[Ur] Polymorphic variants and JSON

[Edward Z. Yang]

Oh, never mind, I'm being silly.

If I understand the current json_record right now, it requires all of
the fields to be present, so this is not so good for the style of encoding
variants I described earlier.  So I'm going to see if I can modify
json_record into a variant json_variant (haha I made a pun), which
takes a type level record but requires only /one/ key to be present.
Or maybe it'll just prefer the first one that shows up?

Edward

Excerpts from Adam Chlipala's message of Sat Apr 14 13:39:34 -0400 2012:
> Edward Z. Yang wrote:
> > I'm a little confused by the definition of json_record;
> > why does it take a (fl : folder ts) as an argument, but then
> > not use it for anything?
> 
> I think this question refers to 
> http://hg.impredicative.com/meta/file/e7d64ea0f922/json.ur .
> 
> In the definition of [json_record] there, I see the argument [fl] used 
> several times.