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Ambiguous grammar [message #1838923]

Tue, 09 March 2021 16:44

John Henbergs

Messages: 239
Registered: October 2020

Senior Member

Hi all,

I have the following grammar:

Machine:

("A" a+=A ("," a+=A )*)*
("B" b+=B ("," b+=B )*)*
goto+=GoTo
;

A:
name=ID;

B:
name=ID;

GoTo:
name=ID ":" (as=[A] | bs=[B]) "to" (as=[A] | bs=[B]) ;

I get the following error: Decision can match input such as RULE_ID using multiple alternatives 1,2 .

I understand that happens because the parser will not understand if it belongs to A or B, but I cannot find a way around it.

Any help is appreciated!

Thank you!

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Re: Ambiguous grammar [message #1838924 is a reply to message #1838923]

Tue, 09 March 2021 16:47

Christian Dietrich

Messages: 14665
Registered: July 2009

Senior Member

you cant. the only way is either to use a different syntax/keyword for the cases
or introduce a common superType e.g.

AorB:A|B; // UNCALLED

GoTo:
name=ID ":" from=[AorB] "to" to=[AorB] ;

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

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