[xquery-talk] arrow operator

[W.S. Hager]

Dear Ghislain,

This I understand, but the only thing that bothers me is that the implicit
binding of the first argument prevents the use of other arguments, whereas
an explicit context would've allowed for the more flexible option of
designating the argument yourself, while the arity would read more clearly:

$position => array:remove($array, .)

This difference with the simple mapping operator is what confuses and
surprises me, but it seems I'm the only one, so let's just leave it at that.

Thanks a lot for your time.

Wouter

2017-08-02 16:08 GMT+02:00 Ghislain Fourny <gfourny at inf.ethz.ch>:

> Dear Wouter,
>
> Indeed, in some cases, whether to use => or ! can be subject to a matter
> of taste.
>
> To put things in perspective, => was introduced in version 3.1, together
> with map and array support. As far as I understand it and looking again at
> the specs, one of the use cases is for => to be used with maps and arrays,
> in an object-oriented style. The XPath and XQuery Functions and Operators
> 3.1 specification [1] explicitly gives a few examples:
>
> ["a", "b", "c"] => array:get(2)
>
> $array => array:remove($position) => array:insert-before($position,
> $member)
>
> Kind regards,
> Ghislain
>
> [1] https://www.w3.org/TR/xpath-functions-31/
>
>
> > On 2 Aug 2017, at 12:09, W.S. Hager <wshager at gmail.com> wrote:
> >
> > That's why, for cases where it's possible, I preferred to write the
> simple mapping operator, as it's easier to read IMO.
> >
> > 2017-08-02 12:07 GMT+02:00 W.S. Hager <wshager at gmail.com>:
> > Hi Ghislain,
> >
> > Alright, I forgot about fn:replace#4, but the implicit binding is
> sometimes hard to detect.
> >
> > Thanks.
> >
> >
> > 2017-08-02 12:04 GMT+02:00 Ghislain Fourny <gfourny at inf.ethz.ch>:
> > ... I didn't get it quite right actually. In @address => string(), there
> is no context item involved, I wrote too fast. :-)
> >
> > New attempt:
> >
> > @address ! string(.) (: explicitly passed context item :)
> > @address ! string() (: context item passed implicitly to string#0, which
> is context-dependent)
> > @address => string() (: @address passed implicitly to string#1 as the
> first parameter via the => operator, but string#1 is context-independent)
> > @address => string(.) (: error: string#2 does not exist :)
> >
> > Kind regards,
> > Ghislain
> >
> >
> > > On 2 Aug 2017, at 12:00, Ghislain Fourny <gfourny at inf.ethz.ch> wrote:
> > >
> > > Dear Wouter,
> > >
> > > There is one more important difference on the syntactic level.
> > >
> > > With the arrow operator, the left-hand-side is implicitly bound to the
> first parameter of the function.
> > >
> > > @address => replace(@postcode, "", "q")
> > >
> > > is the same as
> > >
> > > replace(@address, @postcode, "", "q")
> > >
> > >
> > > With the simple map operator, the context item must be explicitly
> referred to, like so:
> > >
> > > @address ! replace(., @postcode, "", "q")
> > >
> > >
> > > What may create confusion is that some functions have several
> signatures, some of which implicitly refer to the context item. But this is
> a very different mechanism.
> > >
> > > For example :
> > >
> > > @address ! string(.) (: explicitly passed context item :)
> > > @address ! string() (: context item passed implicitly to string#0,
> which is context-dependent)
> > > @address => string() (: context item passed implicitly to string#1 via
> the => operator, but string#1 is context-independent)
> > >
> > > I hope I got it right!
> > >
> > > Kind regards,
> > > Ghislain
> > >
> > >
> > >> On 2 Aug 2017, at 11:27, W.S. Hager <wshager at gmail.com> wrote:
> > >>
> > >> Hi Michael,
> > >>
> > >> The way you used the arrow operator in the example would be the way I
> expected it to work, namely by explicitly addressing the context, but it
> seems that it doesn't. It's actually implicitly binding the first argument
> of the function on the right to the value on the left. Or is there an
> exception I don't know about?
> > >>
> > >> Thanks.
> > >>
> > >> Op 1 aug. 2017 18:58 schreef "Michael Kay" <mike at saxonica.com>:
> > >> In the case of singletons there's very little difference, but (as I
> now see Christian has pointed out), with sequences the effect is quite
> different.
> > >>
> > >> Also, of course, "!" changes the context item, so
> > >>
> > >> @address => replace(@postcode, "", "q") works, while
> > >>
> > >> @address ! replace(@postcode, "", "q") doesn't.
> > >>
> > >> Michael Kay
> > >> Saxonica
> > >>
> > >>> On 1 Aug 2017, at 13:27, W.S. Hager <wshager at gmail.com> wrote:
> > >>>
> > >>> Hi,
> > >>>
> > >>> Is there any advantage to using the 3.1 arrow operator over the
> simple map operator?
> > >>>
> > >>> $string => upper-case() => normalize-unicode() => tokenize("\s+")
> > >>>
> > >>> versus
> > >>>
> > >>> $string ! upper-case(.) ! normalize-unicode(.) ! tokenize(.,"\s+")
> > >>>
> > >>> Thanks,
> > >>> Wouter
> > >>> _______________________________________________
> > >>> talk at x-query.com
> > >>> http://x-query.com/mailman/listinfo/talk
> > >>
> > >>
> > >> _______________________________________________
> > >> talk at x-query.com
> > >> http://x-query.com/mailman/listinfo/talk
> > >
> >
> >
> >
> >
> >
> >
>
>
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