sugoih 8

すごいHaskell読書会 in 大阪 2週目 #8 : ATND
https://atnd.org/events/53833

1. ͍͢͝Haskellಡॻձ in େࡕ 2ि໨ #8 Ӊࠤݟ ެี
2. ୈ7ষ ܕ΍ܕΫϥεΛࣗ෼Ͱ࡞Ζ͏ ʢޙฤʣ
3. લฤͷ͓͞Β͍ 4 ৽͍͠σʔλܕΛఆٛ͢Δ 4 Ϩίʔυߏจ 4 ܕҾ਺ 4 Πϯελϯεͷࣗಈಋग़ 4 ܕγϊχϜ
4. ʢલฤͷ͓͞Β͍ʣ ৽͍͠σʔλܕΛఆٛ͢Δ data ܕ໊ = ஋ίϯετϥΫλ data Bool = False | True data Shape = Circle Float Float Float | Rectangle Float Float Float Float data Point = Point Float Float
5. ʢલฤͷ͓͞Β͍ʣ Ϩίʔυߏจ data Person = Person { firstName :: String , lastName :: String , age :: Int , height :: Float , phoneNumber :: String , flavor :: String }
6. ʢલฤͷ͓͞Β͍ʣ ܕҾ਺ data ܕίϯετϥΫλ = ஋ίϯετϥΫλ ʢܕ໊ ܕҾ਺ʣ data Maybe a = Nothing | Just a data Either a b = Left a | Right b -- ̏࣍ݩϕΫτϧͷྫ data Vector a = Vector a a a
7. ʢલฤͷ͓͞Β͍ʣ Πϯελϯεͷࣗಈಋग़ data Day = Monday | Tuesday | Wednesday | Thursday | Friday | Saturday | Sunday deriving (Eq, Ord, Show, Read, Bounded, Enum) -- ܕΫϥεͷ࣮૷͕ิΘΕɺҎԼ͕ՄೳʹͳΔ ghci> Saturday == Sunday False ghci> show Wednesday Wednesday
8. ʢલฤͷ͓͞Β͍ʣ ܕγϊχϜ type String = [Char] type Name = String type PhoneNumber = String type PhoneBook = [(Name, PhoneNumber)] -- ҎԼͷྫͰ͸ AssocList ͸ܕίϯετϥΫλ type AssocList k v = [(k, v)]
9. ޙฤͷ಺༰ 4 ࠶ؼతͳσʔλߏ଄ 4 ܕΫϥεதڃߨ࠲ 4 Yes ͱ No ͷܕΫϥε 4 Functor ܕΫϥε 4 ܕΛ࢘Δ΋ͷɺछྨ
10. ࠶ؼతͳσʔλܕ
11. ࠶ؼతͳσʔλܕ 4 ஋ίϯετϥΫλͷϑΟʔϧυʹࣗ෼ࣗ਎ͷܕΛ࣋ͨͤΔ 4 ྫ͑͹ɺϦετ͸࠶ؼతͳσʔλܕ 4 [3,4,5,6] ͸ 3:[4,5,6] Ͱ͋Δ 4 3:4:[5,6] Ͱ΋͋Δ 4 3:4:5:[6] 4 3:4:5:6:[]
12. ྫɿಠࣗϦετܕ data List a = Empty | Cons a (List a) deriving (Show, Read, Eq, Ord) -- Ϩίʔυߏจͷ৔߹ data List a = Empty | Cons { listhead :: a , listtail :: List a } deriving (Show, Read, Eq, Ord)
13. ಠࣗϦετܕͷϦετදݱ 4 ઌͷಠࣗఆٛͷ Cons ͸ඪ४ͷ : ʹ͋ͨΔ΋ͷ Empty -- [] ʹ͋ͨΔ 5 `Cons` Empty -- 5:[] ʹ͋ͨΔ 4 `Cons` (5 `Cons` Empty) -- 4:5:[] ʹ͋ͨΔ 3 `Cons` (4 `Cons` (5 `Cons` Empty)) -- 3:4:5:[] ʹ͋ͨΔ
14. ಠࣗϦετܕͷվળ 4 ஋ίϯετϥΫλΛதஔؔ਺ʹʢ: Ͱ࢝ΊΔ͜ͱʣ 4 ݁߹ͷ༏ઌ౓Λఆٛʢinfixl ΍ infixr Λ࢖͏ʣ infixr 5 :-: data List a = Empty | a :-: (List a) deriving (Show, Read, Eq, Ord)
15. վળ݁Ռ 4 ϦετΛ͜͏ॻ͚ΔΑ͏ʹͳͬͨ 5 :-: Empty -- 5 `Cons` Empty 4 :-: 5 :-: Empty -- 4 `Cons` (5 `Cons` Empty) 3 :-: 4 :-: 5 :-: Empty -- 3 `Cons` (4 `Cons` (5 `Cons` Empty))
