无法与实际类型为“[Char]”的预期类型“文本”匹配 [英] Couldn't match expected type `Text' with actual type `[Char]'

问题描述

这可能是一个非常不好的问题，但我无法克服这个问题（正如我刚开始学习Haskell时所说的那样）。

我有一个简单的块代码：

 模块SomeTest其中
导入Data.Text 
 
 str =替换ofo barofofo
  

如果我用 str ，我得到：



 < interactive>：108：19：error ：
 *无法与实际类型`[Char]'相匹配的期望类型'Text'
 *在'​​Data.Text.replace'的第一个参数中，即``ofo''
在表达式中：Data.Text.replaceofobarofofo
在'it'的等式中：it = Data.Text.replaceofobarofofo
 
< interactive>：108：25：error：
 *无法与实际类型为[[Char]'的$ Text'匹配'
 *在Data的第二个参数.Text.replace'，即``bar''
在表达式中：Data.Text.replaceofobarofofo
在a 'it'的等式：it = Data.Text.replaceofobarofofo
 
< interactive>：108：31：error：
 * Could not在'Data.Text.replace'的第三个参数中，即``ofofo''
在预期类型'Text'中匹配实际类型`[Char]'
在表达式：Data.Text中。替换ofobarofofo
在it的等式中：it = Data.Text.replaceofobarofofo
  

我不知道为什么我得到这个错误以及如何通过它。不是文本只是 [Char] ？

的同义词

解决方案

不幸的是，Haskell对于字符串有几种冲突的类型。字符串文字通常是 String 类型，它只是 [Char] 的别名。因为这是字符串的低效表示，所以还有其他选择，比如 Text 。

在这种情况下， code> { - ＃LANGUAGE OverloadedStrings＃ - } 作为程序的第一行将会使其编译。基本上你的字符串文字可以是 Text 然后。

This might be a really noobish question, but I can't get past this problem (as I just started learning Haskell).

I have a simple block of code:

module SomeTest where
import Data.Text

str =  replace "ofo" "bar" "ofofo"

If I call this with str, I get:

<interactive>:108:19: error:
* Couldn't match expected type `Text' with actual type `[Char]'
* In the first argument of `Data.Text.replace', namely `"ofo"'
  In the expression: Data.Text.replace "ofo" "bar" "ofofo"
  In an equation for `it': it = Data.Text.replace "ofo" "bar" "ofofo"

<interactive>:108:25: error:
* Couldn't match expected type `Text' with actual type `[Char]'
* In the second argument of `Data.Text.replace', namely `"bar"'
  In the expression: Data.Text.replace "ofo" "bar" "ofofo"
  In an equation for `it': it = Data.Text.replace "ofo" "bar" "ofofo"

<interactive>:108:31: error:
* Couldn't match expected type `Text' with actual type `[Char]'
* In the third argument of `Data.Text.replace', namely `"ofofo"'
  In the expression: Data.Text.replace "ofo" "bar" "ofofo"
  In an equation for `it': it = Data.Text.replace "ofo" "bar" "ofofo"

I don't know why I'm getting this error and how to get pass it. Isn't Text just a synonym for [Char]?

解决方案

Unfortunately, Haskell has several conflicting types for strings of characters. String literals are usually of type String which is just an alias for [Char]. Because that is an inefficient representation of strings, there are alternatives, like Text.

In your case, adding {-# LANGUAGE OverloadedStrings #-} as the first line of your program will make it compile. Basically your string literals can be of type Text then.

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