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[Bug 22936] New: [XSLT 3.0] Streamability : dynamic calls to context dependent functions

From: <bugzilla@jessica.w3.org>
Date: Tue, 13 Aug 2013 10:35:42 +0000
To: public-qt-comments@w3.org
Message-ID: <bug-22936-523@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=22936

            Bug ID: 22936
           Summary: [XSLT 3.0] Streamability : dynamic calls to context
                    dependent functions
    Classification: Unclassified
           Product: XPath / XQuery / XSLT
           Version: Working drafts
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: XSLT 3.0
          Assignee: mike@saxonica.com
          Reporter: mike@saxonica.com
        QA Contact: public-qt-comments@w3.org

We say that a NamedFunctionRef is motionless.

Similarly we have no special rules for function-lookup().

However, in both cases these constructs are not as innocent as they seem,
because they capture the dynamic context at the point they are evaluated, and
use that dynamic context later when the resulting function is called.

For example:

<xsl:variable name="saved-current" select="current#0"/>
<xsl:for-each select="transaction">
  <xsl:if test="value = $saved-current()/value">
    ...
  </xsl:if>
</xsl:for-each>

is clearly not streamable.

So:

(a) A NamedFunctionRef should be free-ranging if the function is dependent on
(relevant parts of?) the dynamic context

(b) function-lookup() should always be free-ranging (because we have no way of
knowing what it might do).

(c) Partial function application could also be dangerous in the same way if we
had any focus-dependent functions with two or more arguments. Fortunately we
don't, though it seems a little odd to assume that.

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Received on Tuesday, 13 August 2013 10:35:43 UTC

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