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Issue: PUSH-EVALUATION-ORDER (Version 2)
- To: cl-cleanup@SAIL.STANFORD.EDU, peck@Sun.COM
- Subject: Issue: PUSH-EVALUATION-ORDER (Version 2)
- From: David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>
- Date: Sun, 8 Nov 87 15:20 EST
- In-reply-to: <871023-103240-6617@Xerox>
This is fine with me except for a couple of minor corrections noted
Date: 23 Oct 87 10:32 PDT
I removed all but the :ITEM-FIRST
proposal, extended it to include INCF, DECF, PUSHNEW, and macros which
are created with DEFINE-MODIFY-MACRO
You forgot to add these to the References field, although they are
mentioned in the text in a couple of places. It would probably be
better to list everything that's going to be affected in the References
field, so no one gets confused.
Explicitly state that for the macros that manipulate generalized
variables (PUSH, PUSHNEW, INCF, DECF, SHIFTF, ROTATEF, PSETF, SETF and
those defined with DEFINE-MODIFY-MACRO) the subforms of the macro
"of the macro call", to be strictly accurate.
(including but not limited to those of the generalized variable
reference) are evaluated exactly as many times as they appear in the
source program, and in exactly the same order as they appear in the
For example, PUSH is expected to behave as if described as:
(PUSH Item Place) is generally equivalent to (SETF Place (CONS Item
except that the subforms of Place are evaluated only once, and Item
is evaluated before Place."
I wonder why "roughly" changed to "generally".
The phase "subforms of the reference" which appears several times in
CLtL should be made more specific to be "subforms of the
[generalized-variable manipulating macro] arguments".
"subforms of the macro call". Also "subforms" doesn't seem to be
officially defined anywhere, we need to be clear on this (see the
message I sent earlier today, same subject).
Cost of non-adoption:
Obvious programs may be non-portable, although it should be rare that
order of evaluation will effect actual operation.
"affect", unless you're making a very subtle joke here.
David Moon (Symbolics) argues that the unstated intention of page 99
is the definition of the language, while admitting that:
"The quoted paragraphs could be taken to restrict order of evaluation
of the subforms of (CAR (ref2)), not all of the subforms of the PUSH
I think you ought to put back the other part of my comment, since in
removing it my argument is eviscerated. The paragraph on p.99 two
paragraphs after the one referenced makes it clear, at least to me,
that "subforms of generalized-variable references" was a typo, since
it discusses order of things that aren't such subforms.
I'll send out a proposed revision of the discussion in a second message,
in just a moment.