Functional Programming with Arrow in Kotlin

GIDS 2019: https://www.developermarch.com/developersummit/session.html?insert=Raghunath

With a rising trend in programming languages adding more and more functional capabilities, developers are working at a much higher level of abstraction. The declarative style of programming allows us to write readable and maintainable code that focuses on "what" (larger picture) rather than "how" (nuts and bolts). Functional programming also promotes immutability by default which makes dealing with concurrency an easy and a fun affair. Kotlin already supports some of these features like functions as first-class citizens, lambdas, anonymous functions, immutability, persistent collections, explicit nullable and non-nullable types, declarative constructs, etc., However, these features lack capabilities offered by purely functional languages.

Arrow is a Kotlin library that pushes the envelope further by introducing typeclasses, functional data types, optics, etc., It achieves this by clever usage of Kotlin language features and by generating code using annotation processors.

This talk will walk you through several ideas and code examples that will help you get started with functional programming using Arrow.

Audience will be able to:
- Use functional data types from the Arrow library.
- Use functional programming patterns.
- Solve problems using functional ideas and gradually move away from imperative programming.
- Deal with immutability and use optics to modify deeply nested data structures efficiently.

Transcript

1. Functional Programming with
   Arrow in Kotlin
   @ragunathjawahar • Obvious (previously, Uncommon Bangalore)
   

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2. fun findFirst(array: Array, key: Char): Int {
   for (i in array.indices) {
   if (array[i] == key) return i
   }
   return -1
   }
   

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3. fun findFirst(array: Array, key: Char): Int {
   for (i in array.indices) {
   if (array[i] == key) return i
   }
   return -1
   }
   

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4. fun findFirst(array: Array, key: Char): Int {
   for (i in array.indices) {
   if (array[i] == key) return i
   }
   return -1
   }
   

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5. fun findFirst(array: Array, key: Char): Int {
   for (i in array.indices) {
   if (array[i] == key) return i
   }
   return -1
   }
   

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6. fun findFirst(array: Array, key: Char): Int {
   for (i in array.indices) {
   if (array[i] == key) return i
   }
   return -1
   }
   

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7. fun findFirst(array: Array, key: Char): Int {
   for (i in array.indices) {
   if (array[i] == key) return i
   }
   return -1
   }
   

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8. fun findFirst(array: Array, key: Char): Int {
   for (i in array.indices) {
   if (array[i] == key) return i
   }
   return -1
   }
   

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9. fun findFirst(array: Array, key: Char): Int {
   for (i in array.indices) {
   if (array[i] == key) return i
   }
   return -1
   }
   

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10. fun findFirst(array: Array, key: Char): Int {
    for (i in array.indices) {
    if (array[i] == key) return i
    }
    return -1
    }
    

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11. fun findFirst(array: Array, key: Char): Int {
    for (i in array.indices) {
    if (array[i] == key) return i
    }
    return -1
    }
    

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12. fun findFirst(array: Array, key: Char): Int {
    for (i in array.indices) {
    if (array[i] == key) return i
    }
    return -1
    }
    

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13. fun findFirst(array: Array, key: Char): Int {
    for (i in array.indices) {
    if (array[i] == key) return i
    }
    return -1
    }
    

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14. fun findFirst(array: Array, key: Char): Index {
    for (i in array.indices) {
    if (array[i] == key) return i
    }
    return -1
    }
    typealias Index = Int
    

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15. fun findFirst(array: Array, key: Char): Index {
    for (i in array.indices) {
    if (array[i] == key) return i
    }
    return -1
    }
    typealias Index = Int
    

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16. fun findFirst(array: Array, key: Char): Index {
    for (i in array.indices) {
    if (array[i] == key) return i
    }
    return -1
    }
    typealias Index = Int
    

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17. fun findFirst(array: Array, key: Char): Index {
    for (i in array.indices) {
    if (array[i] == key) return i
    }
    return -1
    }
    typealias Index = Int
    // findFirst(chars, ‘e’) != -1
    

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18. fun findFirst(array: Array, key: Char): Index {
    for (i in array.indices) {
    if (array[i] == key) return i
    }
    return -1
    }
    typealias Index = Int
    // findFirst(chars, ‘e’) != -1
    

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19. fun findFirst(array: Array, key: Char): Index {
    for (i in array.indices) {
    if (array[i] == key) return i
    }
    return -1
    }
    typealias Index = Int
    

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20. fun findFirst(array: Array, key: Char): Index? {
    for (i in array.indices) {
    if (array[i] == key) return i
    }
    return null
    }
    typealias Index = Int
    

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21. fun findFirst(array: Array, key: Char): Option {
    for (i in array.indices) {
    if (array[i] == key) return Some(i)
    }
    return None
    }
    typealias Index = Int
    

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22. fun findFirst(array: Array, key: Char): Option {
    for (i in array.indices) {
    if (array[i] == key) return Some(i)
    }
    return None
    }
    typealias Index = Int
    // absence
    // presence
    

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23. fun findFirst(array: Array, key: Char): Option {
    for (i in array.indices) {
    if (array[i] == key) return Some(i)
    }
    return None
    }
    typealias Index = Int
    

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24. fun findFirst(array: Array, key: Char): Option {
    for (i in array.indices) {
    if (array[i] == key) return Some(i)
    }
    return None
    }
    typealias Index = Int
    

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25. fun findFirst(array: Array, key: Char): Option {
    for (i in array.indices) {
    if (array[i] == key) return Some(i)
    }
    return None
    }
    typealias Index = Int
    

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26. fun findFirst(array: Array, key: A): Option {
    for (i in array.indices) {
    if (array[i] == key) return Some(i)
    }
    return None
    }
    typealias Index = Int
    

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27. fun findFirst(array: Array, key: A): Option {
    for (i in array.indices) {
    if (array[i] == key) return Some(i)
    }
    return None
    }
    typealias Index = Int
    

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28. fun findFirst(array: Array, key: A): Option {
    for (i in array.indices) {
    if (array[i] == key) return Some(i)
    }
    return None
    }
    typealias Index = Int
    

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29. fun findFirst(array: Array, p: (A) -> Boolean): Option {
    for (i in array.indices) {
    if (p(array[i])) return Some(i)
    }
    return None
    }
    typealias Index = Int
    

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30. fun findFirst(array: Array, p: (A) -> Boolean): Option {
    for (i in array.indices) {
    if (p(array[i])) return Some(i)
    }
    return None
    }
    typealias Index = Int
    // findFirst(people, { it.firstName == “Ajay” })
    

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31. fun findFirst(array: Array, p: (A) -> Boolean): Option {
    for (i in array.indices) {
    if (p(array[i])) return Some(i)
    }
    return None
    }
    typealias Index = Int
    // findFirst(people) { it.firstName == “Ajay” }
    

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32. fun findFirst(array: Array, p: (A) -> Boolean): Option {
    for (i in array.indices) {
    if (p(array[i])) return Some(i)
    }
    return None
    }
    typealias Index = Int
    

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33. fun findFirst(array: Array, p: (A) -> Boolean): Option {
    for (i in array.indices) {
    if (p(array[i])) return Some(i)
    }
    return None
    }
    typealias Index = Int
    

