Conditionals

With inputs, outputs, and sub-pipelines out of the way, we come,
somewhat indirectly, to conditionals. Despite all the complex drawings
that we had on the board at the f2f, I think a conditional (at least
one where the condition can be evaluated before execution of the
pipeline begins) is fairly simple conceptually.

Let's say we have a p:choose element. If we say that all the branches
of the choice must have the same number of inputs and outputs then
I think it's not too difficult to understand:

  <p:choose>
    <p:input name="schemas" label="s"/>
    <p:input name="document" label="d"/>
    <p:output label="ok"/>

    <p:when test="$status = 'draft'">
      <p:step name="devnull">
        <p:input use="s"/>
      </p:step>
      <p:step name="identity">
        <p:input name="document" use="d"/>
        <p:output/>
      </p:step>
    </p:when>
    <p:when test="$status = 'final'">
      <p:call-pipeline name="expandandvalidate">
        <p:input name="schemas" use="s"/>
        <p:input name="document" use="d"/>
        <p:output/>
      </p:call-pipeline>
    </p:when>
    <p:otherwise>
      <p:error>
        <p:input use="s"/>
        <p:input use="d"/>
        <p:output/>
        <p:message>What the heck did you set $status to exactly?</p:message>
      </p:error>
    </p:otherwise>
  </p:choose>

Like a sub-pipeline, a p:choose defines its inputs and outputs, that
way it fits into the pipeline irrespective of what branch is selected.

I haven't got my head around how to define tests that are evaluated at
runtime based on currently active inputs and outputs.

                                        Be seeing you,
                                          norm

-- 
Norman.Walsh@Sun.COM / XML Standards Architect / Sun Microsystems, Inc.
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