code concurrent structures with… threads (i.e., Java’s legacy to Scala) mailboxes (something like actors) actors
  • 73. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Creating threaded applications by extending class Thread . . . . . .
  • 74. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Creating threaded applications by extending class Thread class PrintProgressMark(val mark: Char, val delay :Int) extends Thread { . . . . . . private var i = 0 override def run(): Unit = try { while (i <= 100) { print(mark); i += 1; Thread.sleep(delay); } } catch { case ex : InterruptedException => return } } object threadExample { def main(args: Array[String]) { new PrintProgressMark('+', 40).start new PrintProgressMark('*', 100).start } }
  • 75. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Creating threaded applications by using trait Runnable . . . . . .
  • 76. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Creating threaded applications by using trait Runnable class PrintProgressMark2(val mark: Char, val delay :Int) extends Runnable { . . . . . . private var i = 0 override def run(): Unit = try { while (i <= 100) { print(mark); i += 1; Thread.sleep(delay_) } } catch { case ex : InterruptedException => return } } object threadExample2 { def main(args: Array[String]) { var plus = new PrintProgressMark2('+', 40) var ast = new PrintProgressMark2('*', 100) new Thread(plus).start(); new Thread(ast).start() } }
  • 77. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of…
  • 78. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors;
  • 79. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors;
  • 80. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and,
  • 81. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and,
  • 82. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created.
  • 83. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created.
  • 84. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created. Thus,
  • 85. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created. Thus, behaviors are history sensitive;
  • 86. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created. Thus, behaviors are history sensitive;
  • 87. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created. Thus, behaviors are history sensitive; there is no presumed sequentiality in the actions an actor performs; and,
  • 88. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created. Thus, behaviors are history sensitive; there is no presumed sequentiality in the actions an actor performs; and,
  • 89. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . What is an actor? An actor is a computational agent which maps each incoming communication to a triple consisting of… a finite set of communications sent to other actors; a new behavior that will govern the response to the next communication processed; and, a finite set of new actors created. Thus, behaviors are history sensitive; there is no presumed sequentiality in the actions an actor performs; and, actor creation is an integral of the computational model.
  • 90. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A first example in actor programming . . . . . .
  • 91. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming A first example in actor programming import scala.actors.Actor._ object actorsExample { def main(args: Array[String]) { var PrintProgressPlus = actor { var i = 0 while (i <= max) { print('+'); i += 1; Thread.sleep(40) } } var PrintProgressTimes = actor { var i = 0 while (i <= max) { print('*'); i += 1; Thread.sleep(100) } } 1 // <--- block must end in result expression, } } // not in definition . . . . . .
  • 92. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Defining a class that subclasses trait Actor . . . . . .
  • 93. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming Defining a class that subclasses trait Actor import scala.actors._ class PrintProgressMark(val mark: Char, val delay :Int) extends Actor { . . . . . . private var i = 0 def act: Unit = { while (i <= 100) { print(mark); i += 1; Thread.sleep(delay_) } } } object actorsExample { def main(args: Array[String]) { new PrintProgressMark('+', 40).start new PrintProgressMark('*', 100).start } }
  • 94. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Carl Hewitt in “Viewing Cotrol Structures as Patterns of Passing Messages” (Artificial Intelligence 8, 3 (1977), 323–364)
  • 95. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Carl Hewitt in “Viewing Cotrol Structures as Patterns of Passing Messages” (Artificial Intelligence 8, 3 (1977), 323–364) “present[s] an approach to modelling intelligence in terms of a society of communicating knowledge-based problem solving experts”;
  • 96. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Carl Hewitt in “Viewing Cotrol Structures as Patterns of Passing Messages” (Artificial Intelligence 8, 3 (1977), 323–364) “present[s] an approach to modelling intelligence in terms of a society of communicating knowledge-based problem solving experts”;
