Re: [vwrap] ECMA-262 and the Real LLSD type

[Meadhbh Hamrick <[e-mail]>]

hmm... the ecmascript 5.0 spec seems to imply the string "-Infinity"
is a valid expression of a number, but note 4 on page 217 of the spec
implies that in JSON, you don't get exceptional values like Infinity
or NaN. or rather, both are represented as nulls.

it could be possible to encode all exceptional real values to null,
but when they're deserialized, there would be no way to tell which
exceptional value it was. so you could serialize a value that's
infinity, and deserialize something taht's NaN. but, in theory, this
should be copacetic for JSON parsers.

or... we could layer something on top of JSON to preserve the NaNs and
Infinities. we could come up with a standard way of representing these
values as strings or binaries. (if strings, then the simple strings
listed in the draft. if binaries, maybe the binary patterns in 754
that represent them.) but this will require asReal() and serialize()
methods in LLIDL libraries to understand the usage.

or we could punt and pretend negative infinities don't exist.

ideas? preferences? john, you're out in front as an implementer. what
works for you?

-cheers
-meadhbh
--
meadhbh hamrick * it's pronounced "maeve"
@OhMeadhbh * http://meadhbh.org/ * [e-mail]



On Thu, May 6, 2010 at 10:36 AM, Hurliman, John <[e-mail]> wrote:
> In draft-hamrick-llsd-00 "3.2. JSON Serialization" it states:
>
>   Real  LLSD 'Real' values are represented by the JSON non-terminal 'number'.
>
> Then later in "Appendix A. ABNF of Real Values" it lists a series of strings that can be converted into real values:
>
>   negative-infinity =  %x2D.49.6E.66.69,6E.69.74.79   ; "-Infinity"
>   negative-zero     =  %x2D.5A.65.72.6F               ; "-Zero"
>   zero              =  %x30.2E.30                     ; "0.0"
>   positive-zero     =  %x2B.5A.65.72.6F               ; "+Zero"
>   positive-infinity =  %x2B.49.6E.66.69,6E.69.74.79   ; "+Infinity"
>   signaling-nan       =  %4E.61.4E.53                   ; "NaNS"
>   quiet-nan         =  %4E.61.4E.51                   ; "NaNQ"
>
> Does this mean that an LLSD real type with a value of -Infinity needs to be converted to a JSON string, and would be decoded on the receiving side as an LLSD string with value "-Infinity" (that happens to have a valid conversion to an LLSD real)? ECMA-262 does not support Infinity, NaN, etc. for the JSON 'number' type so it looks like we need to transmit those values as strings.
>
> John
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