the joy of breaking out from procedural/imperative programming style (was: Re: [xsl] Peculiar Problem in .xsl file

Subject: the joy of breaking out from procedural/imperative programming style (was: Re: [xsl] Peculiar Problem in .xsl file
From: Gunther Schadow <gunther@xxxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 06 Dec 2002 11:31:15 -0500
Hi, on Chandra's issue of month names, etc. I'd like to take
the oportunity to do some XSLT style-evangelism.

I think this case is a particular good example for how ugly
choices are and that one should deliberately try to find other
ways than using xsl:choose, (and xsl:call-template, xsl:for-each
for that matter.)

XSLT is much more fun if you use its own powers rather than
trying to cling on to the weak metaphors of imperative programming
(i.e., case, procedure call and loops.)

So, instead of this ugly choice, you could make tables:

<xsl:variable name="monthNames">
  <month digits="01" name="January"/>
  <month digits="02" name="February"/>
  <month digits="03" name="March"/>
  <month digits="04" name="April"/>
  <month digits="05" name="May"/>
  <month digits="06" name="June"/>
  <month digits="07" name="July"/>
  <month digits="08" name="August"/>
  <month digits="09" name="September"/>
  <month digits="10" name="October"/>
  <month digits="11" name="November"/>
  <month digits="12" name="December"/>
<xsl:variable>

and then you simply go:

<xsl:value-of
  select="$monthNames/month[@digits=substring($date, 5, 2)]/@name"/>

just think of relational model for most of your data, the above
is same as the SQL form

SELECT name FROM monthNames WHERE digits='..'

The advantage: much cleaner code, much less ugly choose/when,
easily reuseable, easily EXTENSIBLE. For instance you could
easily support multi-lingual date representations either by
loading the month name table from an external resource:

<xsl:variable name="monthNames" select="document($monthnamesuri)"/>

or by adding another "column" for language code such as:

  <month digits="01" name="January" xml:lang="en"/>
  <month digits="01" name="Januar" xml:lang="dn"/>
  <month digits="01" name="Janvier" xml:lang="fr"/>

etc.

Just indulge in the many possible ways you could read this data
from XML locale files.

XSLT is so much fun if you can break out of the imperative/
procedural progamming box. (And much pain and suffering if you
don't break out of that box.)

enjoy,
-Gunther


Gunther Schadow wrote:


What you should try is this:

<xsl:when test="$month='01'">

instead of <xsl:when test="$month=01">

that way you avoid the potentially buggy type casting behavior
of your XSLT processor to become manifest. Just leave the values
you compare both strings at all times (it's probably slightly
faster that way anyway :-). That way you are sure to hold on to
the leading zero.

In fact I wonder if it's really buggy type casting? It seem to
be reasonable for this machinery to cast the second operand to
of the = relation to the data type of the first operand. That
would cast the number 1 to a string, which would be '1', then
you compare '01'='1' and the answer is correctly false. XSLT
spec might make a ruling that clarifies that, but it's a subtle
problem, so, I'd expect that to go wrong somewhere. Luckily
your workaround is straight-forward.

regards,
-Gunther


Chandra - wrote:


Hi Guys,
I am trying to print out a html file with a date in words, given date in a xml file in number format
XSL file:
<xsl:variable name='month' select='substring ($date, 5, 2)'/>
<xsl:choose>
<xsl:when test='$month=01'>
<xsl:text>January </xsl:text>
</xsl:when>
<xsl:when test='$month=02'>
<xsl:text>February </xsl:text>
</xsl:when>
<xsl:when test='$month=03'>
<xsl:text>March </xsl:text>
</xsl:when>
<xsl:when test='$month=04'>
<xsl:text>April </xsl:text>
</xsl:when>
<xsl:when test='$month=05'>
<xsl:text>May </xsl:text>
</xsl:when>
<xsl:when test='$month=06'>
<xsl:text>June </xsl:text>
</xsl:when>
<xsl:when test='$month=07'>
<xsl:text>July </xsl:text>
</xsl:when>
<xsl:when test='$month=08'>
<xsl:text>August </xsl:text>
</xsl:when>
<xsl:when test='$month=09'>
<xsl:text>September </xsl:text>
</xsl:when>
<xsl:when test='$month=10'>
<xsl:text>October </xsl:text>
</xsl:when>
<xsl:when test='$month=11'>
<xsl:text>November </xsl:text>
</xsl:when>
<xsl:when test='$month=12'>
<xsl:text>December </xsl:text>
</xsl:when>
</xsl:choose>


When valuepassed into the date variable is 20020516, I don't get a month. Infact if the month is from 01 to 09, I dont get a month in words. If the month is 10 to 12, I get a month displayed. Very very peculiar. I am unable to find the solution. I tried and printed out the value of the month variable. It seems to take the 2 digits correctly. However it doesn't go into the appropraite month code when the month starts with 0!! For example, if the month is 05, it doesnt go into this part of the code:
<xsl:when test='$month=05'>
<xsl:text>May </xsl:text>
</xsl:when>
If the month were 10, 11 or 12, the code works fine.
Can anyone guess what the problem is...
Thanks in advance,
Chandra




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--
Gunther Schadow, M.D., Ph.D.                    gschadow@xxxxxxxxxxxxxxx
Medical Information Scientist      Regenstrief Institute for Health Care
Adjunct Assistant Professor        Indiana University School of Medicine
tel:1(317)630-7960                         http://aurora.regenstrief.org



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