Scala - A Scalable Language

Scala

... a Scalable Language

06.10.2009
XPUG Rhein Main
Mario Gleichmann

Mario Gleichmann XPUG Rhein/Main

Introduction

Mario Gleichmann

site: www.mg-informatik.de

blog: 'brain driven development'
gleichmann.wordpress.com

mail: mario.gleichmann@mg-informatik.de


Motivation

Open your mind ...
• Scala vs. Java 9

• Functional programming for the imperative mind

• Discover the (new) possibilities ...


Motivation

Open your mind ...
“If Java programmers want to
• Scala vs. Java 9
use features that aren't present
• Functional programming forthe language, I think they're
in the imperative mind
probably best off using another
language that targets the JVM,
such as Scala and Groovy“

Joshua Bloch

Motivation

Open your mind ...
● Functions & Closures

• Scala vs. Java 9 ●
Extended Type System

● Extended Module System

• ●
Properties
Discover the (new) possibilities ...
●
Essence over Ceremony

● Extended Control Structs


Motivation

Open your mind ...
• Scala vs. Java 9 “If i were to pick a language
• Functional programming foruse today other than Java,
to the imperative mind
it would be Scala“

James Gosling


Motivation

Open your mind ...

• Discover the possibilities ...
Imparative programming
is a programming paradigm
that describes computation
in terms of statements
that change a programs state


Motivation

Open your mind ...

Functional programming
is a programming paradigm
that describes computation as the
evaluation of mathematical functions
avoiding state and mutable data


Motivation

Open your mind ...

Lazy Evaluation
Continuations
Monads
Recursion
Higher Order Functions
Closures
Currying
Immutable Datatypes


Motivation

Open your mind ...

Control Structure Abstraction
Composition Traits

Pattern Matching Type Variance

Modularity
Type Extentions / Conversions


Motivation

Open your mind !!!
•
“Scala taught me to program and reason about
programming differently. I stopped thinking in terms of
allocating buffers, structs and objects and of changing those
pieces in memory. Instead I learned to think about most of
my programs as transforming input to output.
This change in thinking has lead to lower defect rates,
more modular code, and more testable code“

David Pollak

What is Scala ?

A programming language ...

• Pure Object Oriented

• Statically Typed

• Functional

• Runs on the JVM


What is Scala ?


• Martin Odersky (EPFL Switzerland)
• Functional
•
Pizza, Fummel & Co.

Statically Typed Java
Generic
•
•

• javac Reference Compiler
• Runs on the JVM


What is Scala ?


''Everything is an Object''
1 + 2 <=> 1.+( 2 )

• Functional

• Runs on the JVM


What is Scala ?


1 + 2 <=> 1.+( 2 )
''No primitive Types''
123.hashCode
• Functional

• Runs on the JVM


What is Scala ?


1 + 2 <=> 1.+( 2 )
''No primitive Types''
123.hashCode
• Functional
''Operations are method calls''
• Runs on the JVM actor ! msg <=> actor.!( msg )


What is Scala ?



•
public BigInteger factorial( BigInteger n ){
Functional
Jav

a
if( n.equals( BigInteger.ZERO )
return BigInteger.ONE
else
return
n.multiply(
factorial( n.subtract( BigInteger.ONE ) ) );
• Runs on the JVM
}


What is Scala ?



• Functional
Scal

a
def factorial( n: BigInt ): BigInt = if (n == 0 ) 1 else n * factorial( n – 1 )


• Runs on the JVM


What is Scala ?



• Functionalintroduction
Method Result Type Scal

a

Parameter list Type declaration Definition
• Runs on the JVM


What is Scala ?



• Functional
Scal

a

● (almost) everything is an expression

• Runs on the JVM


What is Scala ?



• Functional
Scal

a

● (almost) everything is an expression

BigInt 'integrates' like a Built-In type (but it's not!)
●
• Runs on the JVM


What is Scala ?



• Functional
class BigInt( val bigInteger: BigInteger ) extends java.lang.Number{

override def hashCode(): Int = this.bigInteger.hashCode()
• Statically Typed BigInt =
def + (that: BigInt):
new BigInt( this.bigInteger.add( that.bigInteger ) )
...
• }
Runs on the JVM


What is Scala ?


