At 2013-01-05 11:35 -0500, Mark Baker wrote:
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Can anyone account for the behavior exhibited by the position function in a predicate in the following code sample:
<xsl:variable name="x" select="'A', 'B', 'C'" as="xs:string*"/> <xsl:variable name="y" select="'a', 'b', 'c'" as="xs:string*"/> <xsl:for-each select="$x"> <xsl:variable name="pos" select="position()"/> <xsl:message select="position()"/> <xsl:message select="., $y[position()]"/> <xsl:message select="., $y[$pos]"/> </xsl:for-each>
As the output below shows, when the value of position is stored in a variable and the variable is used in a predicate, you get what you would expect, the selection of a single item corresponding to the current position. But when position() is used directly in the predicate, it returns all the items in the sequence:
[Saxon-PE] 1 [Saxon-PE] A a b c [Saxon-PE] A a [Saxon-PE] 2 [Saxon-PE] B a b c [Saxon-PE] B b [Saxon-PE] 3 [Saxon-PE] C a b c [Saxon-PE] C c
Any ideas, or is this simply a bug?
I don't see a bug. position() is being re-evaluated *inside* the predicate, whereas $pos is not being re-evaluated inside the predicate. In XPath, position() is always calculated based on the current context. In the predicate, that context is the node test. So when you write: $y[position()] ... the data type of the predicate evaluation is numeric, so that is an abbreviation for position()={value}, where {value} is the current position. Thus, it is evaluated as the sequence: 'a'[position()=1], 'b'[position()=2], 'c'[position()=3] ... which is: 'a'[true()], 'b'[true()], 'c'[true()] ... which is: 'a', 'b', 'c' So, I would expect the result you are seeing. Note for $y[$pos], the data type of $pos is numeric so that also is an abbreviation for $y[position()=$pos], which is true only once in each of the three iterations. You get 'a' for the first, 'b' for the second and 'c' for the third iteration. I hope this has helped. . . . . . . . . . Ken -- Contact us for world-wide XML consulting and instructor-led training Free 5-hour lecture: http://www.CraneSoftwrights.com/links/udemy.htm Crane Softwrights Ltd. http://www.CraneSoftwrights.com/z/ G. Ken Holman mailto:gkholman@CraneSoftwrights.com Google+ profile: https://plus.google.com/116832879756988317389/about Legal business disclaimers: http://www.CraneSoftwrights.com/legal