Functional Programming in Scala

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Functional Programming in Bassam Abd El-Hamid @MrBassam

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Von Neumann architecture

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Von Neumann bottleneck “Can Programming be Liberated from the von Neumann Style?” John Backus 1977

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala History of FP languages

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala A formal system in mathematical logic and computer science for expressing computation by way of variable binding and substitution λ-calculus http://en.wikipedia.org/wiki/Lambda_calculus

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala * Referential transparency * No side effect * Remove unused expression safely Pure functions

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Scalable Language Martin Odersky 2003 www.scala-lang.org

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Why Scala?

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Object-Oriented Functional Statically Typed Runs on the JVM Can Execute Java Code

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala All types are objects Type inference. Nested Functions. Functions are objects. Domain specific language (DSL) support Traits. Closures. Concurrency support inspired by Erlang. vs Java

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Who is using Scala?

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Who is using Scala? And more ...

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Links: Who's using Scala? (March, 2013) http://alvinalexander.com/scala/whos-using-scala-akka-play-framework Scala Adoption by Enterprises http://www.slideshare.net/mslinn/scala-adoption-by-enterprises Scala in the Enterprise http://www.scala-lang.org/node/1658

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Syntax

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala // This is a valid comment /* This is a multiline comment */ Comments:

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala object HelloWorld { def main(args: Array[String]) { println("Hello, world!") } } Hello, world!

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala val s = "hello" // ; not requierd println(s) val s = "hello"; println(s) // ; is REQUIRED Newline Characters

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Keywords

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala package com.bassam.stuff // Import one class import scala.collection.mutable.HashMap // Import more than one import scala.collection.immutable.{TreeMap, TreeSet} // Import all import scala.xml._ Scala Packages

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala var or val VariableName : DataType [= Initial Value] var myVar : String = "mutable variable" val myVal : String = "immutable variable" //Multiple assignments: val (myVar1: Int, myVar2: String) = Pair(5, "Foo") Variable Declaration

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Data Types (the same data types as Java)

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala class Point(xc: Int, yc: Int) { var x: Int = xc var y: Int = yc def move(dx: Int, dy: Int) { x = x + dx y = y + dy println ("Point x location : " + x); println ("Point y location : " + y); } } Classes, Objects and Traits

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala class Point(val xc: Int, val yc: Int) { var x: Int = xc var y: Int = yc def move(dx: Int, dy: Int) { x = x + dx y = y + dy println ("Point x location : " + x); println ("Point y location : " + y); }} class Location(override val xc: Int, override val yc: Int, val zc :Int) extends Point(xc, yc){ var z: Int = zc def move(dx: Int, dy: Int, dz: Int) { x = x + dx y = y + dy z = z + dz println ("Point x location : " + x); println ("Point y location : " + y); println ("Point z location : " + z); }} Classes, Objects and Traits

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala trait someTrait { var somevar: Int=0 def someFun(x: Int): Int = (x*2)/5 } trait anotherTrait { var anothervar: Int=0 def anotherFun(x: Int): Int = (x*7)/100 } class class1(){} class class2() extends class1 with someTrait with anotherTrait {} Classes, Objects and Traits

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala private visible only inside the class or object protected only accessible from subclasses public accessed from anywhere (Default) protected[UpToScope] private[UpToScpoe] Access Modifiers

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala if(Boolean_expression 1){ //Executes when the Boolean expression 1 is true }else if(Boolean_expression 2){ //Executes when the Boolean expression 2 is true }else if(Boolean_expression 3){ //Executes when the Boolean expression 3 is true }else { //Executes when the none of the above condition is true. } IF...ELSE

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala while(condition){ statement(s); } do{ statement(s); }while( condition ); for( x <- Range ){ statement(s); } Loop Types

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala import scala.util.control.Breaks ... var x:Int=1 val brk=new Breaks brk.breakable{ while( x>0 ){ if (x==10) brk.break print(x) x=x+1 }} break a loop

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala def functionName ([list of parameters]) : [return type] = { function body return [expr] } def sum(x:Int,z:Int):Int=z+x def pi=3.14 Sum(5,6) //11 Functions

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala def v:Int=5*6 def sum(x: => Int,z:Int):Int=z+x sum(v,5) //35 Functions Call-by-Name

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala def sum(x: Int,z: Int):Int=z+x sum(z=5,x=6) Functions with Named Arguments

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala def sum( nums : Int* ) :Int ={ var buf:Int=0 for( i <- nums) buf=buf+i } sum(5,2,74,....) Function with Variable Arguments

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala def sum( a:Int=5, b:Int=7 ) : Int = { var s:Int = 0 s = a + b return s } Default Parameter Values for a Function

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala def factorial(i: Int): Int = { def fact(i: Int, accumulator: Int): Int = { if (i <= 1) accumulator else fact(i - 1, i * accumulator) } fact(i, 1) } Nested Functions - local functions

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala def factorial(n: BigInt): BigInt = { if (n <= 1) 1 else n * factorial(n - 1) } Recursion Functions

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala object Test { def main(args: Array[String]) { val date = new Date log(date, "message1" ) log(date, "message2" ) log(date, "message3" ) } def log(date: Date, message: String) = { println(date + "----" + message) } } Partially Applied Functions

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala object Test { def main(args: Array[String]) { val logWithDateBound = log(new Date, _ : String) logWithDateBound("message1" ) logWithDateBound("message2" ) logWithDateBound("message3" ) } def log(date: Date, message: String) = { println(date + "----" + message) } } Partially Applied Functions

