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Re: remaining problem w/ dyn var scoping, as proposed

Subject: Re: remaining problem w/ dyn var scoping, as proposed (and solution?)
From: "Matt G." <matt_g_@xxxxxxxxxxx>
Date: Sun, 06 Jan 2002 23:06:45
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From: Gunther Schadow <gunther@xxxxxxxxxxxxxxxxxxxxxx>
Reply-To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
Subject: Re: remaining problem w/ dyn var scoping, as proposed (and solution?)
Date: Thu, 03 Jan 2002 13:28:30 -0500


I agree that implicit parameters should be scoped by a namespace
just like tags should so there would not be conflicts. I'm not
sure if namespaces should be used for the parameter name or if
the scope attribute should carry the name of the scope. Actually,
I personally like your scope attribute more, but wouldn't namespaces
be more according to common practice?

Of course, the variable names should be QNames. Then, you could use XML Namespaces, instead of (or in addition to) explicitly-named scopes. IMO, the only reasons to use named scopes would be as a way to group variables by concern or to modularize a single stylesheet file. However, I strongly believe that interfaces provided by other stylesheet modules should be well-specified. Therefore, I think dynamically-scoped variables should only be visible within the file containing the template at the root of their scope.

Finally, the variable's visible scope should be bound not only to the originating file, but the originating *instance* of the originating file. What I mean is that if stylesheet A.xslt imports stylesheet B.xslt, which imports stylesheet A.xslt (which I'll take the refer to as A', pardon the abuse), a dynamically-scoped variable passed from a template in A to one in B, won't be visible in any in A' that B may explicitly call.

This way, separate logical instances, at overlapping levels of the call-tree, don't stomp on each other.

BTW, the way you know B is explicitly calling a template in A' would be if it provided a namespace for A, when it imported it. If Bs reference didn't have a namespace qualifier, then the template called would actually be in A. This, of course, is only possible if you can supply a namespace for an imported module.

I also like your proposal for requiring implicit parameters to be
passed on once they are 'caught.' That results in even less dark
magic happening behind the scene without the explicit agreement
by the programmer. It would make implicit parameter even more
closely aligned to explicit parameters.

I don't care if parameter passing is verbose in XSL, everything
is verbose in XML, so I better get used to that :-) The only
purpose of implicit parameters is to pass them through templates
that don't care about them.

Here is an example of all of this:

<xsl:template ...>
  <!-- all implicit parameters used must be declared in the
       current lexical scope. -->
  <xsl:param scope='foo' name='text-color' select="'black'"/>
  <xsl:param scope='foo' name='text-indent' select="''"/>
  <xsl:param scope='foo' name='text-size' select="10pt"/>

<out color="{$text-color}"/>

  <xsl:apply-templates ...>
    <!-- all implicit parameters declared in this lexical
	 scope must be passed forward explicitly. -->
    <xsl:with-param scope='foo' name='text-indent'
                    select="concat($text-indent,'  ')"/>
    <xsl:with-param scope='foo' name='text-size'

Well, just because scope continuation is explicit doesn't mean that it requires separate 'with-param's. It could just as easily be done with a special flag added to the 'param' element.

Matt Gruenke

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