[xquery-talk] [xsl] Re: Random number generation : requirements

Michael Kay mike at saxonica.com
Tue May 6 15:58:43 PDT 2014

The big problem with a nondeterministic random() function is not defining the order of execution, but preventing it being optimised out of a loop. For example, how do we ensure that

$xxx[random() gt 0.5]

doesn't select either all the values or none?

Anyway, we're not planning to do non-determinism. This exercise is about designing a deterministic way to meet the requirement.

Michael Kay

On 6 May 2014, at 23:48, Michael Sokolov <msokolov at safaribooksonline.com> wrote:

> On 5/6/2014 6:41 PM, Michael Kay mike at saxonica.com wrote:
>>> My policy on side effects is: all expressions containing side effects are going to be evaluated in order
>> I do something like that in Saxon as well. But I don't attempt to define what "in order" means; for example, the order in which different global variables are evaluated. Doing this in the spec would be much more problematic.
> You don't think it would be reasonable to say something to the effect that the order in which non-deterministic expressions are evaluated is non-deterministic (ie implementation-defined)? Certainly it would be reasonable enough in the case of a random number generator.  Although I suppose if you are going to seed it, you would like the seed to effect the random numbers that are generated.
> -Mike
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