16. ྫɿಠࣗϦετܕͷ݁߹ infixr 5 ^++ (^++) :: List a -> List a -> List a Empty ^++ ys = ys (x :-: xs) ^++ ys = x :-: (xs ^++ ys) 4 ࣮͸ύλʔϯϚονͱ͸ɺ஋ίϯετϥΫλͷϚον 4 ඪ४ͷ : ΋஋ίϯετϥΫλ
17. ผͷྫɿೋ෼୳ࡧ໦ data Tree a = EmptyTree | Node a (Tree a) (Tree a) deriving (Show) 4 ೋ෼୳ࡧ໦ɿ֤ཁૉʹ͍ͭͯɺ 4 ࠨ෦෼໦ͷશཁૉ͕ͦͷཁૉΑΓখ͍͞ 4 ӈ෦෼໦ͷશཁૉ͕ͦͷཁૉΑΓେ͖͍
18. ໦ʹཁૉΛ௥Ճ͢Δؔ਺ 4 ༩͑ΒΕͨ໦ͷ௚઀ߋ৽͸ෆՄɺ৽͍͠໦Λ࡞ͬͯฦ͢ singleton :: a -> Tree a singleton x = Node x EmptyTree EmptyTree treeInsert :: (Ord a) => a -> Tree a -> Tree a treeInsert x EmptyTree = singleton x treeInsert x (Node y left right) | x == y = Node y left right -- ಉ͡ͳΒૠೖ͠ͳ͍ | x < y = Node y (treeInsert x left) right | x > y = Node y left (treeInsert x right)
19. ໦ͷੜ੒ ghci> let nums = [8,6,4,1,7,3,5] ghci> let numsTree = foldr treeInsert EmptyTree nums 4 tree1 = treeInsert 5 EmptyTree 4 tree2 = treeInsert 3 tree1 4 tree3 = treeInsert 7 tree2 4 ... 4 numsTree = treeInsert 8 tree7
20. ໦ʹཁૉ͕ଐ͢Δ͔ௐ΂Δؔ਺ treeElem :: (Ord a) => a -> Tree a -> Bool treeElem x EmptyTree = False treeElem x (Node y left right) | x == y = True | x < y = treeElem x left | x > y = treeElem x right
21. ܕΫϥεதڃߨ࠲
22. ܕΫϥεதڃߨ࠲ 4 ܕΫϥεͷ෮श 4 ͋Δܕ T ͕͋ΔܕΫϥε C ͷΠϯελϯε = ܕ T ʹରͯ͠ܕΫϥε C ͕ఆٛ͢Δؔ਺Λ࢖͑Δ 4 ܕΫϥεΛࣗ෼Ͱ࡞Δʹ͸ʁ
23. Eq ܕΫϥεͷએݴ class Eq a where (==) :: a -> a -> Bool (/=) :: a -> a -> Bool x == y = not (x /= y) x /= y = not (x == y) 4 a ͸ܕҾ਺ͰɺEq ͷΠϯελϯεͱͳΔܕ
24. Eq ܕΫϥεͷΠϯελϯεએݴ data TrafficLight = Red | Yellow | Green instance Eq TrafficLight where Red == Red = True Yellow == Yellow = True Green == Green = True _ == _ = False 4 ஫ҙɿ௨ৗ͸ deriving Ͱࣗಈಋग़͢Δ
25. ࠷খ׬શఆٛ x == y = not (x /= y) x /= y = not (x == y) 4 Eq ͷΠϯελϯε͸ == ͔ /= ͷͲͪΒ͔Λఆٛ͢Δඞཁ͕ ͋Δ 4 ยํΛఆٛʢσϑΥϧτ࣮૷Λ্ॻ͖ʣ͢Ε͹ɺ΋͏ยํ ΋ఆٛ͞ΕΔ
26. Show ܕΫϥεͷΠϯελϯεએݴ 4 ࣗಈಋग़ͰͷఆٛͰͳ͘ɺࣗલͰఆ͍ٛͨ͠৔߹ʹ instance Show TrafficLight where show Red = "Red light" show Yellow = "Yellow light" show Green = "Green light"
27. ܕΫϥεએݴʹܕΫϥε੍໿Λ͚ͭ Δ 4 Num ܕΫϥε͸ Eq ܕΫϥεͷαϒΫϥε class (Eq a) => Num a where ...
