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From: Michael Heerdegen <michael_heerdegen@web.de>
To: help-gnu-emacs@gnu.org
Subject: Re: Example use of macro to minimize and generalize the code
Date: Tue, 01 Jun 2021 01:37:28 +0200	[thread overview]
Message-ID: <87y2buscef.fsf@web.de> (raw)
In-Reply-To: YLVXslhB17GNcQTT@protected.localdomain

Jean Louis <bugs@gnu.support> writes:

> (defmacro when-tabulated-id (table id &rest body)
>   (declare (indent 2) (debug t))
>   (ignore id)
>   `(if id
>        (progn
> 	 ,@body)
>      (if (or (eq ,table 'any)
> 	     (string-equal ,table rcd-current-table))
> 	 (let ((id (tabulated-list-get-id)))
> 	   (if id
> 	       (progn ,@body)
> 	     (message "Did not get ID")))
>        (message "This function is for table `%s' only" ,table))))

There is something wrong with that definition however: the variable `id'
is completely ignored, specifying something at that argument position is
redundant.

Tt may "work" by accident if the symbol `id' happens to be dynamically
bound to the same thing that you specify as argument, but only when that
exact variable name is used and only in dynamically binding Lisp.
Normally the byte compiler warns about this kind of problem - of course
only if you don't silence it ;-)

Michael.




  reply	other threads:[~2021-05-31 23:37 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-30 22:48 Why is defun not executed during load-file? Drew Adams
2021-05-30 22:57 ` Emanuel Berg via Users list for the GNU Emacs text editor
2021-05-31  2:05   ` [External] : " Drew Adams
2021-05-31  2:56     ` Emanuel Berg via Users list for the GNU Emacs text editor
2021-05-31  5:05       ` Drew Adams
2021-05-31 19:20         ` Emanuel Berg via Users list for the GNU Emacs text editor
2021-05-31 19:47           ` Stefan Monnier via Users list for the GNU Emacs text editor
2021-05-31 20:09             ` Marcin Borkowski
2021-06-07  2:19             ` Emanuel Berg via Users list for the GNU Emacs text editor
2021-06-07  6:27               ` Jean Louis
2021-06-07 14:18               ` FW: " Drew Adams
2021-06-07 14:41                 ` Emanuel Berg via Users list for the GNU Emacs text editor
2021-05-31 21:40           ` Example use of macro to minimize and generalize the code Jean Louis
2021-05-31 23:37             ` Michael Heerdegen [this message]
2021-05-31 23:59               ` Jean Louis
2021-06-01  0:34                 ` Michael Heerdegen
2021-06-01  0:39                   ` Jean Louis
2021-06-01  0:59                     ` Michael Heerdegen
2021-06-01  1:25                       ` Jean Louis
2021-06-01 14:02                         ` Michael Heerdegen
2021-06-01 16:33                           ` Jean Louis
2021-06-01 16:54                             ` Yuri Khan
2021-06-01 17:24                               ` Jean Louis
2021-06-01 17:57                                 ` Yuri Khan
2021-06-01 18:12                                   ` Jean Louis
2021-05-31 21:45           ` Example use of macro to minimize and generalize the code (2) Jean Louis
2021-05-31 21:48           ` [External] : Re: Why is defun not executed during load-file? Michael Heerdegen
2021-05-31 23:41           ` Drew Adams

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