Re: Example use of macro to minimize and generalize the code

[Jean Louis <bugs@gnu.support>]

* Michael Heerdegen <michael_heerdegen@web.de> [2021-06-01 02:38]:
> 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.

I appreciate all comments.

> 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.

You guessed it well, I am using it this way:

(defun hyperscope-tabulated-action (&optional id)
  (interactive)
  (when-tabulated-id "hyobjects" id
    (hyperscope-ring id)
    (hyperscope-action id)))

As there are many different tables which all have its ID, so the macro
has to make sure it is invoked in the right table. There could be
other ways to check that. 

Programs have their lexical binding true, maybe that one you did not
expect.

Such functions can be invoked programmatically or interactively,
interactively there is check if there is right database table in the
tabulated-list-mode, as otherwise it gives a warning that it is not
invoked in that other different table.

> Normally the byte compiler warns about this kind of problem - of course
> only if you don't silence it ;-)

That is why `ignore' is there. Ignore is there to suppress the byte
compiler warning just as you guessed it.

Otherwise:

In when-tabulated-id:
rcd-cf.el:165:45: Warning: Unused lexical argument `id'


-- 
Jean

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