Re: Signature of a function that may throw an error

Best regards,
Christophe

I tried Christophebs function with several Saxon versions, from 9.5 to 9.9, HE and PE, and also XSLT versions 2.0 and 3.0 where available. I slightly changed the error() invocation, using a QName that was in a namespace I was using in the stylesheet at hand. I could only reproduce the message that Christophe was seeing when I returned an empty sequence instead of error(b&). Therefore I can corroborate what you are saying, Michael, at least for my setup.

On 22.01.2019 17:28, Michael Kay mike@xxxxxxxxxxxx wrote:

The XPath spec defines the return type of the error() function as "none", and the role of "none" in the type system is pretty much unspecified. As a result, there was always a steady stream of problems with edge cases in the W3C test suites in this area.

Saxon actually implements the static return type of error() as item(), which is intended to ensure that you won't get a static type error from this sort of construct.

This particular example doesn't seem to give a static error with Saxon 9.9, though the error message looks like it comes from Saxon. The code that produces this error is intended for the case where one of the branches of the conditional always returns an empty sequence (typically, an implicit xsl:otherwise).

What software version are you running?

Michael Kay
Saxonica

On 22 Jan 2019, at 14:36, Christophe Marchand cmarchand@xxxxxxxxxx <mailto:cmarchand@xxxxxxxxxx> <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx <mailto:xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>> wrote:

Hello,

I have a function that must return a xs:string, or raise an error, if result value can not be computed, or is empty-sequence.

Here is function :

B <xsl:function name="conf:getConfVar" as="xs:string">
B B B <xsl:param name="conf" as="element(els-conf:conf)"/>
B B B <xsl:param name="varName" as="xs:string"/>
B B B <xsl:sequence select="
B B B B B if (exists($conf/els-conf:variable[@name=$varName]))
B B B B B then $conf/els-conf:variable[@name=$varName]/@value
B B B B B else (
B B B B B B B error(
B B B B B B B B B $conf:ERROR_MISSING_ENTRY,
B B B B B B B B B concat('Entry ',$varName,' is missing in environment configuration')
B B B B B B B )
B B B B B )
B B B B B "/>
B </xsl:function>

When a variable does not exist in $conf, I expect an error being raised, and expect to catch it in a xsl:try / xsl:catch.

But, in this case, I get this :

XTTE0780: Conditional expression: The condition is not satisfied, so an empty sequence is returned, but this is not allowed as the result of call to conf:getConfVar
in xsl:sequence/@select ....

B * I understand that error() function never return a value, so return
B B B value does not satisfies xsl:function/@as constrint. Is it correct ?
B * How could I write this, as I want the return type being xs:string,
B B B and not xs:string?, and I want my error to be raised when entry is
B B B missing ?

Best regards,
Christophe

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