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Non-LL1 Grammar handling with JvmTypes [message #810326]

Thu, 01 March 2012 00:55

Jens-Uwe Moeller

Messages: 12
Registered: March 2012
Location: Hamburg

Junior Member

Hi,

i would like to define a kind of type definition using xtext, that may either refer to a JvmTypeReference or to an already defined type.

My first idea for the rule looks like

MyTypeDecl returns MyTypeDecl:
	{MyTypeDecl} 'type' name=ValidID 
	(':' type=JvmTypeReference |
	 ':' typesuper=[PmDslTypeDecl]
	);

I know, that a solution could be to use different keywords, like

MyTypeDecl returns MyTypeDecl:
	{MyTypeDecl} 'type' name=ValidID 
	('is' type=JvmTypeReference |
	 'extends' typesuper=[PmDslTypeDecl]
	);

but that is not the solution, I am looking for, as it delegates the problem to the user of my language.

In documentation chapter "The Grammar Language" was a hint to use backtracking, but it was not explained.

I suppose, that this problem is so common, that you already know an elegant solution.

Jens

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