OOP is dead only if FP is dead

It is common to see Functional Programming (FP) presented as the opposite of Object-oriented Programming (OOP). These two programming paradigms have important differences, but they can share a lot in common, so they are not in direct opposition. In this talk, Andre will explore the gray area between OOP and FP, with code samples in JavaScript, TypeScript, and Haskell, kept easy enough enough for any programmer to follow.

Transcript

1. OOP is dead 

   only if FP is dead
   @andrestaltz
   

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2. Is object-oriented programming
   fundamentally different or superficially
   different to functional programming?
   

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3. OOP FP
   

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4. Closures
   Objects
   Immutability
   Mutation
   Assignment

   syntax
   Assignment

   semantics
   Typed
   Dynamic Evaluate
   Execute
   

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5. Evaluate
   Execute
   

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6. Evaluate
   Execute
   Calculate the value
   of an expression
   Perform a sequence
   of get/set actions
   

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7. Evaluate
   Execute
   Calculate the value
   of an expression
   Perform a sequence
   of get/set actions
   Imperative
   Functional
   

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8. Evaluate
   Execute
   (weight =>
   height =>
   weight / 

   (height * height * 0.01 * 0.01)
   )(70)(177)
   var weight = 70;
   var height = 177;
   var bmi = weight;
   bmi /= height;
   bmi /= height;
   bmi /= 0.01;
   bmi /= 0.01;
   

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9. Evaluate
   Execute
   Foundation is
   Lambda calculus
   Foundation is

   Random access machine
   

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10. Closures
    Objects
    

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11. Closures
    Objects
    Put data in an object,
    attach methods to the object
    Put data in a closure,
    functions refer to the closure
    

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12. Closures
    Objects
    const greeter = {
    isFemale: false,
    greet(name) {
    return this.isFemale ?
    "Hi Ms. " + name :
    "Hi Mr. " + name;
    }
    };
    const greet = (isFemale =>
    name => isFemale ?
    "Hi Ms. " + name :
    "Hi Mr. " + name
    )(false);
    

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13. Closures
    Objects
    const greeter = {
    // ...
    };
    greeter.greet.bind({isFemale: true})('Lisa');
    Advantage: allows changing the this object for a method.
    

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14. Closures
    Objects
    const greeter = {
    // ...
    };
    greeter.greet.bind({isFemale: true})('Lisa');
    Advantage: allows changing the this object for a method.
    Disadvantage: allows changing the this object for a method.
    

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15. Immutability
    Mutation
    

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16. Immutability
    Mutation
    

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17. Immutability
    Mutation
    final String s = "ABC";
    s.toLowerCase();
    Java
    

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18. Immutability
    Mutation
    Haskell
    import Data.Char
    str1 = "ABC"
    str2 = map toLower str1
    

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19. Immutability
    Mutation
    Haskell
    import Data.IORef
    f :: Num a => a -> IO a
    f x = do
    y <- newIORef 5 -- :: IORef Int
    writeIORef y 10
    val <- readIORef y -- :: Int
    return 2 * val
    

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20. Immutability
    Mutation
    Haskell
    import Data.STRef
    import Control.Monad.ST
    f :: Num a => a -> a
    f x = runST $ do
    y <- newSTRef 5 -- :: STRef Int
    writeSTRef y 10
    val <- readSTRef y -- :: Int
    return 2 * val
    

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21. Assignment

    syntax
    Assignment

    semantics
    

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22. Assignment

    syntax
    Assignment

    semantics
    Haskell
    do
    text <- readFile "foo"
    writeFile "bar" text
    readFile "foo" >>= writeFile "bar"
    

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23. Assignment

    syntax
    Assignment

    semantics
    Haskell
    do
    text <- readFile "foo"
    writeFile "bar" text
    readFile "foo" >>= writeFile "bar"
    

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24. Assignment

    syntax
    Assignment

    semantics
    JavaScript
    var text = fs.readFileSync('foo');
    fs.writeFileSync('bar', text);
    

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25. Assignment

    syntax
    Assignment

    semantics
    strongConnect v graph index stack indices lowlinks output = do
    i <- readSTRef index
    modifySTRef' indices (I.insert v i)
    modifySTRef' lowlinks (I.insert v i)
    modifySTRef' index (+1)
    push stack v
    forM_ (graph A.! v) $ \w -> do
    wIndex <- I.lookup w <$> readSTRef indices
    if isNothing wIndex
    then do
    strongConnect w graph index stack indices lowlinks output
    vLowLink <- fromJust . I.lookup v <$> readSTRef lowlinks
    wLowLink <- fromJust . I.lookup w <$> readSTRef lowlinks
    modifySTRef' lowlinks (I.insert v $ min vLowLink wLowLink)
    else do
    wOnStack <- elem w <$> readSTRef stack
    when wOnStack $ do
    vLowLink <- fromJust . I.lookup v <$> readSTRef lowlinks
    modifySTRef' lowlinks (I.insert v $ min vLowLink (fromJust wIndex))
    vLowLink <- fromJust . I.lookup v <$> readSTRef lowlinks
    vIndex <- fromJust . I.lookup v <$> readSTRef indices
    when (vLowLink == vIndex) $ do
    scc <- addSCC v [] stack
    modifySTRef' output (scc:)
    http://vaibhavsagar.com/blog/2017/05/29/imperative-haskell/
    

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26. Typed
    Dynamic
    

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27. Typed
    Dynamic
    Clojure (FP)
    Python (OOP)
    Haskell (FP)
    Java (OOP)
    

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28. Typed
    Dynamic
    Is x => 2 * x pure?
    

