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Applied Functional Programming with Scala - Notes

Copyright © 2016-2018 Fantasyland Institute of Learning. All rights reserved.

1. Mastering Functions

A function is a mapping from one set, called a domain, to another set, called the codomain. A function associates every element in the domain with exactly one element in the codomain. In Scala, both domain and codomain are types.

val square : Int => Int = x => x * x

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A sample cla file.

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<?xml version="1.0" encoding="UTF-8"?>
<!--Generated by Standards Editor (build:R1.6.16) on 2020 Mar 05 10:41:58, ISO 20022 version : 2013-->
<xs:schema xmlns="urn:iso:std:iso:20022:tech:xsd:pacs.008.001.09" xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" targetNamespace="urn:iso:std:iso:20022:tech:xsd:pacs.008.001.09">
    <xs:element name="Document" type="Document"/>
    <xs:complexType name="AccountIdentification4Choice">
        <xs:choice>
            <xs:element name="IBAN" type="IBAN2007Identifier"/>
            <xs:element name="Othr" type="GenericAccountIdentification1"/>
        </xs:choice>
    </xs:complexType>

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object TicTocToe {
  sealed trait Action
  object Action {
    case object X extends Action
    case object O extends Action
  }

  sealed trait Player
  object Player {
    case object X extends Player

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import java.util.HashSet;
import java.util.Set;

// This is a Java class with wildcards
public class Wild {
    Set<?> contents() {
        Set<String> languages = new HashSet<>();
        languages.add("Scala");
        languages.add("Haskell");
        languages.add("Closure");

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/**
 * Represents a mode that decides how to deal exceed rate for Throttle operator
 */
sealed abstract class ThrottleMode

object ThrottleMode {

  /**
   *  Tells throttle to make pauses before emitting messages to meet throttle rate
   */

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object Factorial extends App {
  implicit val system = ActorSystem("QuickStart")
  implicit val materializer = ActorMaterializer()

  val source: Source[Int, NotUsed] = Source(1 to 100)

  val factorials: Source[BigInt, NotUsed] = source.scan(BigInt(1))((acc, next) => acc * next)

  val result: Future[IOResult] =
    factorials

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  import org.json4s._
  import org.json4s.jackson.JsonMethods._
  
  implicit val formats: DefaultFormats = new DefaultFormats {
    override  def dateFormatter: SimpleDateFormat = {
      val f = new SimpleDateFormat("EEE MMM dd HH:mm:ss ZZZZZ yyyy")
      f.setTimeZone(DefaultFormats.UTC)
      f
    }

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// More info: http://www.nurkiewicz.com/2014/01/three-flavours-of-request-response.html

import akka.actor.{Actor, ActorLogging, ActorRef, ActorSystem, Cancellable, Props, Terminated}
import akka.event.LoggingReceive
import akka.util.Timeout
import akka.pattern.pipe

import scala.concurrent.duration._
import scala.language.postfixOps

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object QuickSort extends App {
  val list = List(3, 5, 7, 1, 4, 9, 44, 2)
  println(quickSort(list))

  def quickSort(list: List[Int]): List[Int] = {
    list match {
      case Nil => Nil
      case pivot :: tail =>
        val (less, greater) = tail.partition(_ < pivot)
        quickSort(less) ::: pivot :: quickSort(greater)