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34. fun findFirst(array: Array, p: (A) -> Boolean): Option {
    for (i in array.indices) {
    if (p(array[i])) return Some(i)
    }
    return None
    }
    typealias Index = Int
    // findFirst(people) { it.firstName == “Ajay” }
    

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35. fun Array.findFirst(p:,(A) -> Boolean): Option {
    for (i in this.indices) {
    if (p(this[i])) return Some(i)
    }
    return None
    }
    typealias Index = Int
    // people.findFirst { it.firstName == “Ajay” }
    

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36. fun Array.findFirst(p:,(A) -> Boolean): Option {
    for (i in this.indices) {
    if (p(this[i])) return Some(i)
    }
    return None
    }
    typealias Index = Int
    

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37. fun Array.findFirst(p:,(A) -> Boolean): Option {
    for (i in this.indices) {
    if (p(this[i])) return Some(i)
    }
    return None
    }
    fun findFirst(array: Array, key: Char): Int {
    for (i in array.indices) {
    if (array[i] == key) return i
    }
    return -1
    }
    

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38. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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39. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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40. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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41. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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42. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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43. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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44. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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45. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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46. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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47. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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48. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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49. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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50. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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51. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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52. fun findFirst(array: Array, p:,(A) -> Boolean): Option {
    tailrec fun go(array: Array, index: Index): Option {
    return when {
    index == array.size -> None
    p(array[index]) -> Some(index)
    else -> go(array, index + 1)
    }
    }
    return go(array, 0)
    }
    But!
    

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53. Core Ideas
    

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54. Core Ideas
    • Purity
    
    • Referential Transparency
    
    • Immutability
    
    • Lazy Evaluation
    

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55. Notations
    

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56. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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57. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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58. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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59. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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60. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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61. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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62. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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63. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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64. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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65. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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66. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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67. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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68. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    // (a: Int, b: Int) -> Int
    

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69. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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70. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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71. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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72. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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73. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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74. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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75. fun add(a: Int, b: Int): Int = a + b
    val addRef: (Int, Int) -> Int = ::add
    val subtractLambda = { a: Int, b: Int -> a - b }
    

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76. val addRef: (Int, Int) -> Int = ::add
    addRef.invoke(4, 5)
    addRef(4, 5)
    

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77. Arrow Syntax
    compile "io.arrow-kt:arrow-syntax:$arrow_version"
    

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78. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    

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79. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    

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80. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    // bold(“Hello”)
    

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81. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    // Hello
    

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82. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    

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83. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    // italic(“Hello”)
    

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84. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    // Hello
    

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85. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    

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86. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    // boldItalic(“Hello”)
    

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87. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    // Hello
    

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88. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    

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89. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    // italicBold(“Hello”)
    

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90. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    // Hello
    

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91. val bold: (String) -> String = { "$it" }
    val italic: (String) -> String = { "$it" }
    val boldItalic = bold compose italic
    val italicBold = bold forwardCompose italic
    Composition
    

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92. fun multiply(a: Int, b: Int): Int = a * b
    val x2: (Int) -> Int = ::multiply.partially1(2)
    val x5: (Int) -> Int = ::multiply.partially1(5)
    Partial Application
    

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93. fun multiply(a: Int, b: Int): Int = a * b
    val x2: (Int) -> Int = ::multiply.partially1(2)
    val x5: (Int) -> Int = ::multiply.partially1(5)
    Partial Application
    

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94. fun multiply(a: Int, b: Int): Int = a * b
    val x2: (Int) -> Int = ::multiply.partially1(2)
    val x5: (Int) -> Int = ::multiply.partially1(5)
    Partial Application
    

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95. fun multiply(a: Int, b: Int): Int = a * b
    val x2: (Int) -> Int = ::multiply.partially1(2)
    val x5: (Int) -> Int = ::multiply.partially1(5)
    Partial Application
    

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96. fun multiply(a: Int, b: Int): Int = a * b
    val x2: (Int) -> Int = ::multiply.partially1(2)
    val x5: (Int) -> Int = ::multiply.partially1(5)
    Partial Application
    

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97. fun multiply(a: Int, b: Int): Int = a * b
    val x2: (Int) -> Int = ::multiply.partially1(2)
    val x5: (Int) -> Int = ::multiply.partially1(5)
    Partial Application
    

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98. fun multiply(a: Int, b: Int): Int = a * b
    val x2: (Int) -> Int = ::multiply.partially1(2)
    val x5: (Int) -> Int = ::multiply.partially1(5)
    Partial Application
    

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99. fun multiply(a: Int, b: Int): Int = a * b
    val x2: (Int) -> Int = ::multiply.partially1(2)
    val x5: (Int) -> Int = ::multiply.partially1(5)
    Partial Application
    

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100. fun multiply(a: Int, b: Int): Int = a * b
     val x2: (Int) -> Int = ::multiply.partially1(2)
     val x5: (Int) -> Int = ::multiply.partially1(5)
     Partial Application
     // x2(10)
     

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101. fun multiply(a: Int, b: Int): Int = a * b
     val x2: (Int) -> Int = ::multiply.partially1(2)
     val x5: (Int) -> Int = ::multiply.partially1(5)
     Partial Application
     // 20
     

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102. fun multiply(a: Int, b: Int): Int = a * b
     val x2: (Int) -> Int = ::multiply.partially1(2)
     val x5: (Int) -> Int = ::multiply.partially1(5)
     Partial Application
     

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103. fun multiply(a: Int, b: Int): Int = a * b
     val x2: (Int) -> Int = ::multiply.partially1(2)
     val x5: (Int) -> Int = ::multiply.partially1(5)
     Partial Application
     

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104. fun multiply(a: Int, b: Int): Int = a * b
     val x2: (Int) -> Int = ::multiply.partially1(2)
     val x5: (Int) -> Int = ::multiply.partially1(5)
     Partial Application
     

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105. fun multiply(a: Int, b: Int): Int = a * b
     val x2: (Int) -> Int = ::multiply.partially1(2)
     val x5: (Int) -> Int = ::multiply.partially1(5)
     Partial Application
     

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106. fun multiply(a: Int, b: Int): Int = a * b
     val x2: (Int) -> Int = ::multiply.partially1(2)
     val x5: (Int) -> Int = ::multiply.partially1(5)
     Partial Application
     

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107. fun multiply(a: Int, b: Int): Int = a * b
     val x2: (Int) -> Int = ::multiply.partially1(2)
     val x5: (Int) -> Int = ::multiply.partially1(5)
     Partial Application
     

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108. fun multiply(a: Int, b: Int): Int = a * b
     val x2: (Int) -> Int = ::multiply.partially1(2)
     val x5: (Int) -> Int = ::multiply.partially1(5)
     Partial Application
     // x5(10)
     

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109. fun multiply(a: Int, b: Int): Int = a * b
     val x2: (Int) -> Int = ::multiply.partially1(2)
     val x5: (Int) -> Int = ::multiply.partially1(5)
     Partial Application
     // 50
     

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110. fun multiply(a: Int, b: Int): Int = a * b
     val x2: (Int) -> Int = ::multiply.partially1(2)
     val x5: (Int) -> Int = ::multiply.partially1(5)
     Partial Application
     