28. Maybe Λ Eq ͷΠϯελϯεʹ͢ Δʁ class Eq a where (==) :: a -> a -> Bool 4 ܕҾ਺ a ͸۩ମܕͰͳͯ͘͸μϝʢؔ਺ఆٛʹ͋Θͳ͍ʣ 4 Maybe ͸۩ମܕͰͳ͘ଟ૬ܕʢܕίϯετϥΫλʣ 4 ͡Ό͋۩ମܕ Maybe Char Λ Eq ͷΠϯελϯεʹ͢Δʁ 4 ͦΕͰ͸ Maybe Int ͸ʁ ɾɾɾ͖Γ͕ͳ͍
29. ଟ૬ܕΛܕΫϥεͷΠϯελϯεʹ ͢Δ 4 ΠϯελϯεએݴʹܕҾ਺Λ͚ͭΔ instance Eq (Maybe m) where Just x == Just y = x == y Nothing == Nothing = True _ == _ = False 4 ஫ҙɿ͜ͷએݴ͸ෆे෼ʢ࣍ϖʔδࢀরʣ
30. ΠϯελϯεએݴʹܕΫϥε੍໿Λ ͚ͭΔ 4 ܕ m ͕ Eq ܕΫϥεͰͳ͍ͱμϝ 4 ܕΫϥε੍໿Λ͚ͭΔ instance (Eq m) => Eq (Maybe m) where Just x == Just y = x == y Nothing == Nothing = True _ == _ = False
31. ࠶౓੔ཧͯ͠ΈΔ 4 Eq ܕΫϥεએݴͰ͸ɺa ͕۩ମܕͰͳ͍ͱμϝ 4 (==) :: a -> a -> Bool ͱ࢖ΘΕΔ͔Β 4 a ʹ Maybe ͸౉ͤͳ͍ 4 (==) :: Maybe -> Maybe -> Bool ͸μϝ 4 a ʹ Maybe m ͳΒ౉ͤΔ 4 (==) :: (Eq m) => Maybe m -> Maybe m -> Bool
32. ܕΫϥεͷ৘ใ 4 ghci Ͱ :info Maybe ͳͲͱ͢Ε͹৘ใ͕ಘΒΕΔ
33. Yes ͱ No ͷܕΫϥε
34. Yes ͱ No ͷܕΫϥε 4 ͓୊ɿܕΫϥεΛ࡞ͬͯΈΔ
35. Yes ͱ No ͷܕΫϥε 4 Haskell Ͱ͸ਅཧ஋͕ඞཁͳՕॴͰ͸ݫີʹ Bool ܕΛ࢖͏ 4 ଞͷݴޠͰ͸ͦ͏Ͱͳ͍΋ͷ΋͋ΔɿJavaScript ͷྫ 4 if (0) 4 if ("") 4 if (false) 4 ྨࣅͷ͜ͱΛಠࣗͷܕΫϥεͰ࣮ݱͯ͠ΈΔ
36. ܕΫϥεએݴͱΠϯελϯεએݴ class YesNo a where yesno :: a -> Bool instance YesNo Int where yesno 0 = False yesno _ = True instance YesNo [a] where yesno [] = False yesno _ = True
37. instance YesNo Bool where yesno = id -- ͦͷ··ฦ͢ instance YesNo (Maybe a) where yesno Nothing = False yesno (Just _) = True instance YesNo (Tree a) where yesno EmptyTree = False yesno _ = True instance YesNo TrafficLight where yesno Red = False yesno _ = True
38. if ͷ୅ସ yesnoIf :: (YesNo y) => y -> a -> a -> a yesnoIf yesnoVal yesResult noResult = if yesno yesnoVal then yesResult else noResult ghci> yesnoIf [] "YEAH!" "NO!" "NO!" ghci> yesnoIf [2,3,4] "YEAH!" "NO!" "YEAH!"
