RE: [xsl] Ordering of Blocks based on Input/Output

Subject: RE: [xsl] Ordering of Blocks based on Input/Output
From: "Michael Kay" <mhkay@xxxxxxxxxxxx>
Date: Wed, 9 May 2001 17:26:48 +0100
> > >     <xsl:if test="count($todo) > 0">
> >
> > This test does the same as test="$todo", which is
> > much more efficient for larger data,
> > if the processor doesn't optimize it anyway.
> >
> Quite right about the equivalence, though I don't know if
> doing count()
> on a node-set held in a variable will take as long as it would if
> gathering the node-set for the first time.

Many XSLT processors will "gather the node-set for the first time" when
evaluating the count() function - delayed evaluation and pipelining is the
norm in a functional language. That's why test="$todo" (or
test="boolean($todo)" for clarity) is faster, because it can stop as soon as
it sees the first node.

Saxon rewrites "count($todo) > 0" as "boolean($todo)" at compile time,
provided it knows at compile time that $todo is a node-set - which will
generally be the case for a variable, but not for a parameter.

Mike Kay

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