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

[Robin Berjon]

Hi Jeni,

Jeni Tennison wrote:
>   [Issue: Should we have node sets instead of generic lists?]

I prefer generic lists as they tend to be more powerful. I guess we can get set 
functionality with a set() function, or something similar.

>   [Issue: Should we allow only flattened lists rather than allowing
>    lists to hold lists?]

I think lists should be able to hold lists.

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

heterogenous

>   [Issue: Should the string "false" cast to boolean false?]

I think that would be going a bit too far with dwimery.

>   Lists are cast to strings and numbers by converting the first value
>   in the list to a string or number; if the list is empty you get an
>   empty string or NaN. Lists are cast to boolean true if they contain
>   any values, boolean false if they do not.

Defaulting to the first item seems counter intuitive to me.

>   [Issue: Should lists be converted to strings by concatenating the
>    string value of each value, with spaces as separators?]

Yes, I think that is more user friendly (and of course doesn't preclude us from 
providing a separate join() function).

In addition to that, I think that lists should numify to the number of their 
items (flatly, not taking into account the length of their content), and thus 
that empty lists should numify as 0, not NaN. An empty list is still a list, 
even if it's a list of nothing. NaN is not a number, but zero is (I hope the 
parallel is clear).

>   [Issue: Do we need any more built-in data types?]

The only one I can think of is functions. A language that can't pass those 
around is very quickly limited.

-- 
Robin Berjon <robin.berjon at expway.fr>
Research Engineer, Expway
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