Original excellente.hs code to calculate Paypal earnings

excellent.hs

{-# LANGUAGE OverloadedStrings #-}

import Data.Csv
import Data.Fixed
import Data.Vector as Vec (Vector, fromList, sum, length, toList)
import Data.ByteString.Lazy as B (readFile)
import Control.Monad 
import Control.Applicative
import System.Environment

data Receipt = Item String Centi

instance Show Receipt where
show (Item a b) =  Prelude.show a ++ "\n"

toCenti :: String -> Centi
toCenti a = case result of
		[(amt,s)] -> amt
		_ -> 0
	where result = reads (filter (',' /=) a) :: [(Centi, String)]

toReceipt :: String -> String -> Receipt
toReceipt n a = Item n amount 
	where
		amount = toCenti a

instance FromRecord Receipt where
	parseRecord rec
		| Vec.length rec >= 10 = liftA2 toReceipt (rec .! 3) (rec .! 8)
		| otherwise = mzero

main :: IO ()
main = do
	args <- getArgs
	bsFile <- B.readFile (args !! 0)
	receipts <- return $ 
		case (decode HasHeader bsFile :: Either String (Vector Receipt)) of
			Left errorMsg -> [Item "" (0.00 :: Centi)]
			Right receipts -> toList receipts
	print receipts