Question

代码优先：

// I need, but not allowed
o = (<I_EXIT> | <I_RET> | <I_NOP>)

// Work around, the generated code will do double switch
(o = <I_EXIT> | o = <I_RET> | o = <I_NOP>)

// Work around, introduce new token, will warning
// Warning: Line 59, Column 11: Regular Expression choice : XXX can never be matched as : XXX
// Consider this is a bad practice.
TOKEN:{
    <I_NO_OP: <I_EXIT> | <I_RET> | <I_NOP>>
}
o = <I_NO_OP>

// Work around, introduce new grammar, generate double switch with one more function call, looks awful.
Token oneOp():{
    Token t = null;
}{
    (t = <I_CALL> |t = <I_PUSH> |t = <I_POP> |t = <I_JPC>){return t;}
}
...
o = oneOp() a = operand()

我picked

(o = <I_EXIT> | o = <I_RET> | o = <I_NOP>)

看起来更好。有没有其他方法可以做到这一点？我不确定这是正确的做法..

整个jjt是here

Answer 1

(o = <I_EXIT> | o = <I_RET> | o = <I_NOP>)

是一个合理的解决方案。

由于您的三个标记从语法的角度来看是完全可互换的，您还可以定义一个这样的标记类型。

TOKEN:{
    <I_NO_OP: "EXIT" | "RET" | "NOP">
}

在这种情况下，您不会定义I_EXIT，I_RET和I_NOP。

在javacc中如何使用令牌分配执行多选令牌

1 个答案: