Re: Support of lists in PRD

My $0.02:

Sandro Hawke wrote:
> Can lists contain other lists?
>
> Can lists contain objects?  (eg rif:local and rif:iri consts that
> represent frames, or something?)
>   
I think lists should be (individuals) in the domain, and lists should be 
able to contain any individual. I.e., "yes" and "yes" to the above 2 
questions.
> If so, would expect some kind of type/class constraints on these objects?
>   
Yes, and I would like such constraints on frame slots as well.
> Can lists contain variables?  For example, the list [1, ?x, 3], with a
> variable in it, can "contain" anything, but once it does and ?x is
> bound, then it only contains 1, 3, and that thing.  This is Prolog's
> list behavior, and people on the telecon the other day said it was fine
> for PRD, but I suspect on closer inspection it will turn out to be a
> real problem.
>   
Are you asking if lists should be mutable or immutable?  I think mutable 
lists will be too hard to specify.
> Can you construct a list?     Something like:
>          if p(?x) and q(?y) 
>          then 
>             create new list x : [?x ?y]
>             assert pq(x)
>   
yes.
> In terms of functions/operators (getFirst, ...) how does this look:
>      http://www.w3.org/TR/xpath-functions/#sequence-functions
>   
It will take some work but its a good place to start. xpath sequences 
are tailored to holding xml document nodes, and some of the builtins, 
like fn:boolean, don't seem appropriate.  Also, xpath sequences are flat 
(don't contain sequences).