afterthought about the API

Hi all,

last week, we discussed about return values; I asked why use exception 
rather than null values when no value is available.

Chris's answer was that an exception can carry the *reason* why there 
was no value. I guess the rationale is that reasons could be sth like:
  - property has no value in source
  - property is not specified in source
  - property is not supported by source format
  - value of the property could not be converted to the return datatype
  ...

I think this argument makes sense: it is useful to know the reason why 
there is no value.

However, I keep thinking that

   c = md.creator;
   if (c != null) {
     ...
   }

is much easier to write and read than

   try {
     c = md.creator;
     ...
   }
   catch (err) {
     if (err.name != "NoValue") { throw err; }
   }

so I think (again) that for easing the simple cases, we should strick to 
a null value.

I guess the NoValue.message feature could be replace by somethinh like a 
getDiagnoss() method retrieving the reason for the absence of value. For 
example :

   c = md.creator;
   if (c == null) {
     alert(md.get_diagnosis("creator"));
   } else {
     ...
   }


   pa