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Xtext: Trying to check for cross references but get ambiguous grammar [message #1028653]

Thu, 28 March 2013 14:58

Anja Liro

Messages: 3
Registered: March 2013

Junior Member

Hi,

I am trying to implement something like this:
I have two types, individuals and groups. I can assign one individual to another individual and one group to another. Now I want to be able to assign an individual to a group, but it should be forbidden to assign a group to an individual.

Here is an example:

individual ind1;
individual ind2;
group gr1;
group gr2;

ind2 = ind1; //ok
gr2 = gr1; //ok
gr2 = ind2; //ok
ind2 = gr2; //forbidden

I tried to realize this with the following grammar:

VanillaModel:
	statements+=Statement*;
	
Statement:
	Group | Individual | Assignment;
	
Group:
	'group' name=ID ';' ;

Individual:
	'individual' name=ID ';' ;

Assignment:
	left=[Group] '=' right=[Group] ';'
	| left=[Group] '=' right=[Individual] ';'
	| left=[Individual] '=' right=[Individual] ';'
;

However, this grammar is ambiguous and ANTLR complains, which makes sense

warning(200): ../org.xtext.example.vanilladsl.ui/src-gen/org/xtext/example/mydsl/ui/contentassist/antlr/internal/InternalVanillaDsl.g:232:1: Decision can match input such as "RULE_ID '=' RULE_ID ';'" using multiple alternatives: 1, 2, 3
As a result, alternative(s) 3,2 were disabled for that input

However, shouldn't there be a way to somehow realize this setting? I'm pretty new to Xtext, so I might be just missing something. Does anybody have an idea what I could do?

Thanks a lot

-anja

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Re: Xtext: Trying to check for cross references but get ambiguous grammar [message #1028701 is a reply to message #1028653]

Thu, 28 March 2013 16:24

Christian Dietrich

Messages: 14665
Registered: July 2009

Senior Member

Hi,

introduce a supertype

GoI: Group | Individual;
Assignment:
	left=[GoI] '=' right=[GoI] ';'
;

the rest can be done with a semantic validaton

Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

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Re: Xtext: Trying to check for cross references but get ambiguous grammar [message #1033424 is a reply to message #1028701]

Thu, 04 April 2013 08:07

Anja Liro

Messages: 3
Registered: March 2013

Junior Member

Hi,

Thanks for the reply.
The solution looks good so far.
Just one more question: What is a semantic validation? Where does it happen (in which class/file)? When googling this, I only found semantic predicates which is not the same, is it?

Thanks

-anja

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Re: Xtext: Trying to check for cross references but get ambiguous grammar [message #1033434 is a reply to message #1033424]

Thu, 04 April 2013 08:12

Christian Dietrich

Messages: 14665
Registered: July 2009

Senior Member

Hi have a look at MyDslJavaValidator

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Twitter : @chrdietrich
Blog : https://www.dietrich-it.de

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