Haskell IO与数字

任何人都可以帮助这个exersise？Haskell IO与数字

写一个程序，询问用于右成角度三角形的底边和高度的用户，计算出其面积和它打印在屏幕上。该交互看起来应该像：

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

与解决：

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

来源

2009-12-08 Roman Shestakov

你到目前为止尝试了什么？ – 2009-12-08 18:40:42

Haskell IO带有浮点数和数字已经破坏了我的想法，但我已经得到了答案。所以我想现在解决了 – 2009-12-08 19:18:51

然后点击其中一个答案旁边的复选标记。 – 2009-12-09 00:20:32

你有什么作品，但它是更好的Haskell风格从IO分离纯。您的getTriArea计算不需要锁定在IO monad中：将其解除！

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)

应用并非实际必要，它只是提供了一些漂亮的中缀操作符。 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)

在这样一个简短的程序，它并没有真正无论所有的东西，但要注意，即使是那些进口，triArea定义可以保持纯洁。

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)

来源

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

来源

2009-12-08 19:21:35

这些读取的类型注释和参数是多余的。你可以写'读取基地*读取高度/ 2'。函数应用程序是左关联的。 – Chuck 2009-12-08 19:40:46

（B H）/ 2 = B（H/2）=（B/2）ħ= B H/2在数学，它们都是相同的，并且给出相同的结果。所以更好地写简单的基地*高度/ 2

来源

2016-01-09 07:19:18

Haskell IO与数字

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