Introduction to Functional Programing in Kotlin and Arrow

Transcript

1. Welcome
   

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2. Introduction to Functional
   Programing in Kotlin and
   Arrow
   Hadi Tok
   Google Developers Expert (Android)
   Technical Lead, @CitizenMe
   https://haditok.com/
   

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3. Functional
   Programming
   

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4. Functional
   Programming
   In computer science, functional programming is a programming
   paradigm that treats computation as the evaluation of mathematical
   functions and avoids state and mutable data.*
   *https://mauriziostorani.wordpress.com/2008/08/29/functional-programming-examples-methods-and-concepts/
   

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5. Functional
   Programming
   In computer science, functional programming is a programming
   paradigm that treats computation as the evaluation of mathematical
   functions and avoids state and mutable data.
   

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6. Functional
   Programming
   In computer science, functional programming is a programming
   paradigm that treats computation as the evaluation of mathematical
   functions and avoids state and mutable data.
   

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7. Mathematical
   Functions
   A function is a relation for which each value from the set the first
   components of the ordered pairs is associated with exactly one value
   from the set of second components of the ordered pair.
   

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8. Function
   { 1, 2, 3, 4}
   {A, B, C}
   

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9. Function
   { 1, 2, 3, 4}
   {A, B, C}
   

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10. Function
    { 1, 2, 3, 4}
    {A, B, C}
    

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11. Functional
    Programming
    In computer science, functional programming is a programming
    paradigm that treats computation as the evaluation of mathematical
    functions and avoids state and mutable data.
    

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12. State
    class MyClass{
    var list = listOf(1,2,3,4,5)
    fun filterList() {
    list = list.filter { it%2 !=0 }
    }
    }
    

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13. State
    class MyClass{
    val list = listOf(1,2,3,4,5)
    fun filterList(list:List): List {
    return list.filter { it!=0 }
    }
    }
    

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14. Functional
    Programming
    In computer science, functional programming is a programming
    paradigm that treats computation as the evaluation of mathematical
    functions and avoids state and mutable data.
    

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15. Mutable data
    fun filterList(list:List){
    val iterator=list.iterator()
    for(i in iterator){
    if(i%2==0){
    iterator.remove()
    }
    }
    }
    

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16. Mutable data
    val filteredList = list.filter { it % 2 != 0 }
    

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17. Changes in state and
    data
    ● Who is the owner of the data?
    ● What would happen when data changes?
    ● Should other constructs using the data needs to be notified?
    ● How other constructs will be notified?
    ● What happens when there are multiple changes at the same time?
    

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18. Pure functions
    ● Its return value is the same for the same arguments
    ● Has no side effects
    

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19. Side effects
    ● Mutation of local static variables,non-local variables, mutable
    reference arguments
    ● Throwing an exception
    ● I/O operations
    

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20. Kotlin and Functional
    Programming
    

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21. Package Level
    Functions
    class Logger{
    fun log(message: String){
    println(message)
    }
    }
    

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22. Package Level
    Functions
    fun log(message: String){
    println(message)
    }
    

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23. interface Callback{ fun onComplete() }
    fun operationWithACallBack(callback: Callback){
    Thread.sleep(1000L)
    callback.onComplete()
    }
    Higher order
    Functions
    

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24. operationWithACallBack(object : Callback{
    override fun onComplete() {
    println("completed")
    }
    })
    Higher order
    Functions
    

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25. fun operationWithACallBack(callback: () -> Unit) {
    Thread.sleep(1000L)
    callback()
    }
    Higher order
    Functions
    

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26. operationWithACallBack ({
    println("completed")
    })
    Higher order
    Functions
    

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27. operationWithACallBack(){
    println("completed")
    }
    Higher order
    Functions
    

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28. operationWithACallBack{
    println("completed")
    }
    Higher order
    Functions
    

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29. data class Customer(
    val name: String,
    val city: String
    )
    Higher order
    Functions
    

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30. fun printCustomerByCity(city: String) {
    val filteredCustomers = customers.filter { it.city == city }
    filteredCustomers.forEach { println(it) }
    }
    fun printCustomerByName(name: String) {
    val filteredCustomers = customers.filter { it.name == name }
    filteredCustomers.forEach { println(it) }
    }
    Higher order
    Functions
    

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31. fun printCustomers(predicate: (Customer) -> Boolean) {
    val filteredCustomer = customers.filter(predicate)
    filteredCustomers.forEach { println(it) }
    }
    fun main(args: Array) {
    printCustomers { it.city == "Istanbul" }
    printCustomers { it.name == "Hadi" }
    }
    Higher order
    Functions
    

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32. object StringUtils {
    fun getThirdCharacter(string: String): Char {
    if(string.length>2){
    return string[2]
    }
    throw IllegalArgumentException()
    }
    }
    Extension
    Functions
    

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33. val thirdLetter = StringUtils.getThirdCharacter("Kotlin")
    Extension
    Functions
    

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34. fun String.getThirdCharacter(): Char {
    if(length>2){
    return get(2)
    }
    throw IllegalArgumentException()
    }
    Extension
    Functions
    

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35. val thirdCharacter = "Kotlin".getThirdCharacter()
    Extension
    Functions
    

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36. list.forEach { println(it) }
    Extension
    Functions
    

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37. public inline fun Iterable.forEach(action: (T) -> Unit): Unit {
    for (element in this) action(element)
    }
    Extension
    Functions
    

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38. Arrow
    Λrrow is a library for Typed Functional Programming
    in Kotlin.
    https://arrow-kt.io
    

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39. Arrow
    Arrow aims to provide a lingua franca of interfaces
    and abstractions across Kotlin libraries.
    For this, it includes the most popular data types, type
    classes and abstractions such as Option, Either, IO,
    Functor, Applicative, Monad to empower users to
    write pure FP apps and libraries built atop higher
    order abstractions.
    https://arrow-kt.io
    

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40. fun tryGetThirdCharacter(string:String): Try {
    return Try {
    if(string.length<2){
    throw IllegalArgumentException("string is short")
    }else{
    string[3]
    }
    }
    }
    Try
    

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41. tryGetThirdCharacer("Kotlin")
    .getOrElse { println(it.message) }
    Try
    

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42. val thirdCharacter = tryGetThirdLetter("Go")
    .getOrDefault { "a" }
    Try
    

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43. tryGetThirdLetter("Kotlin")
    .fold(
    { println(it.message) },
    { println("third char is $it") }
    )
    Try
    

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44. fun getMessage(useResource: Boolean): Either {
    return if (useResource) {
    Either.right(R.string.start)
    } else {
    Either.left("Start")
    }
    }
    Either
    

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45. val textEither = getMessage(useResource)
    val text: String = when (textEither) {
    is Either.Left -> textEither.a
    is Either.Right -> getString(textEither.b)
    }
    Either
    

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46. fun divide(x: Int, y: Int): Option {
    return if (y == 0) {
    Option.empty()
    } else {
    Option.just(x / y)
    }
    }
    Option
    

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47. val result = divide(x,y).map { it*6 }
    Option
    

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48. Thank you
    

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