--- Jeni Tennison <jeni@[...].com>  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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