[Yaml-core] %IMPLCIT declaration?

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

Regarding implicit types, there are a few things that must be done:

  (a) Update the main specification to make it absolutely clear
      that implicit typing is optional
      
  (b) Update the type repository to be consistent with examples
      and with itself.
      
Personally, I don't like implicit types; at least not the "ambiguous"
ones we currently have.  It makes for a big wart in the specfication
where we carry a plain-type flag all the way into the representation
(aka graph) model for items which could-possibly-be-impliclty-typed.
Frankly, it's ugly.

What I'd like to see is a simple directive, where one "names" the
implicit types you are using.  If a parser doesn't know about one or
more of the implicit types mentioned, it issues a warning, and
continues.  Something like,

  --- %YAML:1.0 %IMPLICIT:bool;number;date;null
  boolean: True     # !bool
  number: 304.34    # !number
  date: 2003-03-02  # !date
  null: Null        # !null
  ...

vs

  --- %YAML:1.0
  boolean: True     # !str
  number: 304.34    # !str
  date: 2003-03-02  # !str
  null: Null        # !str
  ...
 
In this way, no %IMPLICIT, no implict typing.  If you want an implict
type, you declare it using the directive.  It cleans up the model, and
makes the YAML text portable or at least helps parsers issue warnings
when they don't know about an implicit type. 

Later on, we can add a %SCHEMA directive which will be much more
flexible in the declarations, etc.  But for now, a %SCHEMA is just
out-of-scope.  %IMPLICIT is quite simple and straight-forward.

Cheers!

Clark