Re: Problems with xml-parse-string

[Wojciech Meyer]

Sorry, I don't underdand your point at all. did you hear about
abstract data structures?

On 9/24/10, Lars Magne Ingebrigtsen <address@hidden> wrote:
> Chong Yidong <address@hidden> writes:
>
>>> The main difference between sxml and xml.el output is that it has the
>>> weird an unnecessary "@" node for the attributes and that it wastes a
>>> cons in the attributes, isn't it?
>>
>> The xml.el output always has an alist for attributes after each tag; if
>> there are no attributes, the element after the tag name is nil.  In
>> sxml, the `@' denotes an attribute list, which is omitted if no
>> attributes exist.
>
> Yes.  So it's yet another irregularity you have to check for.
>
> To take a concrete example: You want the src of the img node you have.
>
> xml.el:  (cdr (assq 'img (cadr node)))
> sxml.el: (if (and (consp (cadr node))
>                   (eq (caadr node) '@))
>              (cadr (assq 'img node)))
>
> (And I'm not even sure that's correct.  It's probably not.  Which is my
> point.)
>
> libxml: (cdr (assq :img (cdr node)))
>
> (The difference between libxml and xml.c for attributes is minuscule.)
>
>>> Other than that it has the same problem that xml.el has, in that text
>>> nodes have to be special-cased, so you can't say assq or use simple
>>> descent without testing.
>>
>> It is illogical to criticize sxml for wasting conses, while arguing for
>> wrapping each text node in a cons.
>
> No, it is not.  I'm sacrificing space for speed and regularity.  sxml
> wasting cons cells, and adding slowdowns at the same time.
>
>> Anyway, it is difficult to see how real the problem is without a
>> concrete example.  Could you provide one?  I suspect that the real
>> problem, if one exists, is Elisp's relatively weak support for list
>> mapping and reduction; if that's the case, the correct solution is to
>> pull in some of the relevant functions from the CL package.
>
> Here's a pretty piece of code, chosen at random:
>
> (defun nnrss-find-el (tag data &optional found-list)
>   "Find the all matching elements in the data.
> Careful with this on large documents!"
>   (when (consp data)
>     (dolist (bit data)
>       (when (car-safe bit)
>       (when (equal tag (car bit))
>         ;; Old xml.el may return a list of string.
>         (when (and (consp (caddr bit))
>                    (stringp (caaddr bit)))
>           (setcar (cddr bit) (caaddr bit)))
>         (setq found-list
>               (append found-list
>                       (list bit))))
>       (if (and (consp (car-safe (caddr bit)))
>                (not (stringp (caddr bit))))
>           (setq found-list
>                 (append found-list
>                         (nnrss-find-el
>                          tag (caddr bit))))
>         (setq found-list
>               (append found-list
>                       (nnrss-find-el
>                        tag (cddr bit))))))))
>   found-list)
>
> The horror!
>
> --
> (domestic pets only, the antidote for overdose, milk.)
>   address@hidden * Lars Magne Ingebrigtsen
>
>
>

-- 
Sent from my mobile device