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111. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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112. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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113. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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114. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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115. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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116. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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117. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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118. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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119. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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120. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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121. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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122. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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123. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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124. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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125. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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126. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     // findCat(animals)
     

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127. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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128. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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129. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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130. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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131. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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132. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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133. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog } // findDog(animals)
     

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134. Reverse
     fun findFirst(
     animals: List, predicate: (Animal) -> Boolean
     ): Option { /* … */ }
     val findCat: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Cat }
     val findDog: (List) -> Option =
     ::findFirst.reverse().partially1 { it is Dog }
     

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135. Logical Complement
     val onlyCats: (Animal) -> Boolean = { it is Cat }
     val allCats = filter(animals, onlyCats)
     val noCats = onlyCats.complement()
     val allExceptCats = filter(animals, noCats)
     

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136. Logical Complement
     val onlyCats: (Animal) -> Boolean = { it is Cat }
     val allCats = filter(animals, onlyCats)
     val noCats = onlyCats.complement()
     val allExceptCats = filter(animals, noCats)
     

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137. Logical Complement
     val onlyCats: (Animal) -> Boolean = { it is Cat }
     val allCats = filter(animals, onlyCats)
     val noCats = onlyCats.complement()
     val allExceptCats = filter(animals, noCats)
     

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138. Logical Complement
     val onlyCats: (Animal) -> Boolean = { it is Cat }
     val allCats = filter(animals, onlyCats)
     val noCats = onlyCats.complement()
     val allExceptCats = filter(animals, noCats)
     

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139. Logical Complement
     val onlyCats: (Animal) -> Boolean = { it is Cat }
     val allCats = filter(animals, onlyCats)
     val noCats = onlyCats.complement()
     val allExceptCats = filter(animals, noCats)
     

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140. Logical Complement
     val onlyCats: (Animal) -> Boolean = { it is Cat }
     val allCats = filter(animals, onlyCats)
     val noCats = onlyCats.complement()
     val allExceptCats = filter(animals, noCats)
     

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141. Logical Complement
     val onlyCats: (Animal) -> Boolean = { it is Cat }
     val allCats = filter(animals, onlyCats)
     val noCats = onlyCats.complement()
     val allExceptCats = filter(animals, noCats)
     

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142. Logical Complement
     val onlyCats: (Animal) -> Boolean = { it is Cat }
     val allCats = filter(animals, onlyCats)
     val noCats = onlyCats.complement()
     val allExceptCats = filter(animals, noCats)
     

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143. Logical Complement
     val onlyCats: (Animal) -> Boolean = { it is Cat }
     val allCats = filter(animals, onlyCats)
     val noCats = onlyCats.complement()
     val allExceptCats = filter(animals, noCats)
     

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144. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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145. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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146. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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147. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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148. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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149. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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150. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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151. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     // 100
     

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152. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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153. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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154. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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155. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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156. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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157. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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158. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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159. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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160. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1) // 100
     

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161. Currying (1/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     volume(10, 10, 1)
     val curriedVolume: (width: Int) -> (height: Int) -> (length: Int) -> Int =
     ::volume.curried()
     curriedVolume(10)(10)(1)
     

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162. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10)
     

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163. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10)
     

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164. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10)
     

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165. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10)
     // (width, height, length)
     

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166. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10)
     // (length, height, width)
     

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167. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10)
     // (length) -> (height) -> (width)
     

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168. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10)
     // (height) -> (width)
     

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169. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10)
     // (height, width)
     

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170. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10)
     // (width, height)
     

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171. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10)
     

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172. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10)
     

     View Slide

173. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10) // 100
     

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174. Currying (2/2)
     fun volume(width: Int, height: Int, length: Int): Int =
     width * height * length
     val area = ::volume
     .reverse().curried()(1)
     .uncurried().reverse()
     area(10, 10)
     

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175. More…
     • memoize() // FunctionN
     • firstOption() // Array, Sequence, and Iterable
     • flatten() - tail() - prependTo(List) // List
     • plus(C) // TupleN
     • paired() - tripled() // FunctionN
     • pipe() // FunctionN
     

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176. Data Types
     compile “io.arrow-kt:arrow-core-data:$arrow_version”
     

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177. Data Types
     • Option
     • Either
     • Try
     • Validated
     • Eval
     

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178. Option
     sealed class Option {
     object None : Option()
     data class Some(val t: T) : Option()
     }
     Option is an Algebraic Data Type that is used to model the absence of value. In Kotlin
     they are encoded with sealed class hierarchies.
     

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179. Option
     sealed class Option {
     object None : Option()
     data class Some(val t: T) : Option()
     }
     Option is an Algebraic Data Type that is used to model the absence of value. In Kotlin
     they are encoded with sealed class hierarchies.
     

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180. Option
     sealed class Option {
     object None : Option()
     data class Some(val t: T) : Option()
     }
     Option is an Algebraic Data Type that is used to model the absence of value. In Kotlin
     they are encoded with sealed class hierarchies.
     

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181. Option
     sealed class Option {
     object None : Option()
     data class Some(val t: T) : Option()
     }
     Option is an Algebraic Data Type that is used to model the absence of value. In Kotlin
     they are encoded with sealed class hierarchies.
     

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182. Option
     sealed class Option {
     object None : Option()
     data class Some(val t: T) : Option()
     }
     Option is an Algebraic Data Type that is used to model the absence of value. In Kotlin
     they are encoded with sealed class hierarchies.
     

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183. Option (Construction)
     val intOption: Option = Option(1)
     val intOption: Option = None
     val intOption: Option = Option.fromNullable(a) // a: Int?
     val intOption: Option = 1.some()
     val intOption: Option = none()
     

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184. Option (Construction)
     val intOption: Option = Option(1)
     val intOption: Option = None
     val intOption: Option = Option.fromNullable(a) // a: Int?
     val intOption: Option = 1.some()
     val intOption: Option = none()
     

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185. Option (Construction)
     val intOption: Option = Option(1)
     val intOption: Option = None
     val intOption: Option = Option.fromNullable(a) // a: Int?
     val intOption: Option = 1.some()
     val intOption: Option = none()
     

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186. Option (Construction)
     val intOption: Option = Option(1)
     val intOption: Option = None
     val intOption: Option = Option.fromNullable(a) // a: Int?
     val intOption: Option = 1.some()
     val intOption: Option = none()
     

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187. Option (Construction)
     val intOption: Option = Option(1)
     val intOption: Option = None
     val intOption: Option = Option.fromNullable(a) // a: Int?
     val intOption: Option = 1.some()
     val intOption: Option = none()
     

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188. Option (Construction)
     val intOption: Option = Option(1)
     val intOption: Option = None
     val intOption: Option = Option.fromNullable(a) // a: Int?
     val intOption: Option = 1.some()
     val intOption: Option = none()
     

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189. Option (Construction)
     val intOption: Option = Option(1)
     val intOption: Option = None
     val intOption: Option = Option.fromNullable(a) // a: Int?
     val intOption: Option = 1.some()
     val intOption: Option = none()
     

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190. Option (Extraction)
     val intOption: Option = Option(1)
     val nullableResult: Int? = intOption.orNull()
     val result: Int = intOption.getOrElse { 0 }
     

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191. Option (Extraction)
     val intOption: Option = Option(1)
     val nullableResult: Int? = intOption.orNull()
     val result: Int = intOption.getOrElse { 0 }
     

