![Pattern matching
襷れ広 list comprehension 伎 給.
pairToNum :: (Num a) => [(a,a)] -> [a]
pairToNum xs = [a+b | (a,b) <- xs]
*Main> pairToNum [(3,4), (1,2), (5,7), (6,3)]
[7,3,12,9]](https://image.slidesharecdn.com/haskellstudy4-150830145704-lva1-app6892/85/Haskell-study-4-8-320.jpg)
![Pattern matching
螻 觜訣蟆 襴ろ語 襷れ広 伎 給. 觜 襴ろ([]), cons 一一(:)
煙 伎伎 伎 企 襴ろ瑚 螳語 襯 給. 襷れ広 伎伎
覯 head 襯 蟲企.
head' :: [a] -> a
head' [] = error "Can't call head on empty list."
head' (x:_) = x
error 壱 襯 覦る . 覈視 貅伎れ 語 螳牛
覲企ゼ 蠍 襦蠏碁 譯曙 .](https://image.slidesharecdn.com/haskellstudy4-150830145704-lva1-app6892/85/Haskell-study-4-9-320.jpg)
![Pattern matching
るジ 覈 螳讌 覯 危ｴ覺.
length' :: (Num b) => [a] -> b
length' [] = 0
length' (_:xs) = 1 + length' xs
sum' :: (Num a) => [a] -> a
sum' [] = 0
sum' (x:xs) = x + sum' xs](https://image.slidesharecdn.com/haskellstudy4-150830145704-lva1-app6892/85/Haskell-study-4-10-320.jpg)
![Pattern matching
覦 企 一危 豌願 覈 蟆曙 @襯 伎 給.
headFirst :: (Show a) => [a] -> String
headFirst [] = "empty string"
headFirst all@(x:_) = show all ++ "'s first element is " ++ show x
*Main> headFirst [1,2,3,4]
"[1,2,3,4]'s first element is 1"
*Main> headFirst "abcd"
""abcd"'s first element is 'a'"](https://image.slidesharecdn.com/haskellstudy4-150830145704-lva1-app6892/85/Haskell-study-4-11-320.jpg)
![一 覓語
yesNo
Bool 螳 襯 語襦 覦 蠏 螳 True覃 "Yes", False覃 "No"襯 襴危 襯 襷れ 覺.
襯 れ yesNo (True || False) "Yes"襯 襴危伎 .
trueman
Bool 螳 襴ろ碁ゼ 語襦 覦 True 螳襯 襴危 襯 襷れ 覺. 襯 れ
trueman [True,True,False,False,True] 3 襴危伎 .
listToPairs
list襯 語襦 覦 螳 襯 螳 襦 讌 讌 伎 襴ろ碁ゼ 襴危 襯 襷れ
覺. 螳螳 螳 蟆曙 襷讌襷 覯襴暑. 襯 れ listToPairs [1,2,3,4,5]
[(1,2), (3,4)]襯 襴危伎狩.](https://image.slidesharecdn.com/haskellstudy4-150830145704-lva1-app6892/85/Haskell-study-4-12-320.jpg)
![where
where 企 襯 誤 朱, where 企 where 譴豌伎
螻, 襯 襷 覓碁( 襷れ広, 螳 ) 覈 螳ロ.
calcFibos :: (Integral a) => [a] -> a
calcFibos xs = [fibo x | x <- xs]
where fibo 0 = 0
fibo 1 = 1
fibo n = fibo (n-1) + fibo (n-2)](https://image.slidesharecdn.com/haskellstudy4-150830145704-lva1-app6892/85/Haskell-study-4-17-320.jpg)
![let in
譴 螳 覦碁 螻 矩る 碁語襦(;) 伎.
Prelude> let a = 5 in a * a * a
125
Prelude> let squre x = x * x in (squre 5, squre 6)
(25, 36)
Prelude> let a = 100; b = 200; c = 300; in a + b + c
600
list comprehension let 給. let 覦碁 襷 .
Prelude> [f x|x<-[0..10],let f 0=0;f 1=1;f n=f (n-1)+f (n-2)]
[0,1,1,2,3,5,8,13,21,34,55]](https://image.slidesharecdn.com/haskellstudy4-150830145704-lva1-app6892/85/Haskell-study-4-19-320.jpg)
![case expression
head :: [a] -> a
head xs = case xs of [] -> error "Cant call head on empty list."