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29. Typed
    Dynamic
    Is x => 2 * x pure?
    const double = x => 2 * x;
    const lol = {};
    lol.valueOf = Math.random;
    double(lol); // 0.21666564647375441
    double(lol); // 1.4260443726695509
    

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30. Typed
    Dynamic
    Is x => 2 * x pure?
    const double: (x: number) => number =
    x => 2 * x;
    

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31. Typed
    Dynamic
    Abstractions: solving problems on the level of ideas
    

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32. Typed
    Dynamic
    

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33. Typed
    Dynamic
    

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34. Typed
    Dynamic
    Abstraction = flexibility.
    integers = [1, 2..]
    list1 = take 5 integers -- [1,2,3,4,5]
    list2 = take 10 integers -- [1,2,3,4,5,6,7,8,9,10]
    Haskell
    

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35. Typed
    Dynamic
    In Java...
    Objects are concrete. Interfaces are abstract.
    Classes are a bit of both.
    

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36. Typed
    Dynamic
    In Haskell...
    Basic types
    are concrete.
    Type classes are abstract.
    Abstract Data Types too.
    

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37. Typed
    Dynamic
    Inheritance
    In OOP: reusability of classes (= data + methods)
    In FP: reusability of type classes (= functions)
    

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38. Typed
    Dynamic
    Inheritance
    In OOP: reusability of classes (= data + methods)
    In FP: reusability of type classes (= functions)
    

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39. Typed
    Dynamic
    Inheritance
    In OOP: reusability of classes (= data + methods)
    In FP: reusability of type classes (= functions)
    

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40. Typed
    Dynamic
    Inheritance
    In OOP: reusability of classes (= data + methods)
    In FP: reusability of type classes (= functions)
    

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41. Typed
    Dynamic
    Inheritance
    In OOP: reusability of classes (= data + methods)
    In FP: reusability of type classes (= functions)
    

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42. Typed
    Dynamic
    Inheritance
    In OOP: reusability of classes (= data + methods)
    In FP: reusability of type classes (= functions)
    

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43. Typed
    Dynamic
    Diamond problem in typed OOP
    Object
    equals()
    Rectangle
    equals()
    Clickable
    equals()
    Button
    

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44. The real problem is that programmers have spent
    far too much time worrying about efficiency in the
    wrong places and at the wrong times; 

    premature optimization is the root of all evil (or at
    least most of it) in programming. – Donald Knuth
    

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45. Premature concretization is the root of all
    complexity (or at least most of it) in programming.
    – André Staltz
    

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46. Typed
    Dynamic
    Haskell can reliably
    do multiple inheritance.
    

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47. Typed
    Dynamic
    Haskell can reliably
    do multiple inheritance.
    

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48. Typed
    Dynamic
    JavaScript can unreliably
    do multiple inheritance.
    

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49. Typed
    Dynamic
    JavaScript can unreliably
    do multiple inheritance.
    // Creating objects
    var o1, o2, o3,
    obj = multiInherit(o1={a:1}, o2={b:2}, o3={a:3, b:3});
    // Setting properties
    obj.c = 3;
    // Reading properties
    obj.a; // 1 (inherited from o1)
    obj.b; // 2 (inherited from o2)
    obj.c; // 3 (own property)
    obj.d; // undefined (not found)
    https://stackoverflow.com/questions/9163341/multiple-inheritance-prototypes-in-javascript/31236132#31236132
    

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50. Typed
    Dynamic
    JavaScript can unreliably
    do multiple inheritance.
    function multiInherit (...protos) {
    return Object.create(new Proxy(Object.create(null), {
    get (target, prop, receiver) {
    var obj = protos.find(obj => prop in obj);
    return obj ? Reflect.get(obj, prop, receiver) : void 0;
    },
    set (target, prop, value, receiver) {
    var obj = protos.find(obj => prop in obj);
    return Reflect.set(obj || Object.create(null), prop, value, receiver);
    },
    has: (target, prop) => protos.some(obj => prop in obj),
    ownKeys(target) {
    // ...
    },
    getOwnPropertyDescriptor(target, prop) {
    // ...
    },
    *enumerate (target) { yield* this.ownKeys(target); },
    preventExtensions: (target) => false,
    defineProperty: (target, prop, desc) => false,
    }));
    }
    

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51. Typed
    Dynamic
    Strongly typed FP
    Haskell
    

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52. Haskell v1.3 Report
    

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53. Haskell v1.3 Report
    

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54. Evaluate
    Execute
    Calculate the value
    of an expression
    Perform a sequence
    of get/set actions
    Imperative
    Functional
    

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57. OOP FP
    Should we mix everything?
    

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58. OOP FP
    Should we mix everything?
    Languages should be coherent
    

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59. Koka
    Typed
    Evaluate
    Immutability
    Assignment syntax
    Closures
    Object syntax
    

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68. Closures
    Objects
    Immutability
    Mutation
    Assignment

    syntax
    Assignment

    semantics
    Typed
    Dynamic Evaluate
    Execute
    Thanks : )
    

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