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192. Option (Extraction)
     val intOption: Option = Option(1)
     val nullableResult: Int? = intOption.orNull()
     val result: Int = intOption.getOrElse { 0 }
     

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193. Option (Extraction)
     val intOption: Option = Option(1)
     val nullableResult: Int? = intOption.orNull()
     val result: Int = intOption.getOrElse { 0 }
     

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194. Option (Extraction)
     val intOption: Option = Option(1)
     val nullableResult: Int? = intOption.orNull()
     val result: Int = intOption.getOrElse { 0 }
     

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195. Option (Extraction - when)
     val intOption: Option = Option(1)
     when (intOption) {
     is None -> 0
     is Some -> intOption.t
     } // Some(1)
     

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196. Option (Extraction - when)
     val intOption: Option = Option(1)
     when (intOption) {
     is None -> 0
     is Some -> intOption.t
     } // Some(1)
     

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197. Option (Extraction - when)
     val intOption: Option = Option(1)
     when (intOption) {
     is None -> 0
     is Some -> intOption.t
     } // Some(1)
     

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198. Option (Extraction - when)
     val intOption: Option = Option(1)
     when (intOption) {
     is None -> 0
     is Some -> intOption.t
     } // Some(1)
     

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199. Option (Extraction - when)
     val intOption: Option = Option(1)
     when (intOption) {
     is None -> 0
     is Some -> intOption.t
     } // Some(1)
     

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200. Option (Extraction - when)
     val intOption: Option = Option(1)
     when (intOption) {
     is None -> 0
     is Some -> intOption.t
     } // Some(1)
     

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201. Option (Extraction - when)
     val intOption: Option = Option(1)
     when (intOption) {
     is None -> 0
     is Some -> intOption.t
     } // Some(1)
     

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202. Option (Extraction - fold)
     val intOption: Option = Option(1)
     intOption.fold(
     { 0 },
     { it + 1 }
     ) // Some(2)
     

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203. Option (Extraction - fold)
     val intOption: Option = Option(1)
     intOption.fold(
     { 0 },
     { it + 1 }
     ) // Some(2)
     

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204. Option (Extraction - fold)
     val intOption: Option = Option(1)
     intOption.fold(
     { 0 },
     { it + 1 }
     ) // Some(2)
     

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205. Option (Extraction - fold)
     val intOption: Option = Option(1)
     intOption.fold(
     { 0 },
     { it + 1 }
     ) // Some(2)
     

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206. Option (Extraction - fold)
     val intOption: Option = Option(1)
     intOption.fold(
     { 0 },
     { it + 1 }
     ) // Some(2)
     

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207. Option (Extraction - fold)
     val intOption: Option = Option(1)
     intOption.fold(
     { 0 },
     { it + 1 }
     ) // Some(2)
     

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208. Option (Extraction - fold)
     val intOption: Option = Option(1)
     intOption.fold(
     { 0 },
     { it + 1 }
     ) // Some(2)
     

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209. Option (map)
     val intOption: Option = Option(1)
     intOption.map { it * 2 } // Some(2)
     val intOption: Option = None
     intOption.map { it * 2 } // None
     

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210. Option (map)
     val intOption: Option = Option(1)
     intOption.map { it * 2 } // Some(2)
     val intOption: Option = None
     intOption.map { it * 2 } // None
     

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211. Option (map)
     val intOption: Option = Option(1)
     intOption.map { it * 2 } // Some(2)
     val intOption: Option = None
     intOption.map { it * 2 } // None
     

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212. Option (map)
     val intOption: Option = Option(1)
     intOption.map { it * 2 } // Some(2)
     val intOption: Option = None
     intOption.map { it * 2 } // None
     

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213. Option (map)
     val intOption: Option = Option(1)
     intOption.map { it * 2 } // Some(2)
     val intOption: Option = None
     intOption.map { it * 2 } // None
     

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214. Option (map)
     val intOption: Option = Option(1)
     intOption.map { it * 2 } // Some(2)
     val intOption: Option = None
     intOption.map { it * 2 } // None
     

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215. Option (map)
     val intOption: Option = Option(1)
     intOption.map { it * 2 } // Some(2)
     val intOption: Option = None
     intOption.map { it * 2 } // None
     

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216. Option (map)
     val intOption: Option = Option(1)
     intOption.map { it * 2 } // Some(2)
     val intOption: Option = None
     intOption.map { it * 2 } // None
     

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217. Option (flatMap)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     oneOption.flatMap { one ->
     twoOption.map { two ->
     one + two
     }
     } // Some(3)
     

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218. Option (flatMap)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     oneOption.flatMap { one ->
     twoOption.map { two ->
     one + two
     }
     } // Some(3)
     

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219. Option (flatMap)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     oneOption.flatMap { one ->
     twoOption.map { two ->
     one + two
     }
     } // Some(3)
     

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220. Option (flatMap)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     oneOption.flatMap { one ->
     twoOption.map { two ->
     one + two
     }
     } // Some(3)
     

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221. Option (flatMap)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     oneOption.flatMap { one ->
     twoOption.map { two ->
     one + two
     }
     } // Some(3)
     

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222. Option (flatMap)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     oneOption.flatMap { one ->
     twoOption.map { two ->
     one + two
     }
     } // Some(3)
     

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223. Option (flatMap)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     oneOption.flatMap { one ->
     twoOption.map { two ->
     one + two
     }
     } // Some(3)
     

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224. Option (flatMap)
     val oneOption: Option = Option(1)
     val twoOption: Option = None
     oneOption.flatMap { one ->
     twoOption.map { two ->
     one + two
     }
     } // None
     

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225. Option (flatMap)
     val oneOption: Option = Option(1)
     val twoOption: Option = None
     oneOption.flatMap { one ->
     twoOption.map { two ->
     one + two
     }
     } // None
     

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226. Option (flatMap)
     val oneOption: Option = Option(1)
     val twoOption: Option = None
     oneOption.flatMap { one ->
     twoOption.map { two ->
     one + two
     }
     } // None
     

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227. Option (Monad Binding)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     Option.monad().binding {
     val one = oneOption.bind()
     val two = twoOption.bind()
     one + two
     }.fix() // Some(3)
     

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228. Option (Monad Binding)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     Option.monad().binding {
     val one = oneOption.bind()
     val two = twoOption.bind()
     one + two
     }.fix() // Some(3)
     

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229. Option (Monad Binding)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     Option.monad().binding {
     val one = oneOption.bind()
     val two = twoOption.bind()
     one + two
     }.fix() // Some(3)
     

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230. Option (Monad Binding)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     Option.monad().binding {
     val one = oneOption.bind()
     val two = twoOption.bind()
     one + two
     }.fix() // Some(3)
     

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231. Option (Monad Binding)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     Option.monad().binding {
     val one = oneOption.bind()
     val two = twoOption.bind()
     one + two
     }.fix() // Some(3)
     

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232. Option (Monad Binding)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     Option.monad().binding {
     val one = oneOption.bind()
     val two = twoOption.bind()
     one + two
     }.fix() // Some(3)
     

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233. Option (Monad Binding)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     Option.monad().binding {
     val one = oneOption.bind()
     val two = twoOption.bind()
     one + two
     }.fix() // Some(3)
     