(x:_) -> x
descList :: [a] -> String
descList xs = "this List is " ++ case xs of [] -> "Empty List"
[x]-> "Singleton List"
xs -> "Long List"](https://image.slidesharecdn.com/haskellstudy4-150830145704-lva1-app6892/85/Haskell-study-4-21-320.jpg)
![一 覓語
maximum
企 襴ろ瑚 譯殊伎 , 襴ろ語 譴 螳 襯 襴危 襯 蟲 覺. 觜
襴ろ語 蟆曙 error 襯 伎 壱 襯 殊狩り 襷れ 覲伎語.
take
襴ろ瑚 譯殊伎 , 襴ろ語 豌覿 企 襷殊 襯 殊 襴危 襯
襷れ 覺. , 螳 0危 蟆曙 觜 襴ろ([])襯 襴危伎 .
zip
螳 襴ろ瑚 譯殊伎 襴ろ語 螳螳 襦 讌讌 襴ろ碁ゼ 襴危 襯
襷れ 覺.
覈 譴 譟伎 . 企 譟郁 るゴ蟆 燕 .](https://image.slidesharecdn.com/haskellstudy4-150830145704-lva1-app6892/85/Haskell-study-4-22-320.jpg)
![[2010 ChangeON] 語 3 - 企碁](https://cdn.slidesharecdn.com/ss_thumbnails/3-3-101119011311-phpapp01-thumbnail.jpg?width=560&fit=bounds)
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Haskell study 4
- 1. Haskell Study 4. syntax in functions
- 2. Pattern matching 襷れ広 襯 襷 蟲ロ 螳ロ 蟲覓語. 襷れ広 企 一危郁 螳語 伎 覈螻, 一危郁 蠏 一危郁 企 伎 襷豢 覿企 讌 誤 螻殊 蟇一工. Haskell 一危一 伎 磯 襦 るジ 螳 覲語牡襯 螳讌 給. f :: (Integral a, Num b) => a -> b f 0 = 0 f 1 = 1 f n = f (n-1) + f (n-2) Prelude> f 10 55 螳 襷れ広 伎 朱慨豺 襯 蟲ロ 所 讌蟯朱 蟲 給.
- 3. Pattern matching 襷れ広 覿 谿襦襦 企れる 蟆. 讀, 伎 磯ジ 蟲 螳 襦 るゴ覃 蟆郁骸 殊. 襯 覺. f :: (Integral a) => a -> String f n = "must run this function!" f 0 = "its 0" f2 :: (Integral a) => a -> String f2 0 = "its 0" f2 n = "must run this function!" 伎 磯ジ 語 襷 覦蠖 訖伎襷 蟆郁骸螳 殊.
- 4. Pattern matching *Main> f 0 must run this function! *Main> f 1 must run this function! *Main> f2 0 its 0 *Main> f2 1 must run this function! 螳 f 蟆曙 f n 螳 襾殊 企伎覃伎, 覈 語 n企朱 伎 焔渚覩襦 f 0 願讌 螳讌 覈詩螻 螳 ろ. 蠏碁 襷れ広 覈( 轟) 伎 螻, 覲企 朱 伎 れ 蟆 燕 蟆 譬給.
- 5. Pattern matching 襷れ広 ろ 給. 蟆曙 瑚 覦. foo :: Int -> Int foo 0 = 0 foo 1 = 1 foo 2 = 2 *Main> f 0 0 *Main> f 4 *** Exception: test.hs:(2,1)-(4,7): Non-exhaustive patterns in function f 襷れ広 覈 譬襯 伎 襷れ広 蟆 蟆曙 貊伎 .
- 6. Pattern matching 襷れ広 螳ロ. 螳 覯″ 螳 襯 螳企慨譯. addVector :: (Num a) => (a,a) -> (a,a) -> (a,a) addVector a b = (fst a + fst b, snd a + snd b) 覓朱 讌襷, 貊螳 譬 蟾. addVector :: (Num a) => (a,a) -> (a,a) -> (a,a) addVector (x1, y1) (x2, y2) = (x1 + x2, y1 + y2) 企 襷れ広 伎伎 螳 3螳 (碁Μ) 轟 襯 蟶朱伎る 襯 燕 給.
- 7. Pattern matching first :: (a,b,c) -> a first (x, _, _) = x second :: (a,b,c) -> b second (_, y, _) = y third :: (a,b,c) -> c third (_, _, z) = z 襷れ広 企 豺 る 螳 覓企 蟯 蟆曙(覘螳 蟯 蟆曙) _ 蠍壱碁ゼ 伎.
