Haskell：显示时抑制引号 [英] Haskell: Suppress quotes around strings when shown

问题描述

以下代码：

 数据HelloWorld = HelloWorld; 
实例显示HelloWorld其中show _ =hello world; 
 
 hello_world =hello world
 
 main = putStr $ show $（HelloWorld，hello_world）
  

打印：

 （hello world，hello world）
  

我想要打印：

 （hello world，hello world）
  

即我希望以下行为：

  fhello world=hello world
f HelloWorld =hello world 
  

不幸的是， show 不符合这个要求，为：

  showhello world=\hello world \
  

是否有一个像上面描述的 f 的函数？

解决方案

首先，看看这个问题。也许你会对 toString 函数感到满意。其次， show 是一个将某些值映射到 String 的函数。

所以，引用应该是有意义的：

  >显示字符串
\字符串\
  

是否有一个像上面描述的 f 的函数？

好像您正在寻找 id ：

  > putStrLn $ idstring
 string 
> putStrLn $ showstring
string
  

The following code:

data HelloWorld = HelloWorld; 
instance Show HelloWorld where show _ = "hello world";

hello_world = "hello world"

main = putStr $ show $ (HelloWorld, hello_world)

Prints:

(hello world,"hello world")

I'd like it to print:

(hello world,hello world)

i.e. I want behaviour like the following:

f "hello world" = "hello world"
f HelloWorld = "hello world"

Unfortunately, show does not satisfy this, as:

show "hello world" = "\"hello world\""

Is there a function that works like f that I've described above?

解决方案

Firstly, take a look at this question. Maybe you will be satisfied with toString function.

Secondly, show is a function that maps some value to a String.

So, it makes sense that quotes should be escaped:

> show "string"
"\"string\""

Is there a function that works like f that I've described above?

Seems like you're looking for id:

> putStrLn $ id "string"
string
> putStrLn $ show "string"
"string"

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