Introduction of class definition
• Functional val bigInteger: BigInteger ) extends java.lang.Number{
class BigInt(

...
• }
Runs on the JVM


What is Scala ?


class value parameter
• Pure Object Oriented (primary constructor)

class BigInt(

...
• }
Runs on the JVM


What is Scala ?


• Pure Object Oriented Single Inheritance

class BigInt(

...
• }
Runs on the JVM


What is Scala ?



Mandatory !
• Functional

...
• }
Runs on the JVM


What is Scala ?



• Functional

...
• }
Runs ordinary Method
on the JVM


What is Scala ?



• Functional

...
• }
RunsClass Instantiation
on the JVM


What is Scala ?



• Functional

...
• }
Runs on the JVM Self reference


What is Scala ?

Example: Implement your own Type
• Object Oriented
● Stack of Int values

● Immutable (Functional style)
• Functional


• Runs on the JVM


What is Scala ?

• Object Oriented

• Functional
Empty Stack : Non Empty Stack :
[]
• Statically Typed element: Int [ 7 ]
Rest: Stack :
element: Int [ 23 ]
• Runs on the JVM Rest: Stack :
[]


What is Scala ?

• Object Oriented

• Functional
Empty Stack : Non Empty Stack :
[] element: Int [ 10 ]
Rest: Stack :
• Statically Typed element: Int [ 7 ]
Rest: Stack :
element: Int [ 23 ]
• Runs on the JVM Rest: Stack :
[]


What is Scala ?

• Object Oriented
abstract class IntStack {

def push(x: Int): IntStack = new NonEmptyIntStack( x, this )
• Functional
def isEmpty: Boolean

• Statically Typed Int
def top:

def pop: IntStack
}
• Runs on the JVM


What is Scala ?

• Abstract class
Object Oriented
abstract class IntStack {

def push(x: Int): IntStack = new NonEmptyIntStack( x, this )
• Functional
def isEmpty: Boolean Abstract method

• Statically Typed Int
def top: Abstract method

def pop: IntStack Abstract method
}
• Runs on the JVM


What is Scala ?

• Object Oriented
class EmptyIntStack extends IntStack {

def isEmpty = true
• Functional
def top = throw new EmptyStackException

• Statically Typed = throw new EmptyStackException
def pop
}

• Runs on the JVM


What is Scala ?

• Object Oriented Inheritance

def isEmpty = true
• Functional

def pop
}
Throwing a 'checked' Exception
• Runs on the JVM ... but catching is optional


What is Scala ?

• Object Oriented

def isEmpty = true
• Functional

def pop
}
val zeroInts = new EmptyIntStack
• Runs on the JVM
var noInts = new EmptyIntStack


What is Scala ?

• Object Oriented

def isEmpty = true
• Functional

def pop
}
val zeroInts = new EmptyIntStack 'Immutable' value
• Runs on the JVM
var noInts = new EmptyIntStack 'mutable' variable


What is Scala ?

• Object Oriented

def isEmpty = true
• Functional

• Statically Typed = throw new EmptyStackExceptionNo need
def pop
} for multiple
val zeroInts = new EmptyIntStack Instances of
• Runs on the JVM EmptyIntStack


What is Scala ?

• Object Oriented
object EmptyIntStack extends IntStack {
• Functional def isEmpty = true
def pop
}

• Runs on the Singleton Object
●
JVM


What is Scala ?

• Object Oriented
object EmptyIntStack extends IntStack {

• Functional def isEmpty = true

def pop
}
val zeroInts = new EmptyIntStack
• Runs on the JVM


What is Scala ?

• Object Oriented
class NonEmptyIntStack( elem: Int, rest: IntStack )
extends IntStack {
• Functional
def isEmpty = false

def top = elem
def pop = rest
}
• Runs on the JVM


What is Scala ?

• Object Oriented
class NonEmptyIntStack( elem: Int, rest: IntStack )
extends IntStack {
• Functional
def isEmpty = false

def top = elem
def pop = rest
}
• Runs on the JVM
var s = EmptyIntStack push 23 push 7 push 10


What is Scala ?

Refined Type System


• Functional

• Runs on the JVM


What is Scala ?

Refined Type System
• Pure Object Oriented ● Using Stack with other types than Int

● Concept of stacking elements is generic

• Functional

• Runs on the JVM


What is Scala ?

