Example
Labeling the alternatives inside a rule starting with the # operator tells ANTLR to generate listener methods for each label corresponding to the alternative.
By specifying a label for each alternative in the following rule:
// Rule
type : int #typeInt
| short #typeShort
| long #typeLong
| string #typeString
;
// Tokens
int : 'int' ;
short : 'short' ;
long : 'long' ;
string : 'string' ;
Will generate the following methods in the generated interface that extends ParseTreeListener:
public void enterTypeInt(TypeShortContext ctx);
public void enterTypeShort(TypeIntContext ctx);
public void enterTypeLong(TypeLongContext ctx);
public void enterTypeString(TypeStringContext ctx);