39. Functor ܕΫϥε
40. Functor ܕΫϥε class Functor f where fmap :: (a -> b) -> f a -> f b 4 ͜ͷ f ͸۩ମܕͰ͸ͳ͘ɺܕίϯετϥΫλ 4 Ҿ਺̍ : ܕ a ͔Βܕ b ΁ͷؔ਺ܕ 4 Ҿ਺̎ : ܕίϯετϥΫλ f ʹܕҾ਺ a Λద༻ͨ͠ܕ 4 ໭Γ஋ : ܕίϯετϥΫλ f ʹܕҾ਺ b Λద༻ͨ͠ܕ
41. Ϧετͷ map -- Ϧετͷ map map :: (a -> b) -> [a] -> [b] -- Functor ͷ fmap fmap :: (a -> b) -> f a -> f b 4 map ͸ϦετݶఆͰಈ࡞͢Δ fmap ͩͱ͍͑Δ
42. Ϧετͷ Functor Πϯελϯεએݴ instance Functor [] where fmap = map 4 ͜͜Ͱɺ[] ͸ܕίϯετϥΫλͰ͋Δ͜ͱʹ஫ҙ 4 [Int] [String] ͳͲ͕۩ମܕ
43. Maybe ͷ Functor Πϯελϯεએݴ instance Functor Maybe where fmap f (Just x) = Just (f x) fmap f Nothing = Nothing 4 Maybe ͸ܕίϯετϥΫλ
44. ೋ෼୳ࡧ໦ͷ Functor Πϯελϯε એݴ instance Functor Tree where fmap f EmptyTree = EmptyTree fmap f (Node x left right) = Node (f x) (fmap f left) (fmap f right) 4 Tree ͸ܕίϯετϥΫλʢTree a ͕۩ମܕʣ 4 ஫ҙɿ೚ҙͷؔ਺Λద༻ͨ͠ޙ͸ೋ෼୳ࡧ໦ͷੑ࣭Λอͨ ͳ͍
45. Either ͷ৔߹͸ʁ 4 Either ͸ܕҾ਺Λ 2 ͭͱΔܕίϯετϥΫλ 4 Either a b ͕۩ମܕ 4 1 ͚ͭͩ෦෼ద༻͢Δͱ Functor ʹͰ͖Δ 4 Either a ͸ܕҾ਺Λ 1 ͭͱΔܕίϯετϥΫλ
46. Either ͷ Functor Πϯελϯεએݴ instance Functor (Either a) where fmap f (Right x) = Right (f x) fmap f (Left x) = Left x 4 data Either a b = Left a | Right b 4 Left ͱ Right Ͱܕ͕ҧ͏͜ͱʹ஫ҙ 4 fmap Ͱద༻͢Δؔ਺ f ͸ b -> c ܕ 4 Right ଆʹ͸ద༻Ͱ͖Δ͕ɺLeft ଆʹ͸ద༻Ͱ͖ͳ͍
47. Data.Map ͷ৔߹͸ʁʢ࿅श໰୊ʣ 4 Map k v ͸ k ܕ͕Ωʔɺv ܕ͕஋ͷσʔλߏ଄ 4 fmap Ͱద༻͢Δؔ਺͸ v -> v' ܕ 4 ໰୊ɿͲͷΑ͏ʹ Functor ͷΠϯελϯεʹͳΔ͔ʁ 4 MyFunctor ܕΫϥεએݴΛॻ͘ 4 Map ͷ MyFunctor ΠϯελϯεએݴΛॻ͘ 4 Map ʹ myfmap Ͱؔ਺Λద༻͢Δ
48. Functor ʹ͍ͭͯ ΑΓਂ͍಺༰͸ޙͷষͰ
49. ܕΛ࢘Δ΋ͷɺछྨ
50. ܕΛ࢘Δ΋ͷɺछྨ 4 ܕͷछྨʢkindʣ 4 GHCi ͷ :k ίϚϯυͰܕͷछྨΛௐ΂Δ
51. ܕͷछྨ ghci> :k Int Int :: * ghci> :k Maybe Maybe :: * -> * ghci> :k Maybe Int Maybe Int :: * 4 * ͸۩ମܕΛද͢ه߸ 4 Maybe ͸۩ମܕΛҾ਺ʹͱͬͯ۩ମܕΛฦ͢
52. ஋ɺܕɺछྨ 4 ஋ͷϥϕϧ͕ܕ 4 ܕͷϥϕϧ͕छྨ 4 GHCi ͷ :t ίϚϯυ͸஋ͷܕΛௐ΂Δ 4 GHCi ͷ :k ίϚϯυ͸ܕͷछྨΛௐ΂Δ
53. ܕίϯετϥΫλ΁ͷ෦෼ద༻ 4 ܕίϯετϥΫλ͕ΧϦʔԽ͞Ε͍ͯͯ෦෼ద༻Ͱ͖Δ ghci> :k Either Either :: * -> * -> * ghci> :k Either String Either String :: * -> *
54. Functor ʹͳΕΔܕͷछྨ class Functor f where fmap :: (a -> b) -> f a -> f b 4 f a f b ͷछྨ͸ *ʢؔ਺ͷܕએݴʹ࢖ΘΕ͍ͯΔͨΊʣ 4 f ͷछྨ͸ * -> * Ͱͳͯ͘͸ͳΒͳ͍
55. ୈ7ষޙฤ͓ΘΓ 4 ࠶ؼతͳσʔλߏ଄ 4 ܕΫϥεதڃߨ࠲ 4 Yes ͱ No ͷܕΫϥε 4 Functor ܕΫϥε 4 ܕΛ࢘Δ΋ͷɺछྨ