Refined Type System
• Pure Object Oriented ● Using Stack with other types than Int

● Concept of stacking elements is generic

=> Generic Types
• Functional
(Type Parameterization)

• Runs on the JVM


What is Scala ?

Refined Type System
• Pure Object Oriented abstract class Stack[A] { Type Paramter

def push(x: A): Stack[A] =
• Statically Typed new NonEmptyStack[A]( x, this )

def isEmpty: Boolean
• Functional def top: A

def pop: Stack[A]
• Runs on the JVM }


What is Scala ?

Refined Type System
• Pure Object Oriented class NonEmptyStack[A](
elem: A,
rest: Stack[A] ) extends Stack[A] {
def isEmpty = false

• Functional def top = elem

def pop = rest
}
• Runs on the JVM


What is Scala ?

Refined Type System
• Pure Object Oriented val s = new EmptyStack[Int]

val t = s push 1 push 2 push 3
t.pop.top => 2

• Functional

• Runs on the JVM


What is Scala ?

Refined Type System

t.pop.top => 2
Parameterized Type

• Functional

• Runs on the JVM


What is Scala ?

Refined Type System

t.pop.top Mandatory
=> 2
( no Raw Types ! )
• Functional

• Runs on the JVM


What is Scala ?

Refined Type System
• Pure Object Oriented ● A Stack implementation only for numbers


• Functional

• Runs on the JVM


What is Scala ?

Refined Type System

● Restrict the upper Type to Number

• Functional

• Runs on the JVM


What is Scala ?

Refined Type System

●
Upper Type Bound

• Functional

• Runs on the JVM


What is Scala ?

Refined Type System

●
Upper Type Bound

• Functional abstract class Stack[A <: Number]{ ... }

• Runs on the JVM


What is Scala ?

Refined Type System

●
Upper Type Bound

• Functional abstract class Stack[A <: Number]{ ... }

Defined by the implementor,
• Runs on the JVM not by the user !


What is Scala ?

Refined Type System
• Pure Object OrientedIs Stack[String] a super type of Stack[Any] ?


• Functional

• Runs on the JVM


What is Scala ?

Refined Type System

Jav

a
List<String> sList = new ArrayList<String>();

List<Object> oList = sList;
• Functional

• Runs on the JVM


What is Scala ?

Refined Type System

Jav

a

• Functional
Compile Error:
''Type mismatch: cannot convert
• Runs on the JVM List<String> to List<Object>''


What is Scala ?

Refined Type System

Jav

a

• Functional
Generic Types are
• Runs on the JVM INVARIANT


What is Scala ?

Refined Type System
• Pure Object Orientedbut ...

Jav

a
String[] sArray = new String[]{};

Object[] oArray = sArray;
• Functional

• Runs on the JVM


What is Scala ?

Refined Type System

Jav

a

• Functional
Arrays are
• Runs on the JVM COVARIANT


What is Scala ?

Refined Type System

Jav

a

• Functional
oArray[0] = BigDecimal.ONE;

• Runs on the JVM


What is Scala ?

Refined Type System

Jav

a

• Functional
oArray[0] = BigDecimal.ONE;

ArrayStoreException
• Runs on the JVM
at Runtime !


What is Scala ?

Refined Type System
• Pure Object Oriented Scal

a
abstract class Stack[+A]{
• Statically Typed def push(x: A): Stack[A] =
new NonEmptyStack[A]( x, this )
...
• Functional }

• Runs on the JVM


What is Scala ?

Refined Type System
• Pure Object Oriented Covariant subtyping Scal

a
...
• Functional }

• Runs on the JVM


What is Scala ?

Refined Type System
• Pure Object Oriented Covariant subtyping Scal

a
...
• Functional }
Compile Error:
''covariant type A occurs in
• Runs on the JVM contravariant position in type A
of value x''


What is Scala ?

Refined Type System

a
• Statically Typed def push[B >: A](x: B): Stack[B] =
new NonEmptyStack[B](x, this)
...
• Functional }

• Runs on the JVM


What is Scala ?

Refined Type System

a
...
• Functional }
Lower Type Bound
''Parameter B is restricted to range
• Runs on the JVM only over supertypes of type A''


What is Scala ?

Refined Type System

a
...
• Functional }

val s1 = new EmptyStack[Int] push 1 push 2
• Runs on the JVM val s2 = s1 push "x"


What is Scala ?

