A short high level comparison.
either way, i think it's interesting to ask how much difference vocal support makes for a project. his contributions in various places have been useful and interesting (as far as i noticed) and, at least in my mind, that tended to build a positive image of mercury.
I have a theory that Fergus is actually an AI written by the Mercury team. I base this on the fact that no one is humanly possible of being on so many mailing lists and newsgroups. :-) No matter what odd little language I stumble across, if I look in the mailing list archives I find Fergus has already been there.
I mailed him a similar questions a few months ago asking about the state of Mercury (since the web site has not been updated in a while). He said the project is making good progress, and that review of various of its mailing lists provides a better view of its current state.
I did actually meet Fergus once -- many years ago, at a C++ standards meeting. My guess is that he was just there to see how complex a language the committee could come up with. So, while it's certainly possible that a Mercury AI is responsible for the over 8000 USENET articles -- http://tinyurl.com/383w7 -- that claim a "Fergus Henderson" authorship, there is (or was) at least a warm body claiming that identity.
So that's what it takes to get to work for Galois, eh? I guess I have around 7000 more articles to write ... and one more language to invent.
I used to have the desk next to Fergus back in the day. I can confirm that he does exist, and he really does post that much. If it helps, I'm not entirely convinced that he sleeps.
True story: When he was doing his honours year, the only reason he passed was that he gzipped his newsrc file and sent it to two friends, with the instruction that it not be sent back to him until his thesis was finished.