Re: W3C Specification of fn:filter() -- is this a bug

>  You can never guarantee that two expressions are equivalent in your
> sense, because of "errors and optimization". Any construct might raise
> an error - in the case of this example, stack overflow if the recursion
> gets too deep.

What about tail-recursion?

For years we have known recursive expressions whose tail-recursiveness is
correctly recognized in BaseX and it provides correct evaluation regardless
of the input size (recursion depth) but other processors fail miserably...

How much value for the developers would have been provided by the
specification if it mandated proper handling of tail-recursion!!!

The value provided in a document is rather debatable when specifying
"equivalent implementations" that blow up for reasonably long inputs
(several thousand items isn't too high!) when other implementations could
have been provided that demonstrate equivalence with much longer inputs
(millions of items)

Also, why in an XPath specification give "equivalent implementations" in
two different languages neither of which is XPath?

Cheers,
Dimitre

On Sun, Sep 8, 2019 at 5:54 PM Liam R. E. Quin liam@xxxxxxxxxxxxxxxx <
xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:

> On Mon, 2019-09-09 at 00:18 +0000, Dimitre Novatchev
> dnovatchev@xxxxxxxxx wrote:
> > The W3C F&O 3.1 spec (at
> > https://www.w3.org/TR/xpath-functions-31/#func-filter ) says:
> >
> > Rules
> >
> > The effect of the function is equivalent to the following
> [...]
> >
> > Because "equivalent" means the two functions must produce the same
> > result
> > for for all possible values in the same set of arguments,
>
> That is one possible definition of "equivalent" but it is not the one
> used in the Functions and Operators document...
>
> You can never guarantee that two expressions are equivalent in your
> sense, because of "errors and optimization". Any construct might raise
> an error - in the case of this example, stack overflow if the recursion
> gets too deep.
>
> Liam
>
> --
> Liam Quin, https://www.delightfulcomputing.com/
> Available for XML/Document/Information Architecture/XSLT/
> XSL/XQuery/Web/Text Processing/A11Y training, work & consulting.
> Carefoot Web-slave for historical images http://www.fromoldbooks.org/
> 
>


-- 
Cheers,
Dimitre Novatchev
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