- 8. Pattern matching 襷れ広 list comprehension 伎 給. pairToNum :: (Num a) => [(a,a)] -> [a] pairToNum xs = [a+b | (a,b) <- xs] *Main> pairToNum [(3,4), (1,2), (5,7), (6,3)] [7,3,12,9]
- 9. Pattern matching 螻 觜訣蟆 襴ろ語 襷れ広 伎 給. 觜 襴ろ([]), cons 一一(:) 煙 伎伎 伎 企 襴ろ瑚 螳語 襯 給. 襷れ広 伎伎 覯 head 襯 蟲企. head' :: [a] -> a head' [] = error "Can't call head on empty list." head' (x:_) = x error 壱 襯 覦る . 覈視 貅伎れ 語 螳牛 覲企ゼ 蠍 襦蠏碁 譯曙 .
- 10. Pattern matching るジ 覈 螳讌 覯 危ｴ覺. length' :: (Num b) => [a] -> b length' [] = 0 length' (_:xs) = 1 + length' xs sum' :: (Num a) => [a] -> a sum' [] = 0 sum' (x:xs) = x + sum' xs
- 11. Pattern matching 覦 企 一危 豌願 覈 蟆曙 @襯 伎 給. headFirst :: (Show a) => [a] -> String headFirst [] = "empty string" headFirst all@(x:_) = show all ++ "'s first element is " ++ show x *Main> headFirst [1,2,3,4] "[1,2,3,4]'s first element is 1" *Main> headFirst "abcd" ""abcd"'s first element is 'a'"
- 12. 一 覓語 yesNo Bool 螳 襯 語襦 覦 蠏 螳 True覃 "Yes", False覃 "No"襯 襴危 襯 襷れ 覺. 襯 れ yesNo (True || False) "Yes"襯 襴危伎 . trueman Bool 螳 襴ろ碁ゼ 語襦 覦 True 螳襯 襴危 襯 襷れ 覺. 襯 れ trueman [True,True,False,False,True] 3 襴危伎 . listToPairs list襯 語襦 覦 螳 襯 螳 襦 讌 讌 伎 襴ろ碁ゼ 襴危 襯 襷れ 覺. 螳螳 螳 蟆曙 襷讌襷 覯襴暑. 襯 れ listToPairs [1,2,3,4,5] [(1,2), (3,4)]襯 襴危伎狩.
- 13. Guard 襷れ広 一危郁 轟 伎 襷譟燕 讌襯 覦覯 覦覃 螳 一危郁 轟 譟郁唄 襷譟燕 讌襯 覦覯. 螳 if ~ else if螳 企 蟲譟一 觜訣 手 螳覃 . 一 襯 覺. bmiTell :: (Floating a) => a -> String bmiTell bmi | bmi <= 18.5 = "You are underweight." | bmi <= 25.0 = "you are normal." | bmi <= 30.0 = "you are fat." | otherwise = "you are very fat." 螳 語 れ 危(|) 朱Μ 伎 . 覿 襦 語螳 譟郁唄 襷譟燕讌 誤 れ 襷譟燕る 蟇郁鍵 企麹 貊襯 ろ.
- 14. Guard 螳 覲危 螳 譴 螳 螳 譟郁唄螻 蟇郁鍵 企麹 貊襯 危. 譟郁唄 譴 碁危(indent) 譟一 . 螳 危 豺螳 襦 碁危瑚 るゴる 貉危 螳 覦. 覲危 螳 襷 襷讌襷 otherwise. otherwise True襦 朱, るジ 螳螳 豌襴讌 覈詩 譟郁唄 豌襴蠍 譟伎. 願骸 螳襯 螳 蟆曙, 螳 襷譟燕 譟郁唄 蟆曙 れ 伎朱 願. れ 伎 譟伎讌 る 襷谿螳讌襦 瑚 覦. 蠏碁Μ螻 螳襯 譴 覈 貊襯 蟯讌襷, 螳煙 伎蠍 覓語 覲襦 豢豌襷 覦 蟆 螳れ. max' :: (Ord a) => a -> a -> a max' a b | a > b = a | otherwise = b
- 15. where where 企 企 覦覲旧朱 一企 煙 . bmiTell 襯 where襯 伎 企慨蟆給. bmiTell :: (Floating a) => a -> a -> String bmiTell weight height | bmi <= 18.5 = "You are underweight." | bmi <= 25.0 = "You are normal." | bmi <= 30.0 = "You are fat." | otherwise = "You are very fat." where bmi = weight / height ^ 2 れ 覈碁願襯 語襦 覦 bmi讌襯 螻壱伎 蟆 螻, bmi 螻 螻旧 覦覲旧朱 一願鍵 覓語 where 伎給.
