It's not just "LOOP vs DO"...

[Kent M. Pitman <KMP at MIT-MC>]

I might point out that Dick Waters (DICK@ML) is working on some macros
for iteration which looks like it may have much the same expressive
power as LOOP but in a far more natural notation. There is a small
community of users now experimenting with his package (called letS) and
he's working on a paper about it. It is not quite ready even for release
yet and I certainly wouldn't propose it be considered for a standard
anytime soon, but it does show a lot of promise ... On the other hand, I
think there's not a clear concensus that LOOP is the right thing. I'll
agree with LOOP people that more abstraction on LOOPs are needed than
just DO but I'm not sure that LOOP is the right answer (I'd certainly
never use it) ...  and I'd like to avoid people standardizing on
anything so controversial as LOOP while experimentation is still ongoing
with things that may prove as good. So in my mind, LOOP should
definitely not be in the white pages at this time and more importantly I
think people should keep their eyes open to other alternatives. It's not
like DO and LOOP are the only directions that things can go. Dave
Chapman (ZVONA@MC) had a very interesting macro called DO& which was yet
another alternative... I'm sure there are others.  From the point of
view of a standard, I think it's most reasonable to pick accepted
technology for the white pages and there I think DO and DO* are simple,
powerful (computationally adequate for writing any kind of loop), and
perhaps most importantly to the standard, have very well-understood and
well-accepted semantics.
-kmp