• A DSL that is a list of keys and values (with the '=' as the separator between them).
  
• The value field, for sake of simplicity must be an ID type (in reality the value, it will be a custom terminal that consumes tokens up to the end of the line, but not required for the example). IMPORTANT: The implementation cannot use the TERMINAL type to distinguish between a reference an a non-reference. Both a reference value AND a non-reference value are ID type.
  
• There is one global scope for key values. The same key cannot be specified twice (I believe this is the default behaviour anyway).
  
• If the value field starts with 'ref', then the value field should be a reference to a key via the 4th character onward of the text specified for the value. If the value field does not start with 'ref' then the value field is treated as text only.
  
• Holding Ctrl (or the mac equivalent) and clicking a value reference will link to the referenced key, holding ctrl over a non-ref attribute, will do nothing.
  
• Broken links will be flagged as errors.
  
• The 'ref' prefix rule cannot be part of the .xtext file itself, it must be implemented purely in-code (as the purpose of this example is to document how to manipulate such rules)
  

if you have references why dont you use references in the grammar?

Thanks to both that have answered.

Steve: Your answer looks interesting, and its possible this is what I require. Please check my more specific requirements below and let me know if you still believe that this might be a suitable approach.

Christian: Your answer also looks interesting but there are actually scoping rules that come into play here, as a bad reference should be highlighted.

I hate to be bothersome but I feel that scoping is the one area where I can say that, even after reading the manual, and even after reading the previous replies, I am still very unclear as to the way that XText deals with these things. I have lots of questions, but for now, I am confining myself to asking about once concept at a time, which is why the above example looks strange.

Scoping itself is not too much of problem for me. I've written several compilers in JavaCC, some involving very advanced scoping requirements, and I managed to implement these without too much fuss using plain old JDK APIs. Re-implementing the scoping in XText for the purpose of providing an editor is proving more of a challenge.

My own unfamiliarity with the scoping architecture is the problem, not my knowledge of the scoping rules themselves, and that is where I'm having huge issues. I'm eager to understand how all of this works, but unfortunately the documentation lacks concrete examples beyond the scoping-by-rails examples.

So, I'd like to use the above faux-language, and this thread, as a method of possibly adding a concrete example to a future edition of the XText documentation. My understanding in exchange for sharing that understanding so to speak.

So, here are the requirements:

Advanced Scoping Question 1

• A DSL that is a list of keys and values (with the '=' as the separator between them).
  
• The value field, for sake of simplicity must be an ID type (in reality the value, it will be a custom terminal that consumes tokens up to the end of the line, but not required for the example). IMPORTANT: The implementation cannot use the TERMINAL type to distinguish between a reference an a non-reference. Both a reference value AND a non-reference value are ID type.
  
• There is one global scope for key values. The same key cannot be specified twice (I believe this is the default behaviour anyway).
  
• If the value field starts with 'ref', then the value field should be a reference to a key via the 4th character onward of the text specified for the value. If the value field does not start with 'ref' then the value field is treated as text only.
  
• Holding Ctrl (or the mac equivalent) and clicking a value reference will link to the referenced key, holding ctrl over a non-ref attribute, will do nothing.
  
• Broken links will be flagged as errors.
  
• The 'ref' prefix rule cannot be part of the .xtext file itself, it must be implemented purely in-code (as the purpose of this example is to document how to manipulate such rules)
  

Now, this is a completely fake example, but the method to solve this problem is interesting and will reveal how XText works internally to those unfamiliar with EObjects, etc.

Given how limited the requirements are, I'd be happy with a fully working example rather than snippets, and like I said, I'd be willing to document how and why it works.

I'd also like to say, that I have some other more complex concrete scoping examples which upon some answer for this example, I'll be willing to post in a similar fashion. I hope that these examples can be used as a means of documenting the complexities of the scoping architecture of XText. Having a lot of information locked away in these forums is good, but having more single-concept examples in the main documentation is better.

The 'ref' prefix rule cannot be part of the .xtext file itself

ParameterSet:
	param+=Parameter (',' param+=Parameter)*
;
Parameter:
	DataParameter | StringParameter | BareWordParameter | Integer
;

x = y
z = "some string"
w = ref x