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System 72 released

System 72 is now officially released.  It comes with microcode 774.
There are a large number of important changes in this system, so this
message summarizes them first:

The BREAK key is no longer special in Supdup and Telnet
The semantics of RETURN-FROM have been changed
RETURN with one argument treats multiple values differently
Minor compiler changes
New commands in the error handler for special variables, single-stepping,
 and new functions BREAKON, UNBREAKON
New display in the who-line: active network servers
Name changes: process-create, tv:define-blinker, :which-operations-p,
  :handle-message-p, time:chaos-time, time:print-chaos-times obsolete
Changes to patch and make-system systems
Changes to #\ syntax:  #\I is now #\ROMAN-I, #\CONTROL-Q is new
Site configuration changes

>> Supdup and Telnet escape key.

The crock wherein both Network and Break work as the Telnet and Supdup
escape character has finally been declared obsolete.  There is now only
one escape character, and its initial default setting is to the Network
key, which was put on the keyboard precisely for that purpose.


RETURNs inside the arguments of a RETURN-FROM no longer return to the
place specified by the RETURN-FROM.  Now, they return to the innermost
PROG.  Example:

  (SETQ A (PROG ()
            (RETURN-FROM FOO (RETURN 1)))))

returns 1 from the inner PROG, and sets A to 1.

Note well: this improvement is incompatible with something the manual
tells you to do, under RETURN-LIST.

>> Multiple values:

RETURN and RETURN-FROM with only one expression-argument, such as
(RETURN (FOO)) and (RETURN-FROM BAR (FOO)), now pass back all the
values of that argument.  The canonical way to return a specific
sequence of values now is (RETURN (VALUES A B C)), etc.

For compatibility, RETURN and RETURN-FROM with several
expression-arguments still return the first value only of each one.
If you want to make sure to return precisely one value, do

RETURN-LIST is logically superfluous, since it is the same as
(RETURN (VALUES-LIST ...)), but it is still supported.

MULTIPLE-VALUE-RETURN is now the same as RETURN, and will eventually be
flushed.  You'll get a compiler warnings if you are using it.

>> Compiler changes:

An undeclared free variable now gets a "declared special" warning for
each function in which it appears free.

LET, LET*, VALUES and VALUES* are no longer macros.

>> Error handler:

You can now look at the special bindings of a frame with the
Control-Meta-S command, or at the binding of a particular variable as
visible in a given frame with Meta-S.

The error handler can now be used to step through compiled or
interpreted code.  In compiled code it stops on function calls and
returns.  In interpreted code it does essentially what the old stepper
does, though with different commands and output.  Stepping is done using
the "trap on exit" bits of stack frames and the "trap on call" bits
of stack groups.

The commands C-X, M-X and C-M-X control "trap on exit".  C-X toggles
the trap on exit bit of the frame you are looking at.  If the bit is
set, returning from or throwing through the frame causes a trap to the
error handler, which you can continue from with C-C.  M-X sets the bit
for the current frame and all outer frames.  C-M-X clears the bit for
all those frames.  Setting the bit for a lot of frames is useful for
seeing how far out a looping program is getting.

M-D controls "trap on call".  It toggles a bit which, if set, causes
the next function call to trap to the error handler.  You proceed\n from the trap with C-C.  The frame of the call that trapped is
automatically set to trap on exit as well.

C-D continues from an error and sets the "trap on call" bit as well.

You can start stepping at any error using one of the above commands.
Alternatively, do (BREAKON 'FOO) to cause a trap on calling FOO.
(UNBREAKON 'FOO) turns this off.  BREAKON can take a second arg
whose value is a condition on which to trap; if you specify several
conditions for the same function (using multiple calls to BREAKON),
a trap occurs if any condition is true.  UNBREAKON also accepts
a second arg, which says which condition to take away.  With only
one arg, UNBREAKON removes all break conditions.

Every error now signals SOME condition.  Random macrocode errors
signal NIL, and random microcode errors signal condition :ERROR.

