In general, if you're not using the result of a function
but still want it
called, then you should try to hoodwink the optimizer into
thinking that you
are using it. If it's a Java method that returns void, call it as
<xsl:sequence select="my:call(xyz)"/>
or call it as
<xsl:if test="my:call(xyz) = -1"><a/></xsl:if>
when you know the result will never be -1.
Of course, this still doesn't guarantee any specific order of
evaluation or even if the extension function will be called only once,
or am I wrong?
There are things that give predictability with the current release of a
particular processor, but there is almost nothing that gives predictability
for all releases of all processors.
With Saxon today, the order of execution of variable declarations is not
easily predictable. But within a sequence of instructions forming a content
constructor, they are always evaluated sequentially.
Saxon tends to assume the worst case when rearranging expressions involving
extension functions, for example it doesn't move them out of a loop, because
it assumes that they might depend on the loop variables.
Michael Kay
http://www.saxonica.com/
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