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234. Option (Monad Binding)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     Option.monad().binding {
     val one = oneOption.bind()
     val two = twoOption.bind()
     one + two
     }.fix() // Some(3)
     

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235. Option (Monad Binding)
     val oneOption: Option = Option(1)
     val twoOption: Option = Option(2)
     Option.monad().binding {
     val one = oneOption.bind()
     val two = twoOption.bind()
     one + two
     }.fix() // Some(3)
     

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236. Option (Monad Binding)
     val oneOption: Option = Option(1)
     val twoOption: Option = None
     Option.monad().binding {
     val one = oneOption.bind()
     val two = twoOption.bind()
     one + two
     }.fix() // None
     

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237. Option (Monad Binding)
     val oneOption: Option = Option(1)
     val twoOption: Option = None
     Option.monad().binding {
     val one = oneOption.bind()
     val two = twoOption.bind()
     one + two
     }.fix() // None
     

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238. Option (Monad Binding)
     val oneOption: Option = Option(1)
     val twoOption: Option = None
     Option.monad().binding {
     val one = oneOption.bind()
     val two = twoOption.bind()
     one + two
     }.fix() // None
     

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239. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = Option(Foam(0.3))
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // Some(Cappuccino(espresso=Espresso(%=0.3), milk=Milk(%=0.3),
     // foam=Foam(%=0.3)))
     

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240. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = Option(Foam(0.3))
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // Some(Cappuccino(espresso=Espresso(%=0.3), milk=Milk(%=0.3),
     // foam=Foam(%=0.3)))
     

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241. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = Option(Foam(0.3))
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // Some(Cappuccino(espresso=Espresso(%=0.3), milk=Milk(%=0.3),
     // foam=Foam(%=0.3)))
     

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242. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = Option(Foam(0.3))
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // Some(Cappuccino(espresso=Espresso(%=0.3), milk=Milk(%=0.3),
     // foam=Foam(%=0.3)))
     

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243. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = Option(Foam(0.3))
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // Some(Cappuccino(espresso=Espresso(%=0.3), milk=Milk(%=0.3),
     // foam=Foam(%=0.3)))
     

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244. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = Option(Foam(0.3))
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // Some(Cappuccino(espresso=Espresso(%=0.3), milk=Milk(%=0.3),
     // foam=Foam(%=0.3)))
     

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245. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = Option(Foam(0.3))
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // Some(Cappuccino(espresso=Espresso(%=0.3), milk=Milk(%=0.3),
     // foam=Foam(%=0.3)))
     

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246. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = Option(Foam(0.3))
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // Some(Cappuccino(espresso=Espresso(%=0.3), milk=Milk(%=0.3),
     // foam=Foam(%=0.3)))
     

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247. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = Option(Foam(0.3))
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // Some(Cappuccino(espresso=Espresso(%=0.3), milk=Milk(%=0.3),
     // foam=Foam(%=0.3)))
     

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248. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = Option(Foam(0.3))
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // Some(Cappuccino(espresso=Espresso(%=0.3), milk=Milk(%=0.3),
     // foam=Foam(%=0.3)))
     

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249. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = Option(Foam(0.3))
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // Some(Cappuccino(espresso=Espresso(%=0.3), milk=Milk(%=0.3),
     // foam=Foam(%=0.3)))
     

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250. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = None
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // None
     

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251. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = None
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // None
     

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252. Option (Applicative Builder)
     val maybeEspresso: Option = Option(Espresso(0.3))
     val maybeMilkOption: Option = Option(Milk(0.3))
     val foamOption: Option = None
     Option.applicative()
     .map(maybeEspresso, maybeMilk, maybeFoam) { (espresso, milk, foam) ->
     Cappuccino(espresso, milk, foam)
     }.fix()
     // None
     

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253. Either
     sealed class Either {
     data class Left(val a: A) : Either()
     data class Right(val b: B) : Either()
     }
     Either is an Algebraic Data Type that is used to model a return type that may return one of
     two possible values.
     

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254. Either
     sealed class Either {
     data class Left(val a: A) : Either()
     data class Right(val b: B) : Either()
     }
     Either is an Algebraic Data Type that is used to model a return type that may return one of
     two possible values.
     

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255. Either
     sealed class Either {
     data class Left(val a: A) : Either()
     data class Right(val b: B) : Either()
     }
     Either is an Algebraic Data Type that is used to model a return type that may return one of
     two possible values.
     

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256. Either
     sealed class Either {
     data class Left(val a: A) : Either()
     data class Right(val b: B) : Either()
     }
     Either is an Algebraic Data Type that is used to model a return type that may return one of
     two possible values.
     

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257. Either
     sealed class Either {
     data class Left(val a: A) : Either()
     data class Right(val b: B) : Either()
     }
     Either is an Algebraic Data Type that is used to model a return type that may return one of
     two possible values.
     

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258. Either (Construction)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     val result: Either = Left(UnknownUser)
     val result: Either = 1.right()
     val result: Either = UnknownUser.left()
     

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259. Either (Construction)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     val result: Either = Left(UnknownUser)
     val result: Either = 1.right()
     val result: Either = UnknownUser.left()
     

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260. Either (Construction)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     val result: Either = Left(UnknownUser)
     val result: Either = 1.right()
     val result: Either = UnknownUser.left()
     

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261. Either (Construction)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     val result: Either = Left(UnknownUser)
     val result: Either = 1.right()
     val result: Either = UnknownUser.left()
     

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262. Either (Construction)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     val result: Either = Left(UnknownUser)
     val result: Either = 1.right()
     val result: Either = UnknownUser.left()
     

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263. Either (Construction)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     val result: Either = Left(UnknownUser)
     val result: Either = 1.right()
     val result: Either = UnknownUser.left()
     

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264. Either (Construction)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     val result: Either = Left(UnknownUser)
     val result: Either = 1.right()
     val result: Either = UnknownUser.left()
     

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265. Either (Extraction - when)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     when (result) {
     is Left -> 0
     is Right -> result.b
     } // Right(1)
     

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266. Either (Extraction - when)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     when (result) {
     is Left -> 0
     is Right -> result.b
     } // Right(1)
     

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267. Either (Extraction - when)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     when (result) {
     is Left -> 0
     is Right -> result.b
     } // Right(1)
     

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268. Either (Extraction - when)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     when (result) {
     is Left -> 0
     is Right -> result.b
     } // Right(1)
     

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269. Either (Extraction - when)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     when (result) {
     is Left -> 0
     is Right -> result.b
     } // Right(1) F
     

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270. Either (Extraction - when)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     when (result) {
     is Left -> 0
     is Right -> result.b
     } // Right(1)
     

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271. Either (Extraction - when)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     when (result) {
     is Left -> 0
     is Right -> result.b
     } // Right(1)
     

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272. Either (Extraction - fold)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.fold(
     { 0 },
     { it + 1 }
     ) // Right(2)
     

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273. Either (Extraction - fold)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.fold(
     { 0 },
     { it + 1 }
     ) // Right(2)
     

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274. Either (Extraction - fold)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.fold(
     { 0 },
     { it + 1 }
     ) // Right(2)
     

