Learn You a Haskell for Great Good 读书笔记 8

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8. Input & Output

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import Data.Char
main = do 
	putStrLn "What's your first name?" 
	firstName <- getLine 
	putStrLn "What's your last name?" 
	lastName <- getLine 
	let bigFirstName = map toUpper firstName 
		bigLastName = map toUpper lastName 
	putStrLn $ "hey " ++ bigFirstName ++ " " ++ bigLastName ++ ", how are you?"

do 意味着后面进行IO操作

<- 是IO操作，左边取IO行为的结果。

let 与之前的一样，绑定数值。

return 将右边的值作为IO结果返回，如 wahaha <- return “wahaha”

when
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import Control.Monad
main = do 
	input <- getLine 
	when (input == "SWORDFISH") $ do putStrLn input

参数为一个布尔和一个IO行为，布尔为True的时候才进行IO行为，否则返回IO()

sequence
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sequence $ map print [1, 2, 3, 4, 5]

将一组IO行为按顺序进行，并输出结果

mapM & mapM_

相当于sequence $ map，右边不会输出结果

forever

while(true) $ do any IO action…

forM
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forM :: (Monad m, Traversable t) => t a -> (a -> m b) -> m (t b)