Re: can we have last() having a consistent value ?

/ Innovimax SARL <innovimax@gmail.com> was heard to say:
| I think that is the last thing I want to have a consistent story
| around before joining the Dark Side
|
| I hear Norm, and he is true, that WE MUST DEFINE A CONTEXT
|
| My point is, CAN WE MAKE IT THE MOST CONSISTENT AS POSSIBLE
|
| XPath says :
|
| [[
| Expression evaluation occurs with respect to a context. XSLT and
| XPointer specify how the context is determined for XPath expressions
| used in XSLT and XPointer respectively. The context consists of:
|
|    * a node (the context node)
|    * a pair of non-zero positive integers (the context position and
| the context size)
|    * a set of variable bindings
|    * a function library
|    * the set of namespace declarations in scope for the expression
|
| The context position is always less than or equal to the context size..
| ]]
|
| Some thoughts

Here are the options as I see them:

1. We use context position and context size and we make them be
correct. The context size is the number of documents in the sequence
and the context position is the number of the document in that
sequence.

2. We use context position and context size and we accept the fact
that we can't reliably set the context size, so we always make it
equal to the context position. (Or we always make it MAXINT; I don't
much care.)

3. We don't use context position and context size and we always
set them both to "1". We use a separate extension function to return
the number of the document in the sequence.

Only in case 1 do we get complete consistency. But that totally
prevents a streaming implementation and requires (possibly massive
amounts of) buffering. I don't think it'll be difficult to persuade
our users that this is an unattractive option. (What's more, if they
have a step that actually really needs to know how many documents
are in the sequence, they can compute it with p:count.)

In case 2, we get consistency in the sense that, by analogy with the
xsl:for-each case, the context position (and the position() function)
will count the documents, just as a user would expect. We get some
inconsistency because the last() function returns a value that's
possibly smaller than the actual case will ultimately turn out to be.

In case 3, we get literal consistency in the sense that always
returning "1" is consistent. However, whether or not this is more or
less consistent with the users view is an open question. A user who
imagines that processing a sequence of documents with a step is
analagous to performing an xsl:for-each operation over the sequence
may be quite surprised to learn that position() returns "1" even after
more than one document has been processed. And with respect to the
context size, our answer is "consistent" but no more-or-less correct
than in case 2 since last() will always return "1" even when there
were 100 documents in the sequence.

Given that in no case except 1 is the last() function useful, and
given that the definition of p:position() has to exactly mirror what
the user might have expected position() to be in case 2, I think it
makes sense to use the context position.

This also means that steps don't have to understand anything about
extension functions.

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | Things work out best for those who make
http://nwalsh.com/            | the best of the way things work out.