* About setf extensions
@ 2013-02-15 13:07 Xue Fuqiao
0 siblings, 0 replies; 3+ messages in thread
From: Xue Fuqiao @ 2013-02-15 13:07 UTC (permalink / raw)
To: help-gnu-emacs
In (info "(cl) Setf Extensions"):
Most of these have directly corresponding "set" functions, like
`use-local-map' for `current-local-map', or `goto-char' for
`point'. A few, like `point-min', expand to longer sequences of
code when they are used with `setf' (`(narrow-to-region x
(point-max))' in this case).
I don't understand the `point-min' example. What does the "x" mean
here? I know it is the START argument of `narrow-to-region', but where
is it from? And where will it be used? Thanks.
--
Best regards, Xue Fuqiao.
http://www.emacswiki.org/emacs/XueFuqiao
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: About setf extensions
[not found] <mailman.20013.1360933676.855.help-gnu-emacs@gnu.org>
@ 2013-02-15 14:11 ` Michael Heerdegen
2013-02-15 14:48 ` Stefan Monnier
1 sibling, 0 replies; 3+ messages in thread
From: Michael Heerdegen @ 2013-02-15 14:11 UTC (permalink / raw)
To: help-gnu-emacs
Xue Fuqiao <xfq.free@gmail.com> writes:
> In (info "(cl) Setf Extensions"):
>
> Most of these have directly corresponding "set" functions, like
> `use-local-map' for `current-local-map', or `goto-char' for
> `point'. A few, like `point-min', expand to longer sequences of
> code when they are used with `setf' (`(narrow-to-region x
> (point-max))' in this case).
>
> I don't understand the `point-min' example. What does the "x" mean
> here? I know it is the START argument of `narrow-to-region', but where
> is it from? And where will it be used? Thanks.
I guess it's the value the generalized variable `(point-min)' should be
set to. I.e.,
(setf (point-min) x)
is translated to
(narrow-to-region x (point-max))
This seems reasonable, because afterwards, (point-min) will give x.
Regards,
Michael.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: About setf extensions
[not found] <mailman.20013.1360933676.855.help-gnu-emacs@gnu.org>
2013-02-15 14:11 ` About setf extensions Michael Heerdegen
@ 2013-02-15 14:48 ` Stefan Monnier
1 sibling, 0 replies; 3+ messages in thread
From: Stefan Monnier @ 2013-02-15 14:48 UTC (permalink / raw)
To: help-gnu-emacs
> Most of these have directly corresponding "set" functions, like
> `use-local-map' for `current-local-map', or `goto-char' for
> `point'. A few, like `point-min', expand to longer sequences of
> code when they are used with `setf' (`(narrow-to-region x
> (point-max))' in this case).
> I don't understand the `point-min' example. What does the "x" mean
> here?
(setf (point-min) x) gets turned into (narrow-to-region x (point-max)).
Stefan
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