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
Saxonica

On 6 May 2014, at 23:48, Michael Sokolov <msokolov@xxxxxxxxxxxxxxxxxxxxx>
wrote:

> On 5/6/2014 6:41 PM, Michael Kay mike@xxxxxxxxxxxx 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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