Eliminate left recursion in XText

Question

This is part of the grammar of the NuSMV language:

BasicExpression:
Constant | '(' BasicExpression ')' | '!' BasicExpression | BasicExpression '&' BasicExpression;
Constant:
BooleanConstant
BooleanConstant: 
'TRUE' | 'FALSE';

Unfortunately XText is throwing an exception that states there is left recursion in this grammar. How can I fix it?

Thanks.

score 1 · Answer 1 · answered May 24 '15 at 17:57

1

You could simply introduce a new rule (a new tier) like that:

BasicExpression:
    firstContent=ExpressionContent ("&" secondContent=ExpressionContent)?
;

ExpressionContent:
    Constant 
    | '(' BasicExpression ')' 
    | '!' BasicExpression 
;

That way the rule is not left recursive anymore.

Greeting Krzmbrzl

answered May 24 '15 at 17:57

Raven

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This answer rejects `TRUE & TRUE & TRUE` that is allowed in the OP. – Chen Levy Oct 15 '18 at 08:31

score 0 · Answer 2 · answered Apr 18 '14 at 13:24

0

Have a look at this article or the official documentation, it will explain in detail how to handle recursion in language, and taking into account operator precedence.

answered Apr 18 '14 at 13:24

AdrieanKhisbe

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Unfortunately the links are broken. – Chen Levy Oct 15 '18 at 08:37

Eliminate left recursion in XText

2 Answers2