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Common Lisp

Not everyone may be aware of the Common Lisp effort currently going on.
All of the post-Maclisp lisp systems are currently developing a common
subset of lisp which they will all be compatible with, allowing programs
to be written to operate on any of these lisps.  In addition to portability,
an important goal is to fix many of the long-standing problems with the
Maclisp language, providing a cleaner, more consistent language.

There will be a carefully-maintained manual for this Common Lisp
language which all the systems will follow.  This effort is expected to
bear fruit around the end of this year.  The lisp systems currently
involved are Lisp Machine Lisp (in all its incarnations, MIT and
commercial), CMU's Spice Lisp, and the various NILs (VAX and S-1
currently, pdp-10 later).

When the Lisp Machine adopts Common Lisp, there will be a number of
incompatible changes.  These changes will all be made at the same time
and will be announced a couple of months in advance.  As far as possible
changes will be made in an upward-compatible fashion so that old
programs will continue to work, but there will be several cases where
this will not be possible.  Where a Lisp Machine feature is changed,
both the old version and the new version will be present during an
interim period.  I expect that the changed Lisp Machine system will not
be installed until after the Common Lisp manual is published and
available.  We will attempt to make this changeover as painless as
possible, however you should expect some pain.

There are no plans to convert pdp-10 and Multics Maclisp to Common Lisp.
There will be a partial compatibility package, but Maclisp will not be
able to adopt some of the more difficult features of Common Lisp.  The
Lisp Machine will continue to provide for the ability to run programs
that also run in Maclisp.

Details of these changes will be announced later when we know what they are.
This message is just to make sure that everyone knows what is happening.