Re: New axes?

> OTOH, I have often wanted an easier XPath way to construct the equivalent of JQuery nextUntil() and prevUntil() -- that would be another topic I suppose.


The current 4.0 proposal is

items-until(following-sibling::*,  ->{@class="note"})

to select all following siblings until (and including) the first where @class="note". Variants items-before, items-after, and items-from are also offered.

With keyword arguments we could now consider repackaging these four functions as one, for example

select-range(following-siblings::*, until :=  ->{@class="note"})

which would allow both starting and ending conditions in a single call

select-range(following-siblings::*, from := -> {@marker='begin'}, to := ->{@marker='end'})

Could also combine this with the proposed slice() function:

select-range($input, start := 10, end := 3, step := -1)

And the equivalent of subsequence could be thrown into the mix:

select-range($input, start := 10, length := 4)

I'm not entirely convinced by the merits off such all-encompassing functions. There's a useful design principle that a function should do precisely one thing, and do it well, and that different things should be done by different functions. There's a balance somewhere. But the ability to define different starting and ending conditions for a range, and use them in arbitrary combinations, does have some appeal.

Michael Kay
Saxonica

> On 3 Dec 2020, at 04:33, Joel Kalvesmaki <kalvesmaki@gmail.com> wrote:
> 
> From my perspective, the difference between next and following, previous and preceding would introduce confusion, since in common usage each pair of terms is generally regarded as synonymous.
> 
> OTOH, I have often wanted an easier XPath way to construct the equivalent of JQuery nextUntil() and prevUntil() -- that would be another topic I suppose.
> 
> jk
> 
> On Wed, Dec 2, 2020 at 10:11 AM Dimitre Novatchev <dnovatchev@gmail.com <mailto:dnovatchev@gmail.com>> wrote:
>   > An alternative would be to introduce new functions:
>   >   
>   >     fn:next-sibling($node as node()?) as node()?
>   >     fn:previous-sibling($node as node()?) as node()? 
> 
>  
> +1 for the functions vs. new axes.
> This can be conveniently combined with the arrow operator:
> 
> $myXpathExpressionSelectingNode => next-sibling()
> 
> Thanks,
> Dimitre
> 
> On Wed, Dec 2, 2020 at 2:08 AM Christian Grün <cg@basex.org <mailto:cg@basex.org>> wrote:
> An alternative would be to introduce new functions:
> 
>   fn:next-sibling($node as node()?) as node()?
>   fn:previous-sibling($node as node()?) as node()?
> 
> Similar to fn:has-children, we cannot perform straightforward node
> tests. The requirement for such tests may depend on the use cases we
> are trying to solve.
> ____________________________________
> 
> On Wed, Dec 2, 2020 at 10:51 AM Michael Kay <mike@saxonica.com <mailto:mike@saxonica.com>> wrote:
> >
> > It's a fairly cosmetic change to get rid of a minor ugliness. People often forget the [1] qualifier when they only want the immediately following sibling, and the difference between preceding-sibling::*[predicate][1] and preceding-sibling::*[1][predicate] isn't intuitive.
> >
> > The problem of course is that you can never get rid of a danger point on a well-trodden road by providing a new shiny road; the very people who fall into the trap will be unaware of the new features.
> >
> > Michael Kay
> > Saxonica
> >
> > On 2 Dec 2020, at 09:38, Norm Tovey-Walsh <norm@saxonica.com <mailto:norm@saxonica.com>> wrote:
> >
> > Michael Kay <mike@saxonica.com <mailto:mike@saxonica.com>> writes:
> >
> > How would anyone feel about adding new axes next::* and previous::* to
> > get the first following/preceding sibling?
> >
> > Or next-sibling / previous-sibling if people prefer long names.
> >
> > It would have to be that next::* means following-sibling::*[1]
> >
> >
> > Can next::* ever be different from (following-sibling::*)[1]?
> >
> > Another two candidates are following-sibling-or-self::* and
> > preceding-sibling-or-self::*, with hopefully obvious semantics.
> >
> >
> > What are the use cases for these?
> >
> > To me, it feels like adding a new axis is a fairly heavyweight change.
> > There are already quite a few axes and I think users sometimes struggle
> > to understand them. I’m not saying we must not add new axes, but I’d
> > like to be convinced that their utility justifies them.
> >
> >                                        Be seeing you,
> >                                          norm
> >
> > --
> > Norm Tovey-Walsh
> > Saxonica
> >
> >
> 
> 
> 
> -- 
> Cheers,
> Dimitre Novatchev
> ---------------------------------------
> Truly great madness cannot be achieved without significant intelligence.
> ---------------------------------------
> To invent, you need a good imagination and a pile of junk
> -------------------------------------
> Never fight an inanimate object
> -------------------------------------
> To avoid situations in which you might make mistakes may be the
> biggest mistake of all
> ------------------------------------
> Quality means doing it right when no one is looking.
> -------------------------------------
> You've achieved success in your field when you don't know whether what you're doing is work or play
> -------------------------------------
> To achieve the impossible dream, try going to sleep.
> -------------------------------------
> Facts do not cease to exist because they are ignored.
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> -------------------------------------
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>  
> 
> 
> -- 
> Joel Kalvesmaki
> kalvesmaki.com <http://kalvesmaki.com/>