compiler-construction - Jison:二元运算语法冲突

Question

在尝试设置我的 Jison 语法时，我有:

%left 'OR' 'AND'

%%

Expression:
    Operation
;

Operation:
    Expression Operator Expression {$$ = new yy.LogicalExpression($2, $1, $3)}
;

Operator:
    'AND'
|   'OR'
;

但这导致了以下冲突消息:

Conflict in grammar: multiple actions possible when lookahead token is OR in state 6
- reduce by rule: Operation -> Expression Operator Expression
- shift token (then go to state 5)
Conflict in grammar: multiple actions possible when lookahead token is AND in state 6
- reduce by rule: Operation -> Expression Operator Expression
- shift token (then go to state 4)

States with conflicts:
State 6
  Operation -> Expression Operator Expression . #lookaheads= $end OR AND
  Operation -> Expression .Operator Expression
  Operator -> .AND
  Operator -> .OR

当我替换时，删除 Operator 非终结符，而是直接写出表达式模式:

%left 'OR' 'AND'

%%

Expression:
    Operation
;


Operation:
    Expression 'AND' Expression {$$ = new yy.LogicalExpression($2, $1, $3)}
|   Expression 'OR' Expression {$$ = new yy.LogicalExpression($2, $1, $3)}
;

我没有收到这样的错误，为什么第一个语法有冲突，而第二个没有？它们似乎与我的理解相同。

提前致谢!

Answer 1

前瞻太多了，反正第一种形式是错的。第二种形式是正确的。您需要为 AND 和 OR 以及所有其他运算符编写单独的产生式。否则你无法获得运算符优先级。