初めての関数型プログラミング

by petitviolet

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ॳΊͯͷ ؔ਺ܕϓϩάϥϛϯά @petitviolet Fringe81 Co., Ltd.

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

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ॳΊͯͷ ؔ਺ܕϓϩάϥϛϯά

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ॳΊͯͷ ؔ਺ܕϓϩάϥϛϯά

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ॳΊͯͷ Haskell

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

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

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

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ؔ਺ʹ͍ͭͯ

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໋ྩܗݴޠͷؔ਺͸ ίϯϐϡʔλʹରͯ͠ ԿΛ͢Δͷ͔Λ఻͑Δ

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ؔ਺ܕϓϩάϥϛϯάݴޠͰ͸ ίϯϐϡʔλʹରͯ͠ ԿͰ͋Δͷ͔Λ఻͑Δ

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

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

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

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ͳΔ΄Ͳ

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ܕʹ͍ͭͯ

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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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• 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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Ϟφυ

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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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• 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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• 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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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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• 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