
		     Announcing CScheme Release 5

There are many changes with respect to release 4, including:

- The base language is the dialect described in the "Revised^3 Report
on the Algorithmic Language Scheme" (MIT AI Memo 848a, SIGPLAN Vol. 21
Number 12, Dec. 1986), with the following exceptions:

1. (eqv? "" "")   -> unspecified, instead of #T

The reason is because of the non-standard operation SET-STRING-LENGTH!
which MIT Scheme defines, and which makes empty strings not be
operationally equivalent to each other.  The standard may be changed
next time it is revised.

2. Numerical exactness/inexactness is not yet implemented.  Support
for this (reader syntax and procedures) is defined, but for the most
part is unimplemented.  For the most part this means that you can
annotate your programs with exactness information, but it will have no
effect.

- Better performance.  Many subsystems (noticeably the reader) have
been rewritten and the microcode has been tuned in a few places.

- New interface to GNU Emacs.  The scheme runtime system does things
slightly differently when running under GNU Emacs than when running
from a terminal.

- New "cross-syntaxer" with new declarations and more functionality.
The new "cross-syntaxer" performs full beta substitution, available to
users.  USUAL-INTEGRATIONS now includes some standard optimizations
like integrating cadr, caddr, +, -, etc.

	How can it be obtained?

The usual way.  The version distributed from prep.ai.mit.edu is now
the beta test version of rel 5.  You can ftp to prep (log in as
scheme, password scheme) and get the file /scheme/dist.tar (or
/scheme/dist.tar.Z if you have compress/uncompress on your machine).
Alternatively you can get it from zurich.ai.mit.edu, logging in as
guest, password guest.

	Some remarks and notices of upcoming distractions:

CScheme is now MIT's main implementation, so the level of support will
increase.  The main implementation used to be a hand-coded 68k
assembly language interpreter (Chipmunk/Gator Scheme) running under
HP's Pascal workstation system.

A new compiler (Liar 3) is being written for CScheme.  Currently it is
in alpha test, and should be available for beta test soon.  Right now
there are only 2 back ends for the compiler: one for the MC68020
processor (our main development machine is the hp9000s300, which is
68020 based), and one for the HP spectrum processor (the hp9000s800).
We plan to also provide a Vax back end, and later a C back end.  When
the compiler is released, there will be documentation on how to write
a new back end for the compiler, so it can be ported to other
machines.  Please let us know if you would like to receive a beta test
version of the compiler as soon as it is available.

The Edwin editor will be ported to CScheme as soon as the compiler is
released.  Initially it will probably only be supported under the X
window system, but later we may provide a terminal independence
package.  Edwin is a full Emacs-like editor written in Scheme, and
very similar to GNU Emacs (major parts of Edwin were translated from
GNU Emacs).  A restricted version of Edwin runs on the TI and IBM PCs
under TI PC Scheme.

We will also provide an X graphics package sometime soon; the X
library has been ported into Scheme and is being debugged.  Currently
the only graphics we provide are for the hp9000s300, based on starbase
and using a 300h display.