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala ([list of parameters]) => function body object Test { var sum=(x:Int,z:Int) => x+z def main(args: Array[String]) { println(sum(5,6)) } } Anonymous Functions

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala object Test { def main(args: Array[String]) { println( apply( layout, 10) ) } def apply(f: Int => String, v: Int) = f(v) def layout[A](x: A) = "[" + x.toString() + "]" } Higher-Order Functions

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala val multiplier = (i:Int) => i * 10 val multiplier = (i:Int) => i * factor var factor = 3 val multiplier = (i:Int) => i * factor Closures

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Currying transforms a function that takes multiple parameters into a chain of functions, each taking a single parameter Currying Functions schönfinkeling

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala def strcat(s1: String,s2: String) = s1 + s2 def strcat(s1: String) = (s2: String) => s1 + s2 def main(args: Array[String]){ print (strcat ("Hello ")("World")) } Currying Functions schönfinkeling

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala def sum(x: Int,z: Int) = x + z def main(args: Array[String]){ val sumCurried = Function.curried(sum _) print (sumCurried(5)(6)) } Currying Functions schönfinkeling

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala object Test { def main(args: Array[String]) { println(matchTest(3)) } def matchTest(x: Int): String = x match { case 1 => "one" case 2 => "two" case _ => "many" } } Pattern Matching

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala object Test { def main(args: Array[String]) { println(matchTest("two")) println(matchTest("test")) println(matchTest(1)) } def matchTest(x: Any): Any = x match { case 1 => "one" case "two" => 2 case y: Int => "scala.Int" case _ => "many" } } Pattern Matching

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala object Test { def main(args: Array[String]) { val alice = new Person("Alice", 25) val bob = new Person("Bob", 32) val charlie = new Person("Charlie", 32) for (person <- List(alice, bob, charlie)) { person match { case Person("Alice", 25) => println("Hi Alice!") case Person("Bob", 32) => println("Hi Bob!") case Person(name, age) => println("Age: " + age + " year, name: " + name + "?") }}} // case class, empty one. case class Person(name: String, age: Int) } Pattern Matching

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala var x:Array[String] = new Array[String](3) //or var z = new Array[String](3) Arrays

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala var x:Array[String] = new Array[String](3) //or var x = new Array[String](3) //or var x = Array("One", "Two", "Three") x(0)="One" ; x(1)="Two" ; x(2)="Three" Arrays

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala var myMatrix = Array.ofDim[Int](3,3) myMatrix(0)(1)=10 Multi-Dimensional Arrays

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala var myArr1 = Array(1.9, 2.9, 3.4, 3.5) var myArr2 = Array(8.9, 7.9, 0.4, 1.5) var myArr3 = Array.concat( myArr1, myArr2) Arrays

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala var a=(0 to 10) //from 0 to 10 var b=(0 until 10) //from 0 to 9 var c=(0 to 10 by 2) // step 2 ranges

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala // List of Strings val fruit: List[String] = List("apples", "oranges", "pears") // List of Integers val nums: List[Int] = List(1, 2, 3, 4) // Empty List. val empty: List[Nothing] = List() // Two dimensional list val dim: List[List[Int]] = List( List(1, 0, 0), List(0, 1, 0), List(0, 0, 1) ) Lists

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala // List of Integers val nums = 1 :: (2 :: (3 :: (4 :: Nil))) // Empty List. val empty = Nil // Two dimensional list val dim = (1 :: (0 :: (0 :: Nil))) :: (0 :: (1 :: (0 :: Nil))) :: (0 :: (0 :: (1 :: Nil))) :: Nil } } Lists

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala // Empty set of integer type var s : Set[Int] = Set() // Set of integer type var s : Set[Int] = Set(1,3,5,7) //or var s = Set(1,3,5,7) Sets

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala /*Empty hash table whose keys are strings and values are integers:*/ var A:Map[Char,Int] = Map() // A map with keys and values. val colors = Map("red" -> "#FF0000", "azure" -> "#F0FFFF") Maps / Hash tables

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala val tup = (1, "hello", Console) //Which is syntactic sugar for: val t = new Tuple3(1, "hello", Console) val sum = t._1 + t._2 + t._3 t.productIterator.foreach{ i =>println("Value = " + i )} Tuples

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala object Test { def main(args: Array[String]) { val it = Iterator("a", "number", "of", "words") while (it.hasNext){ println(it.next()) } } } Iterators

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala object Test { def findPerson(key: Int): Option[Person] def main(args: Array[String]) { val capitals = Map("France" -> "Paris", "Japan" -> "Tokyo") println("capitals.get( "France" ) : " + capitals.get( "France" )) println("capitals.get( "India" ) : " + capitals.get( "India" )) } } Options

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala import scala.util.matching.Regex object Test { def main(args: Array[String]) { val pattern = "Scala".r val str = "Scala is Scalable and cool" println(pattern findFirstIn str) } } Regular Expressions

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala import java.io.FileReader import java.io.FileNotFoundException import java.io.IOException object Test { def main(args: Array[String]) { try { val f = new FileReader("input.txt") } catch { case ex: FileNotFoundException =>>{ println("Missing file exception") } case ex: IOException => { println("IO Exception") }}}} Exception Handling

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Questions

CAIRO TECH CLUB SESSION 5: Functional Programming in Scala Thank you :)

Functional Programming in Scala

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