CODEWITHSUNDEEP
antlr
Fisherman_Zhu
Fisherman_Zhu

Reputation: 119

Is there a way to know which alternative rule ANTLR parser is currently in?

I want to know which alternative rule antlr is current in .I read "the definitivie antlr4 reference",it use ctx.getChildCount() or ctx.ID()!=null to know which alternative rule antlr is currently in.

But I want to know is there a method which could give the specific index of the alternative rule.

I see this question How to know which alternative rule ANTLR parser is currently in during visit ,but it doesn't have the answer .

Upvotes: 2

Views: 556

Answers (1)

Bart Kiers
Bart Kiers

Reputation: 170138

Either use alt labels to know in which alternative you are, or try to use options {contextSuperClass=org.antlr.v4.runtime.RuleContextWithAltNum;} (link), but that is probably not what you want. The contextSuperClass will only tell you in the child rule what the index in its parent is:

parent
 : child_a
 | child_b
 | child_c
 | child_d
 | child_e
 ;

child_d
 : ... // in a listener, you can now get index 3 from the parent context
 ;

so you cannot do:

parent
 : child_a
 | child_b
 | child_c
 | child_d // get index 3 here
 | child_e
 ;

Note that the contextSuperClass is only available in Java it seems by looking at the remark in the link: "I'm only putting into Java runtime as I'm certain I'm the only one that will really every use this."

Upvotes: 1

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