Access properties defined with in parentheses

Question

I'm using antlr4 with python2 target,

additive_expression returns [value] @init{$value = 0;}
  : multiplicative_expression ((PLUS_OPERATOR | MINUS_OPERATOR) multiplicative_expression)*

Since the ((PLUS_OPERATOR | MINUS_OPERATOR) multiplicative_expression) expression appears zero or multiple times,

I will need to access each of it separately then calculate the final value.

Any ideas? I've tried the following, non of them works

1. use re = (...) and antlr says I can't define it for non-sets
2. use op = (PLUS_OPERATOR | MINUS_OPERATOR) etc. but it always point to the last appearance of the expression

Answer 1

Try something like this:

additive_expression returns [value] 
@init{$value = 0;}
 : e1=multiplicative_expression                  {$value = $e1.value;}
   ( PLUS_OPERATOR e2=multiplicative_expression  {$value += $e2.value;}
   | MINUS_OPERATOR e2=multiplicative_expression {$value -= $e2.value;}
   )*
 ;

Or better, use a visitor instead of embedding target code inside your grammar¹.

¹ ANTLR4 visitor pattern on simple arithmetic example