[Xpath-ng] Proposal for definition of values/lists

[David Rosenborg]

Hi Jeni,
 
>   Every value in XPath NG is a list or an atom. A list is a sequence
>   of zero or more values. Atoms are of two kinds: nodes and data.
>   Nodes are atoms that have identity whereas data are atoms that do
>   not have identity.

What's the purpose of having two kinds of atoms? Yes, nodes have
identity, other data types have not. But there are numerous things
that differentiate value types, what makes the identity property
so special?

>   [Issue: Should we have node sets instead of generic lists?]
Not sure, I think no if we can retain most of the XPath 1.0 semantics.

>   [Issue: Should we allow only flattened lists rather than allowing
>    lists to hold lists?]
No, I think we should allow nested lists

>   [Issue: Should we allow heterogeneous lists or only allow lists
>    whose items are all nodes, all atoms or all lists?]
Heterogeneous

>   [Issue: Should the string "false" cast to boolean false?]
No, defenitely not IMO

>   [Issue: Should lists be converted to strings by concatenating the
>    string value of each value, with spaces as separators?]
No, provide a join function for this instead

>   [Issue: Do we need any more built-in data types?]
Isn't this part of the anticipated modularity? By built-in you
mean some sort of "core" data model?

> 
> Any comments or thoughts on the above issues? Any other issues that
> I've glided over?

Here's one:

[Issue: Singleton lists, are they treated transparently as the value of their only item?]

Cheers,
David