Hi Simon, I found a bug in alex-3.0 and I'm attaching a fixed source file - templates/wrappers.hs (modified against alex-3.0 from cabal unpack). Explanation: I was installing bytestring-lexing 0.2.1 and it failed to install with alex 3.0, which was released on Aug 4. It succeeded, however, with the most recent earlier alex 2.3.5. Turns out that the wrapper for lazy bytestrings (strict are ok) had alexGetByte not doing w2c conversion: alexGetByte (_, cs) | ByteString.null cs = Nothing | otherwise = Just (ByteString.head cs, (ByteString.head cs, ByteString.tail cs)) It should say ByteString.w2c $ ByteString.head cs here. With this and an additional import of Data.ByteString.Internal (w2c), the generated code compiles. To reproduce, cabal unpack bytestring-lexing and try installing it. Installation will fail, then manually alex the .x files in Data/ByteString/Lex{,/Lazy} and try ghci'ing to them, doing the modification I did and ghci'ing again. -- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/