Re: how to create variable by comparing two variables

Eliot writes:

> I also depend heavily on using messages to test my assumptions.

> For example, I might do something like:

> <xsl:message>+ [DEBUG] jpeg_few={$jpeg_few => string-join(',
')}</xsl:message>
> <xsl:message>+ [DEBUG] jpeg_many={$jpeg_many => string-join(',
')}</xsl:message>

This is a key technique when developing XSLT. The language is designed
to "fail gracefully" most of the time -- which puts the burden on the
programmer to ensure things don't fail catastrophically. :-)

Cheers, Wendell

On Sun, Oct 14, 2018 at 7:10 PM Eliot Kimber ekimber@xxxxxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Looking at the XPath 3 Functions and Operators specification and searching
on "intersect" (hoping to also find "disjoint") I find this discussion:
>
> D.4.2.3 eg:value-except
> eg:value-except(        $arg1    as xs:anyAtomicType*,
> $arg2    as xs:anyAtomicType*) as xs:anyAtomicType*
> This function returns a sequence containing all the distinct items that
appear in $arg1 but not in $arg2, in an arbitrary order.
>
> XSLT implementation
>
> <xsl:function name="eg:value-except" as="xs:anyAtomicType*">
>   <xsl:param name="arg1" as="xs:anyAtomicType*"/>
>   <xsl:param name="arg2" as="xs:anyAtomicType*"/>
>   <xsl:sequence
>      select="fn:distinct-values($arg1[not(.=$arg2)])"/>
> </xsl:function>Which is in
https://www.w3.org/TR/xpath-functions-31/#other-functions (Appendix D).
>
> So basically
>
> distinct-values($jpeg_few[not(. = $jpeg_many)]
>
> Should give you the answer you seek.
>
> I agree with Mike that being obsessive about putting data types on all
variables and function return values (and templates when the templates should
return atomic types or specific element types) will help a lot.
>
> If your code is working without types but failing with them it means your
code is "working" but probably not for the reasons you think.
>
> Working carefully through the stages of the expressions by setting each
intermediate result into variable will help a lot.
>
> I also depend heavily on using messages to test my assumptions.
>
> For example, I might do something like:
>
> <xsl:message>+ [DEBUG] jpeg_few={$jpeg_few => string-join(',
')}</xsl:message>
> <xsl:message>+ [DEBUG] jpeg_many={$jpeg_many => string-join(',
')}</xsl:message>
>
> Or if those lists are very long, use count() or get the first n items or
whatever to make it clear that you're working with the values you think you
are.
>
> Also, remember that <xsl:value-of> ({} in string result contexts) is
different from <xsl:sequence>, which returns the actual value, not a string
representation.
>
> For example, given a variable that is an attribute node, value-of will
return string value of the attribute but xsl:sequence will return the
attribute node and Saxon will serialize it as <attribute name="foo"
value="bar"> (or something similar to that.
>
> It's easy to accidently create a sequence of attributes when what you wanted
was a sequence of strings (or visa versa) and using xsl:value-of can obscure
that mistake.
>
> I've also started using the XQuery-required explicating casting of values
even though XSLT usually lets you get away with implicit casting, because it
makes it clearer to me what my intent was (and makes it easier to copy XPath
expressions into XQuery, if that's something you need to do).
>
> Cheers,
>
> Eliot
> --
> Eliot Kimber
> http://contrext.com
>
>
> o;?On 10/14/18, 3:53 PM, "Dave Lang emaildavelang@xxxxxxxxx"
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
>     > That error can only come from an expression that calls tokenize().
It's therefore clearly not your declaration of jpgs_in_xml_not_directories
that's at fault.
>
>     Fair enough - but when I run the transformation without that
declaration
>     everything works fine. Is there something I can do to the variables
that
>     are included in it to make the declaration work?
>
>
>
>



--
Wendell Piez | http://www.wendellpiez.com
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