W3C home > Mailing lists > Public > public-xml-processing-model-wg@w3.org > March 2008

Re: Variable and option binding proposal

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Thu, 27 Mar 2008 17:01:11 +0000
To: Jeni Tennison <jeni@jenitennison.com>
Cc: Norman Walsh <ndw@nwalsh.com>, public-xml-processing-model-wg@w3.org
Message-ID: <f5babkk85k8.fsf@hildegard.inf.ed.ac.uk>

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Jeni Tennison writes:

> Norman Walsh wrote:
>> / Jeni Tennison <jeni@jenitennison.com> was heard to say:
>> | Norman Walsh wrote:
>> [...]
>> |> The document order of steps is irrelevant in practice. That means we'd
>> |> rules about what happens to variables that occur between steps when
>> |> the steps are reordered. I don't think it'd be easy to understand
>> |> those rules.
>> |
>> | Couldn't you say that the bindings visible to any steps within a given
>> | subpipeline are all the variables that are bound within that
>> | subpipeline, and leave it for the implementation to decide whether it
>> | evaluates all the variables before running the steps, or evaluates
>> | them on demand, or what?
>> |
>> | If the order doesn't matter (to the implementation) then we ought to
>> | let people put them in whatever order feels right to them (just as we
>> | have for steps).
>> Yes, I think so. Having concluded that all the variable bindings will
>> come at the beginning, it's not important when or if their values
>> are actually computed (unless they're actually referenced at run time,
>> of course :-)
>
> I was arguing that we shouldn't specify that all the variable bindings
> must come at the beginning if it doesn't matter when or if their
> values are actually computed. Let people put them where it makes sense
> to them.

I'm in two minds -- on the one hand, that will just encourage people
to try to connect variables to the outputs of their siblings, which is
not allowed.  On the other hand, they'll learn soon enough not to do
that, and putting vars near the expressions which use them is a
convenience for authors and readers. . .

ht
- -- 
 Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
                     Half-time member of W3C Team
    2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
            Fax: (44) 131 650-4587, e-mail: ht@inf.ed.ac.uk
                   URL: http://www.ltg.ed.ac.uk/~ht/
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Received on Thursday, 27 March 2008 17:01:57 GMT

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