I'll take a look at assert. I'm not sure static variables address my
requirements since the emitting of the debug messages may be dynamically
controlled within a given template or function using values that couldn't
be known at compile time (e.g., <xsl:variable name="doDebug" select="@id =
'1234'" as="xs:boolean"/>, the equivalent of a watch statement in a
procedural debugger).
With respect to Brian's post: I'm emitting messages to the console, not to
the result, but I like the idea of preprocessing the XSLT itself to add
the logging details--I'll have to think about that.
Cheers,
E.
On 3/24/14, 1:42 PM, "Michael Kay" <mike(_at_)saxonica(_dot_)com> wrote:
On 24 Mar 2014, at 17:31, Eliot Kimber <ekimber(_at_)contrext(_dot_)com> wrote:
For whatever reason I find using interactive debugging unhelpful for
debugging XSLT processing (but I couldn't code a line of Java without
it).
That's my experience too, I have never been sure why the difference.
I think it may be the nature of the apply-templates process makes "step
into" less obvious or practical than in a procedural language where it's
much clearer where you're going to go when you step. I also find that
often when I do try to "step into" that the transform just completes and I
can't figure out where I should have set a breakpoint or why it didn't
work. With messages you can at least trace exactly what's happening.
Thus I depend very heavily on debug messages in my XSLTs. I used to just
emit messages and then comment them out or delete them when I was done,
but then I found myself recreating those messages when I had to return
to
that bit of code.
Then I started using a runtime parameter to turn debugging on or off
globally and using IF checks to output my messages. But that results in
a
lot of messages when you've got a lot of debug messages, most of which
are
not relevant to your current problem, so back to commenting things out
or
disabling the IF check (e.g., test="false() and $doDebug").
There are two things in XSLT 3.0 designed to make this easier:
xsl:assert, and static variables/parameters
xsl:assert is like xsl:message wrapped in an xsl;If.
Static variables can be used in conjunction with xsl:use-when effectively
as an "ifdef", that is a compile-time conditional. So rather than
commenting code out, you tag it with use-when="$DEBUG".
Michael Kay
Saxonica
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