初めての関数型プログラミング

Haskellで始める関数型プログラミング
ざっくりとした紹介とモナド
https://ngineerxiv.doorkeeper.jp/events/29760

Transcript

1. ॳΊͯͷ
   ؔ਺ܕϓϩάϥϛϯά
   @petitviolet
   Fringe81 Co., Ltd.
   
   

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2. About Me
   • খࢵ ߂و(Hiroki Komurasaki)
   • @petitviolet
   • ৽ଔ1೥໨(15ଔ)
   • Fringe81͍ͬͯ͏ΞυςΫͷձࣾ
   • Android/iOSͷ޿ࠂSDK։ൃ
   
   

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3. ॳΊͯͷ
   ؔ਺ܕϓϩάϥϛϯά
   
   

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4. ॳΊͯͷ
   ؔ਺ܕϓϩάϥϛϯά
   
   

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5. ॳΊͯͷ
   Haskell
   
   

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6. What is Haskell
   • ७ਮؔ਺ܕϓϩάϥϛϯάݴޠ
   • ஗ԆධՁ
   • ੩తܕ෇͚/ܕਪ࿦
   • ΋ͳͲ
   
   

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7. ७ਮؔ਺ܕʁ
   • ෭࡞༻͕ແ͍
   • ࢀরಁաੑ
   • ಉ͡ೖྗʹରͯ͠͸ৗʹಉ͡ग़ྗ
   • ؔ਺͸ୈҰڃ
   • jsͷΑ͏ʹؔ਺ΛΦϒδΣΫτͱͯ͠ѻ͑Δ
   
   

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8. ෭࡞༻͕ͳ͍
   • ༩͑ΒΕͨҾ਺ͷΈΛ࢖ͬͯ݁ՌΛฦ͢
   • ΦϒδΣΫτͷঢ়ଶͱ͔جຊతʹແ͍
   
   

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9. ؔ਺ʹ͍ͭͯ
   
   

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10. ໋ྩܗݴޠͷؔ਺͸
    ίϯϐϡʔλʹରͯ͠
    ԿΛ͢Δͷ͔Λ఻͑Δ
    
    

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11. ؔ਺ܕϓϩάϥϛϯάݴޠͰ͸
    ίϯϐϡʔλʹରͯ͠
    ԿͰ͋Δͷ͔Λ఻͑Δ
    
    

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12. ?
    
    

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13. ؔ਺͸ԿͰ͋Δ͔Λ఻͑Δ
    • ϑΟϘφον਺ྻ
    // Python
    def fib(n):
    if n < 2:
    return n
    return fib(n - 1) + fib(n - 2)
    [fib(i) for i in range(1, 11)]
    
    

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14. ؔ਺͸ԿͰ͋Δ͔Λ఻͑Δ
    • ϑΟϘφον਺ྻ
    // Haskell
    fib :: [Int]
    fib = 1 : 1 : zipWith (+) fib (tail fib)
    take 10 fib
    1, 1, 2, 3, 5, 8, 13, …
    1, 1, 2, 3, 5, 8, 13, …
    1, 1, 2, 3, 5, 8, 13,21…
    
    

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15. ஗ԆධՁ
    • ඞཁͳ෼͚ͩΛධՁ͢Δͷ͕஗ԆධՁ
    • ਺ྻࣗମΛఆٛग़དྷΔ
    • fibؔ਺͸ແݶ௕ͷϑΟϘφον਺ྻΛฦ͢
    // Haskell
    fib :: [Int]
    fib = 1 : 1 : zipWith (+) fib (tail fib)
    fib # ࢮ
    take 10 fib
    
    

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16. ؔ਺߹੒
    • Unixత
    • খ͞ͳؔ਺Λ૊Έ߹Θͤͯେ͖ͳ΋ͷΛ࡞Δ
    Prelude> length "hello"
    5
    Prelude> show 100
    "100"
    Prelude> (length . show) 100
    3
    
    

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17. ϥϜμࣜ
    Prelude> let add = \x y -> x + y
    Prelude> foldr add 0 [1..10]
    55
    
