Re: [xsl] () eq () vs () = ()

[David Carlisle <davidc@xxxxxxxxx>]

On 30/09/2011 11:48, Andrew Welch wrote:
> () = () returns false
>
> deep-equals((),()) returns true
>
> That's interesting, I'm guessing it has to be a 'just because'


it can be sort of justified

deep-equals tries to tell you if the sequences passed in as arguments 
are equal or not and () and () being the same are equal as sequences.

eq and = never consider the sequence as a whole, they only consider 
individual items

eq just considers single items and (because if sql heritage, probably, 
empty sequences)  so returns () when given ().

= is an existential quantified comparison and the answer to
"is there an item in the first sequence equal to an item in the second"
is trivially false, since there are no items, so = returns false.

So, each operator (with the possible exception of eq, which would 
perhaps most naturally have been defined to be an error on () eq () )
has a natural justification, and so the user will never be confused and 
order is restored to the universe...

David


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