Re: [xsl] Checking if a variable has a value

["Martin Honnen martin.honnen@xxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Am 8/31/2022 um 10:26 AM schrieb Jean-Paul Rehr rehrjb@xxxxxxxxx:
> >A variable always has a value.
>
> I'm trying to reconcile this statement with Xquery, which I use more
> frequently.
>
> In Xquery the following returns false:
>
> let $x := ()
> return
> B  B  B  if (exists($x)) then true() else false()
>
> Are you stating that the equivalent cannot happen in XSL variables?
> I'm asking this mostly because I've not had the need to explore this
> until now and am ignorant about it.

That variable $x does have a value, the value is the empty sequence. I
think with most people trying to write some check for a null/undefined
or non-existing variable value in XSLT/XQuery/XPath there is no clear
definition of what kind of value a variable can have and for which kind
of values to check.


As for an XQuery variable that might not be bound to a value, if you
have e.g.

declare variable $x external;

and on running the XQuery program with code like

B  exists($x)

without providing a value for x, you will get (at least from Saxon) an
error like "No value supplied for required parameter $x".