Refined Type System

a
...
• Functional } Stack[Int]
val s1 = new EmptyStack[Int] push 1 push 2
• Runs on the JVM val s2 = s1 push "x" Stack[Any]


What is Scala ?

Type inference
• Pure Object Oriented val creator: String = “Odersky“


• Functional

• Runs on the JVM


What is Scala ?

Type inference

val creator = “Odersky“

• Functional

• Runs on the JVM


What is Scala ?

Type inference


• Functional def add( a: Int, b: Int ): Int = a + b

• Runs on the JVM


What is Scala ?

Type inference


• Functional def add( a: Int, b: Int ): Int = a + b

def add( a: Int, b: Int ) = a + b
• Runs on the JVM


What is Scala ?

Implicit Type conversion
• Pure Object Oriented “Scalable Language“ - 'a'

=> Sc l ble L ngu ge

• Functional

• Runs on the JVM


What is Scala ?


• Statically Typed class StringExtension( s: String ){
def -( sub: Char ) = s.replace( sub, ' ' )
}
• Functional
new StringExtension( “Scala“ ).-( 'a' )

• Runs on the JVM


What is Scala ?


}
• Functional
implicit def toStringExtension( s: String ) =
new StringExtension( s )
• Runs on the JVM


What is Scala ?


Implicit conversion to StringExtension
}
• Functional
implicit def toStringExtension( s: String ) =
new StringExtension( s )
• Runs on the JVM


What is Scala ?




•
Functional

• Runs on the JVM


What is Scala ?

●
Lambda Calculus (A. Church)
●
Functions are first class values


•
Functional

• Runs on the JVM


What is Scala ?

●
●

• Statically Typed Function Literals

( x: Int ) => x + 1
•
Functional

• Runs on the JVM


What is Scala ?

●
●


( x: Int ) => x + 1 => λ x . x + 1
•
Functional

• Runs on the JVM


What is Scala ?

●
●


( x: Int ) => x + 1 => λ x . x + 1
•
Functional

Argument list Definition
• Runs on the JVM


What is Scala ?

●
●


( x: Int ) => x + 1 => λ x . x + 1
•
Functional val succ = ( x: Int ) => x + 1

• Runs on the JVM


What is Scala ?

●
●


( x: Int ) => x + 1 => λ x . x + 1
•
succ( 7 ) => 8
• Runs on the JVM


What is Scala ?

●
●


( x: Int ) => x + 1 => λ x . x + 1
•
succ( 7 ) => 8
• Runs on the JVM type of succ: ( Int ) => Int


What is Scala ?

Closures
• Pure Object Oriented val ages = List( 2, 20, 14, 19, 49, 11, 62 )
var barrier = 18
• Statically Typed val minors = { ( x :Int ) => x < barrier }

val germanMinors = ages.filter( minors )
•
Functional

=> List( 2, 14, 11 )
• Runs on the JVM


What is Scala ?

Closures
var barrier = 18 List[Int] (Type inference)

•
Functional
... accepting a function which
=> List( 2, 14, 11 )and results to boolean
accepts an Int
• Runs on the JVM


What is Scala ?

Closures
var barrier = 18 free variable

•
Functional
bound variable

'open term'
• Runs on the JVM


What is Scala ?

Closures
var barrier = 18 capturing

•
Functional
● bound within lexical scope of function
• Runs on the JVM
=> open term is closed

What is Scala ?

Closures
var barrier = 18

•
Functional
barrier = 21
val usMinors = ages.filter( minors )
• Runs on the JVM


What is Scala ?

Closures
var barrier = 18

'dynamic' bound
•
Functional
barrier = 21
val usMinors = ages.filter( minors )
• Runs on the JVM
=> 2, 20, 14, 19, 11

What is Scala ?

Currying
• Pure Object Oriented val add = ( a: Int, b: Int ) => a + b

• Statically Typed A function

... accepting two Args
•
Functional

... resulting in a value of type Int
• Runs on the JVM


What is Scala ?

Currying

type of function add: ( Int, Int ) => Int

•
Functional
'resulting in ...'

• Runs on the JVM


What is Scala ?

Currying

Quiz:

''transform into a function which is accepting
•
Functional only one single Argument after another''

• Runs on the JVM


What is Scala ?

