Hmm :-/

I tried replacing regex-compat with regex-compat-xxx in my configure.ac so as to
simulate the failure, but when I do so the configure script fails as it should.
 Really not sure why it would be passing for aslatter.

Here's the relevant piece of his config.log:
=================================8<=================
configure: failed program was:
-- #line 4647 "configure"
import Text.Regex( mkRegex, matchRegex, Regex )
main = seq (mkRegex undefined) (putStr "Hello world.\n")

end of failed program.
configure:4670: result: no; and neither in package regex-compat
configure:4684: checking for module Network.HTTP( urlEncode )
=================================8<=================

Notice how it keeps going after the regex-compat failure

Antoine, is there any chance this is something we've already fixed?  Could you
try with 2.0.0 + 121 patches or higher? (i.e. darcs get http://darcs.net)