Parameter serialization

When you write an XProc step that has a parameter input port, the XProc
spec does not strictly say how the parameters are serialized on the input
port.

For instance, calabash outputs a sequence of c:param and c:param-set
elements, (basically just giving you whatever you put in, and appends a
c:param-set at the end containing all your p:with-param parameters).
calumet on the other hand gives you a sequence of c:param elements (no
c:param-set wrapping).

I don't know why the spec explicitly states that you can't have a
non-sequence parameter input port, but if it had been possible to declare a
non-sequence parameter input port, then all the parameters would have to be
combined into a c:param-set. I see no reason to have a sequence of
parameters really, since the serialization of the parameters are undefined
and you can't have multiple parameters with the same name (for some reason
- I'm guessing the XSLT use-case).

I would find it easier to work with parameters if they were all wrapped
into a single c:param-set. Alternatively I could live with a sequence of
c:params (like calumet does it); the important thing is that the format is
predictable so that I don't have to preprocess the parameters before
applying any of my own transformations to the set of parameters.

The following XProc script provides some parameters to a step and outputs
how they are serialized. Note also that this script fails if you remove the
sequence attribute from the p:output in the ex:identity step. If you
haven't specified sequence="true" on the parameter input port, then there
are no apparent reason for getting the
XD0006<http://www.w3.org/TR/xproc/#err.D0006>error unless you have
read the part of the spec that states that parameter
ports defaults to sequence="true".
<?xml version="1.0" encoding="UTF-8"?>
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" xmlns:c="
http://www.w3.org/ns/xproc-step" xmlns:ex="http://example.net/ns"
version="1.0">

    <p:output port="result" sequence="true"/>

    <p:declare-step name="main" xmlns:p="http://www.w3.org/ns/xproc"
xmlns:c="http://www.w3.org/ns/xproc-step" xmlns:ex="http://example.net/ns"
type="ex:identity" version="1.0">

        <p:input port="source" primary="true" kind="parameter"
sequence="true"/>

        <p:output port="result" sequence="true">
            <p:pipe port="source" step="main"/>
        </p:output>

        <p:sink>
            <p:input port="source">
                <p:empty/>
            </p:input>
        </p:sink>

    </p:declare-step>

    <ex:identity>
        <p:with-param name="with-param-before"
select="'with-param-before'"/>
        <p:with-param name="param5" select="'value5-1'"/>
        <p:input port="source">
            <p:inline>
                <c:param-set xmlns:c="http://www.w3.org/ns/xproc-step">
                    <c:param name="param1" value="value1"/>
                    <c:param name="param3" value="value3-1"/>
                </c:param-set>
            </p:inline>
            <p:inline>
                <c:param-set xmlns:c="http://www.w3.org/ns/xproc-step">
                    <c:param name="param2" value="value2"/>
                    <c:param name="param3" value="value3-2"/>
                    <c:param name="param4" value="value4-1"/>
                    <c:param name="param5" value="value5-2"/>
                </c:param-set>
            </p:inline>
            <p:inline>
                <c:param name="unwrapped-param"
value="unwrapped-param-value"/>
            </p:inline>
        </p:input>
        <p:with-param name="with-param-after" select="'with-param-after'"/>
        <p:with-param name="param4" select="'value4-2'"/>
    </ex:identity>

</p:declare-step>


This is the result for calabash:
<c:param-set xmlns:c="http://www.w3.org/ns/xproc-step">
    <c:param name="param1" value="value1"/>
    <c:param name="param3" value="value3-1"/>
</c:param-set>
<c:param-set xmlns:c="http://www.w3.org/ns/xproc-step">
    <c:param name="param2" value="value2"/>
    <c:param name="param3" value="value3-2"/>
    <c:param name="param4" value="value4-1"/>
    <c:param name="param5" value="value5-2"/>
</c:param-set>
<c:param xmlns:c="http://www.w3.org/ns/xproc-step" name="unwrapped-param"
value="unwrapped-param-value"/>
<c:param-set xmlns:c="http://www.w3.org/ns/xproc-step">
    <c:param name="param5" namespace="" value="value5-1"/>
    <c:param name="param4" namespace="" value="value4-2"/>
    <c:param name="with-param-after" namespace="" value="with-param-after"/>
    <c:param name="with-param-before" namespace=""
value="with-param-before"/>
</c:param-set>


This is the result for calumet:
<c:param name="with-param-before" namespace="" value="with-param-before"
xmlns:c="http://www.w3.org/ns/xproc-step"/>
<c:param name="param5" namespace="" value="value5-2" xmlns:c="
http://www.w3.org/ns/xproc-step"/>
<c:param name="param1" namespace="" value="value1" xmlns:c="
http://www.w3.org/ns/xproc-step"/>
<c:param name="param3" namespace="" value="value3-2" xmlns:c="
http://www.w3.org/ns/xproc-step"/>
<c:param name="param2" namespace="" value="value2" xmlns:c="
http://www.w3.org/ns/xproc-step"/>
<c:param name="param4" namespace="" value="value4-2" xmlns:c="
http://www.w3.org/ns/xproc-step"/>
<c:param name="unwrapped-param" namespace="" value="unwrapped-param-value"
xmlns:c="http://www.w3.org/ns/xproc-step"/>
<c:param name="with-param-after" namespace="" value="with-param-after"
xmlns:c="http://www.w3.org/ns/xproc-step"/>


I would've liked:
<c:param-set xmlns:c="http://www.w3.org/ns/xproc-step">
    <c:param name="with-param-before" value="with-param-before"/>
    <c:param name="param5" value="value5-2"/>
    <c:param name="param1" value="value1"/>
    <c:param name="param3" value="value3-2"/>
    <c:param name="param2" value="value2"/>
    <c:param name="param4" value="value4-2"/>
    <c:param name="unwrapped-param" value="unwrapped-param-value"/>
    <c:param name="with-param-after" value="with-param-after"/>
</c:param-set>


What do you think?

Jostein