  • 97. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Carl Hewitt in “Viewing Cotrol Structures as Patterns of Passing Messages” (Artificial Intelligence 8, 3 (1977), 323–364) “present[s] an approach to modelling intelligence in terms of a society of communicating knowledge-based problem solving experts”; “each of the experts can be viewed as a society that can be further decomposed in the same way until the primitive actors of the system are reached”;
  • 98. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Carl Hewitt in “Viewing Cotrol Structures as Patterns of Passing Messages” (Artificial Intelligence 8, 3 (1977), 323–364) “present[s] an approach to modelling intelligence in terms of a society of communicating knowledge-based problem solving experts”; “each of the experts can be viewed as a society that can be further decomposed in the same way until the primitive actors of the system are reached”;
  • 99. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Carl Hewitt in “Viewing Cotrol Structures as Patterns of Passing Messages” (Artificial Intelligence 8, 3 (1977), 323–364) “present[s] an approach to modelling intelligence in terms of a society of communicating knowledge-based problem solving experts”; “each of the experts can be viewed as a society that can be further decomposed in the same way until the primitive actors of the system are reached”; he was “investigating the nature of the communication mechanisms needed for effective problem-solving by a society of experts and the conventions of civilized discourse that make this possible.”
  • 100. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials
  • 101. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Hewitt demonstrates these “principles” by showing how to compute the factorial function with actors:
  • 102. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Hewitt demonstrates these “principles” by showing how to compute the factorial function with actors:
  • 103. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Hewitt demonstrates these “principles” by showing how to compute the factorial function with actors: 1. using a resursive procedure, that is, a procedure that uses replication and
  • 104. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Hewitt demonstrates these “principles” by showing how to compute the factorial function with actors: 1. using a resursive procedure, that is, a procedure that uses replication and
  • 105. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Computing Factorials Hewitt demonstrates these “principles” by showing how to compute the factorial function with actors: 1. using a resursive procedure, that is, a procedure that uses replication and 2. an iterative procudure, that is, a procedure that relies on message passing to deliver a result.
  • 106. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Actor Replication
  • 107. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Actor Replication case class Val(a: Actor, n: Int) case class Res(n: Int) class Fact extends Actor { def act = react { case Val(a,0) => a ! Res(1) case Val(a,n) => var p = new Fact p.start p ! Val(self,n-1) react { case Val(_, m) => a ! Val(a, n*m) case Res(m) => a ! Val(a, n*m)} } }
  • 108. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Using Class Fact
  • 109. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Using Class Fact object actorsExample { def main(args: Array[String]) { var factorial = actor { react { case Val(a,n) => var q = new Fact q.start q ! Val(self,n) react { case Val(_,f) => a ! Val(a,f) } } } factorial ! Val(self,6) react { case Val(_, n) => println(n) } } }
  • 110. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Iterative Actor
  • 111. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Iterative Actor case class InitVal(a: Actor, n: Int) case class Val(a: Actor, n: Int, m: Int) object actorsExample { def main(args: Array[String]) { val loopActor = actor { var ResActor : Actor = null loop{ react { case Val(_,acc,1) => ResActor ! acc; exit("done") case Val(a,1,count) => ResActor = a self ! Val(self,count,count-1) case Val(a,acc,count) => self ! Val(self,acc*count,count-1) } } }
  • 112. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Using Class Fact
  • 113. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . Using Class Fact var factorial = actor { react { case InitVal(a,0) => a ! InitVal(a, 1) case InitVal(a,1) => a ! InitVal(a, 1) case InitVal(a,n) => loopActor ! Val(self,1,n) react { case f: Int => a ! InitVal(a,f) } } } factorial ! InitVal(self,6) receive { case InitVal(_, n) => println(n) } } }
  • 114. Scala: An OO Surprise Syropoulos Introduction What is Scala? Object Orientation Scalability Functional Features Parser Builders XML Processing XML Processing Concurrent Program-ming . . . . . . The end! Thank you so much for your attention!