Re: A question about category name in ELisp

[Xue Fuqiao]

On Sat, Oct 5, 2013 at 8:41 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>> Date: Sat, 5 Oct 2013 18:43:27 +0800
>> From: Xue Fuqiao <xfq.free@gmail.com>
>>
>> I have a question about category and category table.  In (info
>> "(elisp) Categories"):
>>
>>     Each category has a name, which is an ASCII printing character in
>>   the range ‘ ’ to ‘~’.  You specify the name of a category when you
>>   define it with ‘define-category’.
>>     The category table is actually a char-table (*note Char-Tables::).
>>   The element of the category table at index C is a "category set"—a
>>   bool-vector—that indicates which categories character C belongs to.
>>   In this category set, if the element at index CAT is ‘t’, that means
>>   category CAT is a member of the set, and that character C belongs to
>>   category CAT.
>>
>> >From the second paragraph, my impression about a category table is
>> something like this:
>>
>> |     | a   | -   | .   | "   |
>> |-----+-----+-----+-----+-----|
>> | bv1 | bv2 | bv3 | bv4 | bv5 |
>>
>> (The first row contains the indices of the char-table (i.e., the
>> "index C" above), and the second row contains the elements at index
>> C1, C2, ... (i.e., it's a category set, which is a bool-vector.))
>>
>> As with all arrays, bool-vector indices start from 0, so CAT should be
>> an integer.  But according to my understanding, CAT is a category
>> name, which should be an ASCII printing character (instead of just an
>> integer, from the first paragraph).  Why?  Am I missing something?
>
> You need to read about char-table, your assumption about its structure
> is wrong.  In particular, a char-table is not a flat array, and it is
> indexed by characters, not by zero-based integers.

Thanks, but IIUC I think bool-vector (the "category set") is not a
char-table.  The "category table" is a char-table.

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