[Bug 26439] [XSLT30] fn:fold-left in streamability rules can take type-determined usage into account (from note in test)

https://www.w3.org/Bugs/Public/show_bug.cgi?id=26439

--- Comment #6 from Michael Kay <mike@saxonica.com> ---
For fn:filter, the rules don't quite work in the same way. By analogy with
filter expressions, filter($seq, $f) has the posture and sweep of $f provided
that a call on $f is motionless. We can be sure that a dynamic call on $f is
motionless only if:

(a) $seq is grounded, or

(b) $f is a known built-in function such as fn:nilled#1 where the argument has
inspection usage, or 

(c) $f is an inline function whose body we are prepared to analyse.

But (b) covers so few useful cases that it really isn't worth bothering,
especially as these cases can always be expressed by a simple filter
expression: emp[nilled()]; and (c) is going into new territory that is best
left untouched for now.

Given that case (a) is already handled, I'm going to make no change for
fn:filter.

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Received on Friday, 5 September 2014 11:43:01 UTC