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275. Either (Extraction - fold)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.fold(
     { 0 },
     { it + 1 }
     ) // Right(2)
     

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276. Either (Extraction - fold)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.fold(
     { 0 },
     { it + 1 }
     ) // Right(2)
     

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277. Either (Extraction - fold)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.fold(
     { 0 },
     { it + 1 }
     ) // Right(2)
     

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278. Either (Extraction - fold)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.fold(
     { 0 },
     { it + 1 }
     ) // Right(2)
     

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279. Either (map)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.map { it * 2 } // Right(2)
     val result: Either = Left(UnknownUser)
     result.map { it * 2 } // Left(UnknownUser)
     

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280. Either (map)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.map { it * 2 } // Right(2)
     val result: Either = Left(UnknownUser)
     result.map { it * 2 } // Left(UnknownUser)
     

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281. Either (map)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.map { it * 2 } // Right(2)
     val result: Either = Left(UnknownUser)
     result.map { it * 2 } // Left(UnknownUser)
     

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282. Either (map)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.map { it * 2 } // Right(2)
     val result: Either = Left(UnknownUser)
     result.map { it * 2 } // Left(UnknownUser)
     

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283. Either (map)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.map { it * 2 } // Right(2)
     val result: Either = Left(UnknownUser)
     result.map { it * 2 } // Left(UnknownUser)
     

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284. Either (map)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.map { it * 2 } // Right(2)
     val result: Either = Left(UnknownUser)
     result.map { it * 2 } // Left(UnknownUser)
     

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285. Either (map)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.map { it * 2 } // Right(2)
     val result: Either = Left(UnknownUser)
     result.map { it * 2 } // Left(UnknownUser)
     

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286. Either (map)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.map { it * 2 } // Right(2)
     val result: Either = Left(UnknownUser)
     result.map { it * 2 } // Left(UnknownUser)
     

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287. Either (map)
     sealed class DomainError { /* ... */ }
     val result: Either = Right(1)
     result.map { it * 2 } // Right(2)
     val result: Either = Left(UnknownUser)
     result.map { it * 2 } // Left(UnknownUser)
     

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288. Either (flatMap)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     result1.flatMap { one ->
     result2.map { two ->
     one + two
     }
     } // Right(3)
     

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289. Either (flatMap)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     result1.flatMap { one ->
     result2.map { two ->
     one + two
     }
     } // Right(3)
     

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290. Either (flatMap)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     result1.flatMap { one ->
     result2.map { two ->
     one + two
     }
     } // Right(3)
     

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291. Either (flatMap)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     result1.flatMap { one ->
     result2.map { two ->
     one + two
     }
     } // Right(3)
     

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292. Either (flatMap)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     result1.flatMap { one ->
     result2.map { two ->
     one + two
     }
     } // Right(3)
     

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293. Either (flatMap)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     result1.flatMap { one ->
     result2.map { two ->
     one + two
     }
     } // Right(3)
     

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294. Either (flatMap)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     result1.flatMap { one ->
     result2.map { two ->
     one + two
     }
     } // Right(3)
     

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295. Either (flatMap)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Left(UnknownUser)
     result1.flatMap { one ->
     result2.map { two ->
     one + two
     }
     } // Left(UnknownUser)
     

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296. Either (flatMap)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Left(UnknownUser)
     result1.flatMap { one ->
     result2.map { two ->
     one + two
     }
     } // Left(UnknownUser)
     

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297. Either (flatMap)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Left(UnknownUser)
     result1.flatMap { one ->
     result2.map { two ->
     one + two
     }
     } // Left(UnknownUser)
     

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298. Either (Monad Binding)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     Either.monad.binding {
     val one = result1.bind()
     val two = result2.bind()
     one + two
     }.fix() // Right(3)
     

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299. Either (Monad Binding)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     Either.monad.binding {
     val one = result1.bind()
     val two = result2.bind()
     one + two
     }.fix() // Right(3)
     

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300. Either (Monad Binding)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     Either.monad.binding {
     val one = result1.bind()
     val two = result2.bind()
     one + two
     }.fix() // Right(3)
     

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301. Either (Monad Binding)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     Either.monad.binding {
     val one = result1.bind()
     val two = result2.bind()
     one + two
     }.fix() // Right(3)
     

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302. Either (Monad Binding)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     Either.monad.binding {
     val one = result1.bind()
     val two = result2.bind()
     one + two
     }.fix() // Right(3)
     

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303. Either (Monad Binding)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     Either.monad.binding {
     val one = result1.bind()
     val two = result2.bind()
     one + two
     }.fix() // Right(3)
     

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304. Either (Monad Binding)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     Either.monad.binding {
     val one = result1.bind()
     val two = result2.bind()
     one + two
     }.fix() // Right(3)
     

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305. Either (Monad Binding)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     Either.monad.binding {
     val one = result1.bind()
     val two = result2.bind()
     one + two
     }.fix() // Right(3)
     

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306. Either (Monad Binding)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Right(2)
     Either.monad.binding {
     val one = result1.bind()
     val two = result2.bind()
     one + two
     }.fix() // Right(3)
     

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307. Either (Monad Binding)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Left(UnknownUser)
     Either.monad.binding {
     val one = result1.bind()
     val two = result2.bind()
     one + two
     }.fix() // Left(UnknownUser)
     

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308. Either (Monad Binding)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Left(UnknownUser)
     Either.monad.binding {
     val one = result1.bind()
     val two = result2.bind()
     one + two
     }.fix() // Left(UnknownUser)
     

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309. Either (Monad Binding)
     sealed class DomainError { /* ... */ }
     val result1: Either = Right(1)
     val result2: Either = Left(UnknownUser)
     Either.monad.binding {
     val one = result1.bind()
     val two = result2.bind()
     one + two
     }.fix() // Left(UnknownUser)
     

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310. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Right(Water(0.6))
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Right(Americano(espresso=Espresso(%=0.4), water=Water(%=0.6)))
     

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311. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Right(Water(0.6))
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Right(Americano(espresso=Espresso(%=0.4), water=Water(%=0.6)))
     

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312. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Right(Water(0.6))
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Right(Americano(espresso=Espresso(%=0.4), water=Water(%=0.6)))
     

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313. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Right(Water(0.6))
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Right(Americano(espresso=Espresso(%=0.4), water=Water(%=0.6)))
     

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314. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Right(Water(0.6))
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Right(Americano(espresso=Espresso(%=0.4), water=Water(%=0.6)))
     

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315. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Right(Water(0.6))
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Right(Americano(espresso=Espresso(%=0.4), water=Water(%=0.6)))
     

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316. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Right(Water(0.6))
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Right(Americano(espresso=Espresso(%=0.4), water=Water(%=0.6)))
     

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317. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Right(Water(0.6))
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Right(Americano(espresso=Espresso(%=0.4), water=Water(%=0.6)))
     

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318. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Right(Water(0.6))
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Right(Americano(espresso=Espresso(%=0.4), water=Water(%=0.6)))
     

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319. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Right(Water(0.6))
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Right(Americano(espresso=Espresso(%=0.4), water=Water(%=0.6)))
     

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320. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Right(Water(0.6))
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Right(Americano(espresso=Espresso(%=0.4), water=Water(%=0.6)))
     

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321. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Left(RefillWater)
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Left(RefillWater)
     

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322. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Left(RefillWater)
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Left(RefillWater)
     

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323. Either (Applicative Builder)
     sealed class CoffeeMakerError { /* ... */ }
     val espressoResult: Either = Right(Espresso(0.4))
     val waterResult: Either = Left(RefillWater)
     Either.applicative()
     .map(espressoResult, waterResult) { (espresso, water) ->
     Americano(espresso, water)
     }.fix()
     // Left(RefillWater)
     

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324. More…
     • Try // Success - Failure
     • Validated // Valid - Invalid
     • Eval // Now - Always - Later - Defer
     • TupleN // Tuple2 - Tuple22
     

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325. Typeclasses
     compile “io.arrow-kt:arrow-typeclasses:$arrow_version”
     kapt “io.arrow-kt:arrow-meta:$arrow_version”
     

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326. Typeclasses
     • Polymorphism in functional programming.
     
