MULTIPLE-VALUE error checking

[JONL at MIT-MC (Jon L White)]

I've refined the error checking for MULTIPLE-VALUE/MULTIPLE-BIND:
    Date: 5 February 1981 00:30-EST
    From: William G. Dubuque <WGD at MIT-MC>
    Why does (MULTIPLE-VALUES (A B) (VALUES 1 2)) lose? Also, why doesn't
    (MULTIPLE-VALUE (A) ...) do the correct thing instead of losing; this
    would be important for automatically generated code. ... also
    for instance, we have (MULTIPLE-VALUE (A) 1) ).
In the cases where 0 or 1 variables are being set, the expander will now 
permit atomic evaluations, and produce a "simple" SETQ or LET.   The
problem with (MULTIPLE-VALUES (A B) (VALUES 1 2)) is more subtle, and
the correction for it is simply to special-case the "evaluations" which
call VALUES or VALUES-LIST;  in particular, VALUES is a macro which
expands into (PROG1 ...)  and in general, a PROG1 can't work there (but
of course this specific prog1 is setting up the values vector ...)
    .  .  .
	    PS, MULTIPLE-VALUE should also work with () as first arg, as it
    does on the Lispm (also with 1 arg).
Right, fixed -- a null varlist just "calls the function", or whatever.
    .  .  .I think the sysp check should either
    by eliminated or changed to an appropriate warning.
It's more accurate now.  But a general problem with these system macros
is that there are many places where "abnormalities" are found, and a
specific diagnosis would require many more words of memory to store
the specific msgs;  until we're willing to give up a lot more address
space, we'll just have to make do with a single message saying that the
expansion didn't make it.  LET, DEFUN& and DEFMACRO are other system
macros which come to mind.