Yayson (proposal for a YAML presentation embedded within JSON for browser clients)

Dear all

Thought I would pop up on this list to sound out people's feelings about the following proposal.

Motivation:

* YAML syntax is quite big and complex to fully support
* No full YAML parser appears to exist for browser Javascript clients
* Web browsers have fast, native JSON parsers which it's nice to use where possible 
* Plain JSON lacks custom data types and graph-based serialization features
* People are reinventing the wheel trying to add these things on top of JSON in assorted poorly-standardised ways
* YAML and JSON are already friendly, this would make them friendlier still :)

Proposed solution is an embedding of YAML inside JSON, which could be implemented as an alternative presentation phase for a YAML library. The goal is that:

* Data which would happily serialize as plain JSON, maps directly to its plain JSON representation (with the exception of some reserved key names required for the embedding)
* Data which is not pure-JSON-compatible (uses types other than map,seq,string,int,float,null, or does not conform to a simple tree structure, containing cyclic references for example) maps to a subset of JSON from which the original YAML node tree can be recovered.

Available cheesy name: Yayson. Sorted.

I'm sure I'm missing some subtleties, but here's an outline of how this could be achieved. First tags:

{
"$tag": "!!timestamp",
"$value": "2001-12-15T02:59:43.1Z"
}

{
"$tag":  "!my-app-specific-type",
"$value": {"is constructed from": "a map"},
}

Or a more concise alternative syntax for this:

{
"$tag":  "!my-app-specific-type",
"is constructed from": "a map"
}

(I would suggest that full support for things like tag namespace aliases via the %TAG directive not be supported here, to keep it simple; ! and !! could have their usual meanings as tag prefixes, or you could use a full tag URI)

Now anchors:

{
"$anchor": "foo",
"$value": "some string"
}

{
"$anchor": "foo",
"$tag":    "!!timestamp",
"$value":  "2001-12-15T02:59:43.1Z"
}

{
"$anchor": "foo",
"$value": {"anchor is for": "a map"},
}

or the alternative in the case of a map:

{
"$anchor": "foo",
"anchor is for": "a map"
}

Now aliases:

{"$alias": "foo"}

Some caveats:

This introduces 4 'reserved' key names for maps. Plain JSON data containing these keys would not actually be able to serialize in the usual way; they'd need to be escaped, via eg:

{"$$anchor": "the key unescapes to $anchor"}
{"$$$anchor": "the key unescapes to $$anchor"}
..

Some more special forms may be needed to express some other YAML features (like arbitary objects as keys of maps) not expressible in JSON, eg:

{
"$tag": "!!map",
"$pairs": [
  [{"key": "object"}, {"value": "object"}],
  [{"other key": "object"}, {"value": "object"}]
]
}

Anyway let me know what you think!

-Matt
------------------------------------------------------------------------------
ThinkGeek and WIRED's GeekDad team up for the Ultimate 
GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the 
lucky parental unit.  See the prize list and enter to win: 
http://p.sf.net/sfu/thinkgeek-promo