要列出的Haskell字符串

Question

["6","","[[1,2,3,4,5,6],[7,8,9,10,11,12],[13,14,15,16,17,18],[19,20,21,22,23,24],[25,26,27,28,29,30],[31,32,33,34,35,36]]"] I must get from this 6 and [[1,2,3,4,5,6],[7,8,9,10,11,12],[13,14,15,16,17,18],[19,20,21,22,23,24],[25,26,27,28,29,30],[31,32,33,34,35,36]] I read from file in file it look

6. [[1,2,3,4,5,6],[7,8,9,10,11,12],[13,14,15,16,17,18],[19,20,21,22,23,24],[25,26,27,28,29,30],[31,32,33,34,35,36]].

I tried with map and read to convert string but it wasnt working. sry for english

Answer 1

The problem with using map and read directly is, that your list elements don't all have the same types. The first element is (or better: should be converted to) an Int , the second an empty list and the third an `[[Int]] .

To convert the first element of the list into an Int , you can say something like read $ head xs :: Int , where xs is your list of strings.

The second element cannot be directly converted by read, since an empty string will result in an exception (Prelude.read: no parse).

To convert the third element, which is a list of lists of integers, you can simply say something like read $ xs !! 2 :: [[Int]] read $ xs !! 2 :: [[Int]] .

This is not safe or elegant, but if your input always has this structure it should work.