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[TCS]Create left-recursive syntax [message #9799]

Mon, 31 March 2008 15:06

T Kruse

Messages: 73
Registered: July 2009

Member

Hi,

assuming I'd have a metamodel like this:

abstract class Expression {
}

class BinaryExpression extends Expression {
attribute left : Expression;
attribute right : Expression;
}

class Value extends Expression {
attribute value: String;
}

And assuming I'd have a syntax like that:
template BinaryExpression
: left "=" right
;

template Value
: value
;

Then this syntax is obviously left-recursive, and ANTLR writes the
following error:
[antlr:antlr3] error(210): The following sets of rules are mutually
left-recursive [binaryExpression, expression]

However, in theory it is possible to create ANTLR Grammars that can do
what I indended above, by using more grammar rules (separating recursive
from non-recursive rules).
Is there any way to achieve this for the scenario above without changing
the metamodel? What would be the best approach to create such a syntax?

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Re: [TCS]Create left-recursive syntax [message #9825 is a reply to message #9799]

Mon, 31 March 2008 16:16

Frédéric Jouault

Messages: 572
Registered: July 2009

Senior Member

Hello,

When you have left recursion, you should use operatorTempltates and the
operator table.
You can for instance have a look at the FPath project from the TCS Zoo.

Regards,

Frédéric Jouault

Thibault a écrit :
> Hi,
>
> assuming I'd have a metamodel like this:
>
> abstract class Expression {
> }
>
> class BinaryExpression extends Expression {
> attribute left : Expression;
> attribute right : Expression;
> }
>
> class Value extends Expression {
> attribute value: String;
> }
>
> And assuming I'd have a syntax like that:
> template BinaryExpression
> : left "=" right
> ;
>
> template Value
> : value
> ;
>
> Then this syntax is obviously left-recursive, and ANTLR writes the
> following error:
> [antlr:antlr3] error(210): The following sets of rules are mutually
> left-recursive [binaryExpression, expression]
>
> However, in theory it is possible to create ANTLR Grammars that can do
> what I indended above, by using more grammar rules (separating recursive
> from non-recursive rules).
> Is there any way to achieve this for the scenario above without changing
> the metamodel? What would be the best approach to create such a syntax?
>

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