bcp2csv in Haskell (with Lazy BtyeStrings)

bcp2csv.hs

import System.Environment
import Data.List.Split
import Data.List.Utils
import Data.List
import qualified Data.ByteString.Lazy.Search as S
import qualified Data.ByteString.Lazy.Char8 as C

-- usage: $ ./bcp2csv input.bcp output.csv
main :: IO ()
main = do
  args <- getArgs
  input <- C.readFile $ head args
  let outputFilename = args !! 1
  C.writeFile outputFilename . C.unlines . map joinWithCommas $ parseAndEscapeBCP input

type Field = C.ByteString
type Line = [Field]

-- runs the escaping code on the nested list data structure generated by parseBCP.
parseAndEscapeBCP :: C.ByteString -> [Line]
parseAndEscapeBCP input = map (map escapeField) $ parseBCP input

-- parses BCP file into nested Lists. top level is lines, next level is fields.
parseBCP :: C.ByteString -> [Line]
parseBCP input = map splitFields $ splitLines input

escapeField :: Field -> Field
escapeField = quoteIfNecessary . escapeQuotes

splitLines :: C.ByteString -> [C.ByteString]
splitLines input = S.split (convertToStrictByteString "&$&") input

splitFields :: C.ByteString -> Line
splitFields input = S.split (convertToStrictByteString "#&#") input

convertToStrictByteString input = S.strictify (C.pack input)

escapeQuotes :: Field -> Field
escapeQuotes input
    | '"' `C.elem` input = S.replace (convertToStrictByteString "\"") (C.pack "\"\"\"") input
    | otherwise = input

quoteIfNecessary :: Field -> Field
quoteIfNecessary input
    | '\n' `C.elem` input || ',' `C.elem` input || '"' `C.elem` input = wrapInQuotes input
    | otherwise = input

wrapInQuotes :: Field -> Field
wrapInQuotes input = C.concat [C.pack "\"", input, C.pack "\""]

joinWithCommas :: Line -> C.ByteString
joinWithCommas list = C.intercalate (C.pack ",") list