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From: Michael Heerdegen <michael_heerdegen@web.de>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: emacs-devel@gnu.org
Subject: Re: Why is FUNC in cl-callf not allowed to be an expression?
Date: Mon, 27 May 2019 02:20:27 +0200	[thread overview]
Message-ID: <877eac3fzo.fsf@web.de> (raw)
In-Reply-To: <jwvlfz3q3ao.fsf-monnier+emacs@gnu.org> (Stefan Monnier's message of "Sat, 18 May 2019 10:09:41 -0400")

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> Indeed, they're closely related but symbol-macrolet does not "evaluates"
> anything at the "binding" site.  Also it can also be used for purposes
> different from "places", e.g. to keep a log of all the accessed to
> a "variable" (tho, we could just as well create a (journaled PLACE)
> pseudo place which would record accesses in the very same way).

I also come to the conclusion that symbol-macrolet and place binding are
two different things.

E.g. in

(macroexpand-all
 '(gv-place-bind ((p (car (cdr x))))
    (progn (cl-incf p) p)))

==>
 (let*
    ((#1=#:v
      (cdr x)))
  (progn
    (setcar #1#
            (1+ #2=(car #1#)))
    #2#))

we want that the (cdr x) "calculation" is factored out because it is
always the same (an "inner place" reference so to say).

OTOH, `symbol-macrolet' might be used for arbitrary calculations.  It
would be surprising (wrong) if in

(symbol-macrolet ((r (list (random))))
  (list r r))

the `random' function would be called only once.

One can't reliably guess from the bound expression which case the coder
wants, so I'll leave s-macrolet as is.

Michael.



  parent reply	other threads:[~2019-05-27  0:20 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-09 21:52 Why is FUNC in cl-callf not allowed to be an expression? Michael Heerdegen
2019-05-10  0:47 ` Stefan Monnier
2019-05-10 11:32   ` Michael Heerdegen
2019-05-10 13:28     ` Stefan Monnier
2019-05-10 14:19       ` Stefan Monnier
2019-05-10 14:22         ` Stefan Monnier
2019-05-10 15:18           ` Michael Heerdegen
2019-05-13 16:47             ` Stefan Monnier
2019-05-14 12:36               ` Michael Heerdegen
2019-05-14 23:32               ` Michael Heerdegen
2019-05-15  2:02                 ` Stefan Monnier
2019-05-15 16:38                   ` Michael Heerdegen
2019-05-15 17:19                     ` Michael Heerdegen
2019-05-16  2:18                       ` Michael Heerdegen
2019-05-16 13:12                     ` Stefan Monnier
2019-05-16 14:37                       ` Michael Heerdegen
2019-05-16 15:09                         ` Michael Heerdegen
2019-05-16 19:34                           ` Stefan Monnier
2019-05-16 21:46                             ` Michael Heerdegen
2019-05-16 23:06                               ` Stefan Monnier
2019-05-17 22:53                                 ` Michael Heerdegen
2019-05-18 14:09                                   ` Stefan Monnier
2019-05-20 23:25                                     ` Michael Heerdegen
2019-05-21  2:01                                       ` Stefan Monnier
2019-05-21  2:47                                         ` Michael Heerdegen
2019-05-21 10:16                                           ` Noam Postavsky
2019-05-21 16:38                                             ` Michael Heerdegen
2019-05-21 17:38                                           ` Stefan Monnier
2019-05-21  7:26                                         ` Andy Moreton
2019-05-23 23:02                                           ` Michael Heerdegen
2019-05-22  1:00                                     ` Michael Heerdegen
2019-05-23  1:50                                       ` Michael Heerdegen
2019-05-23  3:38                                         ` Stefan Monnier
2019-05-23 23:38                                           ` Michael Heerdegen
2019-05-24 15:29                                             ` Stefan Monnier
2019-05-28 19:54                                               ` Michael Heerdegen
2019-05-27  0:20                                     ` Michael Heerdegen [this message]
2019-05-29 17:02                                       ` Stefan Monnier
2019-05-15 19:17                   ` Michael Heerdegen

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