- 16. where where 貊 螳煙 譴 訖襷 螳 螻一 覯襷 螻壱企 蟆 襷れ伎朱 ろ レ蟾讌 螳語給. where 企 伎 企 伎襷 螳ロ. where 襷れ広 伎 給. bmiTell :: (Floating a) => a -> a -> String bmiTell weight height | bmi <= skinny = You are underweight. | bmi <= normal = You are normal. | bmi <= fat = You are fat. | otherwise = You are very fat. where bmi = weight / height ^ 2 (skinny, normal, pat) = (18.5, 25.0, 30.0)
- 17. where where 企 襯 誤 朱, where 企 where 譴豌伎 螻, 襯 襷 覓碁( 襷れ広, 螳 ) 覈 螳ロ. calcFibos :: (Integral a) => [a] -> a calcFibos xs = [fibo x | x <- xs] where fibo 0 = 0 fibo 1 = 1 fibo n = fibo (n-1) + fibo (n-2)
- 18. let in let in where 螻 觜訣 . let (bindings) in (expression) 襯 螻 朱, where れ binding る 覦覃 let binding る 谿伎 給. cylinder :: (Num a) => a -> a -> a cylinder r h = let sideArea = 2 * pi * r * h topArea = pi * r^2 in sideArea + 2 * topArea let in let 覦碁 螳 in れ 給. where 蟲覓語 蟲譟一 覦覃 let in if覓語 貊 企讌 煙ロ 給. 讀, let in 蠏 豌企 螳覃 蟆郁骸 螳 譟伎伎朱 .
- 19. let in 譴 螳 覦碁 螻 矩る 碁語襦(;) 伎. Prelude> let a = 5 in a * a * a 125 Prelude> let squre x = x * x in (squre 5, squre 6) (25, 36) Prelude> let a = 100; b = 200; c = 300; in a + b + c 600 list comprehension let 給. let 覦碁 襷 . Prelude> [f x|x<-[0..10],let f 0=0;f 1=1;f n=f (n-1)+f (n-2)] [0,1,1,2,3,5,8,13,21,34,55]
- 20. case expression case 覈麹 語伎 switch - case 蟲覓瑚骸 觜訣 螳企, 螳ロ 蠍磯レ 螳螻 給. case 願鍵 覓語 螳 螳願, 貊 譴螳 給. 蟲覓語 螳 蟲譟磯ゼ 螳螻 給. case expression of pattern -> result pattern -> result pattern -> result ... 語 襷れ広螻 蟲ロ . 轟 伎 磯ジ 蟆郁骸 螳 case 牛 給. る 襷れ広螻朱 るゴ蟆 case 願鍵 覓語 企讌 螳ロ.
- 21. case expression head :: [a] -> a head xs = case xs of [] -> error "Cant call head on empty list." (x:_) -> x descList :: [a] -> String descList xs = "this List is " ++ case xs of [] -> "Empty List" [x]-> "Singleton List" xs -> "Long List"
- 22. 一 覓語 maximum 企 襴ろ瑚 譯殊伎 , 襴ろ語 譴 螳 襯 襴危 襯 蟲 覺. 觜 襴ろ語 蟆曙 error 襯 伎 壱 襯 殊狩り 襷れ 覲伎語. take 襴ろ瑚 譯殊伎 , 襴ろ語 豌覿 企 襷殊 襯 殊 襴危 襯 襷れ 覺. , 螳 0危 蟆曙 觜 襴ろ([])襯 襴危伎 . zip 螳 襴ろ瑚 譯殊伎 襴ろ語 螳螳 襦 讌讌 襴ろ碁ゼ 襴危 襯 襷れ 覺. 覈 譴 譟伎 . 企 譟郁 るゴ蟆 燕 .
- 23. 一 覓語 quickSort (* hard) 企 襴ろ瑚 譯殊伎 , 蠏 襴ろ碁ゼ quickSort襯 伎 襯 蟲企. 豌 蠍 麹 企れ 覓語 豌豌 螳 れ 螻覩狩企.