On 3 October 2011 11:11, Brandon Ibach
<brandon(_dot_)ibach(_at_)single-sourcing(_dot_)com> wrote:
On Sat, Oct 1, 2011 at 12:01 PM, Andrew Welch
<andrew(_dot_)j(_dot_)welch(_at_)gmail(_dot_)com> wrote:
deep-equal(A, B) means (count(A) eq count(B) and every $i in 1 to count(A)
satisfies A[$i] eq B[$i]). Therefore deep-equal((), ()) is true.
Is it fair to say deep-equal could mean:
every $i in 1 to max((count(A), count(B))) satisfies A[$i] eq B[$i]
which would then return false, as its only the length check that is
causing it to return true (and thats only there to avoid also checking
every item in B is equal to A)
Even if this is a reasonable definition for deep-equal (disregarding
the fact that, as Michael pointed out, it doesn't properly handle
values such as NaN or nodes), your assertion that it would return
false for deep-equal((), ()) does not hold
The point I was trying to make was if you don't compare the lengths,
it won't return true because there is nothing to compare, just like =.
You could of course flip that around and say if you start from a
position of true, there's nothing to make that false, but as = returns
false, it would make sense to me to start from a position of false.
I'd echo the comments of others regarding the purpose of deep-equal
(identifying an equivalent structure with equivalent values, node
names and/or node kinds), the structural equivalence of two empty
sequences, and the very much non-intuitive results that would occur if
it didn't work the way it did in this case.
...but there are no equivalent structures or values?
That said, I agree that () eq () not returning false() is not
necessarily intuitive or always convenient for the XSLT crowd, but as
a nod of compatibility for the database/SQL community, which drives
much of XQuery, it seems a reasonable thorn to bear, given the
seemingly rare situations in which it might cause issues.
Yeah I'm happy with a 'just because' reason, but I don't yet know the
benefit of returning () over false, and in what situation you would
use that.
--
Andrew Welch
http://andrewjwelch.com
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