Currying
• Pure Object Oriented val add = ( a: Int ) => ( b: Int ) => a + b


•
Functional

• Runs on the JVM


What is Scala ?

Currying

• Statically Typed A function

... accepting one Arg
•
Functional

... resulting in another function
• Runs on the JVM


What is Scala ?

Currying


•
Functional

• Runs on the JVM


What is Scala ?

Currying

type of function add: (Int) => (Int) => Int

•
Functional 'resulting in ...'

'resulting in ...'
• Runs on the JVM


What is Scala ?

Currying

• Statically Typed val succ = add( 1 )

succ( 7 ) => 8
•
Functional

• Runs on the JVM


What is Scala ?

Currying
A function ...
val succ = add( 1 ) ... accepting one Arg
... resulting in another function
succ( 7 ) => 8
•
Functional
• Runs on the JVM


What is Scala ?

Curried Methods
• Pure Object Oriented def mult( a: Int )( b: Int ) = a * b


•
Functional

• Runs on the JVM


What is Scala ?

Curried Methods

multiple parameter lists

•
Functional

• Runs on the JVM


What is Scala ?

Curried Methods

multiple parameter lists

•
Functional
Signature: mult ( Int ) ( Int ) : Int
• Runs on the JVM


What is Scala ?

Curried Methods

val double = mult( 2 ) _

•
Functional

• Runs on the JVM


What is Scala ?

Curried Methods


Partially applied 2nd Arg unapplied
•
Functional

• Runs on the JVM


What is Scala ?

Curried Methods


•
Functional Coercion into a function of

type ( Int ) => Int
• Runs on the JVM


What is Scala ?

Curried Methods


double( 6 ) => 12
•
Functional

• Runs on the JVM


What is Scala ?

Curried Methods
• Pure Object Oriented val hours = ( 0 to 23 ).toList

def modulo( n: Int )( x: Int ) = ( x % n ) == 0
hours.filter( modulo( 2 ) _ )

•
Functional

• Runs on the JVM


What is Scala ?

Curried Methods
• Pure Object Oriented val hours = ( 0 to 23 ).toList List[Int]


•
Functional
expects function of type ( Int ) => Boolean

• Runs on the JVM


What is Scala ?

Curried Methods


•
Functional
curried to function of type ( Int ) => Boolean

• Runs on the JVM


What is Scala ?

Curried Methods


=> List( 0, 2, 4, 6, 8, 10, 12, …, 20, 22 )
•
Functional

• Runs on the JVM


What is Scala ?

Curried Methods


=> List( 0, 2, 4, 6, 8, 10, 12, …, 20, 22 )
•
Functional
hours.filter( modulo( 4 ) )
• Runs on the JVM => List( 0, 2, 4, 8, 12, …, 16, 20 )


What is Scala ?

OO + FP Fusion
●


• Functional

• Runs on the JVM


What is Scala ?

OO + FP Fusion
●
• Pure Object Oriented • Everything is an Object


• Functional

• Runs on the JVM


What is Scala ?

OO + FP Fusion
●

• Functions are Objects

• Functional

• Runs on the JVM


What is Scala ?

OO + FP Fusion
●

val succ = ( x: Int ) => x + 1
• Functional

• Runs on the JVM


What is Scala ?

OO + FP Fusion
●

val succ = new Function1[Int, Int]{
override def apply( x: Int ) = x + 1
• Functional }

• Runs on the JVM


What is Scala ?

OO + FP Fusion
●

• Functional }
succ( 7 )
• Runs on the JVM


What is Scala ?

OO + FP Fusion
●

• Functional }
succ.apply( 7 )
• Runs on the JVM


What is Scala ?

... so does Groovy, Clojure, JRuby ...


• Functional

• Runs on the JVM


What is Scala ?

• Pure Object Oriented • Dynamically typed (MOP & Co)
• Significant Performance Overhead !

• Functional

• Runs on the JVM


What is Scala ?

•
Scala is statically typed !

• Functional

• Runs on the JVM


What is Scala ?

•

• Functional
• Compiles to Bytecode
• Seamless Java Interoperability
• Runs on the JVM


What is Scala ?

•

• Functional
• Compiles to Bytecode
• Seamless Java Interoperability
• Runs on the JVM • Performance on par with Java


What is Scala ?


