我有一个 CSV 文件，其中包含我想在 Haskell 中处理的记录数据。 CSV 文件中的数据为十六进制格式。当我将它读入 Haskell 时，我有诸如“0xFF5FFFC8EC5FFEDF”之类的字符串，它代表 8 个字节的数据。
为了处理数据，我想将字符串转换为允许我进行位旋转（按位与、或和异或）的数据类型。然后当我完成后，我想将最终结果转换回十六进制字符串，以便将其写入文件。
这在 Haskell 中容易做到吗？我应该查看哪些模块？
【问题讨论】：
您可以使用read 来解析整数或浮点数。
它位于 Prelude 中，因此您无需任何其他模块即可使用它。
试试：
a = "0xFF5FFFC8EC5FFEDF"
b = read a::Double
（它给出 b = 1.8401707840883393e19）
另外，为了解析 CSV，您也可以创建自己的函数来执行此操作。 一周前我刚刚写了一个简单的 CSV 解析器。
module CSVUtils
( parseCSV, showCSV
, readCSV , writeCSV
, colFields
, Separator, Document
, CSV , Entry
, Field
)
where
import Data.Char
import Data.List
{-
A simple utility for working with CSV (comma-separated value) files. These
are simple textual files where fields are delimited with a character (usually a comma
or a semicolon). It is required that the CSV document is well-formed, i.e., that
it contains an equal number of fields per row.
-}
type Separator = String
type Document = String
type CSV = [Entry]
type Entry = [Field]
type Field = String
doc = "John;Doe;15\nTom;Sawyer;12\nAnnie;Blake;20"
brokenDoc = "One;Two\nThree;Four;Five"
{-
(a) Takes a separator and a string representing a CSV document and returns a
CSV representation of the document.
-}
-- !! In the homework text is said Separator is going to be Char and now the type is String
-- !! so I'm just going to take head
parseCSV :: Separator -> Document -> CSV
parseCSV sep doc
| (head sep) `notElem` doc = error $ "The character '"++sep++"' does not occur in the text"
| 1 /= length ( nub ( map length (lines doc))) = error $ "The CSV file is not well-formed"
| otherwise = [splitOn sep wrd | wrd <- lines doc ]
{-
(b) Takes a separator and a CSV representation of
a document and creates a CSV string from it.
-}
showCSV :: Separator -> CSV -> Document
showCSV sep = init . unlines . map (intercalate sep)
{-
(c) Takes a CSV document and a field number
and returns a list of fields in that column.
-}
colFields :: Int -> CSV -> [Field]
colFields n csv = [ if length field > n
then field !! n
else error $ "There is no column "++(show n)++" in the CSV document"
| field <- csv]
{-
(d) Takes a file path and a separator and returns the CSV representation of the file.
-}
readCSV :: Separator -> FilePath -> IO CSV
readCSV sep path = do
file <- readFile path
return $ parseCSV sep file
{-
(e) Takes a separator, a file path, and a CSV document and writes the document into a file.
The return type of writeCSV is a special case of IO { we need to wrap an impure
action, but do not actually have to return anything when writing. Thus, we
introduce (), or the unit type, which holds no information (consider it a 0-
tuple).
-}
writeCSV :: Separator -> FilePath -> CSV -> IO ()
writeCSV sep path csv = writeFile path (showCSV sep csv)
【讨论】：
我将假设您的二进制数据可以是任意长度。例如，如果您的二进制数据适合 Int64，则可以简化事情。
我会推荐以下库和模块：
有关如何对 ByteStrings 执行按位运算的示例，请查看 Haskell 学院本教程的结尾：
https://www.fpcomplete.com/school/to-infinity-and-beyond/pick-of-the-week/bytestring-bits-and-pieces
cassava的使用示例，请查看源repo的examples目录：
【讨论】：