Typelevel: the past, the present, the future

The early 2010’s were exciting times for Scala. The language & ecosystem started to professionalize, both from a technical (binary compatibility) and a community point of view (many conferences were started). Not too long after Lightbend – then Typesafe – was founded, I registered the typelevel.org domain on a whim and put together a rudimentary website advertising a few FP-minded Scala libraries. Fast forward to today: Typelevel is known for a wealth of functional libraries, beginner-friendly educational resources, a series of conferences and a distinct ecosystem – including a custom compiler – within the Scala community. In this talk, I’d like to examine what got us there and how you could help shape the future.

Transcript

1. T y p e l e v e l : t h e
   p a s t , t h e
   p r e s e n t , t h e
   f u t u r e
   L a r s H u p e l
   S c a l a C o n
   2 0 2 1 - 1 1 - 0 3
   

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2. View Slide

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4. H u m b l e b e g i n n i n g s
   F o u n d e d i n 2 0 1 3 a t N o r t h e a s t S c a l a S y m p o s i u m
   

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5. H u m b l e b e g i n n i n g s
   F o u n d e d i n 2 0 1 3 a t N o r t h e a s t S c a l a S y m p o s i u m
   T o d a y : 7 0 + p r o j e c t s , v i b r a n t e c o s y s t e m
   

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6. T y p e l e v e l p r o j e c t s
   C e n t r a l t h e m e : S c a l a - i d i o m a t i c F u n c t i o n a l P r o g r a m m i n g
   

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7. T y p e l e v e l p r o j e c t s
   C e n t r a l t h e m e : S c a l a - i d i o m a t i c F u n c t i o n a l P r o g r a m m i n g
   • . . . w i t h a s l i t t l e h a s s l e a s p o s s i b l e
   

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8. T y p e l e v e l p r o j e c t s
   C e n t r a l t h e m e : S c a l a - i d i o m a t i c F u n c t i o n a l P r o g r a m m i n g
   • . . . w i t h a s l i t t l e h a s s l e a s p o s s i b l e
   • . . . w i t h a s l i t t l e r u n t i m e o v e r h e a d a s p o s s i b l e
   

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9. T y p e l e v e l p r o j e c t s
   C e n t r a l t h e m e : S c a l a - i d i o m a t i c F u n c t i o n a l P r o g r a m m i n g
   • . . . w i t h a s l i t t l e h a s s l e a s p o s s i b l e
   • . . . w i t h a s l i t t l e r u n t i m e o v e r h e a d a s p o s s i b l e
   • . . . a s s a f e a s p o s s i b l e
   

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11. C a t s
    

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12. T y p e c l a s s e s
    S u p r e m e l y u s e f u l t o o l , p i o n e e r e d i n H a s k e l l
    

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13. T y p e c l a s s e s
    S u p r e m e l y u s e f u l t o o l , p i o n e e r e d i n H a s k e l l
    class Semigroup a => Monoid a where
    mempty :: a
    mconcat :: [a] -> a
    mconcat = foldr mappend mempty
    

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14. T y p e c l a s s e s
    S u p r e m e l y u s e f u l t o o l , p i o n e e r e d i n H a s k e l l
    class Semigroup a => Monoid a where
    mempty :: a
    mconcat :: [a] -> a
    mconcat = foldr mappend mempty
    I t J u s t W o r k s ™ !
    

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17. T y p e c l a s s e s i n S c a l a
    . . . n o w w e j u s t n e e d t o e n c o d e t h e m i n S c a l a
    

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18. T y p e c l a s s e s i n S c a l a
    . . . n o w w e j u s t n e e d t o e n c o d e t h e m i n S c a l a
    • m u l t i p l e i n h e r i t a n c e ?
    

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19. T y p e c l a s s e s i n S c a l a
    . . . n o w w e j u s t n e e d t o e n c o d e t h e m i n S c a l a
    • m u l t i p l e i n h e r i t a n c e ?
    • s y n t a x ? ?
    

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20. T y p e c l a s s e s i n S c a l a
    . . . n o w w e j u s t n e e d t o e n c o d e t h e m i n S c a l a
    • m u l t i p l e i n h e r i t a n c e ?
    • s y n t a x ? ?
    • g l o b a l c o n f l u e n c e ? ? ?
    

