So as a first comment (will look at details later, though I have confidence
it's well thought-out given the background work you've done, Frank; thanks
for that), let me explain why the syntax is the way it is. E.g. it wasn't
an accident.
Given that CSL is an XML language, I really wanted to keep the language as
clean to process as possible using the most pure XML processing language
extant: XSLT.
So the idea was any significant CSL logic was represented in terms of
native XML structures: nodes (elements and attributes) and values.
Going this route, where the values themselves take on core logical
semantics, and where those values themselves must be processed (though
admittedly, the processing is simple here; just split on a colon and treat
as key-value), is a change in direction.
I suggest if we do go this route we have a firm logical basis on which we
do this, so that we can have a consistent answer on what's OK, and what's
not, going forward.
Bruce
On Mon, Apr 15, 2013 at 11:41 AM, Frank Bennett <[email protected]>wrote:
> Several months ago, I posted an issue on the schema tracker concerning
> the "none" attribute. After giving it some more thought, I've come up
> with the fuller proposal below. The changes proposed are
> backward-compatible with the current schema.
>
> At Rintze's suggestion I ran this past Sebastian and processor
> developers before posting here for broader review. The response has
> been positive: Sebastian is in favour; Sylvester has implement the
> syntax in citeproc-ruby; and Andrea and Charles have indicated that
> they are ready to go forward with implementation.
>
> Open issues are:
>
> * Whether to include a *-none suffix on attributes in addition to
> *-any and *-all (I left this out, Sylvester suggested including it,
> and I can't see a problem); and
> * Constraints to be imposed by the schema.
>
>
>
> A test that exercises the syntax is available here:
>
>
> https://bitbucket.org/fbennett/citeproc-js/src/tip/tests/fixtures/local/condition_PlusMinus.txt?at=default
>
> The proposal would introduce two changes:
>
> * An optional not: prefix on elements of the list argument to
> certain condition attributes; and
>
> * Alternative forms of several condition attributes, identified
> by an *-all or *-any suffix.
>
> Under the proposal, conditional evaluation would take place as
> follows:
>
> (1) Each attribute argument list element is evaluated, returning
> "true" or "false";
>
> (2) For each attribute, the results from (1) are evaluated using "all"
> (if the attribute suffix is "-all") or "any" (if the attribute
> suffix is "-any"), following the rules described in the CSL
> Specification. Legacy attributes with no suffix follow the value
> of the "match" attribute, or "all" if no companion "match"
> attribute is present).
>
> (3) The "match" attribute evaluates the results from (2) using
> "all" or "any" as described in the CSL Specification,
> returning an overall test value of "true" or "false".
>
> This would allow two testing patterns that are not currently possible:
>
> * A single test can require both true and false values; and
>
> * Attributes can set an evaluation method ("all" or "any") independent
> of the "match" attribute that controls inter-attribute evaluation.
>
> This flexibility makes it possible to reduce the bulk of CSL code.
> As one example, the construct below is found in several styles in the
> CSL repository:
>
> <macro name="year-date">
> <choose>
> <if type="webpage">
> <choose>
> <if variable="issued">
> <date variable="issued">
> <date-part name="year"/>
> </date>
> </if>
> <else>
> <date variable="accessed">
> <date-part name="year"/>
> </date>
> </else>
> </choose>
> </if>
> <else>
> <date variable="issued">
> <date-part name="year"/>
> </date>
> </else>
> </choose>
> </macro>
>
> What the code does is to print the "accessed" date if the item is a
> webpage and has no "issued" date, and otherwise to print the "issued"
> date, regardless of item type. A nested cs:choose statement is needed,
> because negative and positive conditions cannot be declared together
> on the same cs:if or cs:else-if element.
>
> With the proposed syntax, the code sample above can be rewritten as a
> single cs:choose statement:
>
> <macro name="year-date">
> <choose>
> <if type="webpage" variable="not:issued" match="all">
> <date variable="accessed">
> <date-part name="year"/>
> </date>
> </if>
> <else>
> <date variable="issued">
> <date-part name="year"/>
> </date>
> </else>
> </choose>
> </macro>
>
> Condition attributes that would accept a not: prefix on argument
> elements and be given alternative *-all and *-any forms under the
> proposal are the following:
>
> * is-numeric
> * is-uncertain-date
> * locator
> * type
> * variable
> * jurisdiction (MLZ only)
> * page (MLZ only)
>
> Frank
>
>
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