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creating sequences: defaults, surprises, syntax and semantics

From: Tobias Reif <tobiasreif@pinkjuice.com>
Date: Thu, 08 May 2003 11:53:33 +0200
Message-ID: <3EBA291D.8050005@pinkjuice.com>
To: public-qt-comments@w3.org

Contary to what the grandiose-sounding subject line suggests, this is 
neither an exhaustive description of the issue, nor a complete solution. 
It's just an impression I got while working with the current draft for 
XSLT 2.

1. Why do I get a string for my sequence?

I needed to send a sequence of strings to a template.

This worked

   ...
   <xsl:call-template name="elements">
     <xsl:with-param name="choices" select="('div', 'p', 'span')"/>
   ..

Those didn't

   <xsl:with-param name="choices"/>
     <xsl:sequence select="('div', 'p', 'span')"/>
   </xsl:with-param>

   <xsl:with-param name="choices"/>
     <xsl:copy-of select="('div', 'p', 'span')"/>
   </xsl:with-param>

Why? I was surprised and confused.
(look below for why the former example didn't fully cut it in this case)

Mike explained to me that the enclosing instruction turns the sequence 
into a string.

This is counter-intuitive IMHO: if I supply a sequence, and there is no 
"as" attribute, then I think it's a confusing surprise that I get a 
string instead of a sequence.

So I need to write

   <xsl:with-param name="choices" as="xs:string*"/>
     <xsl:sequence select="'div', 'p', 'span'"/>
   </xsl:with-param>

or alternatively (copy-of, optional parentheses around sequence)

   <xsl:with-param name="choices" as="xs:string*"/>
     <xsl:copy-of select="('div', 'p', 'span')"/>
    </xsl:with-param>

and when assigning a sequence to a variable, I'd do

   <xsl:variable name="choices" as="xs:string*"/>
     <xsl:sequence select="'div', 'p', 'span'"/>
   </xsl:variable>

If I omit the "as" attribute and supply a sequence I get a string; not 
what I want.
If I want to get a sequence for my sequence, I need to specify 
as="xs:string*".
I think it would be much more clear if the default behaviour would be to 
return a sequence for a sequence,
just as in
   <xsl:with-param name="choices" select="('div', 'p', 'span')"/>)
.

When I write

  ...
  <xsl:variable name="out">
    <xsl:choose>
      <xsl:when test="$in='phrase'">
        <xsl:sequence select="('span','p','div')"/>
      </xsl:when>
      <xsl:when test="$in='div'">
        <xsl:sequence select="('div','p','span')"/>
      </xsl:when>
      <xsl:otherwise>
        <xsl:copy-of select="('baar', 'blamm')"/>
      </xsl:otherwise>
    </xsl:choose>
  </xsl:variable>

   ...
   <xsl:call-template name="elements">
     <xsl:with-param name="choices" select="$out"/>
   ..

I'd like the have a sequence assigned to the variable and send to the 
called template, not a string. *If* I would like to turn the sequence 
into something else, I would say so by adding an "as" attribute.

The issue lies in an area where ease of use an intuitiveness of XSLT 2 
can be improved. AFAIK a nice solution would probably involve breaking 
XSLT 1.0 backwards compatibility, but I think it would be worth it.

2. A question:

Can a sequence consist of numbers, strings, etc, mixed? (Didn't yet read 
through all ten specs :)

Tobi

-- 
http://www.pinkjuice.com/
Received on Thursday, 8 May 2003 05:54:45 GMT

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