About elements in `format-alist'

About elements in `format-alist'

[Xue Fuqiao]

Hi list,

In the doc string of `format-alist':

  Elements are of the form
  (NAME DOC-STR REGEXP FROM-FN TO-FN MODIFY MODE-FN PRESERVE).

There should be 8 elements in each list.  But there are only 7 elements
in each list of the default value.  Which one is absent?  If there's an
optional element, I think we should mention it in the doc string.

--
Best regards, Xue Fuqiao.
http://www.gnu.org/software/emacs/

Re: About elements in `format-alist'

[Michael Heerdegen]

Xue Fuqiao <xfq.free@gmail.com> writes:

> Hi list,
>
> In the doc string of `format-alist':
>
>   Elements are of the form
>   (NAME DOC-STR REGEXP FROM-FN TO-FN MODIFY MODE-FN PRESERVE).
>
> There should be 8 elements in each list.  But there are only 7 elements
> in each list of the default value.  Which one is absent?  If there's an
> optional element, I think we should mention it in the doc string.

Looks like missing elements are just treated as if they were nil (the
code uses `nth').

Dunno if it's worth the trouble of making a bug report - since holding
the convention doesn't make problems (does it?).


Regards,

Michael.

Re: About elements in `format-alist'

[Xue Fuqiao]

On Tue, Jun 18, 2013 at 6:24 AM, Michael Heerdegen
<michael_heerdegen@web.de> wrote:
> Xue Fuqiao <xfq.free@gmail.com> writes:
>
>> Hi list,
>>
>> In the doc string of `format-alist':
>>
>>   Elements are of the form
>>   (NAME DOC-STR REGEXP FROM-FN TO-FN MODIFY MODE-FN PRESERVE).
>>
>> There should be 8 elements in each list.  But there are only 7 elements
>> in each list of the default value.  Which one is absent?  If there's an
>> optional element, I think we should mention it in the doc string.
>
> Looks like missing elements are just treated as if they were nil (the
> code uses `nth').

Thanks.  May I install the following patch to trunk?

=== modified file 'lisp/format.el'
--- lisp/format.el    2013-01-01 09:11:05 +0000
+++ lisp/format.el    2013-06-17 22:57:24 +0000
@@ -101,6 +101,7 @@
   "List of information about understood file formats.
 Elements are of the form
 \(NAME DOC-STR REGEXP FROM-FN TO-FN MODIFY MODE-FN PRESERVE).
+If an element list is not that long, the excessive part is taken as nil.

 NAME    is a symbol, which is stored in `buffer-file-format'.

--
Best regards, Xue Fuqiao.
http://www.gnu.org/software/emacs/

Re: About elements in `format-alist'

[Stefan Monnier]

>  \(NAME DOC-STR REGEXP FROM-FN TO-FN MODIFY MODE-FN PRESERVE).
> +If an element list is not that long, the excessive part is taken as nil.

It's OK to add it, but at the same time it's not worth the trouble,
because it's a general convention: in 99% of the cases nil is treated
identically to (cons nil nil).  I.e. it's only when this equivalence is
not followed that we should mention it.


        Stefan