In javacc How to do multi choice token with token assignment

Question

Code first:

// 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()

I picked

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

It's looks better. Is there any other way to do this ? I'm not sure is this the right way to do this..

The whole jjt is here

Answer 1

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

is a reasonable solution.

Since your three tokens are completely interchangeable from a syntactic point of view, you could also define one token kind like this.

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

In this case, you would not define I_EXIT , I_RET , and I_NOP .