Create a list of strings from a CSV line. Requires the DList library installed. Usage example: ghc csv.hs; ./csv 'foo,bar,"foo,bar","foo bar "" foo,,bar",bar'

csv.hs

import Control.Monad (forM_)
import qualified Data.DList as DL
import System.Environment (getArgs,getProgName)
import System.Exit (exitSuccess)

data CSVState = OutsideQuote | InsideQuote | AfterQuote

listFromCSV :: String
            → [String]
listFromCSV = toResult ∘ foldl parseChar (OutsideQuote,DL.empty,DL.empty)
 where
  parseChar (OutsideQuote,res,curr) ',' = (OutsideQuote,snocBS res curr,DL.empty)
  parseChar (OutsideQuote,res,curr) '"' = (InsideQuote,res,curr)
  parseChar (OutsideQuote,res,curr)   c = (OutsideQuote,res,DL.snoc curr c)
  parseChar (InsideQuote ,res,curr) '"' = (AfterQuote,res,curr)
  parseChar (InsideQuote ,res,curr)   c = (InsideQuote,res,DL.snoc curr c)
  parseChar (AfterQuote  ,res,curr) '"' = (InsideQuote,res,DL.snoc curr '"')
  parseChar (AfterQuote  ,res,curr) ',' = (OutsideQuote,snocBS res curr,DL.empty)
  parseChar (AfterQuote  ,res,curr)   c = (OutsideQuote,res,DL.snoc curr c)
  toResult :: (CSVState,DL.DList String,DL.DList Char) → [String]
  toResult = DL.toList ∘ addLast
  addLast (_,res,curr) = snocBS res curr
  snocBS dl b = DL.snoc dl (DL.toList b)

main :: IO 𐌏
main = do
  args ← getArgs
  if null args
    then do
      progName ← getProgName
      putStrLn $ "Usage: " ++ progName ++ " <csv_string> [<csv_string>...]"
    else do
      forM_ args $ λarg → do
        let csv = listFromCSV arg
        putStrLn $ show arg ++ " ⇒ " ++ show csv