现在应该移到表达式"的左边.

The <assoc> should now be moved left of the "expression".

它必须始终放在周围 | 的右侧:

It must be placed always right to the surrounding |:

看这里:https://theantlrguy.atlassian.net/wiki/display/ANTLR4/左递归+规则

 ...
 |   expression '&&' expression
    |   expression '||' expression
    |   expression '?' expression ':' expression
    |<assoc=right>   expression
        (   '='
        |   '+='
        |   '-='
        |   '*='
        |   '/='
        |   '&='
        |   '|='
        |   '^='
        |   '>>='
        |   '>>>='
        |   '<<='
        |   '%='
        )
        expression