Haskell IO與數字

任何人都可以幫助這個exersise？Haskell IO與數字

寫一個程序，詢問用於右成角度三角形的底邊和高度的用戶，計算出其面積和它打印在屏幕上。該交互看起來應該像：

The base? 
3.3 
The height? 
5.4 
The area of that triangle is 8.91

與解決：

getTriArea :: IO Float 
getTriArea = do 
putStr "The base? " 
base <- getLine 
putStr "The height? " 
height <- getLine 
let ar = ((read base :: Float) * (read height :: Float))/ 2 
return ar 

main = do 
result <- getTriArea 
putStr $ "The area of that triangle is " ++ show result

來源

2009-12-08 Roman Shestakov

你到目前爲止嘗試了什麼？ – 2009-12-08 18:40:42

Haskell IO帶有浮點數和數字已經破壞了我的想法，但我已經得到了答案。所以我想現在解決了 – 2009-12-08 19:18:51

然後點擊其中一個答案旁邊的複選標記。 – 2009-12-09 00:20:32

你有什麼作品，但它是更好的Haskell風格從IO分離純。您的getTriArea計算不需要鎖定在IO monad中：將其解除！

import Control.Applicative 

prompt :: (Read a) => String -> IO a 
prompt s = putStr s >> read <$> getLine 

triArea :: (Fractional a) => a -> a -> a 
triArea base height = (base * height)/2 

main :: IO() 
main = do 
    area <- triArea <$> prompt "The base? " <*> prompt "The height? " 
    putStrLn $ "The area of that triangle is " ++ show (area :: Float)

應用並非實際必要，它只是提供了一些漂亮的中綴操作符。 Monad工作得很好。

import Control.Monad 

prompt :: (Read a) => String -> IO a 
prompt s = putStr s >> fmap read getLine 

triArea :: (Fractional a) => a -> a -> a 
triArea base height = (base * height)/2 

main :: IO() 
main = do -- pick one of the following two lines 
    area <- liftM2 triArea (prompt "The base? ") (prompt "The height? ") 
    area <- return triArea `ap` prompt "The base? " `ap` prompt "The height? " 
    putStrLn $ "The area of that triangle is " ++ show (area :: Float)

在這樣一個簡短的程序，它並沒有真正無論所有的東西，但要注意，即使是那些進口，triArea定義可以保持純潔。

prompt :: (Read a) => String -> IO a 
prompt s = putStr s >> getLine >>= return . read 

triArea :: (Fractional a) => a -> a -> a 
triArea base height = (base * height)/2 

main :: IO() 
main = do 
    base <- prompt "The base? " 
    height <- prompt "The height? " 
    let area = triArea base height 
    putStrLn $ "The area of that triangle is " ++ show (area :: Float)

來源

2009-12-08 19:55:26 ephemient

getTriArea :: IO Float 
getTriArea = do 
putStr "The base? " 
base <- getLine 
putStr "The height? " 
height <- getLine 
let ar = ((read base :: Float) * (read height :: Float))/ 2 
return ar 

main = do 
result <- getTriArea 
putStr $ "The area of that triangle is " ++ show result

來源

2009-12-08 19:21:35

這些讀取的類型註釋和參數是多餘的。你可以寫'讀取基地*讀取高度/ 2'。函數應用程序是左關聯的。 – Chuck 2009-12-08 19:40:46

（B H）/ 2 = B（H/2）=（B/2）ħ= B H/2在數學，它們都是相同的，並且給出相同的結果。所以更好地寫簡單的基地*高度/ 2

來源

2016-01-09 07:19:18

Haskell IO與數字

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