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

[Philip Müller]

Achim Schneider schrieb:
 > Philip Müller <mail at philip.in-aachen.net> wrote:
 >
 >> I do not know how to compare a Word8 to a Char. Or maybe I don't need
 >> to?
 >>
 > You don't need to, just use ByteString.Char8 or ByteString.Lazy.Char8.

Could you give a short example of how to check whether a ByteString 
starts with a comma (',')?

I tried this

import qualified Data.ByteString.Char8 as B

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


But now I get strange errors when compiling, like

Main.o: In function `rTD_info':
(.text+0x5a): undefined reference to 
`bytestringzm0zi9zi1zi0_DataziByteStringziInternal_zdf2_closure'

Is this a problem with my Code or is it just GHC unable to find the 
ByteString package?

Regards
Philip