[antlr-interest] Rewind one token?

[Monty Zukowski]

Giving different rules a try is exactly what syntactic predicates are 
for.  Perhaps if you could post a small example that shows the problem 
we can help out.

Monty

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On Aug 16, 2004, at 9:21 AM, Ingo Maier wrote:

> On Mon, 2004-08-16 at 04:54, Ric Klaren wrote:
>> On Mon, Aug 16, 2004 at 09:03:42AM -0400, Ingo Maier wrote:
>>> Well, my question seemed to be misleading. I don't want to know where
>>> mark/rewind is used (a call hierarchy check tells me that, I use 
>>> eclipse
>>> :)). I want to know, if there is a possibility to
>>> rewind/backtrack/whatever an already read token?
>>>
>>> I use two lexers on the same stream with a multiplexer. First lexer
>>> starts. When it passes a specific token (sequence) to the parser, 
>>> lexers
>>> will be switched. But the tokens already read by the first lexer and
>>> indicating the switch will be needed by the second one.
>>>
>>> Any ideas how to do that?
>>
>> Call mark at the start of the switch sequence then switch to the other
>> lexer and rewind directly at the start of the second lexer (e.g. pass 
>> the
>> mark id and call rewind in the init action of the startrule)?
>>
>> I'm not sure wether you do but.. it sounds like you switch lexers 
>> from the
>> parser. In general this does not work (especially if there's some
>> predicates in the parser (mark/rewind again)) (just checking)
>
> Well, sorry, I think I was on the wrong level. The second lexer should
> get a chance to "rescan" the last tokens, read by the first lexer. It
> might get totally different tokens from the same input sequence. This
> have to be done on the level of a CharBuffer or InputBuffer, probably.
> So, I want to put back the last tokens, character by character.
>
> Just to clarify, I want to do the following:
>
> 1) give parser1/lexer1 a try
> 2) when they fail, put back all tokens since failure, can be several 
> due
> to lookahead etc
> 3) give parser2/lexer2 a try, beginning from the point of failure, as 
> if
> nothing happened before
>
> I hope this makes it clearer,
> Ingo
>
>
>
>
> Yahoo! Groups Links
>
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