How to iterate over a production in ANTLR

Question

Lets suppose the following scenarios with 2 ANTLR grammars:

1)

expr     : antExp+;
antExpr  : '{' T '}' ;
T        : 'foo';

2)

expr     : antExpr; 
antExpr  : '{' T* '}' ;
T        : 'bar';

In both cases I need to know how to iterate over antExp+ and T*, because I need to generate an ArrayList of each element of them. Of course my grammar is more complex, but I think that this example should explain what I'm needing. Thank you!

Answer 1

Production rules in ANTLR can have one or more return types which you can reference inside a loop (a (...)* or (...)+). So, let's say you want to print each of the T's text the antExp rule matches. This could be done like this:

expr
 : (antExp {System.out.println($antExp.str);} )+
 ;

antExpr returns [String str]
 : '{' T '}' {$str = $T.text;}
 ;

T : 'foo';

The same principle holds for example grammar #2:

expr     : antExpr; 
antExpr  : '{' (T {System.out.println($T.text);} )* '}' ;
T        : 'bar';

EDIT

Note that you're not restricted to returning a single reference. Running the parser generated from:

grammar T;  

parse
 : ids {System.out.println($ids.firstId + "\n" + $ids.allIds);}
 ;

ids returns [String firstId, List<String> allIds]
@init{$allIds = new ArrayList<String>();}
@after{$firstId = $allIds.get(0);}
 : (ID {$allIds.add($ID.text);})+
 ;

ID    : ('a'..'z' | 'A'..'Z')+;
SPACE : ' ' {skip();};

on the input "aaa bbb ccc" would print the following:

aaa
[aaa, bbb, ccc]