     • Separates data from behaviour.
     
     • Maybe governed by algebraic / category theoretic laws.
     
     • Implemented as interfaces in Kotlin.
     
     • One Typeclass instance per type.
     

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327. Typeclasses
     • Show
     • Eq
     • Semigroup
     • Functor
     • Monad
     • …
     

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328. Show
     interface Show {
     fun A.show(): String
     }
     The Show typeclass abstracts the ability to obtain a String representation of any object.
     

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329. Show
     interface Show {
     fun A.show(): String
     }
     The Show typeclass abstracts the ability to obtain a String representation of any object.
     

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330. Show
     interface Show {
     fun A.show(): String
     }
     The Show typeclass abstracts the ability to obtain a String representation of any object.
     

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331. Show
     interface Show {
     fun A.show(): String
     }
     The Show typeclass abstracts the ability to obtain a String representation of any object.
     

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332. Eq
     interface Eq {
     fun F.eqv(b: F): Boolean
     fun F.neqv(b: F): Boolean = !eqv(b)
     }
     The Eq typeclass abstracts the ability to compare two instances of any object. It can be
     compared to the typeclass equivalent of Java’s Object#equals.
     

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333. Eq
     interface Eq {
     fun F.eqv(b: F): Boolean
     fun F.neqv(b: F): Boolean = !eqv(b)
     }
     The Eq typeclass abstracts the ability to compare two instances of any object. It can be
     compared to the typeclass equivalent of Java’s Object#equals.
     

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334. Eq
     interface Eq {
     fun F.eqv(b: F): Boolean
     fun F.neqv(b: F): Boolean = !eqv(b)
     }
     The Eq typeclass abstracts the ability to compare two instances of any object. It can be
     compared to the typeclass equivalent of Java’s Object#equals.
     

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335. Eq
     interface Eq {
     fun F.eqv(b: F): Boolean
     fun F.neqv(b: F): Boolean = !eqv(b)
     }
     The Eq typeclass abstracts the ability to compare two instances of any object. It can be
     compared to the typeclass equivalent of Java’s Object#equals.
     

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336. Eq
     interface Eq {
     fun F.eqv(b: F): Boolean
     fun F.neqv(b: F): Boolean = !eqv(b)
     }
     The Eq typeclass abstracts the ability to compare two instances of any object. It can be
     compared to the typeclass equivalent of Java’s Object#equals.
     

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337. Semigroup
     interface Semigroup {
     fun A.combine(b: A): A
     operator fun A.plus(b: A): A = this.combine(b)
     }
     The Semigroup for some given type A has a single operation combine which takes two
     values of type A, and returns a value of type A. This operation must be associative.
     

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338. Semigroup
     interface Semigroup {
     fun A.combine(b: A): A
     operator fun A.plus(b: A): A = this.combine(b)
     }
     The Semigroup for some given type A has a single operation combine which takes two
     values of type A, and returns a value of type A. This operation must be associative.
     

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339. Semigroup
     interface Semigroup {
     fun A.combine(b: A): A
     operator fun A.plus(b: A): A = this.combine(b)
     }
     The Semigroup for some given type A has a single operation combine which takes two
     values of type A, and returns a value of type A. This operation must be associative.
     

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340. Semigroup
     interface Semigroup {
     fun A.combine(b: A): A
     operator fun A.plus(b: A): A = this.combine(b)
     }
     The Semigroup for some given type A has a single operation combine which takes two
     values of type A, and returns a value of type A. This operation must be associative.
     

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341. Semigroup
     interface Semigroup {
     fun A.combine(b: A): A
     operator fun A.plus(b: A): A = this.combine(b)
     }
     The Semigroup for some given type A has a single operation combine which takes two
     values of type A, and returns a value of type A. This operation must be associative.
     

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342. Creating Instances
     data class Person(val firstName: String, val lastName: String) {
     companion object
     }
     @extension interface PersonShow : Show {
     override fun Person.show(): String = "$firstName $lastName"
     }
     val john = Person("John", "Doe")
     Person.show().run {
     john.show()
     } // John Doe
     

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343. Creating Instances
     data class Person(val firstName: String, val lastName: String) {
     companion object
     }
     @extension interface PersonShow : Show {
     override fun Person.show(): String = "$firstName $lastName"
     }
     val john = Person("John", "Doe")
     Person.show().run {
     john.show()
     } // John Doe
     

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344. Creating Instances
     data class Person(val firstName: String, val lastName: String) {
     companion object
     }
     @extension interface PersonShow : Show {
     override fun Person.show(): String = "$firstName $lastName"
     }
     val john = Person("John", "Doe")
     Person.show().run {
     john.show()
     } // John Doe
     

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345. Creating Instances
     data class Person(val firstName: String, val lastName: String) {
     companion object
     }
     @extension interface PersonShow : Show {
     override fun Person.show(): String = "$firstName $lastName"
     }
     val john = Person("John", "Doe")
     Person.show().run {
     john.show()
     } // John Doe
     

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346. Creating Instances
     data class Person(val firstName: String, val lastName: String) {
     companion object
     }
     @extension interface PersonShow : Show {
     override fun Person.show(): String = "$firstName $lastName"
     }
     val john = Person("John", "Doe")
     Person.show().run {
     john.show()
     } // John Doe
     

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347. Creating Instances
     data class Person(val firstName: String, val lastName: String) {
     companion object
     }
     @extension interface PersonShow : Show {
     override fun Person.show(): String = "$firstName $lastName"
     }
     val john = Person("John", "Doe")
     Person.show().run {
     john.show()
     } // John Doe
     

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348. Creating Instances
     data class Person(val firstName: String, val lastName: String) {
     companion object
     }
     @extension interface PersonShow : Show {
     override fun Person.show(): String = "$firstName $lastName"
     }
     val john = Person("John", "Doe")
     Person.show().run {
     john.show()
     } // John Doe
     

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349. Creating Instances
     data class Person(val firstName: String, val lastName: String) {
     companion object
     }
     @extension interface PersonShow : Show {
     override fun Person.show(): String = "$firstName $lastName"
     }
     val john = Person("John", "Doe")
     Person.show().run {
     john.show()
     } // John Doe
     

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350. Creating Instances
     data class Person(val firstName: String, val lastName: String) {
     companion object
     }
     @extension interface PersonShow : Show {
     override fun Person.show(): String = "$firstName $lastName"
     }
     val john = Person("John", "Doe")
     Person.show().run {
     john.show()
     } // John Doe
     

