Re: Assignment no, dynamic scoping si (was: Re: RE: Wi

Gunther Schadow <gunther at aurora dot regenstrief dot org> wrote:

[snip]

| Here is Terje Norderhaug's use case again for your convenience:

> Being able to simplify the stylesheet by removing repeated parameter
> passing is reason enough for me. However, I have also missed variables
> with dynamic scope when extending predefined stylesheets.
> 
> Dynamic scoped variables may reduce the redundancy between imported
> and importing stylesheets, with associated benefits. It makes
> imported/importing stylesheets less dependent on each other by
> allowing passing of values between templates in a stylesheet without
> demands on the templates in the other stylesheet.
> 
> Say you have a stylesheet "book.xsl" containing templates to process
> the various element types in a book (e.g. book, chapter, paragraph,
> ...) where each template applies templates recursively, like this:
> 
> <xsl:template match="chapter">
>   <fo:block>
>     <xsl:apply-templates/>
>   </fo:block>
> </xsl:template>
> 
> Consider the case that you need to make a stylesheet that imports a
> third party "book.xsl" then overrides its templates for 'book' and
> 'paragraph' elements with custom processing but with a minimum of
> duplication. For some reason, you would like to pass a parameter from
> the 'book' template to the 'paragraph' template.
> 
> Unfortunately, today this requires that you duplicate and modify the
> 'chapter' template (and possibly others) from the "book.xsl"
> stylesheet to pass along the parameter. You end up with a stylesheet
> that contains most or all of the imported stylesheet.
> 

Duplicating and modifying the 'chapter' template (and possibly others) ***is not
required***.

Just declare a global variable and access it in the 'paragraph' template.

One may argue that within the 'book' template the necessary value can be obtained
"dynamically", while the value of a global variable is "static". This is clearly not
true, as any variable (global included) can have templates instantiated/called
within its body in order to define its value.

> With support for dynamic scope, the 'book' template would be able to
> bind variables that are visible for the 'paragraph' template without
> requiring modifications of other templates in "book.xsl".

As pointed out above, this is also possible ***without support for dynamic scope***
by using a global variable.

Another disadvantage of dynamic-scoped variables is that separating and making
remote the definition of a parameter/variable from its reference/use may present
difficulties to its type-checking.

Also, any such separation/remoting makes the code more difficult to understand and
maintain.

Cheers,
Dimitre Novatchev.




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