Re: [Accumulators] Another stupid question

Thanks a lot, Michael, for this precision. I've just forgot it !

Best regards,
Christophe

Le 07/10/2020 ` 00:33, Michael Kay mike@xxxxxxxxxxxx a icrit :
> It's fundamental to accumulators that the value of an accumulator at a 
> particular node in a document is a pure function of the preceding 
> nodes in that document (or in the case of an "after" value, the 
> descendant nodes), and nothing else (other than constant data such as 
> global variables). You can't inject values into this calculation in 
> the way you are trying to do. Accumulators were invented, of course, 
> for streaming, and represent "things that are remembered from earlier 
> in the stream".
>
> Your private:block element is matched by a different "accumulator 
> instance" from the one that matches the page element; an accumulator 
> instance corresponds to one document, and accumulator instances for 
> different documents don't interact. Otherwise, there would be a 
> terrible dependency on order of processing.
>
> Saxon evaluates unstreamed accumulators lazily: the first time you 
> evaluate accumulator-before, or accumulator-after, on any node in a 
> particular document, the accumulator values are computed for all nodes 
> in that document.
>
> Michael Kay
> Saxonica
>
>
>> On 6 Oct 2020, at 21:58, Christophe Marchand cmarchand@xxxxxxxxxx 
>> <mailto:cmarchand@xxxxxxxxxx> 
>> <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx 
>> <mailto:xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>> wrote:
>>
>> Hello !
>>
>> I have another question with accumulators. I use accumulators to 
>> calculate block height, and then to calculate block locations (y).
>>
>> I have this XSL for a repro...
>>
>> <?xml version="1.0" encoding="UTF-8"?>
>> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
>>   xmlns:xs="http://www.w3.org/2001/XMLSchema"
>>   xmlns:private="top:marchand"
>>   exclude-result-prefixes="#all"
>>   version="3.0">
>>
>>   <xsl:output method="xml" indent="true"/>
>>
>>   <xsl:mode on-no-match="shallow-copy" use-accumulators="#all"/>
>>
>>   <xsl:accumulator name="blockHeight" as="xs:double" initial-value="0.0">
>>     <xsl:accumulator-rule match="page">
>>       <xsl:message>Reset block height to 3.2</xsl:message>
>>       <xsl:sequence select="3.2"/>
>>     </xsl:accumulator-rule>
>>     <xsl:accumulator-rule match="private:block">
>>       <xsl:message>Adding block height {@id} : {@height}</xsl:message>
>>       <xsl:sequence select="$value + xs:double(@height)"/>
>>     </xsl:accumulator-rule>
>>   </xsl:accumulator>
>>
>>   <xsl:template match="block">
>>     <xsl:variable name="height" as="xs:double" select="3.5"/>
>>     <!-- produce some output -->
>>     <xsl:variable name="TempTree" as="element(private:block)">
>>       <private:block height="{$height}"/>
>>     </xsl:variable>
>>     <xsl:apply-templates select="$TempTree"/>
>>     <xsl:copy>
>>       <xsl:attribute name="y" select="accumulator-after('blockHeight')"/>
>>       <xsl:apply-templates select="node() | @*"/>
>>     </xsl:copy>
>>   </xsl:template>
>>
>>   <xsl:template match="private:block">
>>     <xsl:message>private:block matched</xsl:message>
>>   </xsl:template>
>>
>>   <xsl:template name="xsl:initial-template">
>>     <xsl:variable name="content" as="document-node()">
>>       <xsl:document>
>>         <doc>
>>           <page id="p1">
>>             <block id="b1">
>>               <!-- arbitrary content -->
>>             </block>
>>             <block id="b2">
>>               <!-- another arbitrary content -->
>>             </block>
>>           </page>
>>           <page id="p2">
>>             <block id="b3">
>>               <!-- arbitrary content -->
>>             </block>
>>             <block id="b4">
>>               <!-- another arbitrary content -->
>>             </block>
>>           </page>
>>         </doc>
>>       </xsl:document>
>>     </xsl:variable>
>>     <xsl:apply-templates select="$content"/>
>>   </xsl:template>
>> </xsl:stylesheet>
>>
>> When I run this XSL on the sample XML, I have messages displayed : 
>> "Reset block height to 3.2", "private:block matched", but never the 
>> "Adding block height..."
>>
>> According to specification [1], I expect private:block matches 
>> accumulator rule, and accumulator value being augmented by block/@height.
>>
>> What am I doing wrong ?
>>
>> Thanks in advance,
>> Christophe
>>
>> [1] : 18.2.2 
>> https://www.w3.org/TR/xslt-30/#applicability-of-accumulators list item 1
>>
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