Data.ByteString in base fails to build?

[Malcolm Wallace]

Hi,

I'm just building ghc from scratch with the latest darcs sources, and
getting a build failure on Data.ByteString in the base package.  The
error is multiple copies of

     Data/ByteString.hs:301:14: Not in scope: `empty'

at different locations.  Indeed, the module does appear to both export
"empty" and use it many times, but does not define it.

Regards,
    Malcolm