    

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18. \͸ࢥ͍͖ͬΓ໨ΛࡉΊΔͱ
    ΪϦγϟจࣈͷϥϜμλʹ
    ݟ͑·͢ΑͶɻ
    ͍͢͝Haskellֶָ͘͠΅͏ʂ p73
    

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19. ͳΔ΄Ͳ
    
    

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20. ܕʹ͍ͭͯ
    
    

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21. ੩తܕ෇͚ && ܕਪ࿦
    Prelude> let a = 5 + 4
    Prelude> :t a
    a :: Num a => a
    Prelude> let b :: Num a => a; b = (5 :: Num a
    => a) + (4 :: Num a => a)
    Prelude> :t b
    b :: Num a => a
    
    

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22. • ܕͷ࣋ͭੑ࣭Λද͢ΠϯλʔϑΣʔεͬΆ͍
    • Numʹଐ͢ܕ͸”਺”ͱͯ͠ͷੑ࣭Λ࣋ͭ
    ܕΫϥε
    Prelude> :t 10
    10 :: Num a => a
    Prelude> :t 10 :: Int
    10 :: Int :: Int
    Prelude> :t 10 :: Double
    10 :: Double :: Double
    
    

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23. Ϟφυ
    
    

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24. Ϟφυͷલʹཧղ͍ͨ͠΍ͭ
    • ϑΝϯΫλʔ
    • ΞϓϦΧςΟϒϑΝϯΫλʔ
    class Functor f where
    fmap :: (a -> b) -> f a -> f b
    class (Functor f) => Applicative f where
    pure :: a -> f a
    (<*>) :: f (a -> b) -> f a -> f b
    
    

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25. • จ຺Λ࣋ͭܭࢉΛ࣮ݱ͢Δ࢓૊Έ
    • Maybe͸͋Δ͔΋͠Εͳ͍͠ɺͳ͍͔΋
    • List͸ෳ਺ͷ஋͕͋Δ͔΋͠Εͳ͍
    Ϟφυ
    Prelude> Just 10 >>= (\x -> Just(x + 4))
    Just 14
    Prelude> Nothing >>= (\x -> Just(x + 4))
    Nothing
    
    

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26. • จ຺Λ࣋ͭܭࢉΛ࣮ݱ͢Δ࢓૊Έ
    • Maybe͸͋Δ͔΋͠Εͳ͍͠ɺͳ͍͔΋
    • List͸ෳ਺ͷ஋͕͋Δ͔΋͠Εͳ͍
    Ϟφυ
    Prelude> [1, 2] >>= (\x -> [10, 20] >>= (\y -> [x, y]))
    [1,10,1,20,2,10,2,20]
    Prelude> [1, 2] >>= (\x -> [] >>= (\y -> [x, y]))
    []
    
    

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27. class Monad m where
    return :: Monad m => a -> m a
    (>>=) :: Monad m => m a -> (a -> m b) -> m b
    …
    B
    monad
    C
    monad
    
    Just 10 >>= (\x -> Just(show x)) = Just “10”
    B
    monad
    SFUVSOB
    return 10 :: Maybe Int = Just 10
    
    C
    monad
    B
    
    
    

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28. • จ຺Λ࣋ͭ஋ಉ࢜ͷܭࢉΛ៉ྷʹ΍ΔͨΊͷ࢓૊Έ
    • Ϟφυ஋ͱɺϞφυ஋ΛฦΓ஋ͱ͢Δؔ਺Λ
    ͍͍ײ͡ʹ૊Έ߹ΘͤͯϞφυ஋ΛಘΔ
    • ܭࢉ݁ՌΛϞφυ஋ʹ͢Δ
    • Just 10 ͱ show Λ࢖ͬͯJust “10”
    • ࣦഊͯͨ͠ΒશମΛࣦഊͤ͞Δ
    • Nothing Λ show ͠Α͏ͱ͢Δͱ Nothing
    Ϟφυ
    
    

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29. 
    

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30. We are hiring!
    fringe81.com/recruit
    
    

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