Thank you very much for the error report. I have tracked down the cause. You are searching against an empty Bytestring. This is now represented by
-- | /O(1)/ The empty 'ByteString' empty :: ByteString empty = PS nullForeignPtr 0 0
And while the useAsCString and useAsCStringLen functions never reveal the null pointer, the current library uses unsafeUseAsCStringLen, which returns the null pointer. And this is getting caught by a null pointer check resulting in your crash. I will post a fix later tonight, and announce it. Which regex-prce version are you using? Perhaps from hackage? I want to prioritize the version you need fixed. The earlier repository holds up to version 0.81 at http://darcs.haskell.org/packages/regex-pcre/ The newer repository holds up to version 0.92 at http://darcs.haskell.org/packages/regex-unstable/regex-pcre/regex-pcre.cabal Out of further curiosity: Which version of the pcre library does it use? And what version of ghc? Which version of Data.ByteString? Cheers, Chris Kuklewicz