[xquery-talk] Adaptive serialization of an empty sequence

[Joe Wicentowski]

Thank you, Mike.  That explanation is perfectly reasonable; this handling
certainly meets the stated intention.

Joe

On Sat, Apr 14, 2018 at 2:58 PM Michael Kay <mike at saxonica.com> wrote:

> As always with "why?" questions, it's difficult to know what kind of
> answer you want, between
>
> (a) Where does the spec say this should happen?
>
> (b) Why does the the spec say this should happen?
>
> and (b) breaks down to either
>
> (b1) Why would this be a reasonable choice for the spec-writers to make?
>
> (b2) As a matter of historical record, who proposed that it should be like
> this and what justification did they put forward?
>
> Regarding (a), the spec says:
>
> <quote>
> Each item in the supplied sequence is serialized individually as follows,
> with an occurrence of the chosen item-separator between successive items.
> </quote>
>
> I think it's a reasonable reading of that that adaptive(S) ==
> string-join(S!adaptive(.), item-separator), which leads to the conclusion
> that the serialization of () is "".
>
> Regarding (b2), my main recollection of relevant discussions concerns
> streamability: specifically, it should be possible to serialize each item
> independently without knowing what follows. But if someone had proposed
> serializing () as "()", I don't think that could really have been opposed
> on streamability grounds. But I don't think anyone proposed it.
>
> Regarding (b1), the main clue about the WG's thinking is the sentence
>
> <quote>
> The intention of this is to allow any valid XDM instance to be serialized
> without raising a serialization error.
> </quote>
>
> So you find that the adaptive method focuses on how to serialize cases
> that otherwise would fail. Serializing the empty sequence wouldn't
> otherwise fail, so I guess it didn't receive much attention. Whether a
> proposal to serialize () as "()" would have been accepted is anyone's guess.
>
> Michael Kay
> Saxonica
>
>
> > On 14 Apr 2018, at 19:14, Joe Wicentowski <joewiz at gmail.com> wrote:
> >
> > Hi all,
> >
> > Many thanks, as always, for the very helpful feedback here.
> >
> > I have noticed that Saxon, eXist, and BaseX all serialize the empty
> sequence `()` not as `()` but instead as the empty string ``.  Sample code:
> >
> >   serialize((), map { "method": "adaptive" })
> >
> > I was expecting to see `()` because when serializing a map entry, the
> empty sequence is serialized as `()`:
> >
> >   serialize(map { "test": () }, map { "method": "adaptive" })
> >
> > This returns `map{"blah":()}`.
> >
> > Can anyone enlighten me on why the empty sequence is serialized as `()`
> in the latter context and the empty string in the former?
> >
> > Thanks,
> > Joe
> > _______________________________________________
> > talk at x-query.com
> > http://x-query.com/mailman/listinfo/talk
>
>
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