Re: Re: . in for

--- Jeni Tennison <jeni@xxxxxxxxxxxxxxxx> wrote:
> Hi Dimitre,
> 
> >> I imagine that a processor would be able to spot situations where
> >> the position() or last() function had been called and only compose
> >> the steps that were composable.
> >
> > It seems to me obviously not so -- I mean the general task of
> > spotting ***any*** function in the expression, that could reference
> > not only the specific item in the sequence. This includes any
> > user-defined functions.
> 
> Yes, you're right of course - the focus at the point at which the
> user-defined function is called provides the focus for the body of the
> function when it's defined by xsl:function, and that will propagate
> through function (and named template) calls from those functions and
> so on, making it impractical for the processor to spot.
> 
> I do think that the position of an item in a sequence is going to be
> an important piece of information, particularly because items in
> sequences can't be sequences themselves. Yet another
> usability/optimisability trade-off I suppose.
> 

Yes, and this actually means that a piped 'mapping operator' would not be possible
to optimise by the XSLT processor and to convert it into a single map applying a
composition of functions. Piped/composed map-s will require big space, proportional
to the number of map-s, as compared with the single map operation.

Cheers,
Dimitre.

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