I am having a problem with an ambiguous Xtext grammar, but I just cannot find the correct solution.
Program: (statements+=Statement)+
Statement: (AssignmentStatement | ResetStatement);
ResetStatement returns Statement:
'RESET' (fields+=Identifier)+
;
AssignStatement returns Statement:
target=Identifier ':=' object=Identifier
;
The problem I get is that the RESET statement may have several fields to RESET; however, when a ':=' token is located, the parser should detect the beginning of an AssignmentStatement instead. I have tried using syntactic predicates, but I was only able to disambiguate the grammar doing:
ResetStatement returns Statement:
'RESET' =>(fields+=Identifier)+
;
However, as you might notice that is not the expected behavior, as:
RESET ID1 ID2
ID3 := ID1
Returns an error at the ':=' token. I tried adding the predicate marker to the AssignmentStatement:
Statement: (=>AssignmentStatement | ResetStatement);
And also:
AssignStatement returns Statement:
=>(target=Identifier ':=') object=Identifier
;
But with no success. The error is in all the cases:
[fatal] rule ruleResetStatement has non-LL(*) decision due to recursive rule invocations reachable from alts 1,2. Resolve by left-factoring or using syntactic predicates or using backtrack=true option.
I am quite lost so any hints are well appreciated.
