[antlr-interest] Lexer rule with alternatives (Newbie question)

[Петров Александр]

> but there can be problems as '+' used in to different rules will create
> two distinct token types which will cause a MismatchedTokenTypeException
> later.

This is exactly what happens with my grammar.
Thank you very much.

2008/11/22 Johannes Luber <jaluber at gmx.de>:
> Петров Александр schrieb:
>> Hello,
>> why such grammar doesn't work properly:
>> --------------------------------------------------------------------------------------
>> expr  :
>>         operand ((oper) operand)*
>>               ;
>> //Correct operands
>> operand       :
>>       INT
>>       ;
>> OPER: ('+'|'-'|'*'|'/')
>>       ;
>> INT   :
>>       ('0'..'9')+
>>       ;
>> --------------------------------------------------------------------------------------
>>> t+1
>> line 0:3 mismatched input '+' expecting EOF
>>
>> But if I replace the Lexer rule by Parser rule:
>>
>> oper: ('+'|'-'|'*'|'/');
>>
>> All work as it should. Why I should't use Lexer rule with alternatives ?
>
> The problem with your example is that in the expr rule you use oper, but
> define OPER as rule. Did you overlook this while posting or does even
>
> expr    :
>         operand (OPER operand)*
>        ;
>
> not work? Nonetheless, the usual way to define operands is to create a
> single rule for each operand and reference those lexer rules in a single
> parser rule for convenience. As "oper: ('+'|'-'|'*'|'/');" creates
> implicit lexer rules doing it this way simulates the described approach,
> but there can be problems as '+' used in to different rules will create
> two distinct token types which will cause a MismatchedTokenTypeException
> later.
>
> Johannes
>>
>> Thank you
>>
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