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351. Creating Instances
     data class Person(val firstName: String, val lastName: String) {
     companion object
     }
     @extension interface PersonShow : Show {
     override fun Person.show(): String = "$firstName $lastName"
     }
     val john = Person("John", "Doe")
     Person.show().run {
     john.show()
     } // John Doe
     

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352. Creating Instances
     data class Person(val firstName: String, val lastName: String) {
     companion object
     }
     @extension interface PersonShow : Show {
     override fun Person.show(): String = "$firstName $lastName"
     }
     val john = Person("John", "Doe")
     Person.show().run {
     john.show()
     } // John Doe
     

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353. Creating Instances
     data class Person(val firstName: String, val lastName: String) {
     companion object
     }
     @extension interface PersonShow : Show {
     override fun Person.show(): String = "$firstName $lastName"
     }
     val john = Person("John", "Doe")
     Person.show().run {
     john.show()
     } // John Doe
     

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354. More…
     • Hash
     • Order
     • Traverse
     • Applicative
     • And many more…
     

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355. Optics
     compile “io.arrow-kt:arrow-optics:$arrow_version”
     kapt “io.arrow-kt:arrow-meta:$arrow_version”
     

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356. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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357. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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358. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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359. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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360. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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361. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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362. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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363. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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364. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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365. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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366. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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367. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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368. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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369. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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370. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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371. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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372. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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373. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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374. Lens
     @optics data class UserProfile(
     val name: Name, /* Not shown for brevity */
     val contact: Contact
     ) { companion object }
     @optics data class Contact(
     val email: String,
     val phone: String
     ) { companion object }
     

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375. Without Lens
     val profile = UserProfile(
     Name("John", "Doe"),
     Contact("john.doe@personal.com", "6483920164")
     )
     val updatedProfile = profile.copy(
     contact = profile.contact.copy(
     email = "john.doe@work.com"
     )
     )
     

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376. Without Lens
     val profile = UserProfile(
     Name("John", "Doe"),
     Contact("john.doe@personal.com", "6483920164")
     )
     val updatedProfile = profile.copy(
     contact = profile.contact.copy(
     email = "john.doe@work.com"
     )
     )
     

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377. Without Lens
     val profile = UserProfile(
     Name("John", "Doe"),
     Contact("john.doe@personal.com", "6483920164")
     )
     val updatedProfile = profile.copy(
     contact = profile.contact.copy(
     email = "john.doe@work.com"
     )
     )
     

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378. Without Lens
     val profile = UserProfile(
     Name("John", "Doe"),
     Contact("john.doe@personal.com", "6483920164")
     )
     val updatedProfile = profile.copy(
     contact = profile.contact.copy(
     email = "john.doe@work.com"
     )
     )
     

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379. Without Lens
     val profile = UserProfile(
     Name("John", "Doe"),
     Contact("john.doe@personal.com", "6483920164")
     )
     val updatedProfile = profile.copy(
     contact = profile.contact.copy(
     email = "john.doe@work.com"
     )
     )
     

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380. Without Lens
     val profile = UserProfile(
     Name("John", "Doe"),
     Contact("john.doe@personal.com", "6483920164")
     )
     val updatedProfile = profile.copy(
     contact = profile.contact.copy(
     email = "john.doe@work.com"
     )
     )
     

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381. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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382. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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383. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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384. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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385. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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386. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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387. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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388. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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389. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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390. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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391. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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392. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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393. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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394. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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395. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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396. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile) // “john.doe@work.com”
     

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397. With Lens
     val profile = UserProfile( /* … */ )
     val emailLens: Lens = UserProfile.contact.email
     val workEmail = "john.doe@work.com"
     val updatedProfile = emailLens.modify(profile) { workEmail }
     val email = emailLens.get(profile)
     

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398. Optional
     @optics data class ShoppingCart(
     val id: String,
     val cartItems: ListK
     ) { companion object }
     @optics data class CartItem(
     val product: Product, /* Not shown for brevity */
     val quantity: Int
     ) { companion object }
     

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399. Optional
     @optics data class ShoppingCart(
     val id: String,
     val cartItems: ListK
     ) { companion object }
     @optics data class CartItem(
     val product: Product, /* Not shown for brevity */
     val quantity: Int
     ) { companion object }
     

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400. Optional
     @optics data class ShoppingCart(
     val id: String,
     val cartItems: ListK
     ) { companion object }
     @optics data class CartItem(
     val product: Product, /* Not shown for brevity */
     val quantity: Int
     ) { companion object }
     

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401. Optional
     @optics data class ShoppingCart(
     val id: String,
     val cartItems: ListK
     ) { companion object }
     @optics data class CartItem(
     val product: Product, /* Not shown for brevity */
     val quantity: Int
     ) { companion object }
     

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402. Optional
     @optics data class ShoppingCart(
     val id: String,
     val cartItems: ListK
     ) { companion object }
     @optics data class CartItem(
     val product: Product, /* Not shown for brevity */
     val quantity: Int
     ) { companion object }
     

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403. Optional
     @optics data class ShoppingCart(
     val id: String,
     val cartItems: ListK
     ) { companion object }
     @optics data class CartItem(
     val product: Product, /* Not shown for brevity */
     val quantity: Int
     ) { companion object }
     

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404. Optional
     @optics data class ShoppingCart(
     val id: String,
     val cartItems: ListK
     ) { companion object }
     @optics data class CartItem(
     val product: Product, /* Not shown for brevity */
     val quantity: Int
     ) { companion object }
     

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405. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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406. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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407. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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408. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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409. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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410. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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411. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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412. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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413. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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414. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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415. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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416. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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417. Optional (Set)
     val shoppingCart = ShoppingCart("CRT19321", cartItems)
     val quantityOptional: Optional = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .quantity
     val updatedCart = quantityOptional.modify(shoppingCart) { it + 1 }
     

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418. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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419. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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420. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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421. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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422. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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423. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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424. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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425. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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426. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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427. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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428. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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429. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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430. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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431. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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432. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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433. Optional (Get)
     val cartItemOption = ShoppingCart
     .cartItems
     .index(ListK.index(), productIndex)
     .getOption(shoppingCart)
     val sameCartItemOption = ListK.index().run {
     ShoppingCart.cartItems[productIndex].getOption(shoppingCart)
     }
     

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434. More…
     • Iso
     • Prism
     • Getter / Setter
     • Fold
     • Each
     • And others …
     

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435. That’s not it…
     • Arrow Fx
     
     • Effects
     
     • Arrow Query Language
     
     • Generic
     
     • Integrations
     
     • Free
     
     • Recursion Schemes
     

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436. Resources
     • https://arrow-kt.io/docs/
     
     • http://learnyouahaskell.com/
     
     • https://caster.io/courses/functional-programming-in-kotlin-with-arrow
     
     • https://github.com/hemanth/functional-programming-jargon#function
     
     • https://wiki.haskell.org/Typeclassopedia
     
     • http://nealford.com/functionalthinking.html
     
     • https://prod.packtpub.com/in/application-development/functional-kotlin
     

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437. end;
     @ragunathjawahar
     Twitter / Medium / GitHub
     

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