Hi Wouter, > That's why, for cases where it's possible, I preferred to write the simple > mapping operator, as it's easier to read IMO.
In practice, in our trainings and courses, we usually present the arrow operator as alternative for nested functions. It turned out that most people seem to love it. Some don’t… As it’s always the case if a language provides more than one syntactic solution. Personally, I tend to stick with the old-school syntax, but I switch to the arrow operator if I believe that the too much nesting makes the code difficult to read. As Ghislain indicated, the semantics of the two operators differs pretty much (although there are surely some cases in which they can serve as equivalent alternatives). Actually, the mapping operator is much closer to XPath steps. There are even good reasons for replacing / with !, e.g. if you do not want to have duplicate-free and ordered results. Christian > > 2017-08-02 12:07 GMT+02:00 W.S. Hager <[email protected]>: >> >> 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 <[email protected]>: >>> >>> ... 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 <[email protected]> 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 <[email protected]> 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" <[email protected]>: >>> >> 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 <[email protected]> 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 >>> >>> _______________________________________________ >>> >>> [email protected] >>> >>> http://x-query.com/mailman/listinfo/talk >>> >> >>> >> >>> >> _______________________________________________ >>> >> [email protected] >>> >> http://x-query.com/mailman/listinfo/talk >>> > >>> >> >> > > > _______________________________________________ > [email protected] > http://x-query.com/mailman/listinfo/talk _______________________________________________ [email protected] http://x-query.com/mailman/listinfo/talk
