[pmwiki-users] RFC: hypothetical PageVariableExtensions recipe

[Patrick R. Michaud]

On Wed, Apr 12, 2006 at 05:28:49PM +0200, Dominique Faure wrote:
>   (:initvars myvariable='my value' answer=42:)
> 
> This markup defines two variables. Despite their values are provided
> with the regular syntax: {$myvariable} or {$answer}, they couldn't be
> reached directly from other pages as in {Group.Page$answer} (BTW, this
> is the 1st and I fear unavoidable issue).

It can be made to be reachable from other pages; the variables
just have to be turned into page attributes.  This isn't that
difficult -- PmWiki already does this for the (:title:), (:keywords:),
and (:description:) pages, and in the Cookbook it does it for
the "Summary:", "Version:", and "Votes:" properties.  (I.e., someone
can write {Cookbook.RandomQuote$Summary} to get the summary of the
Cookbook.RandomQuote page.)

> The second issue is that I couldn't (for now) mix variables
> and conditions:
>   (:initvars var='something':)
>   (:if false:)
>   (:initvars var='nothing':)
>   (:if:)
>   var's value is {$var}
> renders as:
>   var's value is nothing
> which is not what is expected.

...welcome to PmWiki's chicken-and-egg problem.  The question is
one of ordering -- in this case, the ordering between the
(:initvars:) markup and the (:if:) markup.

If we say that (:initvars:) is to be processed before (:if:), 
then one cannot use conditional markups to control (:initvars:).

If we say that (:initvars:) is to be processed after (:if:),
then we cannot use page variables set by (:initvars:) as part
of an (:if:) conditional -- i.e., we cannot do

    (:initvars super=hello:)
    (:if equal {$super} "hello":)
    Alas, we'll never see this.
    (:if:)

As I've mentioned a couple of times before -- I don't yet have a 
good answer to these problems except by drastically re-working 
PmWiki's formatting engine (likely breaking a lot of recipes 
and sites in the process).

However, I do have some mediocre answers to the problem, such as 
using different directives depending on when we want the variable
to be initialized, but I fear that approach will simply end up 
being too confusing to be practical.

Adding this sort of capability is something I definitely want to
do for PmWiki, but I'm waiting for a good answer.

What order are you planning to use for (:initvars:), {$...},
and (:if:) markups?

Pm