I was just about to post about this.
In my XSLT 2 code I have historically used this pattern:
<xsl:template match="foo">
<xsl:param name="doDebug" as="xs:boolean" tunnel="yes" select="false()"/>
<xsl:if test="$doDebug">
<xsl:message>+ [DEBUG] Handling <xsl:value-of name="concat(name(..), '/',
name(.))"/>...</xsl:message>
<xsl:apply-templates>
<xsl:with-param name="doDebug" as="xsl:boolean" tunnel="yes"
select="$doDebug"/>
</xsl:apply-templates>
</xsl:template>
This allows me to selectively turn debugging on and off in specific parts of
the code but does require this somewhat heavy weight code.
With @use-when, can I get the same level of local control?
That is, with the above, I can add:
<xsl:variable name="doDebug" as="xs:Boolean" select="true()"/>
In any block to turn debugging on just there.
If I understand the implications of static variables allowed in @use-when, the
debugging switch is globally all-or-nothing, or at least global within a given
package.
Is that correct?
If that is correct, is there a better way to do the selective,
dynamically-controlled debug messaging shown above?
Cheers,
E.
--
Eliot Kimber
http://contrext.com
On 10/15/18, 9:08 AM, "Michael Kay mike(_at_)saxonica(_dot_)com"
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
These days you can do
<xsl:message use-when="$DEBUG" ....>
with $DEBUG defined as a static parameter.
<xsl:param name="DEBUG" as="xs:boolean" static="true" select="false()"/>
No need for the run-time check with xsl:if.
You can also use xsl:assert to define assertions. In Saxon, assertion
checking can be enabled from the command line using -ea.
Michael Kay
Saxonica
> On 15 Oct 2018, at 14:54, Dave Pawson
dave(_dot_)pawson(_at_)gmail(_dot_)com
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
>
> MIght even surround it with
> <xsl:if test="$debug">
>
> To ease insertion / removal when testing?
>
> HTH
> On Mon, 15 Oct 2018 at 14:31, Wendell Piez
wapiez(_at_)wendellpiez(_dot_)com
> <xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
>>
>> 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(_at_)contrext(_dot_)com
>> <xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> 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
>>>
>>>
>>> On 10/14/18, 3:53 PM, "Dave Lang emaildavelang(_at_)gmail(_dot_)com"
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> 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
>> XML | XSLT | electronic publishing
>> Eat Your Vegetables
>> _____oo_________o_o___ooooo____ooooooo_^
>>
>
>
>
> --
> Dave Pawson
> XSLT XSL-FO FAQ.
> Docbook FAQ.
>
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