[Haskell-cafe] ByteString comparison question (was: another Newbie performance question)

[Philip Müller]

Hi,

I'm changing my CSV program to use ByteStrings, but I have problems with 
this:


readCSVLine       :: String   -- line as String
                   -> [String] -- line broken down into the value Strings
readCSVLine       = unfoldr builder
                       where
                         builder [] = Nothing
                         builder xs = Just $ readField xs

                         readField []       = ([],[])
                         readField (',':xs) = ([],xs)
                         readField ('"':xs) = (field,rest)
                           where
                             (field,'"':rest) = break (== '"') xs


So far, I have something like this - doesn't look too good to me, and 
doesn't compile:


import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as C8

type CSV = [[B.ByteString]]

readCSVLine :: B.ByteString   -- line as String
             -> [B.ByteString] -- line broken down into the value Strings
readCSVLine = unfoldr builder
                 where
                   builder xs | xs == B.empty = Nothing
                              | otherwise     = Just $ readField xs

                   readField xs | xs == B.empty    = ([],[])
                                | B.head xs == ',' = ([], B.tail xs)
                                | B.head xs == '"' = (field, B.tail rest)
                                     where
                                        field,rest) = B.break (== '"') xs


I do not know how to compare a Word8 to a Char. Or maybe I don't need to?

Regards
Philip