You can now declare that a function is an "error reporter".  This
means that its function is to test for and report errors, and errors
detected inside it should be reported as having happened in the
error-reporting function's caller rather than in the error-reporting
function itself.  FOr example, FERROR is now an error-reporting
function.  Make this declaration by giving the function name
a non-nil :ERROR-REPORTER property.

>> Who-line display.

The who-line now displays information about any servers which are
running at the present time.  This information is displayed in the same
portion of the who-line as file transactions.  For instance, if your
who-line says "BAND-TRANSFER serving CADR-3", then CADR-3 is currently
using your BAND-TRANSFER server.  If your wholine says "3 Active
Servers", then there are three other processes trying to use your
machine remotely.  You can find out more about them by saying
(TV:DESCRIBE-SERVERS).  Should you wish to make them go away, the
incantation is (TV:CLOSE-ALL-SERVERS <reason>), where <reason> is a
string.  This is done automatically in such functions as DISK-RESTORE.

>> Naming.

The battle for naming consistency continues to be waged: PROCESS-CREATE
has been renamed to MAKE-PROCESS, and TV:DEFINE-BLINKER has been renamed
to TV:MAKE-BLINKER.  The old names will continue to work indefinitely.

DEFSELECT and the STREAM-DEFAULT-HANDLER now both understand the
:OPERATION-HANDLED-P and :SEND-IF-HANDLES messages, just as all flavor
instances do.  So it should now be safe to use these messages on
any stream in the system.  The old names :WHICH-OPERATIONS-P and
:HANDLE-MESSAGE-P have been flushed; use :OPERATION-HANDLED-P.

>> Marking Systems as experimental, released, obsolete, etc.

Systems (of the patch and make- sort) now have a status associated with
them, which is displayed when the machine boots and in the label.  It is
updated by (SI:LOAD-PATCHES).  Currently defined statuses are
recompiled, the status of the new system version that creates is set to
:EXPERIMENTAL.  (This can in fact be overridden by the :INITIAL-STATUS
argument to DEFSYSTEM.)  The function SI:SET-SYSTEM-STATUS can then be
used to declare the system released or broken as needed.  The format of
patch directories is not compatible, but the old format is recognized
and converted (giving a status of :RELEASED) when necessary (e.g. Add
Patch or SET-SYSTEM-STATUS), so users should not need to do anything to
their systems that don't need compiling.

>> Syntax for characters.

The names of the Roman numeral keys have been changed from #\I, #\II,
etc. to #\ROMAN-I, #\ROMAN-II, etc.  The old names will no longer work.
If you have a program that uses these names, you will get an error if
you try to recompile it or load its source; all you have to do is switch
to the new names.  The reason for this change is to remove an ambiguity
regarding the letter "I" in the following new feature:

It works to say #\Control-Meta-B, #\HYPER-SUPER-CTRL-, and so on.  In
specifying the names of the shift keys, case is ignored, they cn be in
any order, and CTRL can be spelled either "CONTROL" or "CTRL".  If the
last character is non-alphanumeric (e.g. a parenthesis), it should be
slashified as usual.  (The old way to do this was with things like
#/B and #/.  This old syntax will continue to work, but the new
one is, for obvious reasons, preferrable in new programs.)

>> Various new functions and macros on the GLOBAL package.

A macro that helps you define macros, ONCE-ONLY, has been installed.
See LMMAN; MACROS > for documentation.  PROCESS-WAIT-WITH-TIMEOUT is
like PROCESS-WAIT but lets you specify a timeout as well; see LMMAN;
PROCES >.  FIXNUMP and FLONUMP of one argument exist and have the
obvious meanings.

ZWEI:LOAD-FILE-INTO-ZMACS allows loading a file into the file editor\n from an init file or otherwise outside the editor context.

The functions TIME:CHAOS-TIME and TIME:PRINT-CHAOS-TIMES have been
renamed to CHAOS:HOST-TIME and CHAOS:PRINT-HOST-TIMES for the sake of
systems without chaosnets.

>> Site configuration changes

The way the system keeps track of network hosts, console locations, file and
time servers, default host for logging in, presence of special devices such
as dover and elevator, and other details of the site-specific configuration
has been changed.  See MMcM if this affects you (it probably doesn't).