No more parameter ports

Hi folks,

I expect many of you have seen the requirements document (still an
unofficial draft) that the XProc WG produced in Edinburgh:

  http://www.w3.org/XML/XProc/docs/xproc-v2-req.html

I want to draw particular attention to the "simplify parameters"
requirement:

  Experience with parameters in XProc 1.0 reveals that they are too
  complicated. They often cause user confusion and introduce syntactic
  complexity not justified by their function. XProc v2.0 must
  dramatically simplify parameters, perhaps simply removing parameter
  ports altogether without replacing them with a new mechanism of
  equivalent power (and complexity).

Not inventing a new mechanism would mean that p:with-param would still
exist but parameter ports would not. Consider this pipeline:

  <p:declare-step name="main">
    <p:input port="source"/>
    <p:output port="result"/>
    <p:option name="page-size" select="'A4'"/>

    <p:xslt>
      <p:input port="stylesheet">
        <p:document href="style.xsl"/>
      </p:input>
      <p:with-param name="page-size" select="$page-size"/>
      <p:with-param name="style" select="'draft'"/>
    </p:xslt>
  </p:declare-step>

Without parameter ports that would be valid (no more stupid warnings
about unbound parameter input ports, thank you very much!)

The pipeline caller could change the value of the 'page-size'
parameter by passing in the page-size option to the pipeline. They
could not change the value of the 'style' parameter or pass in any
other parameters.

On the one hand, this is a decrease in functionality. On the other,
the complexity of parameters VASTLY outweighs the practical utility of
that functionality (in the experience of the members of the WG present
in Edinburgh).

Your thoughts on this trade off would be most appreciated.

                                        Be seeing you,
                                          norm

-- 
Norman Walsh
Lead Engineer
MarkLogic Corporation
Phone: +1 512 761 6676
www.marklogic.com