[xquery-talk] arrow operator

[W.S. Hager]

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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