Re: Signature of a function that may throw an error

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
<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 :
>
>   <xsl:function name="conf:getConfVar" <conf:getConfVar> as="xs:string">
>     <xsl:param name="conf" as="element(els-conf:conf)"/>
>     <xsl:param name="varName" as="xs:string"/>
>     <xsl:sequence select="
>       if (exists($conf/els-conf:variable[@name=$varName]))
>       then $conf/els-conf:variable[@name=$varName]/@value
>       else (
>         error(
>           $conf:ERROR_MISSING_ENTRY <conf:ERROR_MISSING_ENTRY>,
>           concat('Entry ',$varName,' is missing in environment
configuration')
>         )
>       )
>       "/>
>   </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 <conf:getConfVar>
> in xsl:sequence/@select ....
>
> I understand that error() function never return a value, so return value
does not satisfies xsl:function/@as constrint. Is it correct ?
> How could I write this, as I want the return type being xs:string, and not
xs:string?, and I want my error to be raised when entry is missing ?
> Best regards,
> Christophe
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