[xquery-talk] arrow operator

[W.S. Hager]

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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