如何解析雅虎歷史CSV與Attoparsec

Question

我是哈斯克爾的初學者，如何與attoparsec成開放數組解析，高陣列等

module CsvParser (
     Quote (..) 
    , csvFile 
    , quote 
    ) where 
import System.IO 
import Data.Attoparsec.Text 
import Data.Attoparsec.Combinator 
import Data.Text (Text, unpack) 
import Data.Time 
import System.Locale 
import Data.Maybe 

data Quote = Quote { 
     qTime  :: LocalTime, 
     qAsk  :: Double, 
     qBid  :: Double, 
     qAskVolume :: Double, 
     qBidVolume :: Double 
    } deriving (Show, Eq) 

csvFile :: Parser [Quote] 
csvFile = do 
    q <- many1 quote 
    endOfInput 
    return q 

quote :: Parser Quote 
quote = do 
    time  <- qtime 
    qcomma 
    ask   <- double 
    qcomma 
    bid   <- double 
    qcomma 
    askVolume <- double 
    qcomma 
    bidVolume <- double 
    endOfLine 
    return $ Quote time ask bid askVolume bidVolume 

qcomma :: Parser() 
qcomma = do 
    char ',' 
    return() 

qtime :: Parser LocalTime 
qtime = do 
    tstring  <- takeTill (\x -> x == ',') 
    let time = parseTime defaultTimeLocale "%d.%m.%Y %H:%M:%S%Q" (unpack tstring) 
    return $ fromMaybe (LocalTime (fromGregorian 0001 01 01) (TimeOfDay 00 00 00)) time 

--testString :: Text 
--testString = "01.10.2012 00:00:00.741,1.28082,1.28077,1500000.00,1500000.00\n" 

quoteParser = parseOnly quote 

main = do 
    handle <- openFile "C:\\Users\\ivan\\Downloads\\0005.HK.csv" ReadMode 
    contents <- hGetContents handle 
    let allLines = lines contents 
    map (\line -> quoteParser line) allLines 
    --putStr contents 
    hClose handle 

錯誤消息：

testhaskell.hs:89:5: 
    Couldn't match type `[]' with `IO' 
    Expected type: IO (Either String Quote) 
     Actual type: [Either String Quote] 
    In the return type of a call of `map' 
    In a stmt of a 'do' block: 
     map (\ line -> quoteParser line) allLines 
    In the expression: 
     do { handle <- openFile 
         "C:\\Users\\ivan\\Downloads\\0005.HK.csv" ReadMode; 

      contents <- hGetContents handle; 
      let allLines = lines contents; 
      map (\ line -> quoteParser line) allLines; 
      .... } 

testhaskell.hs:89:37: 
    Couldn't match type `[Char]' with `Text' 
    Expected type: [Text] 
     Actual type: [String] 
    In the second argument of `map', namely `allLines' 
    In a stmt of a 'do' block: 
     map (\ line -> quoteParser line) allLines 
    In the expression: 
     do { handle <- openFile 
         "C:\\Users\\ivan\\Downloads\\0005.HK.csv" ReadMode; 

      contents <- hGetContents handle; 
      let allLines = lines contents; 
      map (\ line -> quoteParser line) allLines; 
      .... } 

Answer 1

您可以使用attoparsec-csv包，或者你可以看看它的source code有一些想法如何寫你自己。

的代碼會像

import qualified Data.Text.IO as T 
import Text.ParseCSV 

main = do 
    txt <- T.readFile "file.csv" 
    case parseCSV txt of 
    Left err -> error err 
    Right csv -> mapM_ (print . mkQuote) csv 

mkQuote :: [T.Text] -> Quote 
mkQuote = error "Not implemented yet" 

Answer 2

在錯誤無關秒差距或attoparsec。該錯誤消息指出該生產線是不是IO動作，所以當您嘗試使用它作爲一個它會導致錯誤：

main = do 
    handle <- openFile "C:\\Users\\ivan\\Downloads\\0005.HK.csv" ReadMode 
    contents <- hGetContents handle 
    let allLines = lines contents 
    map (\line -> quoteParser line) allLines -- <== This is not an IO action 
    --putStr contents 
    hClose handl 

你忽略map調用的結果。您應該將其存儲在let的變量中，就像您使用lines的結果一樣。

第二個錯誤是因爲您試圖使用Text作爲String這是不同的類型，即使它們都表示有序的字符集合（它們也有不同的內部表示形式）。你可以用pack和unpack兩種類型之間的轉換：http://hackage.haskell.org/package/text/docs/Data-Text.html#g:5

此外，你應該始終明確給出main類型簽名main :: IO()。如果你不這樣做，它有時會導致微妙的問題。

但正如其他人所說，你應該使用csv解析器包。