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21. T y p e c l a s s e s i n S c a l a
    . . . n o w w e j u s t n e e d t o e n c o d e t h e m i n S c a l a
    • m u l t i p l e i n h e r i t a n c e ?
    • s y n t a x ? ?
    • g l o b a l c o n f l u e n c e ? ? ?
    

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22. View Slide

23. T y p e c l a s s e s , e n c o d e d
    I n 2 0 1 5 , M i c h a e l P i l q u i s t s t a r t e d s i m u l a c r u m .
    G o a l : c o n s i s t e n t e n c o d i n g a c r o s s d i f f e r e n t p r o j e c t s , 0 b o i l e r p l a t e
    

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24. S i m u l a c r u m
    I n p u t
    import simulacrum._
    @typeclass trait Semigroup[A] {
    @op("|+|") def append(x: A, y: A): A
    }
    

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25. S i m u l a c r u m
    O u t p u t
    object Semigroup {
    def apply[A](implicit instance: Semigroup[A]): Semigroup[A] = instance
    // ...
    }
    

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26. S i m u l a c r u m
    M o r e o u t p u t
    object Semigroup {
    trait Ops[A] {
    def typeClassInstance: Semigroup[A]
    def self: A
    def |+|(y: A): A = typeClassInstance.append(self, y)
    }
    }
    

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27. S i m u l a c r u m
    E v e n m o r e o u t p u t
    object Semigroup {
    trait ToSemigroupOps {
    implicit def toSemigroupOps[A](target: A)(implicit tc: Semigroup[A]): Ops[A]
    val self = target
    val typeClassInstance = tc
    }
    }
    object nonInheritedOps extends ToSemigroupOps
    }
    

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28. S i m u l a c r u m
    Y e t m o r e o u t p u t
    object Semigroup {
    trait AllOps[A] extends Ops[A] {
    def typeClassInstance: Semigroup[A]
    }
    object ops {
    implicit def toAllSemigroupOps[A](target: A)(implicit tc: Semigroup[A]): AllO
    val self = target
    val typeClassInstance = tc
    }
    }
    }
    

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30. B u t i t w o r k s !
    S i m u l a c r u m s o l v e d a t o n o f i s s u e s
    W e c a n w r i t e x |+| y!
    

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31. B u t i t w o r k s !
    S i m u l a c r u m s o l v e d a t o n o f i s s u e s
    W e c a n w r i t e x |+| y!
    U s e d b y C a t s a n d t o n s o f t h i r d - p a r t y
    l i b r a r i e s
    

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32. S p i r e
    

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33. N u m e r i c s f o r S c a l a
    • s t a r t e d o u t a s a S I P i n 2 0 1 1 ( ! )
    • e v o l v e d i n t o a d e d i c a t e d l i b r a r y
    • “ w h a t i f f u n c t i o n a l b u t a l s o f a s t ”
    

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34. W h a t a b o u t p e r f o r m a n c e ?
    S i m u l a c r u m d i d n ’ t s o l v e t h e p e r f o r m a n c e i s s u e o f t y p e c l a s s e s .
    

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35. W h a t a b o u t p e r f o r m a n c e ?
    S i m u l a c r u m d i d n ’ t s o l v e t h e p e r f o r m a n c e i s s u e o f t y p e c l a s s e s .
    I n p u t
    x |+| y
    

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36. W h a t a b o u t p e r f o r m a n c e ?
    S i m u l a c r u m d i d n ’ t s o l v e t h e p e r f o r m a n c e i s s u e o f t y p e c l a s s e s .
    O u t p u t
    Semigroup.ops.toAllSemigroupOps(x).|+|(y)
    

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37. E n t e r M a c h i n i s t
    S p l i t o u t o f S p i r e b y E r i k O s h e i m i n 2 0 1 4
    

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38. E n t e r M a c h i n i s t
    S p l i t o u t o f S p i r e b y E r i k O s h e i m i n 2 0 1 4
    N o w ( 2 0 2 0 ) a r c h i v e d a n d r e - i n c o r p o r a t e d i n t o S p i r e
    

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39. S h a p e l e s s
    

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40. • s t a r t e d o u t a s a s e r i e s o f t a l k s
    i n 2 0 1 1 ( ! )
    • s c r a t c h e d a n i t c h :
    h o w t o a b s t r a c t o v e r d a t a ?
    • p i o n e e r e d “ t y p e c l a s s d e r i v a t i o n ”
    • m a n y c o n c e p t s i n c o r p o r a t e d
    i n t o S c a l a 3
    

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41. T y p e C l a s s D e r i v a t i o n
    P r o b l e m : Y o u w a n t t o s e r i a l i z e a b u n c h o f c a s e c l a s s e s t o J S O N .
    S o l u t i o n : B o i l e r p l a t e ?
    

