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Re: Controlling Debugging Messages (was Re: [xsl] how to create variable by comparing two variables using [not])
2018-10-15 12:11:38
With static variables you can of course have multiple switches but they will be
statically scoped rather than dynamically scoped. You could use multiple
variables or you could use flags within a single variable
(use-when="contains($DEBUG_FLAGS, 'g')").
I have to confess I'm not usually that organized. I tend to have a single
variable $DEBUG which is false, and then switch on individual debug lines using
use-when="$DEBUG or true()". I tend to find that debug statements are rarely
useful once you've solved the bug that they were invented for; except in rare
cases where you persistently have problems with some particular intermediate
result passed across a key interface in your application - in which case there
may be better approaches than xsl:message to monitoring what's passed across
that boundary.
But I wouldn't recommend anyone to be as disorganised as me.
Michael Kay
Saxonica
On 15 Oct 2018, at 17:05, Eliot Kimber ekimber(_at_)contrext(_dot_)com
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
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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