首页 \ 问答 \ 为什么要将Reader的构造函数参数定义为函数？(Why to define the constructor parameter of Reader as a function?)

为什么要将Reader的构造函数参数定义为函数？(Why to define the constructor parameter of Reader as a function?)

 在学习Reader Monad时，我发现它被定义为：  
newtype Reader r a = Reader { runReader :: r -> a }

instance Monad (Reader r) where
  return a = Reader $ \_ -> a
  m >>= k  = Reader $ \r -> runReader (k (runReader m r)) r
 
 我想知道为什么使用函数作为构造函数参数而不是其他东西，如元组：  
newtype Reader r a = Reader { runReader :: (r, a) }

instance Monad (Reader r) where
  -- Here I cannot get r when defining return function, 
  -- so does that's the reason that must using a function whose input is an "r"?
  return a = Reader (r_unknown, a) 
  m >>= k = Reader (fst $ runReader m) (f (snd $ runReader m))
 
 根据Reader的定义，我们需要一个“环境”来生成“价值”。 我认为Reader类型应该包含“environment”和“value”的信息，所以元组看起来很完美。 

When learning the Reader Monad, I find that it is defined as: 
newtype Reader r a = Reader { runReader :: r -> a }

instance Monad (Reader r) where
  return a = Reader $ \_ -> a
  m >>= k  = Reader $ \r -> runReader (k (runReader m r)) r
 
I want to known why using function as constructor parameter instead of something else such as a tuple: 
newtype Reader r a = Reader { runReader :: (r, a) }

instance Monad (Reader r) where
  -- Here I cannot get r when defining return function, 
  -- so does that's the reason that must using a function whose input is an "r"?
  return a = Reader (r_unknown, a) 
  m >>= k = Reader (fst $ runReader m) (f (snd $ runReader m))
 
According to the Reader definition, we need a "environment" which we can use to generate a "value". I think a Reader type should contain the information of "environment" and "value", so the tuple seems perfect.

原文：https://stackoverflow.com/questions/42310931

更新时间：2023-10-14 22:10

最满意答案

 我认为您需要添加更多信息，但只需使用您所拥有的信息即可尝试这种方法  
Import-Csv C:\temp\test.csv -Header server,1,2,3,4 | ForEach-Object{
    $_.server  = (($_.server).split("(")[0]).Trim()
    $_
} 
 
 我们导入csv数据并分配标头。 如果您已经有一个，则可以省略此参数。  
 然后我们将每行数据作为对象进行检查。 通过将其分隔为空格来更改server数据。 如果此数据用于服务器名称，则可以安全地假设第一个空格之前的所有内容都是服务器名称。 这种方法取决于那里的空间。 我们也可以使用相同的逻辑(但如果空间是保证，这将更容易。  
 因此，我们更新server ，然后使用$_将数据发送回管道。  
 示例输出  
server        1 2  3   4               
------        - -  -   -               
GDR01W01SQ004 1 4  63  NY-TER-PLN-P-5N 
GDR01L02D001  4 12 129 CO-FDP-STE-NP-5N
 
 根据评论进行编辑  
 由于它是服务器显示名称，因此我根据“（”）将逻辑更改为拆分。还使用Split()方法而不是-split运算符。 

I think you need to add more information but just using what you have let try this one approach 
Import-Csv C:\temp\test.csv -Header server,1,2,3,4 | ForEach-Object{
    $_.server  = (($_.server).split("(")[0]).Trim()
    $_
} 
 
We import the csv data and assign a header. If you already have one then this parameter can be omitted.  
Then we examine each row of data as an object. Change the server data by splitting it up by its spaces. If this data is for server names then it is safe to assume that that everything before the first space is the server name. This approach is dependent on the space being there. We could also use the same logic with the ( but this would be easier if the space was a guarantee.  
So we update the server and then send the data back down the pipe with $_. 
Sample Output 
server        1 2  3   4               
------        - -  -   -               
GDR01W01SQ004 1 4  63  NY-TER-PLN-P-5N 
GDR01L02D001  4 12 129 CO-FDP-STE-NP-5N
 
Edit based on comments 
Since it is a server display name I changed the logic to split based on the "(". Also using the Split() method instead of the -split operator.

为什么要将Reader的构造函数参数定义为函数？(Why to define the constructor parameter of Reader as a function?)

最满意答案

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