“I can honestly say if someone
had shown me the Programming
in Scala book ... back in 2003
I'd probably have never created
Groovy“
• Functional

James Strachan
• Runs on the JVM


Characteristics

•
Expressive

•
High Level

•
Concise

•
Extensible

•
Pragmatic


Characteristics

•
Expressive
case class Person( name: String, age: Int )

•
High Level var persons = List( Person( "Hans", 11 ),
Person( "Hugo", 19 ),
Person( "Helga", 16 ),
Person( "Heinz", 38 ) )
•
Concise
val (adults, minors) = persons.partition( _.age > 18 )

•
Extensible
Can you spot the intention ?

•
Pragmatic


Characteristics

•
Expressive

•
•
Concise

•
Extensible
''Split Persons into minors and adults by their age''

•
Pragmatic


Characteristics

•
Expressive

•
Results into a Tuple2[List[Person],List[Person]]
•
Concise

•
Extensible

•
Pragmatic


Characteristics

•
Expressive

•
Results into a Tuple2[List[Person],List[Person]]
•
Concise

•
Extensible Pattern Matching:
bound to single elements of a Tuple2

•
Pragmatic


Characteristics

•
Expressive

•
•
Concise

•
Extensible

adults => List(Person(Hugo,19), Person(Heinz,38))
•
Pragmatic minors => List(Person(Hans,11), Person(Helga,16))


Characteristics

•
Expressive val bookPrices = Map(
“Prag. Programmer“ -> 20 USD,
•
High Level “Systems Thinking“ -> 30 EUR,
“Code Complete“ -> 25 USD )
•
Concise
bookPrices += ( “Clean Code“ -> 20 EUR )

•
Extensible println( bookPrices( “Systems Thinking“ ) )

•
Pragmatic for( (book, price) <- bookPrices ){
if( price in EUR ) println( book )
}

Characteristics

Create a new Map
•
•
•
Concise

•

•
}

Characteristics

Create a new Map
•
•
Implicit Conversion into a Tuple2
•
Concise

•

•
}

Characteristics

Create a new Map
•
•
Implicit Conversion into a Currency
•
Concise

•

•
}

Characteristics

•
Compagnion Object
•
High Level object Map{
“Systems Thinking“ -> 30 EUR,
def apply[A, B]( elems: (A, B)* ) : Map[A, B] = ...
...
•
Concise }

•

•
}

Characteristics

•
Map instance
•
class <xxx>Map[A, B] extends Map[A, B] {
override def apply(key: A): B = ...
...
•
Concise }

•

•
}

Characteristics

Upper Case in given name ? Jav
•
Expressive

a
boolean hasUpperCase = false;
•
High Level for( int i=0; i < name.length; i++ ){
if( Character.isUpperCase( name.charAt( i ) {
•
Concise hasUpperCase = true;
break;
}
•
Extensible
}

•
Pragmatic


Characteristics

Upper Case in given name ? Scal
•
Expressive

a
val hasUpperCase =
name.exists( c: Char => c.isUpperCase )
•
High Level

•
Concise

•
Extensible

•
Pragmatic


Characteristics

•
Expressive

a
val hasUpperCase =
•
High Level

•
Concise 'Higher Order Method' Function

•
Extensible

•
Pragmatic


Characteristics

•
Expressive

a
val hasUpperCase =
•
High Level

•

val hasUpperCase =
•
Extensible
name.exists( c => c isUpperCase )

•
Pragmatic Type inference


Characteristics

•
Expressive

a
val hasUpperCase =
•
High Level

•

val hasUpperCase =
•
Extensible
name.exists( _ isUpperCase )

•
Pragmatic parameter shortcut


Characteristics
Find maximal Distance Jav
•
Expressive

a
List<Integer> distances =
new ArrayList<Integer>();
•
High Level distances.add( 12 );
distances.add( 17 ); ...
•
Concise
Integer maxDistance = 0;
•
Extensible for( Integer distance : distances ){
if( distance > maxDistance ){
•
Pragmatic }
maxDistance = distance

}


Characteristics
Find maximal Distance Scal
•
Expressive

a
val distances = List( 12, 17, 14, 21, ...)

•
High Level val maxDistance =
distances.foldLeft( 0 ){ Math.max }
•
Concise

•
Extensible

•
Pragmatic


Scala - A Scalable Language

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Scala - A Scalable Language