Trying to build from the current repo with ghc 6.8.2 on Ubuntu 8.10, I
get this:

  $ runghc Setup build
  Preprocessing library darcs-2.2.0...
  Preprocessing executables for darcs-2.2.0...
  Building darcs-2.2.0...
  /usr/bin/ar: creating dist/build/libHSdarcs-2.2.0.a
  [ 17 of 134] Compiling Context          ( src/Context.hs, dist/build/darcs/darcs-tmp/Context.o )

  src/Context.hs:3:55:
      lexical error in string/character literal at character '/'

Here are the first few lines of src/Context.hs:

------
module Context (context) where
context :: String
context ="# configured Tue Feb 10 22:04:27 GMT 2009\n\
\./configure /usr/local/share/config.site /usr/local/etc/config.site\n\
\\n\
\Context:\n\
\\n\
\[add list_authors-style canonicalizing to the show authors command\n\
\Simon Michael <simon@joyful.com>**20090207232835\n\
\ Ignore-this: deac150ed2e2de58442e8fd398c9b14e\n\
\] \n\
\\n\
\[add .authorspellings file appropriate for our repo\n\
\Simon Michael <simon@joyful.com>**20090207235751\n\
\ This .authorspellings file is equivalent to the old hard-coded\n\
\ spellings in list_authors.hs. With this in place, darcs show authors\n\
\ gives the same output as list_authors.\n\
\] \n\

I can't reproduce this on GHC 6.8.2 on a Slackware box with the fragment you
give. Could you attach the entire failing Context.hs file?

Please run make maintainer-clean and try again. Building with cabal from 
"dirty" working directory (with existing autoconf build in it) is not supported.