(Sorry for the late reply; have been on holiday.)
No problem. Your email system was kind enough to say when you'd be back :-)
I've used it to diff fairly large files (hundreds of K's, if not Megs) where there were few differences. It seemed to perform OK, and in cases where GNU diff (or whatever comes with MSYS) failed.
Thanks for posting the code. It works on pretty large data sets (for example, a thousand Strings each) and I have a hunch that if I use Data.ByteString it would even work fast enough on my quarter meg text files (split on words, ~40,000 and ~50,000 words each) to use in place of GNU sdiff or diff. Did you use FastPackedString or ByteString to get performance you alluded to? I'll return with the results of my experiments with ByteString and Diff, although I imagine it should be pretty fast since darcs is able to get acceptable speed on large datasets using (I think) ByeString and a Haskell implementation of Myers diff. Cheers, Jared. -- http://www.updike.org/~jared/ reverse ")-:"