Haskell从文件中读取Integer和列表列表 [英] Haskell read Integer and list of lists from file

问题描述

让我说我有一个文件

8 [[1,2,3,4],[1,2]]

其中包含数字和列表列表.

with number and list of lists in it.

此代码允许我从中读取所有行或第n个元素.

This code allow me to read all line or n-th element from it.

import System.IO

main = do
      x <- openFile "file.txt" ReadMode
      cont <- hGetContents x
      let fLines = lines cont
      let numb = fLines !! 0 !! 0
      print numb

这里numb是'8'.

如何在不使用其他库的情况下从numb获取整数8?

How can I get integer 8 from numb without using other libraries?

是否有可能读取列表列表并将其用作列表列表?

And is there a possibility to read list of lists and use it as list of lists?

还是我最好将每个列表写在新行中，并逐行阅读并添加到空列表中?

Or should I better write each list in a new row, and read them row by row and add to empty list?

也许这是一个愚蠢的问题，但是我没有找到在互联网上进行类似操作的任何例子.

Maybe it's a stupid question, but I didn't find any example of doing something like that on internet.

更新

感谢分形的回答，我设法写了这篇文章

Thanks to Fractal answer I've managed to write this

rList :: String -> [[Int]]    
rList = read

适用于列表列表！

但是，当我无法使用单个Int时.

However, when I cant make it work with single Int.

into :: String -> Int
into = read

不知道为什么，但是不适用于numb T_T

Don't know why, but it doesn't work for numb T_T

更新2

好吧，这有点愚蠢. numb在这里是Char，因此要使其正常工作，就可以编写

Ok, it was kinda stupid. numb is Char here, so to make it work it will be enough to write

print (into [numb])

谢谢大家的回答.

推荐答案

您可以使用

You can use read to parse String representations of Haskell data structures. This should work for your list of lists as well.

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