antlr-3.4/runtime/ObjC/Framework/examples/hoistedPredicates/T.g

/** Demonstrates how semantic predicates get hoisted out of the rule in 
 *  which they are found and used in other decisions.  This grammar illustrates
 *  how predicates can be used to distinguish between enum as a keyword and
 *  an ID *dynamically*. :)

 * Run "java org.antlr.Tool -dfa t.g" to generate DOT (graphviz) files.  See
 * the T_dec-1.dot file to see the predicates in action.
 */
grammar T;

options {
	language=ObjC;
}

@memVars {
/* With this true, enum is seen as a keyword.  False, it's an identifier */
BOOL enableEnum;
}

@init {
enableEnum = NO;
}

stat: identifier    {NSLog(@"enum is an ID");}
    | enumAsKeyword {NSLog(@"enum is a keyword");}
    ;

identifier
    : ID
    | enumAsID
    ;

enumAsKeyword : {enableEnum}? 'enum' ;

enumAsID : {!enableEnum}? 'enum' ;

ID  :   ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'_')*
    ;

INT :	('0'..'9')+
    ;

WS  :   (   ' '
        |   '\t'
        |   '\r'
        |   '\n'
        )+
        { $channel=99; }
    ;