Re: [Yaml-core] unspecified plain scalars - a simple proposal

[Clark C. E. <cc...@cl...>]

Ok.  Another pass; borrowing T.Onoma's idea to use '?' to signify an
unspecified tag. We define parser syntax-shorthand rules, from the
untagged varieties of each node/style to a final tag reported:

  untagged mapping      ->  ?mapping
  untagged sequence     ->  ?sequence
  untagged plain scalar ->  ?scalar
  untagged other scalar ->  tag:yaml.org,2002:str    # Unicode String
         ! other scalar ->  ?scalar

Examples:

  ---                                  # ?sequence
  - unspecified                        # ?scalar
  - "string"                           # tag:yaml.org,2002:str
  - {}                                 # ?mapping
  - ! "implicit but quoted"            # ?scalar
  - 'also string'                      # tag:yaml.org,2002:str
  - !!str unquoted but specified       # tag:yaml.org,2002:str
  - >                                  # tag:yaml.org,2002:str
    folded scalar
  - ! >                                # ?scalar
    implicit folded scalar
  ...

Advantages:

  - no syntax production changes, just parser cooking rules
 
  - no way to accidently ask for a ?tag via the !tag mechanism,
    since !tag only makes global:uri or !private sorts of tags.

  - ?tag as reported signifies it is a 'meta' or 'unknown',
    the ? serves as a clear warning that this was an "implicit"
    tag and not provided by the author of the document.

  - ?tag has a _kind_ just like every other tag, this
    makes implementation easy for lookup tables, etc.

  - no special model or processing rules, application can do
    what ever it wishes with the 'implict' tags, which are
    neither private nor global.

That's it.

Clark

P.S. If Oren wishes to include a 'resolution' phase that is in the spec
that talks about how all '?tags' are converted to private or global
tags... that is _fine_ with me.  However, let's be perfectly clear here.
I'm not asking for anyhthing other than a simple syntax parsing rule
here.  In particular, I'm not asking about "extra" steps, or anything
else that is special.  If an _application_ wishes to treat these
bloddy ?implicti tags in a special manner... good for them.