how to parse yahoo historical csv with Attoparsec - haskell

Question

i am a beginner of haskell, how to parse with attoparsec into open array, high array etc
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
Error message:
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

The error has nothing to do with parsec or attoparsec. The line the error message points to is not an IO action, so it causes the error when you try to use it as one:
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
You ignore the result of the map call. You should store it in a variable with let, like you do with the result of lines.
The second error is because you are trying to use Text as String which are different types, even though they both represent ordered collections of characters (they also have different internal representations). You can convert between the two types with pack and unpack: http://hackage.haskell.org/package/text/docs/Data-Text.html#g:5
Also, you should always explicitly give main the type signature main :: IO (). It can sometimes lead to subtle problems if you don't.
As other people have said, though, you should probably use a csv parser package.

Answer 2

You can use attoparsec-csv package or you can take a look at its source code to have some idea on how to write it by yourself.
The code will be like
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"