Re: custom non-atomic steps?

I'm not sure if I'm a fan of introducing a precompiler (I like to think of
this feature as higher order functions rather than macros, even though what
I outlined might be closer to a way to define macros). The XProc processor
needs to be able to throw a meaningful error with the filename and line
number of where the error occured.


Jostein


On 31 July 2013 18:14, Florent Georges <fgeorges@fgeorges.org> wrote:

> On 30 July 2013 19:52, Norman Walsh wrote:
> > Jostein Austvik Jacobsen writes:
>
>   Hi,
>
> >> Has custom non-atomic steps (steps where you can provide one or more
> >> subpipelines upon invocation) been discussed as a possibility in
> >> XProc v.Next? It would for instance allow us to define our own
> >> custom syntactic sugar.
>
> > I don't think it's been discussed. It's not clear how to describe a
> > custom step in a standard way.
>
>   If we are considering the "macro" approach, if we take the
> initial example again:
>
>     <my:if test="...">
>        <my:xpath-context .../>
>        [ sub-pipeline ]
>     </my:if>
>
> being equivalent to:
>
>     <p:choose>
>        <p:when test="...">
>           <px:xpath-context .../>
>           [ sub-pipeline ]
>        </p:when>
>        <p:otherwise>
>           <p:identity/>
>        </p:otherwise>
>     </p:choose>
>
>   What about the following?:
>
>     <p:declare-macro type="my:if">
>        <p:input  port="source" primary="true"/>
>        <p:output port="result" primary="true"/>
>        <p:xslt>
>           <p:input port="stylesheet">
>              <p:inline>
>                 <xsl:stylesheet version="2.0">
>                    <xsl:template match="/my:if">
>                       <a:choose>
>                          <a:when>
>                             <xsl:copy-of select="@*"/>
>                             <xsl:apply-templates/>
>                          </a:when>
>                          <a:otherwise>
>                             <a:identity/>
>                          </a:otherwise>
>                       </a:choose>
>                    </xsl:template>
>                    <xsl:template match="my:xpath-context">
>                       <a:xpath-context>
>                          <xsl:copy-of select="node()"/>
>                       </a:xpath-context>
>                    </xsl:template>
>                    <xsl:template match="node()" priority="-1">
>                       <xsl:message terminate="yes">
>                          Unknown: <xsl:copy-of select="."/>
>                       </xsl:message>
>                    </xsl:template>
>                 </xsl:stylesheet>
>              </p:inline>
>           </p:input>
>           <p:input port="parameters">
>              <p:empty/>
>           </p:input>
>        </p:xslt>
>     </p:declare-macro>
>
>   This defines a "step like", but which is evaluated at compile-
> time (instead of at run-time), with the corresponding XML as input
> (here the my:if element), and the result is inserted in the lexer
> tree, replacing the initial "macro call".  Here the macro is just
> a stylesheet transforming the my:if into corresponding p:choose
> (actually in an alias namespace, here bound to "a:").
>
>   Regards,
>
> --
> Florent Georges
> http://fgeorges.org/
> http://h2oconsulting.be/
>
>