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42. T y p e C l a s s D e r i v a t i o n
    P r o b l e m : Y o u w a n t t o c o m p a r e a b u n c h o f c a s e c l a s s e s .
    S o l u t i o n : B o i l e r p l a t e . . . a g a i n ? !
    

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43. case class Account(owner: Person, balance: Int)
    case class Person(name: String, address: Address)
    case class Address(lines: List[String], country: Country)
    case class Country(code: String)
    

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44. type Account = Person :: Int :: HNil
    type Person = String :: Address :: HNil
    type Address = List[String] :: Country :: HNil
    type Country = String :: HNil
    

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45. I n A c t i o n
    

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46. C a t s E f f e c t
    

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47. • f u l l h i s t o r y a l m o s t i m p o s s i b l e t o t r a c e
    • d r a w s f r o m m u l t i t u d e o f i n f l u e n c e s
    • s u p p o r t s t h e r i s e o f a s y n c h r o n o u s
    s o f t w a r e c o n s t r u c t i o n
    

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48. View Slide

49. C o m m u n i t y
    

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50. W h a t h a p p e n e d s i n c e 2 0 1 3 ?
    • i n 2 0 1 4 , w e f o r k e d S c a l a
    • i n 2 0 1 5 , E r i k s t a r t e d C a t s
    • i n 2 0 1 6 , w e o r g a n i z e d o u r f i r s t c o n f e r e n c e
    • i n 2 0 1 6 , L a r s j o i n e d t h e S c a l a C e n t e r A d v i s o r y B o a r d
    • i n 2 0 1 7 , w e s h u t d o w n t h e S c a l a f o r k
    • i n 2 0 1 7 , w e r e l e a s e d C a t s 1 . 0 . 0
    • i n 2 0 1 9 , w e l a u n c h e d a d o n a t i o n c a m p a i g n
    • i n 2 0 2 0 , T y p e l e v e l l i b r a r i e s w e r e a t t h e f o r e f r o n t o f D o t t y
    

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51. 2 0 1 3
    

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52. 2 0 1 4
    

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53. 2 0 1 5
    

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54. 2 0 1 6
    

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55. S o o n
    

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56. F u t u r e
    

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58. s e r i o u s l y t h e a n s w e r i s a l m o s t a l w a y s . t r a v e r s e
    S o a r e w e n o t f l a t m a p p i n g t h a t s h i t a n y m o r e ?
    t r a v e r s e i s f l a t m a p p i n g t h a t s h i t o n o u r b e h a l f
    

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59. Q & A
    L a r s H u p e l
    �
    l a r s . h u p e l @ i n n o q . c o m
    � @ l a r s r _ h
    w w w . i n n o q . c o m
    

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60. L A R S H U P E L
    S e n i o r C o n s u l t a n t
    i n n o Q D e u t s c h l a n d G m b H
    L a r s i s k n o w n a s o n e o f t h e f o u n d e r s o f t h e T y p e -
    l e v e l i n i t i a t i v e w h i c h i s d e d i c a t e d t o p r o v i d i n g
    p r i n c i p l e d , t y p e - d r i v e n S c a l a l i b r a r i e s i n a f r i e n d l y ,
    w e l c o m i n g e n v i r o n m e n t . A f r e q u e n t c o n f e r e n c e
    s p e a k e r , t h e y a r e a c t i v e i n t h e o p e n s o u r c e c o m -
    m u n i t y , p a r t i c u l a r l y i n S c a l a .
    

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61. S o u r c e s
    • https://pixabay.com/photos/people-business-meeting-1979261/
    • https://unsplash.com/photos/FaNUdWGJqBg
    • https://twitter.com/bodil/status/1383908807588204552/photo/1
    • https://twitter.com/milessabin/status/1364523756601937921
    • https://www.manning.com/books/functional-programming-in-scala
    • https://impurepics.com/posts/2021-03-31-cats-effect-3.html
    • https://twitter.com/tpolecat/status/721019769869045760
    

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