Flat Infix Operator

[Robert Jacobson]

I have a silly question about writing an ANTLR4 expression grammar with a flat infix operator. I want "1+2+3" to parse as (PLUS 1 2 3) rather than (PLUS (PLUS 1 2) 3). So consider this grammar:

expr

: LEAF

| LPAREN expr RPAREN //parentheses

| <assoc=right> expr POWER expr //exponentiation

| expr MUL expr //multiplication

| expr PLUS expr //addition

;

This of course gives the left associativity I'm trying to avoid. If I modify the addition alternative as follows,

| expr (PLUS expr)+ //addition

then PLUS becomes right associative! Is there a way to coax ANTLR to give me (PLUS 1 2 3)? Or do I need to "flatten" after the fact?

Best,

Robert