* * * * *

                         Convenience vs. Correctness

I'm not sure how I feel about this.

I've been wanting to update my website [1] for some time now, but the latest
version of xsltproc hates me [2]. Or rather, it hates the XSL (eXtensible
Stylesheet Language) files that worked fine under an earlier version of the
code.

It took a few hours of debugging (XSL makes COBOL look terse [3]) but I
figured out the issues, and most of them relate to attributes. Or rather, the
lack of attributes when testing them.

I had a bit of code:

> <xsl:if test="count($objects[@listindex != 'no'])">
>  ...
> </xsl:if>
>

I was passing in a bunch of entities (think DOM (Document Object Model)
objects, or if that's too obscure, things similar to HTML (HyperText Markup
Language) tags):

> <section id="News" directory="news/"> ... </section>
> <section id="People" directory="people/"> ... </section>
> <section id="Software" directory="software/" pubdate="yes"> ... </section>
> <section id="Projects" directory="projects/"> ... </section>
> <section id="Merchandise" location=" ... "> ... </section>
> <section id="Reference" directory="refs/"> ... </section>
> <section listindex="no" id="Errors" directory="errors/"> .. </section>
>

(the neat thing about XML (eXtensible Markup Language)—you get to create your
own tags) and as you can see, there are several sections, with one I don't
really care to list, thus the listindex attribute. It avoids creating links
to those sections I don't care about.

The old version of xsltproc would attempt to compare the attribute listindex
index against the value “no”, and if the attribute was missing, then it just
assumed the attribute was there, but the value was something other than “no”.
The function count() counts the number of nodes that match, and would return
“6”, because there were six entities where the attribute listindex was not
equal to “no” (despite the fact that the attribute listindex didn't exist in
most cases).

The newer version would only check those entities that had the listindex
attribute, and here, the function count() returned “0”, because of all the
entities that had the listindex attribute, none had a value other than “no”.

And that's why I'm conflicted on this.

The earlier interpretation makes things convenient. I want to ignore entities
that have listindex='no' and include everything else. The number of entities
that I want to ignore is small, so it is easier to just add this when I want
to ignore something than to add listindex='yes' to everything.

On the other hand, I prefer strict type checking and having everything
explicitly spelled out. Nothing hidden, no surprises. So I can see that I'm
asking for all entities that have the listindex attribute, and only those
entities that have the listindex attribute.

And on the gripping hand, having to check the existence of an attribute
before checking it's value every single time is making a verbose language
even more verbose and seriously changes the logic in the code (and I'm only
half done, sigh).

[1] http://www.conman.org/
[2] gopher://gopher.conman.org/0Phlog:2009/02/17.1
[3] gopher://gopher.conman.org/0Phlog:2004/01/26.1

Email author at [email protected]

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