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Re: About setf extensions


From: Michael Heerdegen
Subject: Re: About setf extensions
Date: Fri, 15 Feb 2013 15:11:21 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux)

Xue Fuqiao <address@hidden> 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.



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