[no subject]

	I understand your worry about sequences etc. Maybe we could try
to split the effort of studying issues a little. I dunno. It was just
a spur of the moment thought.
			-rpg-

â??19-Jan-82  1448	Feigenbaum at SUMEX-AIM 	more on common lisp
Date: Tue, 19 Jan 1982 18:43:00 -0000
From: Feigenbaum at SUMEX-AIM
Subject: more on common lisp
To:   gabriel at SU-AI

Mail-from: ARPANET host PARC-MAXC rcvd at 19-Jan-82 1331-PST
Date: Tue, 19 Jan 1982 17:12:00 -0000
From: Masinter at PARC-MAXC
to: Feigenbaum@sumex-aim
Subject: Common Lisp- reply to Hedrick

It is a shame that such misinformation gets such rapid dissemination....

Date: Tue, 19 Jan 1982 16:57:00 -0000
From: Masinter at PARC-MAXC
Subject: Re: CommonLisp at Rutgers
To: Hedrick@Rutgers
cc: Masinter

A copy of your message to "bboard at RUTGERS, griss at UTAH-20, admin.mrc at
SU-SCORE, jsol at RUTGERS" was forwarded to me. I would like to rebut some of
the points in it:

I think that Common Lisp has the potential for being a good lisp dialect which
will carry research forward in the future. I do not think, however, that people
should underestimate the amount of time before Common Lisp could possibly be a
reality.

The Common Lisp manual is nowhere near being complete. Given the current
rate of progress, the Common Lisp language definition would probably not be
resolved for two years--most of the hard issues have merely been deferred (e.g.,
T and NIL, multiple-values), and there are many parts of the manual which are
simply missing. Given the number of people who are joining into the discussion,
some drastic measures will have to be taken to resolve some of the more serious
problems within a reasonable timeframe (say a year).

Beyond that, the number of things which would have to be done to bring up a
new implementation of CommonLisp lead me to believe that the kernel for
another machine, such as the Dec-20, would take on the order of 5 man-years at
least. For many of the features in the manual, it is essential that the be built
into the kernel (most notably the arithmetic features and the multiple-value
mechanism) rather than in shared Lisp code. I believe that many of these may
make an implementation of Common Lisp more "difficult to implement efficiently
and cleanly" than Interlisp.

I think that the Interlisp-VAX effort has been progressing quite well. They have
focused on the important problems before them, and are proceeding quite well. I
do not know for sure, but it is likely that they will deliver a useful system
complete with a programming enviornment long before the VAX/NIL project,
which has consumed much more resources. When you were interacting with the
group of Interlisp implementors at Xerox, BBN and ISI about implementing
Interlisp, we cautioned you about being optimistic about the amount of
manpower required. What seems to have happened is that you have come away
believing that Common Lisp would be easier to implement.  I don't think that is
the case by far.

Given your current manpower estimate (one full-time person and one RA) I do
not believe you have the critical mass to bring off a useful implemention of
Common Lisp. I would hate to see a replay of the previous situation with
Interlisp-VAX, where budgets were made and machines bought on the basis of a
hopeless software project. It is not that you are not competent to do a reasonable
job of implementation, it is just that creating a new implementation of an already
specified language is much much harder than merely creating a new
implementation of a language originally designed for another processor.

I do think that an Interlisp-20 using extended virtual addressing might be
possible, given the amount of work that has gone into making Interlisp
transportable, the current number of compatible implementations (10, D, Jericho,
VAX) and the fact that Interlisp "grew up" in the Tenex/Tops-20 world, and that
some of the ordinarily more difficult problems, such as file names and operating
system conventions, are already tuned for that operating system. I think that a
year of your spare time and Josh for one month seems very thin.

Larry
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